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Influence of different environmental factors on the germination and seedling emergence of Ipomoea eriocarpa R. Br.
Crop Protection 130 (2020) 105070
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Influence of different environmental factors on the germination and seedling emergence of Ipomoea eriocarpa R. Br. Asif Tanveer a, Mujahid Abbas Khan a, Hafiz Haider Ali b, *, Muhammad Mansoor Javaid b, Ali Raza b, Bhagirath Singh Chauhan c a b c
Department of Agronomy, University of Agriculture, Faisalabad, Pakistan Department of Agronomy, College of Agriculture, University of Sargodha, Sargodha, Punjab, Pakistan The Centre for Crop Science, Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Gatton, Queensland, 4343, Australia
A R T I C L E I N F O
A B S T R A C T
Keywords: Germination Temperature Salinity Drought stress pH Sowing depth
Ipomoea eriocarpa R. Br., an annual prostrate plant, is a troublesome weed species in the tropical and sub-tropical regions of Asia, Africa, and Australia. For a better understanding of the plant’s ecology, a seed germination study was conducted in order to predict the weed’s ability to increase its global distribution, as well as presenting suitable management strategies for combating its spread. Germination and emergence of I. eriocarpa were examined in order to investigate the impact of abiotic factors such as temperature, salinity, moisture, soil pH, and burial depth on seeds. Germination and growth experiments were conducted under a completely randomized design with four replications. Maximum germination (77.5%) of I. eriocarpa occurred at 25 � C, decreasing ac cording to an increase in temperature. A decrease in germination from 77.5 to 27.5% was observed where salinity increased from 0 to 200 mM of sodium chloride (NaCl). Germination of I. eriocarpa was 75% in no-water stress conditions; however, it gradually decreased with increasing water stress, with 32.5% germination at 0.8 MPa osmotic potential and no germination at 0.1 MPa osmotic potential. Germination was similar (74–76%) at pH levels ranging from 5 to 8 and decreased to 38% at pH 10. Optimal sowing depths ranged from 2 to 6 cm. Emergence decreased to 37.5% and 12.5% at burial depths of 8 and 10 cm, respectively. Our results suggest that I. eriocarpa has the potential to germinate, emerge and survive under different ecological conditions. Soil solarisation, organic manure application, and deep ploughing all respectively assist in altering the soil tem perature, soil pH, and seed burial depths of I. eriocarpa, contributing towards the effective management of this weed species.
1. Introduction Ipomoea eriocarpa R. Br., a member of the Convolvulaceae family, is an annual, aggressive and invasive herb in cropping systems. It is a vigorous climber, tolerant to drought and cold snaps that prefers well-drained, moist and rich alluvial and sandy loam soils (Tanveer et al., 2012; Webster and MacDonald, 2001). It is widely distributed across tropical Africa, extending from Egypt to South Africa, including Madagascar (Firehun and Tamado, 2006; Grubben, 1978). It occurs as a weed in maize (Zea mays. L) and cotton (Gossypium hirsutum L.) production across Pakistan, India and northern Australia (Marwat et al., 2010; Sekar et al., 2012; Webster and MacDonald, 2001). Ipomoea eriocarpa is also a common weed in sugarcane (Saccharum officinarum L.), pearl millet (Pennisetum americanum (L.) Leeke), and guar (Cyamopsis tetragonoloba
(L.) Tauber) (Burkill, 1985; Firehun and Tamado, 2006). Ipomoea erio carpa was introduced to Pakistan as an ornamental and is commonly found in warm climates of the northwest region of the country (Marwat et al., 2010). In the life cycle of a plant, germination and emergence are consid ered significant stages in determining the successful survival and effi cient utilization of plant-available nutrients and water (Gan et al., 1996). They are the key phenological stages of plant survival in an agro-environment and are generally affected by environmental factors such as temperature, soil salinity, soil pH and soil moisture (Canossa et al., 2008; Chauhan et al., 2006a, 2006b; Chauhan and Johnson, 2010; Ikeda et al., 2008). There exists a wide body of research into the seed ecology of different Ipomoea species. Oliveira and Norsworthy (2006) found a closely related species, Ipomoea lacunosa L., successfully
* Corresponding author. Department of Agronomy, College of Agriculture, University of Sargodha, Sargodha, Pakistan. E-mail addresses: [email protected], [email protected] (H.H. Ali). https://doi.org/10.1016/j.cropro.2019.105070 Received 18 April 2018; Received in revised form 15 December 2019; Accepted 21 December 2019 Available online 24 December 2019 0261-2194/© 2019 Elsevier Ltd. All rights reserved.
