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Avena fatua L. escapes and delayed emergence in wheat (Triticum aestivum L.) crops of Argentina
Crop Protection 103 (2018) 30e38
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Avena fatua L. escapes and delayed emergence in wheat (Triticum aestivum L.) crops of Argentina s N. Martín, Julio A. Scursoni* Andre tedra de Produccio n Vegetal, Departamento de Produccio n Vegetal, Facultad de Agronomía, U.B.A., Av. San Martín 4453, C.A.B.A., Argentina Ca
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 October 2016 Received in revised form 13 August 2017 Accepted 26 August 2017
Avenafatua (L.) is one of the most important weed grasses in wheat crops on the most important wheat (Triticum aestivum L.) production area of Argentina. It is present in 60% of the fields of an area of 750,000 ha not only reducing crop yields but also contaminating the wheat and barley (Hordeum vulgare L.) grain. The most frequent practice for its control is the application of ACCase inhibitors or ALS inhibitors herbicides. However, the presence of wild oat is frequent in wheat crops at harvest even in those fields where herbicides were applied and thus, regarded as resistant individuals. Thus, the objective of this study was to identify the processes that explain the persistence of wild oat individuals during the crop cycle. Seeds from cultivated and from uncultivated areas were harvested and then the response to ACCase inhibitors and ALS inhibitors herbicides was studied over 20 selected populations from different areas of both conditions (cultivated and uncultivated). Emergence dynamic from seeds of both conditions was also studied and in addition, the effect of mature environment on seeds germination was also assessed. The results indicate that none of the populations were resistant to herbicides studied. However, emergence dynamic was different depending on the seeds coming from agricultural fields or not cropping condition. Seeds from cultivated areas had higher dormancy and emerged later in the field than those from no cropped areas. The ripening environment did not modify the emergence pattern suggesting differences in emergence dynamic are based on genetic nature. These results show dormancy levels and therefore germination and establishment dynamic on the field was hierarchically more important than response to herbicides to favor the persistence of this weed in wheat production systems. Thus, it is still possible to apply proactive agronomic strategies with the aim of avoiding the growth of wild oat populations resistance to herbicides. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Avenafatua Weeds escapes Emergence dynamic Resistance
1. Introduction Avenafatua (L.) is a troublesome annual grass weed regarded to be one of the most wide-spread and harmful weeds of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rice (Oryza sativa L.) and flax (Linumusitatissimum L.). It is considered one of the ten most important weed species in the world because of its wide distribution and competitive effect on crop yield worldwide (Holm et al., 1977; Simpson, 1990). In addition, Avenafatua seeds are frequently found in wheat or barley grain at harvest, thus, representing significant commercial discounts. In the United States, it is present in approximately 11,000,000 ha, generating losses over a trillion dollars (Evans et al., 1991). In Western Australia, 24% of
* Corresponding author. E-mail address: [email protected] (J.A. Scursoni). http://dx.doi.org/10.1016/j.cropro.2017.08.020 0261-2194/© 2017 Elsevier Ltd. All rights reserved.
samples of wheat, barley and lupine (Lupinusalbus L.) seeds contained Avenafatua seeds (Michael et al., 2010). In western Canada, more money is spent on Avenafatua herbicides than on any other weed species. In addition, Avenafatua resistance to herbicides is the most widespread issue (Harker et al., 2016). In Spain, more than 27% of the area planted with winter cereals were considered severely affected by Avenafatua (Fernandez Quintanilla et al., 1984). It is also the main weed in winter cereals in the UK (Wilson et al., 1990) and in China, it is one of the most important weeds in wheat crops, considering its presence in about 5 million ha. grown, resulting in a loss of 1.75 million tons per year (Li et al., 2007). In Argentina, Avenafatua and Loliummultiflorum (Lam.) are the most important grass weeds in wheat and barley crops. Scursoni et al. (2014) reported presence of Avenafatua in 60% of the wheat crops in the main wheat production area, representing an increase of 24% compared to surveys conducted 30 years ago by Catullo et al. (1983). In this area, Scursoni and Benech-Arnold (1998) estimated
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losses of 25% in barley and wheat with Avenafatua densities of 60 plants m2. Scursoni and Satorre (2005) reported similar losses in barley with Avenafatua at 70 plants m2. More recently, Scursoni et al. (2011) found 20% wheat yield reduction with Avenafatua densities of 100 plants m2. Interestingly, Scursoni et al. (1999) found significant differences on Avenafatua fecundity between barley crop densities. Crop density, time of wild oat emergence, fertilization, crop species are agronomic factors that influence on crop yield reduction by Avena fatua and the amount of seeds produced and returned to the soil (Satorre and Snaydon, 1992; Scursoni and Benech-Arnold, 1998; Scursoni and Satorre, 2005; Willenborg et al., 2005). Manipulating these factors to favor the crop against the weed and integrating them with reduced herbicide use and cultural control measures has the potential to simultaneously reduce Avenafatua competition and weed seed production (Thill et al., 1994). Nevertheless, Avenafatua control in Argentina is strongly based on herbicide application. The first herbicides applied were the ACCase inhibitors such as diclofop methyl, clodinafoppropargyl, fenoxaprop p ethyl and in the last ten years pinoxaden. Currently, although pinoxaden is the most applied, ALS inhibitors such as iodosulfuron plus mesosulfuron and pyroxsulam are also recommended to control Avenafatua in wheat crops. In spite of the successful results achieved by herbicide application, it must be considered the selection pressure for resistant biotypes due to continue use of herbicides with the same mode of action (Burgos et al., 2013). Avenafatua resistance to ACCase inhibitors clodinafop-propargyl, diclofop-methyl, and fenoxaprop-P-ethyl was reported in 2010 in Argentina. In addition, 35 biotypes are registered in the entire world. Regarding ALS inhibitors, there are 19 biotypes resistant to ALS inhibitors herbicides in the world (Heap, 2016). Avenafatua individuals are frequently present on wheat crops at harvest and are considered resistant individuals. However, escapes to herbicide application can be explained by demographic processes such as delay weed emergence and establishment (Scursoni et al., 2007). In this sense, Payne and Oliver (2000) recorded control lower than 85% for Echinochloacruss-galli [L.] Beauv. with two applications of glyphosate during the crop cycle as a consequence of late-emerging cohorts. In addition, later application of glyphosate gave better control of Digitariasanguinalis (L.) at the end of the season due to control of individuals emerging after earlier applications (Arnold et al., 1997). To identify what processes regulate the escape of weeds during crop cycle is relevant to design suitable weed management strategy avoiding confusion between resistance and demographic escape. Thus, the hypothesis is that resistance to herbicides is the most relevant processes that explain escapes of wild oat in wheat crops. The objectives of these experiments were to study: (i) the response to different herbicides of 20 populations of Avenafatua present at preharvest of wheat crops, (ii) to study the germination dynamic of Avenafatua seeds harvested from individuals present in pre-harvest of wheat crops and, in contrast, from individuals present in uncultivated sites, (iii) to identify the nature of possible differences associated with the emergence dynamic of different source of seeds and (iv) to study morphological development (phyllochron) on individuals from both origin of plants (uncultivated and cultivated sites). 2. Materials and methods 2.1. Seed harvest During 2008, 2009 and 2011 field surveys were conducted at preharvest of wheat crops in different sites of southeast of Buenos Aires Province representing almost 400,000 ha of wheat crops between 36 ,770 S e 38 ,550 S and 61,280 W- 57,830 W. This region
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is characterized by an average of 25% of grazing and the rest of the area is winter (wheat, barley) and spring-summer (soybean, sunflower, maize) crops. Rainfall ranges between 650 mm/year in the west to 740 mm/year in the east of the region. It is the zone of Argentina with greater surface planted with wheat and barley. Avenafatua seeds were harvested by hand from individuals present in different fields. Seeds were collected from 20 fields located in a radius of 180 miles and at each field 40 individual plants were randomly selected and harvested. In addition, seeds from individuals on uncultivated areas were also harvested and regarded as susceptible biotypes. The non-cultivated areas were abandoned areas, without cultivation or in some cases close to routes without presence of near cultivation. The seeds were classified according to geographical location and by their origin (cultivated or uncultivated conditions) and were kept dry at room temperature. 2.2. Response to herbicides in the field From 2009 to 2012, 57 experiments were carried out with the aim of studying the efficacy on Avenafatua control of different herbicides applied in each field during the last growing seasons on 18 wild oat populations (Tables 1e3). The experiments were performed considering in each individual population seeds from cultivated and non-cultivated areas. In each experiment different herbicides frequently applied were tested once. The experiments were carried out in split-plot design with the origin of the population as the main factor and the rate of the herbicides the second factor. All the experiments were conducted in the experimental field of the Faculty of Agronomy (UBA) 34 350 3700 S, 58 290 2.500 W. Avenafatua seedlings were obtained from seeds germinated in chambers at constant 12 C and when the plumule reached 2 cm long these seedlings were planted in pots 14 cm diameter and 2.1 L volume. After that, pots were placed for ten days in greenhouse and then were placed outdoors. Each pot was filled with a mixture of fertile soil, peat and sand and was fertilized with 0.1539 g and 0.1847 g, diammonium phosphate and urea, equivalent to 100 kg ha1diammonium phosphate and 120 kg urea ha1, respectively. The plants were watered throughout its entire life cycle and the herbicides were applied when the plants were at 13 Z stage (Zadoks et al., 1974). All treatments were applied with a CO2 pressurized backpack sprayer consisting of a handheld boom that contained four 110015 flat-fan nozzles and calibrated to deliver 140 L/ha at 276 kPa. The experimental design was in split plot regarding the origin of the seeds as the main factor and the rates as the subfactor. The rates tested of each herbicide were 0.5 , 1 and 2 regarding (x) the recommended rate. In addition a control dose (0 without application of herbicides) was included. Each rate was replicated five times. Herbicide response was evaluated assessing relative individual dry weight 30 days after herbicide application. 2.3. Germination under controlled conditions With the aim of studying the germination rate at different temperatures, 20 seeds from 12 populations and each condition (cultivated and uncultivated) were incubated at constant 12 C and 20 C dark, in petri dishes in a medium of distillated water. Completely randomized design was applied with three replicates were used for each treatment (population x condition) and germination (radical emergence) was recorded 20 days after incubation. In addition, two populations were recorded daily to calculate the germination rate for different fractions of the population and thus, to estimate the base temperature (Bradford, 1995). These experiments were carried out with post maturated and no post maturated seeds. The covers were removed and placed at constant 25 C dry for 10 days. All the seeds that did not germinate
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Table 1 Responses of wild oat populations from different origins (cultivated and no cultivated environment) to different herbicides at recommended rate (2009e2010). Plants were treated at 3e4 leaf stage (Z 13e14). P-value indicate significance of ANOVA (<0.05).a Population
Herbicide
Treatment day
Dry Weight (% of nontreated control) Cultivated
No Cult.
El Porvenir Medano Seco Medano Seco Azul Azul Azul Azul El Diez L4 El Diez L4 El Diez L4 El Diez L4 El Diez L6 El Diez L6 El Diez L6 El Diez L6 El Porvenir La Gauchita
Fenoxaprop Fenoxaprop Fenoxaprop Diclofop-metil Imazamox Iodosulfuron þ Metsulfuron Pinoxaden Diclofop-metil Imazamox Iodosulfuron þ Metsulfuron Pinoxaden Diclofop-metil Imazamox Iodosulfuron þ Metsulfuron Pinoxaden Diclofop-metil Diclofop-metil
26/11/09 26/11/09 26/10/10 01/07/10 28/11/10 28/11/10 28/11/10 01/07/10 28/11/10 28/11/10 28/11/10 01/07/10 28/11/10 28/11/10 28/11/10 30/09/10 17/08/10
62.16 66.32 34.71 50.84 42.21 11.06 12.32 87.63 18.77 25.03 9.75 77.2 6.07 8.53 5.78 29.97 93.07
52.4 52.4 48.48 75.39 14.37 5.89 6.8 73.04 24.75 19.75 12.12 73.04 24.75 19.75 12.12 52.1 84.26
a
P-value
0.5117 0.1946 0.193 0.0676 0.4681 0.3172 0.4845 0.6214 0.1613 0.0614 0.2394 0.6214 0.1613 0.0614 0.2394 0.192 0.1027
All the population x herbicide combinations are non-significant (P > 0.05).
Table 2 Responses of wild oat populations from different origins (cultivated and no cultivated environment) to different herbicides at recommended rate (2011e2012). Plants were treated at 3e4 leaf stage (Z 13e14). P-value indicate significance of ANOVA (<0.05). Population
Adelante MS CosMalal Don Luis El Diez L6 El Diez L6 El Diez L6 Enfrente Huincahue La Legua Medano Seco Pailche Izquierdo Pailche Izquierdo Pailche Izquierdo Saco Saco Saco Tupungato Tupungato a
Herbicide
Iodosulfuron Iodosulfuron Pinoxaden Iodosulfuron Fenoxaprop pyroxsulam Pinoxaden Fenoxaprop Fenoxaprop Pinoxaden Imazamox pyroxsulam Fenoxaprop Iodosulfuron Iodosulfuron pyroxsulam Iodosulfuron Pinoxaden
Application date
þ metsulfuron-metil þ metsulfuron-metil þ metsulfuron-metil
þ metsulfuron-metil þ metsulfuron-metil þ metsulfuron-metil
10/06/11 10/06/11 10/06/11 02/09/11 02/09/11 02/09/11 10/06/11 10/06/11 10/06/11 10/06/11 10/06/11 10/06/11 10/06/11 22/08/11 22/08/11 22/08/11 10/06/11 10/06/11
Dry Weight (% of nontreated control) Cultivated
No Cult.
22.47 34.5 4.74 7.66 0 6.46 1.79 1.09 4.15 5.29 10.5 19.39 10.99 15.4 13.13 10.7 29.79 6.41
16.22 16.22 19.31 6.47 9.45 0.87 19.31 10.91 10.91 19.31 12.93 20.64 15.85 16.22 13.28 11.25 16.22 19.31
P value
0.1394 0.1394 0.3354 0.7138 0.0452a 0.0226a 0.3354 0.5943 0.5943 0.3354 0.829 0.7799 0.4021 0.7986 0.966 0.86 0.1394 0.3354
Populations with significant differences between cultivated and uncultivated conditions.
were analyzed through a test of Tetrazolium Chloride 0.1% v/for 24 h at 30 C in darkness (Grabe, 1970). Those seeds that became red or pink in the embryo were considered viable. 2.4. Germination dynamic in the field During 2011, 2012 three experiments were carried out with the aim of studying the emergence dynamic in field conditions of five populations of Avenafatua. The experimental design was a Complete Random Design (CRD). Each population was evaluated with seeds from uncultivated and cultivated conditions. Fifty seeds were placed in small bags, 10 20 cm made with air and moisture permeable plastic thread, filled with sand and soil mix. The bags were shallowly buried into pots 14 cm in diameter and 2.1 L volume and then, each pot was buried in the experimental site in early
summer. Since April, and at intervals of 45e60 days, the bags were exhumed and germinated seeds were counted. Each treatment (population x condition) was repeated three times for each sample date. The last exhumation was conducted during spring. Seeds were assessed five times with the exception of the San Joaquin population in 2012, which, due to lack of seeds, only three samples were carried out. During 2011, experiments were carried out on the experimental field of FAUBA (Faculty of Agronomy, U.B.A.). On the other hand, in 2012, experiments were performed simultaneously on the campus of the EEA INTA Balcarce and at the experimental field of FAUBA. During the experiments, daily temperature and rainfall were assessed from meteorological station. In all cases, the viability of those seeds which were not germinated at the end of the experiment was analyzed through a chloride tetrazolium test. Seeds whose embryos were stained red were classified as viable.
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Table 3 Responses of wild oat populations from different origins (cultivated and no cultivated environment) to different herbicides at recommended rate (2012). Plants were treated at 3e4 leaf stage (Z 13e14). P-value indicate significance of ANOVA (<0.05).a Population
Herbicide
Application date
Dry Weight (% of nontreated control) Cultivated
No Cult.
Avenida Grande Avenida Grande Azul Azul CosMalal CosMalal CosMalal Km 17 Km 17 Km 17 La Gauchita La Gauchita La Gauchita Medano Seco Medano Seco Medano Seco San Jose San Jose San Jose Tupungato Tupungato Tupungato
Imazamox pyroxsulam Imazamox pyroxsulam Imazamox Pinoxaden pyroxsulam Imazamox Pinoxaden pyroxsulam Imazamox Iodosulfuron þ Mesosulfuron pyroxsulam Imazamox Iodosulfuron þ Mesosulfuron pyroxsulam Imazamox Pinoxaden pyroxsulam Imazamox Iodosulfuron þ Mesosulfuron pyroxsulam
01/08/12 01/08/12 01/08/12 01/08/12 04/08/12 04/08/12 04/08/12 04/08/12 04/08/12 04/08/12 10/08/12 10/08/12 10/08/12 10/08/12 10/08/12 10/08/12 04/08/12 04/08/12 04/08/12 10/08/12 10/08/12 10/08/12
20.28 52.46 16.93 35.49 15.31 13.12 21.43 31.24 8.05 15.11 24.48 18.14 32.1 19.75 15.31 25.94 20.27 17.13 6.19 31.39 28.58 9.26
21.21 21.55 21.21 21.55 21.2 1.01 21.55 21.2 1.01 21.55 17.54 13.03 17.82 17.54 13.03 17.82 21.2 1.01 21.55 17.54 13.03 17.82
a
P value
0.7584 0.0644 0.7584 0.0644 0.8491 0.8348 0.252 0.8491 0.8348 0.252 0.0619 0.0791 0.15 0.0619 0.0791 0.15 0.8491 0.8348 0.252 0.0619 0.0791 0.15
All the population x herbicide combinations are non-significant (P > 0.05).
2.7. Analysis
2.5. Dynamics of seed germination from different maturation environments The experiment was a RCD conducted in the experimental field of FAUBA during 2012 and 2013. Seeds of Avenafatua individuals from Necochea (South East Buenos Aires) from both conditions (cultivated and uncultivated) were incubated at 12 C in chambers. When the plumule was 2 cm long, these seedlings were planted randomly in an uncultivated area of the Experimental Field of FAUBA with the aim of simulating no cultivated condition. These individuals were harvested at maturity in December and with these seeds a field dynamic emergence experiment, as was described in 2.4, was performed. In January 2013, seeds and buried treatments were: i) Cultivated condition - progeny uncultivated condition (CCUC) and ii) Uncultivated conditions-progeny uncultivated condition (UC-UC). Seeds were sampled three times over year and percentage germination was recorded. In all cases, non-germinated seeds were analyzed through a tetrazolium chloride test.
2.6. Phyllochron
Y ¼ Ymax e (Ymax e Y0). exp (-(k.x)g)
Four experiments were carried out with five plants from two populations located at the greatest distance harvested in 2011 and from both conditions (cultivated and uncultivated fields). Main stem leaf appearance was counted when the leaf tip first became visible (Frank and Bauer, 1995) in five pants for each population. The thermal time interval between appearance of successive leaves (phyllochron, C d/leaf) was estimated from the inverse of slope of a linear regression of main-stem leaf number versus accumulated degree-days (Bertero, 2001). Degree-days (C d) were calculated using Equation (1) (Ritchie and NeSmith, 1991). We consider in this case Tb ¼ 0 C d ¼ (day temperature þ night temperature)/2eTb
For each response to herbicides experiments, analysis of variance was performed for each trial separately regarding relative dry weight as variable response, comparing sources (cultivated vs. uncultivated) for each herbicide and rate on each population. Dry weight values were expressed relative to those registered with the control dose (0). When the F value was significant (P < 0,05), LSD corrected by Fisher was used for the comparison between means. Total germination over 20 days under controlled conditions was analyzed by ANOVA, for each population and temperature regime. The treatments were cultivated and uncultivated conditions. When necessary, percentage values were angular transformed (y ¼ arcsin√x) to increase normality and variance homogeneity. Treatment means were separated using Tukey's honestly significant difference (HSD) (a ¼ 0.05). These were carried out using Infostat® (Di Rienzo et al., 2008). For cumulative seed germination in field values for each treatment were fitted to Weibull growth model using least-squares nonlinear regression. The model used was:
(1)
Where Y is cumulative seed germination over thermal time x, Ymax is the maximum seed germination, Y0 is the lower asymptote, k is the growth rate and g is the slope. Statistical differences between uncultivated and cultivated conditions were found by testing the null hypothesis of one regression model for both conditions. F-test was performed and p-values less than 0.05 conclude that each condition had a different model. These data were analyzed using GraphPad Prism v5.0 (GraphPad Software, San Diego, CA). Regression analyses were carried out for the fitted models of number of leaves versus degree daysusing Infostat® (Di Rienzo et al., 2008). Regression analysis was carried out for the phyllochron to test differences on parameter b (leaf expanded/thermal time).