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germinated across temperatures ranging from 7.5 to 52.5 � C with opti mum germination occurring between 20 and 25 � C; Ipomoea coccinea L. germinated best at 20–30 � C (Hardcastle, 1978); Ipomoea hederacea L. var. hederacea, I. lacunosa, and Ipomoea hederacea (L.) var. integriuscula Gray germinated at constant temperatures of 20, 25, 35, and 40 � C (Gomes et al., 1978). Germination of the scarified seeds of Ipomoea tri loba L. was similar (96–99%) at different day/night temperature ranges of 25/15, 30/20 and 35/25 � C (Chauhan and Abugho, 2012). However, such information is not available for I. eriocarpa. Different species of Ipomoea were found to have varying levels of tolerance to osmotic stress. Ipomoea lacunosa presented greater tolerance to osmotic stress than Jacquemontia tamnifolia L. (Oliveira and Nors worthy, 2006; Shaw et al., 1987). Non-stressed seeds (0 MPa osmotic potential) in Ipomoea obscura L. were observed to have the greatest germination rate after 2 days (Hoveland and Buchanan, 1973). The maximum germination of I. obscura occurred at 0.2 MPa after 4 days, at 0.4 MPa after 6 days and at 0.6 and 0.8 MPa after 8 days. The maximum emergence of three Ipomoea species, I. hederacea, I. lacunosa, and I. hederacea occurred at burial depths ranging from 1.3 to 2.5 cm (Gomes et al., 1978). There was no significant effect of the tested burial depths (1–10 cm) on seedling emergence of Ipomoea asarifolia (Desr.) Roem. & Schult (Dias-Filho, 1996). Minimal emergence (five percent germination) was observed for seeds placed on the soil surface, possibly due to low seed and soil interaction, as well as desiccation. It is reported that various Ipomoea species have the potential to germinate and emerge at relatively significant depths (Suwanketnikom and Jula kasewee, 2004). Seedling emergence of I. obscura has been shown to gradually decrease when sowing depth exceeds 1 cm. Only 7% of seedlings emerged when sown at a depth of 8 cm, with no germination occurring at 12 cm depth. The germination of I. lacunosa occurred at a pH range of 3–10, with optimum germination occurring at pH 6 to 8 (Oliveira and Norsworthy, 2006). Ipomoea pandurata L. germinated best in soils ranging from 6 to 8.5 pH, levels commonly present in agricul tural systems (Horak and Wax, 1991). No such information is available for I. eriocarpa. While the germination ecology of several Ipomoea species have already been studied, no work has been done on the germination ecol ogy of I. eriocarpa. To better understand the agro-ecological threats presented by this emerging and problematic weed species, it is essential to acquire information related to its seed germination in response to environmental conditions. The aims of this study were to evaluate the germination and growth of I. eriocarpa in response to the ecological factors of temperature, salinity, drought, soil pH and burial depth.