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3. Results
3.4. Germination dynamics of seeds progeny
3.1. Dose response experiments
The progeny of individuals from uncultivated conditions when they were grown in uncultivated conditions showed more germinability than those from cultivated conditions grown in uncultivated conditions (Fig. 5). At 2400 days ( Cd) (Tb ¼ 0) from 1 January there were 78% and 54.6% emergence in seeds from uncultivated and cultivated conditions, respectively. At the last sample these figures were 80% and 62% for seeds from uncultivated and cultivated conditions, respectively. As was found in controlled experiments, few seeds were found not viable at the end of the experiment (data not shown).
Regarding relative the dry weight (% of nontreated control) there were significant differences (P < 0.05) only in two cases among individuals from cultivated conditions (CC) and uncultivated ones (NC) in response to herbicides. This was the case of El Diez L6 population with pyroxsulam and fenoxaprop applied at the recommended rates in 2011 (Tables 1e3). However, when the double rate was applied in these individuals there were no significant differences between those from cultivated (CC) and uncultivated conditions (NC). Dry Weight (% of nontreated control) was 5.12 and 3.29 with pyroxsulam and 3.29 and 7.98 for fenoxaprop for cultivated and uncultivated conditions, respectively (Table 4). The herbicide with the highest efficacy in terms of reducing Avenafatua biomass was pinoxaden. On the average of all the treatments with pinoxaden biomass reduction was 90.2% compared to the untreated control. In addition, the lowest variability between populations was recorded. In contrast, diclofop methyl showed the worst performance with an average biomass reduction of 69.6% compared to the untreated control and greatest variability between populations. Other herbicides with high variability in the response were fenoxaprop and pyroxsulam. 3.2. Germination under controlled conditions When the seed coats were removed and seeds were postmatured, there were significant differences in germination percentage between seeds from cultivated and uncultivated conditions on 9 from 12 populations when were incubated at 20 C (Fig. 1). On the average of all populations these figures were 56% and 74% for seeds from cultivated and uncultivated conditions, respectively. However, incubated at 12 C there was no differences between populations (Fig. 2). Regarding the emergence rate, base temperature ranged between -4 C to 6.03 C. When germination tests were performed without cover extraction, no differences were observed between the different backgrounds (data not shown). Regarding all the populations, there were 74% and 26% germinated and not germinated seeds, respectively. In addition 3.3% of not germinated seeds were not viable seeds. 3.3. Germination dynamic on the field In both years (2011 and 2012), seeds from uncultivated conditions (UC) germinated and emerged earlier than those from cultivated conditions (CC) regardless the experimental site. In 2011 almost 70% of the seeds form uncultivated conditions emerged at the beginning of winter while only a little bit more than 20% seeds from the cultivated conditions (Fig. 3, Table 5). In 2012, there were also differences in germination percentages comparing both conditions. The germination percentage at the beginning of winter was higher on seeds buried in Balcarce (51%) than those buried in FAUBA (35%) (Fig. 4, Table 5).
3.5. Phyllochron On both populations evaluated, the phyllochron ( C day/leaf) was higher in plants from cultivated than uncultivated conditions (Fig. 6). 4. Discussion In this study none of the populations of Avena fatua L. from wheat crops showed different response compared with individuals that had not been treated with herbicides, proving that these populations should not be considered resistant to these herbicides (Tables 1e3). Thus, other demographic processes explain persistence of Avenafatua in the fields crops studied at Southern Buenos Aires. In 2010 a Avenafatua population resistant to ACCase inhibiting herbicides was identified in Coronel Dorrego (South west of Buenos Aires) (Vigna et al., 2011; Heap, 2016). Moreover, this population showed cross resistance to clodinafop propargyl, diclofop-methyl, and fenoxaprop-P-ethyl. However, this was not the case with the populations studied in this work. Although the results showed similar response between ALS and ACCase inhibitors, the highest efficacy of pinoxaden was also registered on field experiments by Scursoni et al. (2011). On field, application is usually carried out on a higher growth stage than three expanded leaves and ALS inhibitors are more dependent on weed growth stage than pinoxaden (Scursoni et al., 2011). In agreement with our results studies carried out in Australia by Owen and Powles (2009) also recorded the best control with pinoxaden and the worst with diclofop methyl. As described above, the presence of individuals of Avenafatua at preharvest of wheat crops is explained by another demographic process different to herbicides resistance. In this study, seeds maturated in uncultivated conditions showed a lower level of dormancy than those from field crops. This difference was evidenced in this study in which there were differences in thermal time for different germination levels (Figs. 1e4). Interestingly, differences in dormancy in controlled conditions were only shown when seeds were without seed coats and incubated at 20 C. Mechanisms enforcing Avenafatua seed dormancy have been shown to include floret structures, seed coat and immature embryo (Sawhney and Naylor, 1982). The seed coats or maternal structures
Table 4 Responses of two two wild oat populationsa from different origins (cultivated and no cultivated environment) to herbicides at double of recommended rate (2011). Plants were treated at 3e4 leaf stage (Z 13/14). P-value indicate significance of ANOVA (<0.05). Population
El Diez L6 El Diez L6 a
Herbicide
Fenoxaprop Pyroxsulam
Application date
2-9-2011 2-9-2011
Populations with significant differences at recommended rate in 2011 (Table 2).
Dry Weight (% of nontreated control) Cultivated
Uncultivated
3.29 5.12
7.98 3.29
P value
0.1572 0.1673
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Fig. 1. Cumulative germination of 12 wild oat populations registered at twenty days incubated at 20 C constant in darkness from two different conditions, uncultivated (striped bars) and cultivated (black bars). Different letters indicate significant differences between conditions within each population, according to Tuckey HSD test (a ¼ 0.05). Bars indicate the standard error of mean.
Fig. 2. Cumulative germination of 12 wild oat populations registered at twenty days incubated at 12 C constant in darkness from two different conditions, uncultivated (striped bars) and cultivated (black bars). Different letters indicate significant differences between conditions within each population, according to Tuckey HSD test (a ¼ 0.05). Bars indicate the standard error of mean.
can interfere with water uptake or gas exchange and act as mechanical barriers that regulate the movement of inhibitor chemicals to and from the embryo (Lehnhoff et al., 2013). However, the results reported here showed that even without seed coats levels of dormancy are still different between populations, suggesting embryo dormancy may plays a significant role in the germination
dynamics of this weed. Regarding the base temperature there were no differences between conditions. As average the value 1 C as base temperature is in agreement with data published by Cousens et al. (1992) and used by Blanco et al. (2014) for predicting Avena fatua L. field emergence. Scursoni et al. (1999) found higher emergence rate of Avenafatua
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Fig. 3. Cumul ative emergence (%) on field experiment in two wild oat transplanted populations during 2011. Solid lines (cultivated conditions); dashed lines (uncultivated conditions). Circle (Km17 population); triangle (Azul population). Arrows indicate the beginning of autumn, winter and spring respectively. Fitted lines represent predicted values from non-linear regression analysis (Weibull growth model) and bars the standard error of mean.
Fig. 4. Cumulative emergence (%) on field experiment in two transplanted wild oat populations during 2012. Experiments were carried out in two locations, Balcarce and FAUBA (Buenos Aires). Solid lines (cultivated conditions); dashed lines (uncultivated conditions). Circle (SanJoaquín-Balcarce); diamond (San Joaquín-FAUBA); triangle (Stella Maris-Balcarce); square (Stella Maris-FAUBA). Arrows indicate the beginning of autumn, winter and spring respectively. Fitted lines represent predicted values from non-linear regression analysis (Weibull growth model) and bars the standard error of mean.
Table 5 Parameters from non-linear regression analysis (Weibull growth model) from field emergence experiments in 2011 and 2012. Population Km17
Condition
cultivated uncultivated Azul cultivated uncultivated Stella Maris FAUBA cultivated uncultivated Stella Maris Balcarce cultivated uncultivated San Joaquin FAUBA cultivated uncultivated San Joaquin Balcarce cultivated uncultivated
YM
Y0
K
g
P-value
65.8 95.4 61.9 105.1 47.4 129.2 52.5 93.7 42.7 92.8 78.5 83
0.26 0.98 0.02 0.7 1.37 4.63 0.51 2.82 0 0.35 1.48 0.14
0.00028 0.00043 0.00031 0.00028 0.00028 0.00021 0.00031 0.00042 0.00031 0.00035 0.00027 0.00048
5.48 2.81 5.819 2.49 8.678 1.44 2.3 2.177 10.01 4.14 2.43 13.05
<0.0001 0.0003 <0.0001 <0.0001 <0.0001 <0.0001
after crop harvest in plots treated with herbicides than those untreated, suggesting lower dormancy of seeds from individuals' survival to the herbicide. These results could mean a direct effect of the herbicides on seed physiology (Peters et al., 1975) or a relation between herbicide tolerance and dormancy. Similarly, O'Donovan et al. (1999) registered higher germinability of seeds from individuals tolerant to difenzoquat than those susceptible to it. Thus, it is possible that herbicides make a selection of plants with lower seed dormancy (Scursoni et al., 1999). However, our results here suggest that those individuals that escape the herbicide treatment have this behavior because of the higher dormancy and consequently emergence after the herbicide application. Coincidentally with the results presented (Hilgenfeld et al., 2004), and (Scursoni et al., 2007) proved that the emergence dynamics of Chenopodium album, Ipomoea sppand Amaranthussp. was what explained the presence of individuals at preharvest of the soybean crops escaping herbicides application. Owen et al. (2015) also found that populations from non-
Fig. 5. Field Cumulative emergence (%) of two wild oat populations during 2013. Solid lines (seeds from cultivated conditions maturing at uncultivated conditions); dashed lines (seeds from uncultivated conditions maturing at uncultivated conditions). Arrows indicate the beginning of autumn, winter and spring respectively. Bars represent standard error of mean.
cropped fields or with low cropping intensity showed higher and faster germination than populations from fields with a medium- or high-intensity cropping regime. However, resistance to selective herbicides was higher in the medium- and high-intensity cropping
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37
Fig. 6. Phyllocron (Thermal time for leaf appearance) in plants of two populations (A) Necochea and (B) Azul for both conditions, cultivated (,) and uncultivated () conditions.
fields than in the low-intensity cropping fields. That was because late-emerging seedlings avoid preplanting weed control practices (tillage and non-selective herbicide application) but are exposed to selective in-crop herbicides. However, this is not the case in our field crop conditions. The environment on uncultivated conditions is characterized by more diverse species and lower availability of sites for the establishment of new individuals. Thus, the low level of seed dormancy in these environments may response to an ecological strategy that successfully ensures the establishment detecting light conditions (R/FR) that are better to establish (Sanchez et al., 1993). On the other hand, cultivated environment is characterized by disturbances caused by management practices that are often repeated year after year, especially where there is no crop rotation. The fallow period, the crop chosen and date of sowing, timing and type of tillage and control with herbicides are usually repeated at the same time or similar over time. Thus, higher dormancy can be interpreted as a convenient adjustment strategy in emergence dynamic for a weed successfully established in crop conditions. That is to say that these cases could be interpreted as escape to herbicide mediated by functional phenological attributes. Interestingly, when seeds from cultivated areas were established and grew up in uncultivated areas, differences in level of dormancy was still evident (Fig. 5). The environment in which the mother plant grows (maternal environment) during seed development influence seed viability, seed dormancy, and survival in the
seedbank (Kegode and Pearce, 1998; Baskin and Baskin, 2006; Luzuriaga et al., 2006; Williams et al., 2012). The results reported here demonstrate that maternal effect was less relevant than the inherent genetic basis of different populations. Thus, the effect of seed maturation environment on dormancy was dependent on the genotype. This was also demonstrated in wild oat by Sawhney and Naylor (1979), Adkins et al. (1986) and also in Chenopodium quinoa (Ceccato et al., 2011). Phyllochron data showed higher thermal time by leaf in plants form cultivated conditions. This means flowering and consequently seeds maturation is delayed and possibly converge with the crop. The knowledge of the phenology of weeds bring possibility to design weed management strategies such as in this case to avoid the seed return to the soil. Practices with this purpose have been developed and are applied in crop production conditions of Australia (Walsh et al., 2013). Moreover, the harvest advance is an adequate strategy to reduce the fall of seeds in the soil (Scursoni et al., 1999). In summary, from the results obtained in these experiments it was shown that dormancy levels and therefore germination and establishment dynamic on the field was hierarchically more important than the response to herbicides to favor the persistence of Avenafatua in wheat production systems. This can be interpreted as an ecological functional survival mechanism possibly heritable without selection by herbicides in cultivated areas. As emergence studies continue and emergence prediction tools improve,
38
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application dates can be determined for the most effective results. In addition, knowing the demographic processes regulating the population growth it can be design proactive management to avoid the increase of weed resistant populations. Thus, it is still possible to apply proactive agronomic strategies with the aim of avoiding the growth of Avenafatua populations resistance to herbicides. Acknowledgement Experiments were supported by the University Of Buenos Aires UBACyT G (2011e2014) (00440) and Ministerio de Ciencia y Tecnología, PICT: 2012-0936. The authors would like to thank particularly Ing.Agr. Juan Quistre and E. Iorio for their collaboration in experimental activities. References Adkins, S.W., Loewen, M., Symons, S.J., 1986. Variation within pure lines of wild oats (Avena fatua L.) in relation to degree of primary dormancy. Weed Sci. 34, 859e864. Arnold, J.C.D., Shaw, R., Scharer, S.M., 1997. Influence of application timing on efficacy of glyphosate in Roundup Ready soybean. Proc. South. Weed Sci. Soc. 50, 176e177. Baskin, C.C., Baskin, J.M., 2006. The natural history of soil seed banks of arable land. Weed Sci. 54, 549e557. Bertero, H.D., 2001. Effects of photoperiod, temperature and radiation on the rate of leaf appearance in Quinoa (Chenopodium quinoa Willd.) under field conditions. Ann. Bot. 87, 495e502. pez, R., Blanco, A.M., Chantre, G.R., Lodovichi, M.V., Bandoni, J.A., Sabbatini, M.R., Lo n, R., 2014. Modeling seed dormancy release & germination for Vigna, M., Gigo predicting Avena fatua L. field emergence: a genetic algorithm approach. Ecol. Model. 272, 293e300. Bradford, K., 1995. Water relations in seed germination. In: Kigel, J., Galili, G. (Eds.), Seed Development and Germination. Marcel Dekker Inc., pp. 351e396 Burgos, N.R., Tranel, P.J., Streibig, J.C., Davis, V.M., Shaner, D., Norsworthy, J.K., Ritz, C., 2013. Review: confirmation of resistance to herbicides and evaluation of resistance levels. Weed Sci. 61, 4e20. Catullo, J., Valleti, O., Rodríguez, M., Sosa, C., 1983. Relevamiento de malezas en cultivos comerciales de trigo y girasol en el centro sur bonaerense. In: Actas de n Argentina sobre la Maleza y su control, pp. 204e235. Santa Fe IX Reunio agosto de 1982. Ceccato, D.V., Bertero, D.H., Batlla, D., 2011. Environmental control of dormancy in quinoa (Chenopodium quinoa) seeds: two potential genetic resources for preharvest sprouting tolerance. Seed Sci. Res. 21, 133e141. Cousens, R., Weaver, S.E., Porter, J.R., Rooney, J.M., Butler, D.R., Johnson, M.P., 1992. Growth & development of Avenafatua (wild-oat) in the field. Ann. Appl. Biol. 120, 339e351. Di Rienzo, J.A., Casanoves, F., Balzarini, M.G., Gonzalez, L., Tablada, M., Robledo, C.W., n 2008, Grupo InfoStat. FCA, Universidad Nacional de 2008. InfoStat, Versio rdoba, Argentina. Co Evans, R.M., Thill, D.C., Tapia, L., Shafill, B., Lish, J.M., 1991. Wild oat (Avenafatua) &spring barley (Hordeum vulgare) density affect spring barley grain yield. Weed Technol. 5, 33e39. Fernandez Quintanilla, C., Navarrete, L., Torner, C., 1984. The influence of crop rotation on the population dynamics of Avenasterilis spp. ludiviciana in Central Spain. In: Proceedings of 3rd EWRS Symposium on Weed Problems in Mediterranean Area, 16/09/1984, Lisboa, Portugal. Frank, A.B., Bauer, A., 1995. Phyllochron differences in wheat, barley, and forage grasses. Crop Sci. 35, 19e23. Grabe, D.F., 1970. Tetrazolium Testing Handbook for Agricultural Seed [S.l.]. Association of Official Seed Analysts, p. 62. Harker, K.N., O'Donovan, J.T., Turkington, K., Blackshaw, R.E., Lupwayi, N.Z., Smith, E.G., Johnson, E.N., Pageau, D., Shirtliffe, S.J., Gulden, R.H., Rowsell, J., Hall, L.M., Willenborg, C.J., 2016. Diverse rotations and optimal cultural practices control wild oat (Avena fatua L.). Weed Sci. 64, 170e180. Heap, I., (2016). http://weedscience.com/Summary/Species.aspx?WeedID¼28. Accessed 1August 10, 2016. Hilgenfeld, K.L., Martin, A.R., Mortensen, D., Mason, S., 2004. Weed management in glyphosate resistant soybean: weed emergence patterns in relation to glyphosate treatment timing. Weed Technol. 18, 277e283. Holm, L.G., Plucknett, D.L., Pancho, J.V., Herberger, J.P., 1977. Avena fatua L. and other members of the “wild oat” group. In: World's Worst Weeds: Distribution and Biology. University of Hawaii Press, Honolulu, 105 e 113. Kegode, G.O., Pearce, R.B., 1998. Influence of environment during maternal plant
growth on dormancy of shattercane (Sorghum bicolor) and giant foxtail (setariafaberi) seed. Weed Sci. 46, 322e329. Lehnhoff, E.A., Miller, Z.J., Brelsford, M.J., White, S., Maxwell, B.D., 2013. Relative canopy height influences wild oat (Avenafatua) seed viability, dormancy, and germination. Weed Sci. 2013 (61), 564e569. Li, R., Wang, S., Duan, L., Li, Z., Christoffers, M.J., Mengistu, L.W., 2007. Genetic diversity of wild oat (Avenafatua) populations from China and the United States. Weed Sci. 55, 95e101. Luzuriaga, A.L., Escudero, A., Perez-Garcia, F., 2006. Environmental maternal effects on seed morphology and germination in Sinapsisarvensis (Cruciferae). Weed Res. 46, 163e174. Owen, M.J., Goggin D.E, Powles S.B., 2015. Intensive cropping systems select for greater seed dormancy and increased herbicide resistance levels in Lolium (annual ryegrass). 71, 966e971 rigidum. Owen, M.J., Powles, S.B., 2009. Distribution and frequency of herbicide-resistant wild oat (Avena spp.) across the Western Australian grain belt. Crop Pasture Sci. 60, 25e31. O'Donovan, J.T., Newman, J.C., Blackshaw, R.E., Harker, K.N., Derksen, D.A., Thomas, A., 1999. Growth, competitiveness, & seed germination of triallate/ difenzoquat -susceptible & resistant wild oat populations. Can. J. Plant Sci. 79, 303e312. Payne, S.A., Oliver, L.R., 2000. Weed control programs in drilled glyphosate-resistant soybean. Weed Technol. 14, 413e422. Peters, N.C.B., Chancellor, R.J., Drennan, D.S.H., 1975. Dormancy of seeds from wild oat plants sprayed with sub-lethal levels of herbicides and giberellic acid. In: Synposium on the Status and Control of Grass Weeds in Europe. Proc. Eur. Weed Res. Soc. Symp., Paris, vol. 1. EWRS.Wageningen, Netherlands, pp. 87e94. Ritchie, J.T., NeSmith, D.S., 1991. Temperature and crop development. In: Hanks, J., Ritchie, J.T. (Eds.), Modeling Plant and Soil Systems. Agronomy Monograph, vol. 31. ASA, CSSA and SSSA, Madison. , C.L., Scopel, A.L., 1993. Plant responses to canopy Sanchez, R.A., Casal, J.J., Ballare density mediated by photomorphogenic processes. Int. Crop Sci. 779e786 chapter 103. Satorre, E.H., Snaydon, R.W., 1992. A comparison of root and shoot competition between spring cereals and Avena fatua L. Weed Res. 32, 45e55. Sawhney, R., Naylor, J.M., 1979. Dormancy studies in seeds of Avenafatua. Demonstration of genetic variability affecting the response to temperature during seed development. Can. J. Bot. 57, 59e63. Sawhney, R., Naylor, J.M., 1982. Dormancy studies in seed of Avena fatua L. Influence of drought stress during seed development on duration of seed dormancy. Can. J. Bot. 60, 1016e1020. Scursoni, J.A., Benech-Arnold, R., 1998. Rendimiento de cultivos de trigo y cebada y n nitrocrecimiento de Avena fatua en distintas condiciones de fertilizacio genada. In: IV Congreso Nacional de Trigo y II Simposio Nacional de Cereales de ~ o-Invernal, pp. 3e48. Mar del Plata. Siembra Oton Scursoni, J., Benech-Arnold, R., Hirchoren, H., 1999. Demography of wild oat in barley crops: effect of crop, sowing rate, and herbicide treatment. Agron. J. 91, 478e485. Scursoni, J.A., Forcella, F., Gunsolus, J., 2007. Weed escapes and delayed weed emergence in glyphosate-resistant soybean. Crop Prot. 26, 212e218. n, R., Martín, A.N., Vigna, M., Leguizamo n, E.S., Istilart, C., Scursoni, J.A., Gigo pez, R., 2014. Changes in weed communities of spring wheat crops of Buenos Lo Aires Province of Argentina. Weed Sci. 62, 51e62. Scursoni, J.A., Martín, A., Catanzaro, M.P., Quiroga, J., Goldar, F., 2011. Evaluation of post-emergence herbicides for the control of wild oat (Avena fatua L.) in wheat and barley in Argentina. Crop Prot. 30, 18e23. Scursoni, J.A., Satorre, E.H., 2005. Barley (Hordeum vulgare) and wild oat (Avenafatua)competition is affected by crop and weed density. Weed Technol. 19, 790e795. Simpson, G.M., 1990. Seed Dormancy in Grasses. Cambridge University Press, Cambridge, United Kingdom, p. 297. Thill, D.C., O'Donovan, J.V., Mallory-Smith, C.A., 1994. Integrated weed management strategies for delaying herbicide resistance. Phytoprotection 75 (Suppl. l.), 61e70. Vigna, M., Lopez, R., Gigon, R., 2011. Resistencia de Loliummultiflorum a diclofopmetil en el SO de Buenos Aires, Argentina. In: XX Congreso de la ALAM. 5 al 9 de diciembre de 2011. Vina del Mar, Chile. Walsh, M., Newman, P., Powles, S., 2013. Targeting weed seeds in-crop: a new weed control paradigm for global agriculture. Weed Technol. 27, 431e436. Williams, M.M., Schutte, B.J., So, Y.F., 2012. Maternal corn environment influences wild-proso millet (Panicummiliaceum) seed characteristics. Weed Sci. 60, 69e74. Willenborg, C.J., May, W.E., Gulden, R.H., Lafond, G.P., Shirtliffe, S.J., 2005. Influence of wild oat (Avenafatua) relative time of emergence and density on cultivated oat yield, wildoat seed production, and wildoat contamination. Weed Sci. 53, 342e352. Wilson, B.J., Cousens, R., Wright, K.J., 1990. The response of spring barley and winter wheat to Avenafatua population density. Ann. App. Biol. 116, 601e609. Zadoks, J.C., Chang, T.T., Konzak, C.F., 1974. A decimal code for the growth stages of cereals. Weed Res. 14, 415e421.