above) were placed in incubators at five constant temperatures (25, 30, 35, 40 and 45 � C). Each Petri dish was first rinsed with 5 ml of distilled water. Subsequent water was added if necessary to avoid drought. 2.3. Salt stress The salinity levels utilized to observe the impact of salt stress on germination were 0, 25, 50, 75, 100, 125, 150, 175, and 200 mM sodium chloride (NaCl). Each Petri dish received an initial application of 5 ml of saline solution to dampen the filter paper, as well as subsequent appli cations to maintain moisture. Petri dishes were stored in an incubator at 25 � C. 2.4. Drought stress Ipomoea eriocarpa seeds were checked for germination in aqueous solutions having osmotic potential of 0, -0.2, 0.4, 0.6, 0.8, and 1.0 MPa, Polyethylene glycol 6000 (PEG, Sigma Aldrich Co., Spruce St., MO, 63103, USA) was dissolved in distilled water to develop solu tions for osmotic potential. From the known concentration levels of PEG 6000, the undersigning equation (Michel and Kaufmann, 1973) was used to observe water potentials. Water potential ¼ - (1.18 � 10 2) C - (1.18 � 10 4) C2 þ (2.67 � 10 4) 18CT þ (8.39 � 10 7) C2T where C represents the concentration levels of PEG (g per kg of distilled water) and T shows temperature (� C). Petri dishes were stored in an incubator at 25 � C. 2.5. pH A 2-mM solution of MES [2-(N-morpholino) ethanesulfonic acid] was used to prepare the pH of 5 and 6 with an aqueous form of 1 N NaOH. Similarly, a 2 mM solution of HEPES [N-(2-hydroxymethyl) piperazineN-(2-ethane sulfonic acid)] was fixed for the pH of 7 and 8 with one N NaOH. The pH solutions from 9 to 10 were prepared with 2-mM tricine [N-tris (hydroxymethyl) methyl glycine] and fixed with 1 N NaOH. The seeds of I. eriocarpa were prepared according to the method described for preceding tests. Aqueous solutions of pH 5, 6, 7, 8, 9, and 10 were added to each Petri dish individually. An additional solution of pH was used on demand. Petri dishes were stored in an incubator at 25 � C. 2.6. Sowing depth
2. Materials and methods
Twenty-five seeds of I. eriocarpa were sown at depths of 0 (surface), 2, 4, 6, 8, and 10 cm in plastic pots (14 cm diameter and 15 cm height). A sandy loam soil of 0.7% organic carbon and a pH of 7.2 was collected from a nearby field, and used for this study. In each pot, 100 ml of distilled water was applied at sowing, with additional water added to avoid drought stress. These pots were subjected to a minimum and maximum temperature of 25 and 29 � C, respectively. Seedlings at the soil surface were considered to have emerged when cotyledons were visible. Time for 50% germinating or emergence (T50 or E50) was based on Coolbear et al. (1984): � � N=2 ni ðtj ti T50 ¼ nj ni
2.1. Seed description and germination tests Mature I. eriocarpa seeds were collected from several consenting farmers’ fields in the Bhakkar District of Punjab Province, Pakistan (31� N, 71� E) during the start of the winter season of 2014. After har vesting, seeds were properly threshed, cleaned, and dried in the shade at room temperature for seven days prior to being stored in paper bags. Seeds damaged by insects or pathogens were discarded. Before the establishment of each experiment, seeds were soaked in a 10% sodium hypochlorite solution for 5 min to sterilize the seed coat and then rinsed with distilled water. For each treatment, 25 seeds were placed in 9 cm diameter Petri dishes with Whatman No. 10 filter paper for germination. Petri dishes were sealed with a strip of parafilm to reduce water loss. Seeds with radicles of 2 mm were counted as germi nated and removed daily over the course of three weeks.
where N is the total number of germinated seeds or emerged seedlings, nj and ni represent the cumulative number of germinated seeds by adjacent sampling dates, day tj, and ti, respectively, when ni is less than N/2, but N/2 is less than nj. Mean germination or emergence time (MGT or MET) is a measure of the rate and time-spread of germination and was calculated using Ellis and Roberts (1981) equation:
2.2. Temperature In order to evaluate the impact of temperature on seed germination and the emergence of I. eriocarpa, Petri dishes (prepared as explained 2
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MGT / MET ¼
Crop Protection 130 (2020) 105070
P
(Dn) /
P
n
where n shows the number of germinated seeds on day D and Dn in dicates the number of days from the beginning of germination/emer gence. The germination or emergence index (GI or EI) is the sum of the ratios of the un-germinated seeds from the day of first count until the final counting day and was recorded as defined by the Association of Official Seed Analysts (1983) applying the undersigning formula. GI ¼ EI ¼
No:of germinated seeds þ Days of first count No:of germinated seeds þ Days of final count
2.7. Statistical analyses All experiments were conducted in a completely randomized design with four replications. All trials were repeated within 20 days of termination of the first run. From the repeated tests, data was subjected to one-way analysis of variance (ANOVA) followed by the use of least significant difference (LSD) at p ¼ 0.05 (Steel et al., 1997), by using SAS (Statistical Analysis Systems), (2002). Nonlinear regression analysis was applied to calculate the effect of NaCl concentration, osmotic/water stress, or soil depth on germination or emergence. At various levels of NaCl and osmotic stress, the germi nation value (%) was fixed to a functional model of three-parameter logistics using SigmaPlot 11.0 software (Systat Software, Inc., Point Richmond, CA, 94801, USA) for analysis:
Fig. 1. Effect of temperature on seed germination of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and the dotted lines show 95% confidence intervals. Vertical bars represent � standard error of the mean. Table 1 Effect of temperature on germination traits of Ipomoea eriocarpa.