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Avena fatua L. escapes and delayed emergence in wheat (Triticum aestivum L.) crops of Argentina s N. Martín, Julio A. Scursoni* Andre tedra de Produccio n Vegetal, Departamento de Produccio n Vegetal, Facultad de Agronomía, U.B.A., Av. San Martín 4453, C.A.B.A., Argentina Ca
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 October 2016 Received in revised form 13 August 2017 Accepted 26 August 2017
Avenafatua (L.) is one of the most important weed grasses in wheat crops on the most important wheat (Triticum aestivum L.) production area of Argentina. It is present in 60% of the fields of an area of 750,000 ha not only reducing crop yields but also contaminating the wheat and barley (Hordeum vulgare L.) grain. The most frequent practice for its control is the application of ACCase inhibitors or ALS inhibitors herbicides. However, the presence of wild oat is frequent in wheat crops at harvest even in those fields where herbicides were applied and thus, regarded as resistant individuals. Thus, the objective of this study was to identify the processes that explain the persistence of wild oat individuals during the crop cycle. Seeds from cultivated and from uncultivated areas were harvested and then the response to ACCase inhibitors and ALS inhibitors herbicides was studied over 20 selected populations from different areas of both conditions (cultivated and uncultivated). Emergence dynamic from seeds of both conditions was also studied and in addition, the effect of mature environment on seeds germination was also assessed. The results indicate that none of the populations were resistant to herbicides studied. However, emergence dynamic was different depending on the seeds coming from agricultural fields or not cropping condition. Seeds from cultivated areas had higher dormancy and emerged later in the field than those from no cropped areas. The ripening environment did not modify the emergence pattern suggesting differences in emergence dynamic are based on genetic nature. These results show dormancy levels and therefore germination and establishment dynamic on the field was hierarchically more important than response to herbicides to favor the persistence of this weed in wheat production systems. Thus, it is still possible to apply proactive agronomic strategies with the aim of avoiding the growth of wild oat populations resistance to herbicides. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Avenafatua Weeds escapes Emergence dynamic Resistance
1. Introduction Avenafatua (L.) is a troublesome annual grass weed regarded to be one of the most wide-spread and harmful weeds of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rice (Oryza sativa L.) and flax (Linumusitatissimum L.). It is considered one of the ten most important weed species in the world because of its wide distribution and competitive effect on crop yield worldwide (Holm et al., 1977; Simpson, 1990). In addition, Avenafatua seeds are frequently found in wheat or barley grain at harvest, thus, representing significant commercial discounts. In the United States, it is present in approximately 11,000,000 ha, generating losses over a trillion dollars (Evans et al., 1991). In Western Australia, 24% of
* Corresponding author. E-mail address: [email protected] (J.A. Scursoni). http://dx.doi.org/10.1016/j.cropro.2017.08.020 0261-2194/© 2017 Elsevier Ltd. All rights reserved.
samples of wheat, barley and lupine (Lupinusalbus L.) seeds contained Avenafatua seeds (Michael et al., 2010). In western Canada, more money is spent on Avenafatua herbicides than on any other weed species. In addition, Avenafatua resistance to herbicides is the most widespread issue (Harker et al., 2016). In Spain, more than 27% of the area planted with winter cereals were considered severely affected by Avenafatua (Fernandez Quintanilla et al., 1984). It is also the main weed in winter cereals in the UK (Wilson et al., 1990) and in China, it is one of the most important weeds in wheat crops, considering its presence in about 5 million ha. grown, resulting in a loss of 1.75 million tons per year (Li et al., 2007). In Argentina, Avenafatua and Loliummultiflorum (Lam.) are the most important grass weeds in wheat and barley crops. Scursoni et al. (2014) reported presence of Avenafatua in 60% of the wheat crops in the main wheat production area, representing an increase of 24% compared to surveys conducted 30 years ago by Catullo et al. (1983). In this area, Scursoni and Benech-Arnold (1998) estimated
A.N. Martín, J.A. Scursoni / Crop Protection 103 (2018) 30e38
losses of 25% in barley and wheat with Avenafatua densities of 60 plants m2. Scursoni and Satorre (2005) reported similar losses in barley with Avenafatua at 70 plants m2. More recently, Scursoni et al. (2011) found 20% wheat yield reduction with Avenafatua densities of 100 plants m2. Interestingly, Scursoni et al. (1999) found significant differences on Avenafatua fecundity between barley crop densities. Crop density, time of wild oat emergence, fertilization, crop species are agronomic factors that influence on crop yield reduction by Avena fatua and the amount of seeds produced and returned to the soil (Satorre and Snaydon, 1992; Scursoni and Benech-Arnold, 1998; Scursoni and Satorre, 2005; Willenborg et al., 2005). Manipulating these factors to favor the crop against the weed and integrating them with reduced herbicide use and cultural control measures has the potential to simultaneously reduce Avenafatua competition and weed seed production (Thill et al., 1994). Nevertheless, Avenafatua control in Argentina is strongly based on herbicide application. The first herbicides applied were the ACCase inhibitors such as diclofop methyl, clodinafoppropargyl, fenoxaprop p ethyl and in the last ten years pinoxaden. Currently, although pinoxaden is the most applied, ALS inhibitors such as iodosulfuron plus mesosulfuron and pyroxsulam are also recommended to control Avenafatua in wheat crops. In spite of the successful results achieved by herbicide application, it must be considered the selection pressure for resistant biotypes due to continue use of herbicides with the same mode of action (Burgos et al., 2013). Avenafatua resistance to ACCase inhibitors clodinafop-propargyl, diclofop-methyl, and fenoxaprop-P-ethyl was reported in 2010 in Argentina. In addition, 35 biotypes are registered in the entire world. Regarding ALS inhibitors, there are 19 biotypes resistant to ALS inhibitors herbicides in the world (Heap, 2016). Avenafatua individuals are frequently present on wheat crops at harvest and are considered resistant individuals. However, escapes to herbicide application can be explained by demographic processes such as delay weed emergence and establishment (Scursoni et al., 2007). In this sense, Payne and Oliver (2000) recorded control lower than 85% for Echinochloacruss-galli [L.] Beauv. with two applications of glyphosate during the crop cycle as a consequence of late-emerging cohorts. In addition, later application of glyphosate gave better control of Digitariasanguinalis (L.) at the end of the season due to control of individuals emerging after earlier applications (Arnold et al., 1997). To identify what processes regulate the escape of weeds during crop cycle is relevant to design suitable weed management strategy avoiding confusion between resistance and demographic escape. Thus, the hypothesis is that resistance to herbicides is the most relevant processes that explain escapes of wild oat in wheat crops. The objectives of these experiments were to study: (i) the response to different herbicides of 20 populations of Avenafatua present at preharvest of wheat crops, (ii) to study the germination dynamic of Avenafatua seeds harvested from individuals present in pre-harvest of wheat crops and, in contrast, from individuals present in uncultivated sites, (iii) to identify the nature of possible differences associated with the emergence dynamic of different source of seeds and (iv) to study morphological development (phyllochron) on individuals from both origin of plants (uncultivated and cultivated sites). 2. Materials and methods 2.1. Seed harvest During 2008, 2009 and 2011 field surveys were conducted at preharvest of wheat crops in different sites of southeast of Buenos Aires Province representing almost 400,000 ha of wheat crops between 36 ,770 S e 38 ,550 S and 61,280 W- 57,830 W. This region
31
is characterized by an average of 25% of grazing and the rest of the area is winter (wheat, barley) and spring-summer (soybean, sunflower, maize) crops. Rainfall ranges between 650 mm/year in the west to 740 mm/year in the east of the region. It is the zone of Argentina with greater surface planted with wheat and barley. Avenafatua seeds were harvested by hand from individuals present in different fields. Seeds were collected from 20 fields located in a radius of 180 miles and at each field 40 individual plants were randomly selected and harvested. In addition, seeds from individuals on uncultivated areas were also harvested and regarded as susceptible biotypes. The non-cultivated areas were abandoned areas, without cultivation or in some cases close to routes without presence of near cultivation. The seeds were classified according to geographical location and by their origin (cultivated or uncultivated conditions) and were kept dry at room temperature. 2.2. Response to herbicides in the field From 2009 to 2012, 57 experiments were carried out with the aim of studying the efficacy on Avenafatua control of different herbicides applied in each field during the last growing seasons on 18 wild oat populations (Tables 1e3). The experiments were performed considering in each individual population seeds from cultivated and non-cultivated areas. In each experiment different herbicides frequently applied were tested once. The experiments were carried out in split-plot design with the origin of the population as the main factor and the rate of the herbicides the second factor. All the experiments were conducted in the experimental field of the Faculty of Agronomy (UBA) 34 350 3700 S, 58 290 2.500 W. Avenafatua seedlings were obtained from seeds germinated in chambers at constant 12 C and when the plumule reached 2 cm long these seedlings were planted in pots 14 cm diameter and 2.1 L volume. After that, pots were placed for ten days in greenhouse and then were placed outdoors. Each pot was filled with a mixture of fertile soil, peat and sand and was fertilized with 0.1539 g and 0.1847 g, diammonium phosphate and urea, equivalent to 100 kg ha1diammonium phosphate and 120 kg urea ha1, respectively. The plants were watered throughout its entire life cycle and the herbicides were applied when the plants were at 13 Z stage (Zadoks et al., 1974). All treatments were applied with a CO2 pressurized backpack sprayer consisting of a handheld boom that contained four 110015 flat-fan nozzles and calibrated to deliver 140 L/ha at 276 kPa. The experimental design was in split plot regarding the origin of the seeds as the main factor and the rates as the subfactor. The rates tested of each herbicide were 0.5 , 1 and 2 regarding (x) the recommended rate. In addition a control dose (0 without application of herbicides) was included. Each rate was replicated five times. Herbicide response was evaluated assessing relative individual dry weight 30 days after herbicide application. 2.3. Germination under controlled conditions With the aim of studying the germination rate at different temperatures, 20 seeds from 12 populations and each condition (cultivated and uncultivated) were incubated at constant 12 C and 20 C dark, in petri dishes in a medium of distillated water. Completely randomized design was applied with three replicates were used for each treatment (population x condition) and germination (radical emergence) was recorded 20 days after incubation. In addition, two populations were recorded daily to calculate the germination rate for different fractions of the population and thus, to estimate the base temperature (Bradford, 1995). These experiments were carried out with post maturated and no post maturated seeds. The covers were removed and placed at constant 25 C dry for 10 days. All the seeds that did not germinate
32
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Table 1 Responses of wild oat populations from different origins (cultivated and no cultivated environment) to different herbicides at recommended rate (2009e2010). Plants were treated at 3e4 leaf stage (Z 13e14). P-value indicate significance of ANOVA (<0.05).a Population
Herbicide
Treatment day
Dry Weight (% of nontreated control) Cultivated
No Cult.
El Porvenir Medano Seco Medano Seco Azul Azul Azul Azul El Diez L4 El Diez L4 El Diez L4 El Diez L4 El Diez L6 El Diez L6 El Diez L6 El Diez L6 El Porvenir La Gauchita
Fenoxaprop Fenoxaprop Fenoxaprop Diclofop-metil Imazamox Iodosulfuron þ Metsulfuron Pinoxaden Diclofop-metil Imazamox Iodosulfuron þ Metsulfuron Pinoxaden Diclofop-metil Imazamox Iodosulfuron þ Metsulfuron Pinoxaden Diclofop-metil Diclofop-metil
26/11/09 26/11/09 26/10/10 01/07/10 28/11/10 28/11/10 28/11/10 01/07/10 28/11/10 28/11/10 28/11/10 01/07/10 28/11/10 28/11/10 28/11/10 30/09/10 17/08/10
62.16 66.32 34.71 50.84 42.21 11.06 12.32 87.63 18.77 25.03 9.75 77.2 6.07 8.53 5.78 29.97 93.07
52.4 52.4 48.48 75.39 14.37 5.89 6.8 73.04 24.75 19.75 12.12 73.04 24.75 19.75 12.12 52.1 84.26
a
P-value
0.5117 0.1946 0.193 0.0676 0.4681 0.3172 0.4845 0.6214 0.1613 0.0614 0.2394 0.6214 0.1613 0.0614 0.2394 0.192 0.1027
All the population x herbicide combinations are non-significant (P > 0.05).
Table 2 Responses of wild oat populations from different origins (cultivated and no cultivated environment) to different herbicides at recommended rate (2011e2012). Plants were treated at 3e4 leaf stage (Z 13e14). P-value indicate significance of ANOVA (<0.05). Population
Adelante MS CosMalal Don Luis El Diez L6 El Diez L6 El Diez L6 Enfrente Huincahue La Legua Medano Seco Pailche Izquierdo Pailche Izquierdo Pailche Izquierdo Saco Saco Saco Tupungato Tupungato a
Herbicide
Iodosulfuron Iodosulfuron Pinoxaden Iodosulfuron Fenoxaprop pyroxsulam Pinoxaden Fenoxaprop Fenoxaprop Pinoxaden Imazamox pyroxsulam Fenoxaprop Iodosulfuron Iodosulfuron pyroxsulam Iodosulfuron Pinoxaden
Application date
þ metsulfuron-metil þ metsulfuron-metil þ metsulfuron-metil
þ metsulfuron-metil þ metsulfuron-metil þ metsulfuron-metil
10/06/11 10/06/11 10/06/11 02/09/11 02/09/11 02/09/11 10/06/11 10/06/11 10/06/11 10/06/11 10/06/11 10/06/11 10/06/11 22/08/11 22/08/11 22/08/11 10/06/11 10/06/11
Dry Weight (% of nontreated control) Cultivated
No Cult.
22.47 34.5 4.74 7.66 0 6.46 1.79 1.09 4.15 5.29 10.5 19.39 10.99 15.4 13.13 10.7 29.79 6.41
16.22 16.22 19.31 6.47 9.45 0.87 19.31 10.91 10.91 19.31 12.93 20.64 15.85 16.22 13.28 11.25 16.22 19.31
P value
0.1394 0.1394 0.3354 0.7138 0.0452a 0.0226a 0.3354 0.5943 0.5943 0.3354 0.829 0.7799 0.4021 0.7986 0.966 0.86 0.1394 0.3354
Populations with significant differences between cultivated and uncultivated conditions.
were analyzed through a test of Tetrazolium Chloride 0.1% v/for 24 h at 30 C in darkness (Grabe, 1970). Those seeds that became red or pink in the embryo were considered viable. 2.4. Germination dynamic in the field During 2011, 2012 three experiments were carried out with the aim of studying the emergence dynamic in field conditions of five populations of Avenafatua. The experimental design was a Complete Random Design (CRD). Each population was evaluated with seeds from uncultivated and cultivated conditions. Fifty seeds were placed in small bags, 10 20 cm made with air and moisture permeable plastic thread, filled with sand and soil mix. The bags were shallowly buried into pots 14 cm in diameter and 2.1 L volume and then, each pot was buried in the experimental site in early
summer. Since April, and at intervals of 45e60 days, the bags were exhumed and germinated seeds were counted. Each treatment (population x condition) was repeated three times for each sample date. The last exhumation was conducted during spring. Seeds were assessed five times with the exception of the San Joaquin population in 2012, which, due to lack of seeds, only three samples were carried out. During 2011, experiments were carried out on the experimental field of FAUBA (Faculty of Agronomy, U.B.A.). On the other hand, in 2012, experiments were performed simultaneously on the campus of the EEA INTA Balcarce and at the experimental field of FAUBA. During the experiments, daily temperature and rainfall were assessed from meteorological station. In all cases, the viability of those seeds which were not germinated at the end of the experiment was analyzed through a chloride tetrazolium test. Seeds whose embryos were stained red were classified as viable.
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Table 3 Responses of wild oat populations from different origins (cultivated and no cultivated environment) to different herbicides at recommended rate (2012). Plants were treated at 3e4 leaf stage (Z 13e14). P-value indicate significance of ANOVA (<0.05).a Population
Herbicide
Application date
Dry Weight (% of nontreated control) Cultivated
No Cult.
Avenida Grande Avenida Grande Azul Azul CosMalal CosMalal CosMalal Km 17 Km 17 Km 17 La Gauchita La Gauchita La Gauchita Medano Seco Medano Seco Medano Seco San Jose San Jose San Jose Tupungato Tupungato Tupungato
Imazamox pyroxsulam Imazamox pyroxsulam Imazamox Pinoxaden pyroxsulam Imazamox Pinoxaden pyroxsulam Imazamox Iodosulfuron þ Mesosulfuron pyroxsulam Imazamox Iodosulfuron þ Mesosulfuron pyroxsulam Imazamox Pinoxaden pyroxsulam Imazamox Iodosulfuron þ Mesosulfuron pyroxsulam
01/08/12 01/08/12 01/08/12 01/08/12 04/08/12 04/08/12 04/08/12 04/08/12 04/08/12 04/08/12 10/08/12 10/08/12 10/08/12 10/08/12 10/08/12 10/08/12 04/08/12 04/08/12 04/08/12 10/08/12 10/08/12 10/08/12
20.28 52.46 16.93 35.49 15.31 13.12 21.43 31.24 8.05 15.11 24.48 18.14 32.1 19.75 15.31 25.94 20.27 17.13 6.19 31.39 28.58 9.26
21.21 21.55 21.21 21.55 21.2 1.01 21.55 21.2 1.01 21.55 17.54 13.03 17.82 17.54 13.03 17.82 21.2 1.01 21.55 17.54 13.03 17.82
a
P value
0.7584 0.0644 0.7584 0.0644 0.8491 0.8348 0.252 0.8491 0.8348 0.252 0.0619 0.0791 0.15 0.0619 0.0791 0.15 0.8491 0.8348 0.252 0.0619 0.0791 0.15
All the population x herbicide combinations are non-significant (P > 0.05).
2.7. Analysis
2.5. Dynamics of seed germination from different maturation environments The experiment was a RCD conducted in the experimental field of FAUBA during 2012 and 2013. Seeds of Avenafatua individuals from Necochea (South East Buenos Aires) from both conditions (cultivated and uncultivated) were incubated at 12 C in chambers. When the plumule was 2 cm long, these seedlings were planted randomly in an uncultivated area of the Experimental Field of FAUBA with the aim of simulating no cultivated condition. These individuals were harvested at maturity in December and with these seeds a field dynamic emergence experiment, as was described in 2.4, was performed. In January 2013, seeds and buried treatments were: i) Cultivated condition - progeny uncultivated condition (CCUC) and ii) Uncultivated conditions-progeny uncultivated condition (UC-UC). Seeds were sampled three times over year and percentage germination was recorded. In all cases, non-germinated seeds were analyzed through a tetrazolium chloride test.