Y ¼ A / [1 þ (x/x50)B] where Y is the percentage (%) of germination or emergence at NaCl or osmotic potential x, A is the maximum germination or emergence (%), x50 is the NaCl or osmotic potential concentration required for 50% suppression, and B shows the slope.
Temperature � C
Time to start germination (days)
T50 (days)
MGT (days)
GI
25 30 35 40 45 LSD ¼ 0.05
1.00 1.00 1.00 1.25 1.25 NS
1.48 1.61 1.72 1.65 1.68 NS
4.22 4.17 4.16 4.27 4.45 NS
16.57 16.34 12.78 9.17 3.95 2.95
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index, NS ¼ non-significant.
3. Results 3.1. Temperature A logistic model of three-parameters {G (%) ¼ 79.6/[1 þ (x/ 40.5)7.9], R2 ¼ 0.97} was fixed to check the germination (%) of I. eriocarpa obtained at different temperature ranges (Fig. 1). Germina tion of I. eriocarpa seeds occurred between 25 and 45 � C. Maximum germination (77.5%) was recorded at 25 � C followed by 30 � C (75%). Germination significantly decreased with the increase of temperature. Minimum germination (22.5%) was attained at the highest temperature (45 � C). A 50% reduction from the maximum germination rate (x50) at a temperature of 40.5 � C was observed. The germination index (GI) of I. eriocarpa was maximum (16.57) at 25 � C, which was statistically similar to those at 30 � C. While minimum GI (3.95) was observed at 45 � C (Table 1). 3.2. Salt stress A three-parameter logistic model {G (%) ¼ 68.9/[1 þ (x/190)4.5], R2 ¼ 0.88} was used to model the ability of I. eriocarpa to germinate at various NaCl concentrations (Fig. 2). Salinity tolerance was observed in I. eriocarpa seeds up to a concentration of 125 mM NaCl, with germi nation steadily decreasing according to an increase in salinity. Ipomoea eriocarpa germination was 67.5% at 75 mM NaCl, and low germination (27.50%) followed at 200 mM NaCl. A 50% reduction from the maximum germination rate was achieved at 190 mM of NaCl (Fig. 2). The outset of I. eriocarpa germination was significantly affected by salinity (Table 2). Maximum time to start germination (2.8 days) and T50 (3.5 days) of I. eriocarpa was recorded at 200 mM NaCl followed by 175
Fig. 2. Effect of sodium chloride concentration on seed germination of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and the dotted lines show 95% confidence intervals. Vertical bars represent � standard error of the mean.
mM NaCl (Table 2). The minimum starting time for germination (1.0 day) and T50 (1.6 days) was observed at 0 mM NaCl. The highest germination time for the mean (5.3 days) of I. eriocarpa was noted at 200 mM NaCl, followed by 175 mM NaCl. The lowest mean germination time (3.9 days) was recorded at 0 mM (distilled water), which remained 3
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Table 2 Effect of salinity levels on germination traits of Ipomoea eriocarpa.
Table 3 Effect of drought stress on germination traits of Ipomoea eriocarpa.
NaCl concentration (mM)
Time to start germination (days)
T50 (days)
MGT (days)
GI
Osmotic potential (MPa)
Time to start germination (days)
T50 (days)
MGT (days)
GI
0 (control) 25 50 75 100 125 150 175 200 LSD ¼ 0.05
1.00 1.00 1.00 1.00 1.00 1.00 1.25 2.25 2.75 0.70
1.60 1.62 1.88 1.66 1.91 2.22 2.32 2.79 3.50 0.730
3.93 4.08 4.12 4.16 4.12 4.19 4.42 4.87 5.28 0.30
17.84 15.47 15.62 15.12 13.93 13.33 9.00 5.75 2.52 2.67
0 (control) 0.2 0.4 0.6 0.8 1.0 LSD ¼ 0.05
1.00 1.00 1.25 2.25 3.00 NG 0.73
1.94 2.04 2.27 2.92 3.02 NG 1.00
3.36 3.89 4.50 4.53 5.31 NG NS
16.69 14.04 9.89 6.25 3.0 NG 1.96
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index, NG ¼ no germination; NS ¼ non-significant.
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index.
3.4. Effect of pH Seeds of I. eriocarpa germinated under a range of pH conditions, with maximum germination (77.5%) observed at pH 7 followed by 75% at pH 5 and 6 (Fig. 4). Minimum germination (40%) was calculated at pH 10. At different pH levels, the GI was efficiently affected (Table 4). The maximum GI of I. eriocarpa (17.59) was recorded at pH 7, while the minimum GI (4.37) occurred at pH 10.
similarly consistent up to 125 mM NaCl. The maximum GI (17.84) was recorded at 0 mM, which was similar to those observed at 25 and 50 mM (Table 2). The lowest GI (2.52) was recorded at 200 mM NaCl. 3.3. Osmotic stress A three-parameter logistic model {G (%) ¼ 67.29/[1 þ x/-0.75]7.0, R2 ¼ 0.90} revealed a 50% reduction from maximum germination at 0.75 MPa (Fig. 3). Germination was reduced from 75 to 32% as os motic stress increased from 0 to 0.8 MPa. Similar levels of germination were observed in I. eriorcarpa up to 0.4 MPa, with germination pro gressively decreasing according to an increase in stress. At 1.0 MPa, seed germination was completely suppressed (Fig. 3). The minimum starting time for germination (1 day) of I. eriocarpa was achieved in the control treatment (0 MPa) and at 0.2 MPa (Table 3). At 0.8 MPa, the beginning of germination was delayed to three days. The maximum time for 50% germination was observed at 0.8 MPa (3 days), while minimum time was observed at 0 MPa (1.9 days), being similar to 0.2, 0.4 and 0.6 MPa. The maximum time for mean germination was observed at a maximum of 0.8 MPa (5.3 days) which was followed by 4.5 days at 0.6 and 0.4 MPa. The minimum time for germination was observed at 0 MPa (3.4 days). In the control treatment, the maximum GI was recorded (16.7) while minimum GI (3) was observed at 0.8 MPa (Table 3).
3.5. Sowing depth A three-parameter logistic model {E (%) ¼ 68.20/[1þ(x/8.6)7.9, R2 ¼ 0.82} was fixed for the observation of the seedling emergence data of I. eriocarpa (Fig. 5). Seeds of I. eriocarpa placed at the soil surface pro duced lower rates of germination compared to those buried at 2 cm depth. Seed germination and emergence increased from 55 to 75% as the depth of seed burial increased from 0 to 2 cm. Seedling emergence was 17.5% at 10 cm. According to the model values, suppression of 50% would be achieved at 8.6 cm (Fig. 5). Emergence started earlier at 2 cm (one DAS), similar to 0, 4, 6 and 8 cm, while the beginning of seedling emergence at 10 cm was delayed to 4.3 DAS. Minimum time to 50% emergence (1.4 days) and time to mean emergence (3.0 days) of I. eriocarpa was recorded at the sowing depth of 2 cm while the highest time to 50% emergence (5.1 days) and time to mean emergence (6.6 days) of I. eriocarpa was observed at a sowing depth of 10 cm. This was statistically equivalent to that of 0 cm of sowing depth (Table 5). The maximum EI of I. eriocarpa was calculated at 2 cm sowing depth, while the minimum EI (0.92) was recorded at 10 cm sowing depth. Generally, the EI reduced with increased sowing depth.