2.6. Phyllochron
Y ¼ Ymax e (Ymax e Y0). exp (-(k.x)g)
Four experiments were carried out with five plants from two populations located at the greatest distance harvested in 2011 and from both conditions (cultivated and uncultivated fields). Main stem leaf appearance was counted when the leaf tip first became visible (Frank and Bauer, 1995) in five pants for each population. The thermal time interval between appearance of successive leaves (phyllochron, C d/leaf) was estimated from the inverse of slope of a linear regression of main-stem leaf number versus accumulated degree-days (Bertero, 2001). Degree-days (C d) were calculated using Equation (1) (Ritchie and NeSmith, 1991). We consider in this case Tb ¼ 0 C d ¼ (day temperature þ night temperature)/2eTb
For each response to herbicides experiments, analysis of variance was performed for each trial separately regarding relative dry weight as variable response, comparing sources (cultivated vs. uncultivated) for each herbicide and rate on each population. Dry weight values were expressed relative to those registered with the control dose (0). When the F value was significant (P < 0,05), LSD corrected by Fisher was used for the comparison between means. Total germination over 20 days under controlled conditions was analyzed by ANOVA, for each population and temperature regime. The treatments were cultivated and uncultivated conditions. When necessary, percentage values were angular transformed (y ¼ arcsin√x) to increase normality and variance homogeneity. Treatment means were separated using Tukey's honestly significant difference (HSD) (a ¼ 0.05). These were carried out using Infostat® (Di Rienzo et al., 2008). For cumulative seed germination in field values for each treatment were fitted to Weibull growth model using least-squares nonlinear regression. The model used was:
(1)
Where Y is cumulative seed germination over thermal time x, Ymax is the maximum seed germination, Y0 is the lower asymptote, k is the growth rate and g is the slope. Statistical differences between uncultivated and cultivated conditions were found by testing the null hypothesis of one regression model for both conditions. F-test was performed and p-values less than 0.05 conclude that each condition had a different model. These data were analyzed using GraphPad Prism v5.0 (GraphPad Software, San Diego, CA). Regression analyses were carried out for the fitted models of number of leaves versus degree daysusing Infostat® (Di Rienzo et al., 2008). Regression analysis was carried out for the phyllochron to test differences on parameter b (leaf expanded/thermal time).
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3. Results
3.4. Germination dynamics of seeds progeny
3.1. Dose response experiments
The progeny of individuals from uncultivated conditions when they were grown in uncultivated conditions showed more germinability than those from cultivated conditions grown in uncultivated conditions (Fig. 5). At 2400 days ( Cd) (Tb ¼ 0) from 1 January there were 78% and 54.6% emergence in seeds from uncultivated and cultivated conditions, respectively. At the last sample these figures were 80% and 62% for seeds from uncultivated and cultivated conditions, respectively. As was found in controlled experiments, few seeds were found not viable at the end of the experiment (data not shown).
Regarding relative the dry weight (% of nontreated control) there were significant differences (P < 0.05) only in two cases among individuals from cultivated conditions (CC) and uncultivated ones (NC) in response to herbicides. This was the case of El Diez L6 population with pyroxsulam and fenoxaprop applied at the recommended rates in 2011 (Tables 1e3). However, when the double rate was applied in these individuals there were no significant differences between those from cultivated (CC) and uncultivated conditions (NC). Dry Weight (% of nontreated control) was 5.12 and 3.29 with pyroxsulam and 3.29 and 7.98 for fenoxaprop for cultivated and uncultivated conditions, respectively (Table 4). The herbicide with the highest efficacy in terms of reducing Avenafatua biomass was pinoxaden. On the average of all the treatments with pinoxaden biomass reduction was 90.2% compared to the untreated control. In addition, the lowest variability between populations was recorded. In contrast, diclofop methyl showed the worst performance with an average biomass reduction of 69.6% compared to the untreated control and greatest variability between populations. Other herbicides with high variability in the response were fenoxaprop and pyroxsulam. 3.2. Germination under controlled conditions When the seed coats were removed and seeds were postmatured, there were significant differences in germination percentage between seeds from cultivated and uncultivated conditions on 9 from 12 populations when were incubated at 20 C (Fig. 1). On the average of all populations these figures were 56% and 74% for seeds from cultivated and uncultivated conditions, respectively. However, incubated at 12 C there was no differences between populations (Fig. 2). Regarding the emergence rate, base temperature ranged between -4 C to 6.03 C. When germination tests were performed without cover extraction, no differences were observed between the different backgrounds (data not shown). Regarding all the populations, there were 74% and 26% germinated and not germinated seeds, respectively. In addition 3.3% of not germinated seeds were not viable seeds. 3.3. Germination dynamic on the field In both years (2011 and 2012), seeds from uncultivated conditions (UC) germinated and emerged earlier than those from cultivated conditions (CC) regardless the experimental site. In 2011 almost 70% of the seeds form uncultivated conditions emerged at the beginning of winter while only a little bit more than 20% seeds from the cultivated conditions (Fig. 3, Table 5). In 2012, there were also differences in germination percentages comparing both conditions. The germination percentage at the beginning of winter was higher on seeds buried in Balcarce (51%) than those buried in FAUBA (35%) (Fig. 4, Table 5).
3.5. Phyllochron On both populations evaluated, the phyllochron ( C day/leaf) was higher in plants from cultivated than uncultivated conditions (Fig. 6). 4. Discussion In this study none of the populations of Avena fatua L. from wheat crops showed different response compared with individuals that had not been treated with herbicides, proving that these populations should not be considered resistant to these herbicides (Tables 1e3). Thus, other demographic processes explain persistence of Avenafatua in the fields crops studied at Southern Buenos Aires. In 2010 a Avenafatua population resistant to ACCase inhibiting herbicides was identified in Coronel Dorrego (South west of Buenos Aires) (Vigna et al., 2011; Heap, 2016). Moreover, this population showed cross resistance to clodinafop propargyl, diclofop-methyl, and fenoxaprop-P-ethyl. However, this was not the case with the populations studied in this work. Although the results showed similar response between ALS and ACCase inhibitors, the highest efficacy of pinoxaden was also registered on field experiments by Scursoni et al. (2011). On field, application is usually carried out on a higher growth stage than three expanded leaves and ALS inhibitors are more dependent on weed growth stage than pinoxaden (Scursoni et al., 2011). In agreement with our results studies carried out in Australia by Owen and Powles (2009) also recorded the best control with pinoxaden and the worst with diclofop methyl. As described above, the presence of individuals of Avenafatua at preharvest of wheat crops is explained by another demographic process different to herbicides resistance. In this study, seeds maturated in uncultivated conditions showed a lower level of dormancy than those from field crops. This difference was evidenced in this study in which there were differences in thermal time for different germination levels (Figs. 1e4). Interestingly, differences in dormancy in controlled conditions were only shown when seeds were without seed coats and incubated at 20 C. Mechanisms enforcing Avenafatua seed dormancy have been shown to include floret structures, seed coat and immature embryo (Sawhney and Naylor, 1982). The seed coats or maternal structures
Table 4 Responses of two two wild oat populationsa from different origins (cultivated and no cultivated environment) to herbicides at double of recommended rate (2011). Plants were treated at 3e4 leaf stage (Z 13/14). P-value indicate significance of ANOVA (<0.05). Population
El Diez L6 El Diez L6 a
Herbicide
Fenoxaprop Pyroxsulam
Application date
2-9-2011 2-9-2011
Populations with significant differences at recommended rate in 2011 (Table 2).
Dry Weight (% of nontreated control) Cultivated
Uncultivated
3.29 5.12
7.98 3.29
P value
0.1572 0.1673
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Fig. 1. Cumulative germination of 12 wild oat populations registered at twenty days incubated at 20 C constant in darkness from two different conditions, uncultivated (striped bars) and cultivated (black bars). Different letters indicate significant differences between conditions within each population, according to Tuckey HSD test (a ¼ 0.05). Bars indicate the standard error of mean.
Fig. 2. Cumulative germination of 12 wild oat populations registered at twenty days incubated at 12 C constant in darkness from two different conditions, uncultivated (striped bars) and cultivated (black bars). Different letters indicate significant differences between conditions within each population, according to Tuckey HSD test (a ¼ 0.05). Bars indicate the standard error of mean.
can interfere with water uptake or gas exchange and act as mechanical barriers that regulate the movement of inhibitor chemicals to and from the embryo (Lehnhoff et al., 2013). However, the results reported here showed that even without seed coats levels of dormancy are still different between populations, suggesting embryo dormancy may plays a significant role in the germination
dynamics of this weed. Regarding the base temperature there were no differences between conditions. As average the value 1 C as base temperature is in agreement with data published by Cousens et al. (1992) and used by Blanco et al. (2014) for predicting Avena fatua L. field emergence. Scursoni et al. (1999) found higher emergence rate of Avenafatua
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Fig. 3. Cumul ative emergence (%) on field experiment in two wild oat transplanted populations during 2011. Solid lines (cultivated conditions); dashed lines (uncultivated conditions). Circle (Km17 population); triangle (Azul population). Arrows indicate the beginning of autumn, winter and spring respectively. Fitted lines represent predicted values from non-linear regression analysis (Weibull growth model) and bars the standard error of mean.
Fig. 4. Cumulative emergence (%) on field experiment in two transplanted wild oat populations during 2012. Experiments were carried out in two locations, Balcarce and FAUBA (Buenos Aires). Solid lines (cultivated conditions); dashed lines (uncultivated conditions). Circle (SanJoaquín-Balcarce); diamond (San Joaquín-FAUBA); triangle (Stella Maris-Balcarce); square (Stella Maris-FAUBA). Arrows indicate the beginning of autumn, winter and spring respectively. Fitted lines represent predicted values from non-linear regression analysis (Weibull growth model) and bars the standard error of mean.