Fig. 3. Effect of osmotic potential (MPa) on seed germination of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and the dotted lines show 95% confidence intervals. Vertical bars represent � standard error of the mean.
Fig. 4. Effect of pH on seed germination of Ipomoea eriocarpa. Vertical lines on the top of bars represent � standard error of the mean. 4
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Generally, germination is delayed under critical concentrations of salt (Ungar, 1991). The level of critical concentration which affects germination varies according to species, biotype, ecological conditions, osmotic potential and specific ions present. (Gomez et al., 2008). Our results also suggest that as salt concentration increased, the time to start germination, T50, and the MGT of I. eriocarpa was delayed. The GI and germination percentage of I. eriocarpa were reduced with an increasing rate of salt solution. Significant decreases in the rate and percentage of germination in response to salinity in other Ipomoea spp. were confirmed earlier by Horak and Wax (1991), Oliveira and Norsworthy (2006), Shaw et al. (1987) and Singh et al. (2012). Salinity may also affect germination due to reduced water uptake during imbibition; through high toxicity due to poor ion selectivity or decreased nutrient absorption as a result of ionic imbalance (Romo and Eddleman, 1985). This decrease in germination might be due to an increase in the absorption of toxic substances with water at maximum concentrations of salt (Smith and Comb, 1991; Younis et al., 1991). Similarly, our study suggests that time start to germination, T50, germination index, and MGT of I. eriocarpa increased according to the level of drought stress, while the percentage of germination and GI of I. eriocarpa decreased. In 1978, Gomes et al. reported that I. lacunosa showed 3% germination at 1.0 MPa drought stress. This could be attributed to species-specific behaviour. The literature revealed that some species of Ipomoea have different levels of tolerance to osmotic stress (Hoveland and Buchanan, 1973; Suwanketnikom and Julaka sewee, 2004). In previous studies, germination was delayed due to os motic stress and was faster at 0 MPa in different I. eriocarpa species, including I. purpurea, I. hederacea, I. lacunosa, I. hederacea, J. tamnifolia, and I. obscura (Crowley and Buchanan, 1980; Hoveland and Buchanan, Oliveira and Norsworthy, 2006, 1973; Shaw et al., 1987; Suwanketni kom and Julakasewee, 2004). This study also demonstrated that I. eriocarpa seeds can germinate under variable soil moisture conditions in sub-tropical areas of Pakistan. The survival and germination of I. eriocarpa under a wide pH range indicates that this could not be considered a restrictive factor in the germination and emergence of the weed under varying soil conditions in Pakistan. Ipomoea eriocarpa showed similar results to those reported for I. pandurata, which germinated well in the soil at a pH of 6–8.5 (Horak and Wax, 1991). Ipomoea lacunosa germinated at a pH range from 3 to 10, but optimal germination was recorded at 6–8 pH (Oliveira and Norsworthy, 2006). Pakistani soils are generally alkaline in nature and have low amounts of organic matter, especially in irrigated areas near canals and tubewells (Niaz et al., 2007). The results of this study indicate that seed germination and emer gence increased as sowing depth increased from 0 to 2 cm, whilst it decreased as burial increased towards a maximum sowing depth of 10 cm. Similarly, at a sowing depth of 10 cm, I. eriocarpa seedling emer gence was delayed. The minimum starting time to emergence, T50 for emergence and MGT for this species were observed at a burial depth of 2 cm. Similarly, the EI was reduced by increasing sowing depth. The germination and emergence of various species of Ipomoea have been observed from greater soil depths (Suwanketnikom and Julakasewee, 2004). When the seed burial depth increased from 1.3 to 5 cm in the soil, the seedling emergence of I. purpurea was delayed (Cole, 1976). Ipomoea hederacea, I. lacunosa, and I. hederacea (all closely related to I. eriocarpa) had maximum emergence at sowing depths between 1.3 and 2.5 cm (Gomes et al., 1978). The seedling emergence of I. obscura was also low (5%) at the soil surface. The highest emergence of I. lacunosa was 87% for the seeds planted at a depth of 1 cm (Suwanketnikom and Julaka sewee, 2004). The emergence of Ipomoea tricolor Cav. was greatest for sowing depths between 2.5 and 7.5 cm (Chandler et al., 1977). Greater emergence at shallow depths indicates that zero-tillage farming prac tices can improve the germination and survival of this weed under field conditions. Our results also suggest that the placement of seeds on the soil surface may decay faster because of increased predation activity and variations in temperature and moisture conditions (Chauhan and
Table 4 Effect of pH on germination traits of Ipomoea eriocarpa. pH
Time to start germination (days)
T50 (days)
MGT (days)
GI
5 6 7 8 9 10 LSD ¼ 0.05
1.00 1.00 1.00 1.25 1.25 1.25 NS
1.75 1.70 1.73 1.80 1.74 2.20 NS
4.16 4.13 4.14 4.26 4.42 4.37 NS
16.94 17.07 17.59 14.35 9.52 7.37 2.64
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index, NS ¼ non-significant.