Table 5 Parameters from non-linear regression analysis (Weibull growth model) from field emergence experiments in 2011 and 2012. Population Km17
Condition
cultivated uncultivated Azul cultivated uncultivated Stella Maris FAUBA cultivated uncultivated Stella Maris Balcarce cultivated uncultivated San Joaquin FAUBA cultivated uncultivated San Joaquin Balcarce cultivated uncultivated
YM
Y0
K
g
P-value
65.8 95.4 61.9 105.1 47.4 129.2 52.5 93.7 42.7 92.8 78.5 83
0.26 0.98 0.02 0.7 1.37 4.63 0.51 2.82 0 0.35 1.48 0.14
0.00028 0.00043 0.00031 0.00028 0.00028 0.00021 0.00031 0.00042 0.00031 0.00035 0.00027 0.00048
5.48 2.81 5.819 2.49 8.678 1.44 2.3 2.177 10.01 4.14 2.43 13.05
<0.0001 0.0003 <0.0001 <0.0001 <0.0001 <0.0001
after crop harvest in plots treated with herbicides than those untreated, suggesting lower dormancy of seeds from individuals' survival to the herbicide. These results could mean a direct effect of the herbicides on seed physiology (Peters et al., 1975) or a relation between herbicide tolerance and dormancy. Similarly, O'Donovan et al. (1999) registered higher germinability of seeds from individuals tolerant to difenzoquat than those susceptible to it. Thus, it is possible that herbicides make a selection of plants with lower seed dormancy (Scursoni et al., 1999). However, our results here suggest that those individuals that escape the herbicide treatment have this behavior because of the higher dormancy and consequently emergence after the herbicide application. Coincidentally with the results presented (Hilgenfeld et al., 2004), and (Scursoni et al., 2007) proved that the emergence dynamics of Chenopodium album, Ipomoea sppand Amaranthussp. was what explained the presence of individuals at preharvest of the soybean crops escaping herbicides application. Owen et al. (2015) also found that populations from non-
Fig. 5. Field Cumulative emergence (%) of two wild oat populations during 2013. Solid lines (seeds from cultivated conditions maturing at uncultivated conditions); dashed lines (seeds from uncultivated conditions maturing at uncultivated conditions). Arrows indicate the beginning of autumn, winter and spring respectively. Bars represent standard error of mean.
cropped fields or with low cropping intensity showed higher and faster germination than populations from fields with a medium- or high-intensity cropping regime. However, resistance to selective herbicides was higher in the medium- and high-intensity cropping
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Fig. 6. Phyllocron (Thermal time for leaf appearance) in plants of two populations (A) Necochea and (B) Azul for both conditions, cultivated (,) and uncultivated () conditions.
fields than in the low-intensity cropping fields. That was because late-emerging seedlings avoid preplanting weed control practices (tillage and non-selective herbicide application) but are exposed to selective in-crop herbicides. However, this is not the case in our field crop conditions. The environment on uncultivated conditions is characterized by more diverse species and lower availability of sites for the establishment of new individuals. Thus, the low level of seed dormancy in these environments may response to an ecological strategy that successfully ensures the establishment detecting light conditions (R/FR) that are better to establish (Sanchez et al., 1993). On the other hand, cultivated environment is characterized by disturbances caused by management practices that are often repeated year after year, especially where there is no crop rotation. The fallow period, the crop chosen and date of sowing, timing and type of tillage and control with herbicides are usually repeated at the same time or similar over time. Thus, higher dormancy can be interpreted as a convenient adjustment strategy in emergence dynamic for a weed successfully established in crop conditions. That is to say that these cases could be interpreted as escape to herbicide mediated by functional phenological attributes. Interestingly, when seeds from cultivated areas were established and grew up in uncultivated areas, differences in level of dormancy was still evident (Fig. 5). The environment in which the mother plant grows (maternal environment) during seed development influence seed viability, seed dormancy, and survival in the
seedbank (Kegode and Pearce, 1998; Baskin and Baskin, 2006; Luzuriaga et al., 2006; Williams et al., 2012). The results reported here demonstrate that maternal effect was less relevant than the inherent genetic basis of different populations. Thus, the effect of seed maturation environment on dormancy was dependent on the genotype. This was also demonstrated in wild oat by Sawhney and Naylor (1979), Adkins et al. (1986) and also in Chenopodium quinoa (Ceccato et al., 2011). Phyllochron data showed higher thermal time by leaf in plants form cultivated conditions. This means flowering and consequently seeds maturation is delayed and possibly converge with the crop. The knowledge of the phenology of weeds bring possibility to design weed management strategies such as in this case to avoid the seed return to the soil. Practices with this purpose have been developed and are applied in crop production conditions of Australia (Walsh et al., 2013). Moreover, the harvest advance is an adequate strategy to reduce the fall of seeds in the soil (Scursoni et al., 1999). In summary, from the results obtained in these experiments it was shown that dormancy levels and therefore germination and establishment dynamic on the field was hierarchically more important than the response to herbicides to favor the persistence of Avenafatua in wheat production systems. This can be interpreted as an ecological functional survival mechanism possibly heritable without selection by herbicides in cultivated areas. As emergence studies continue and emergence prediction tools improve,
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application dates can be determined for the most effective results. In addition, knowing the demographic processes regulating the population growth it can be design proactive management to avoid the increase of weed resistant populations. Thus, it is still possible to apply proactive agronomic strategies with the aim of avoiding the growth of Avenafatua populations resistance to herbicides. Acknowledgement Experiments were supported by the University Of Buenos Aires UBACyT G (2011e2014) (00440) and Ministerio de Ciencia y Tecnología, PICT: 2012-0936. The authors would like to thank particularly Ing.Agr. Juan Quistre and E. Iorio for their collaboration in experimental activities. References Adkins, S.W., Loewen, M., Symons, S.J., 1986. Variation within pure lines of wild oats (Avena fatua L.) in relation to degree of primary dormancy. Weed Sci. 34, 859e864. Arnold, J.C.D., Shaw, R., Scharer, S.M., 1997. Influence of application timing on efficacy of glyphosate in Roundup Ready soybean. Proc. South. Weed Sci. Soc. 50, 176e177. Baskin, C.C., Baskin, J.M., 2006. The natural history of soil seed banks of arable land. Weed Sci. 54, 549e557. Bertero, H.D., 2001. Effects of photoperiod, temperature and radiation on the rate of leaf appearance in Quinoa (Chenopodium quinoa Willd.) under field conditions. Ann. Bot. 87, 495e502. pez, R., Blanco, A.M., Chantre, G.R., Lodovichi, M.V., Bandoni, J.A., Sabbatini, M.R., Lo n, R., 2014. Modeling seed dormancy release & germination for Vigna, M., Gigo predicting Avena fatua L. field emergence: a genetic algorithm approach. Ecol. Model. 272, 293e300. Bradford, K., 1995. Water relations in seed germination. In: Kigel, J., Galili, G. (Eds.), Seed Development and Germination. Marcel Dekker Inc., pp. 351e396 Burgos, N.R., Tranel, P.J., Streibig, J.C., Davis, V.M., Shaner, D., Norsworthy, J.K., Ritz, C., 2013. Review: confirmation of resistance to herbicides and evaluation of resistance levels. Weed Sci. 61, 4e20. Catullo, J., Valleti, O., Rodríguez, M., Sosa, C., 1983. Relevamiento de malezas en cultivos comerciales de trigo y girasol en el centro sur bonaerense. In: Actas de n Argentina sobre la Maleza y su control, pp. 204e235. Santa Fe IX Reunio agosto de 1982. Ceccato, D.V., Bertero, D.H., Batlla, D., 2011. Environmental control of dormancy in quinoa (Chenopodium quinoa) seeds: two potential genetic resources for preharvest sprouting tolerance. Seed Sci. Res. 21, 133e141. Cousens, R., Weaver, S.E., Porter, J.R., Rooney, J.M., Butler, D.R., Johnson, M.P., 1992. Growth & development of Avenafatua (wild-oat) in the field. Ann. Appl. Biol. 120, 339e351. Di Rienzo, J.A., Casanoves, F., Balzarini, M.G., Gonzalez, L., Tablada, M., Robledo, C.W., n 2008, Grupo InfoStat. FCA, Universidad Nacional de 2008. InfoStat, Versio rdoba, Argentina. Co Evans, R.M., Thill, D.C., Tapia, L., Shafill, B., Lish, J.M., 1991. Wild oat (Avenafatua) &spring barley (Hordeum vulgare) density affect spring barley grain yield. Weed Technol. 5, 33e39. Fernandez Quintanilla, C., Navarrete, L., Torner, C., 1984. The influence of crop rotation on the population dynamics of Avenasterilis spp. ludiviciana in Central Spain. In: Proceedings of 3rd EWRS Symposium on Weed Problems in Mediterranean Area, 16/09/1984, Lisboa, Portugal. Frank, A.B., Bauer, A., 1995. Phyllochron differences in wheat, barley, and forage grasses. Crop Sci. 35, 19e23. Grabe, D.F., 1970. Tetrazolium Testing Handbook for Agricultural Seed [S.l.]. Association of Official Seed Analysts, p. 62. Harker, K.N., O'Donovan, J.T., Turkington, K., Blackshaw, R.E., Lupwayi, N.Z., Smith, E.G., Johnson, E.N., Pageau, D., Shirtliffe, S.J., Gulden, R.H., Rowsell, J., Hall, L.M., Willenborg, C.J., 2016. Diverse rotations and optimal cultural practices control wild oat (Avena fatua L.). Weed Sci. 64, 170e180. Heap, I., (2016). http://weedscience.com/Summary/Species.aspx?WeedID¼28. Accessed 1August 10, 2016. Hilgenfeld, K.L., Martin, A.R., Mortensen, D., Mason, S., 2004. Weed management in glyphosate resistant soybean: weed emergence patterns in relation to glyphosate treatment timing. Weed Technol. 18, 277e283. Holm, L.G., Plucknett, D.L., Pancho, J.V., Herberger, J.P., 1977. Avena fatua L. and other members of the “wild oat” group. In: World's Worst Weeds: Distribution and Biology. University of Hawaii Press, Honolulu, 105 e 113. Kegode, G.O., Pearce, R.B., 1998. Influence of environment during maternal plant
growth on dormancy of shattercane (Sorghum bicolor) and giant foxtail (setariafaberi) seed. Weed Sci. 46, 322e329. Lehnhoff, E.A., Miller, Z.J., Brelsford, M.J., White, S., Maxwell, B.D., 2013. Relative canopy height influences wild oat (Avenafatua) seed viability, dormancy, and germination. Weed Sci. 2013 (61), 564e569. Li, R., Wang, S., Duan, L., Li, Z., Christoffers, M.J., Mengistu, L.W., 2007. Genetic diversity of wild oat (Avenafatua) populations from China and the United States. Weed Sci. 55, 95e101. Luzuriaga, A.L., Escudero, A., Perez-Garcia, F., 2006. Environmental maternal effects on seed morphology and germination in Sinapsisarvensis (Cruciferae). Weed Res. 46, 163e174. Owen, M.J., Goggin D.E, Powles S.B., 2015. Intensive cropping systems select for greater seed dormancy and increased herbicide resistance levels in Lolium (annual ryegrass). 71, 966e971 rigidum. Owen, M.J., Powles, S.B., 2009. 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