Fig. 5. Effect of sowing depth (cm) on seedling emergence of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and thin lines show 95% confidence intervals. Vertical bars repre sent � standard error of the mean. Table 5 Effect of sowing depth on emergence traits of Ipomoea eriocarpa. Sowing depth (cm)
Time to start germination (days)
E50 (days)
MET (days)
EI
0 2 4 6 8 10 LSD ¼ 0.05
1.25 1.00 1.00 1.25 1.50 4.25 0.942
4.06 1.43 1.53 3.08 3.22 5.12 1.145
5.72 2.95 3.43 4.53 4.59 6.63 1.185
4.75 17.19 14.29 10.71 6.43 0.92 1.883
E50 ¼ time to obtain 50% germination, MET ¼ mean germination time, EI ¼ germination index.
4. Discussion The results obtained from our study suggest that I. eriocarpa is able to germinate over a range of temperatures, allowing its emergence over the spring, summer, and autumn seasons in a majority of the sub-tropical areas of Pakistan. Such temperature adaptation may provide I. eriocarpa with competitive advantages under varying environmental conditions. Results also indicate that the GI of I. eriocarpa decreased as the temperature increased. Reduced germination with increasing tem perature has also been reported in other Ipomoea species (Cole and Coats, 1973; Horak and Wax, 1991; Oliveira and Norsworthy, 2006; Shaw et al., 1987). These studies reported maximum germination of I. pandurata at 20 � C, Ipomoea purpurea (L.) Roth. at 24 � C, I. lacunosa at 25 � C and finally J. tamnifolia at 35 � C. 5
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Johnson, 2010). Tillage determines the vertical spread of seed in the soil structure and this, in turn, affects seedling establishment through factors such as seed predation, dormancy, longevity, and potential of seedling emergence from a given depth (Chauhan et al., 2006b). The emergence of this weed can be suppressed at burial depths of 8–10 cm under deep tillage operations.
Cole, A.W., Coats, G.E., 1973. Tall morning glory germination response to herbicides and temperature. Weed Sci. 21, 443–446. Cole, A.W., 1976. Tall morning glory response to planting depth. Weed Sci. 24, 489–492. Coolbear, P., Francis, A., Grierson, D., 1984. The effect of low temperature pre- sowing treatment on the germination performance and membrane integrity of artificially aged tomato seeds. J. Exp. Bot. 35, 1609–1617. Crowley, R.H., Buchanan, G.A., 1980. Responses of Ipomoea spp and small flower morningglory (Jacquenontia tamnifolia) to temperature and osmotic stress. Weed Sci. 28, 87-82. Dias-Filho, M.B., 1996. Germination and emergence of Stachytarpheta cayennensis and Ipomoea asarifolia. Planta Daninha 14, 183–188. Ellis, R.A., Roberts, E.H., 1981. The quantification of ageing and survival in orthodox seeds. Seed Sci. Technol. 9, 373–409. Firehun, Y., Tamado, T., 2006. Weed flora in the Rift Valley sugarcane plantations of Ethiopia as influenced by soil types and agronomic practises. Weed Biol. Manag. 6, 139–150. Gan, Y.E., Stobbe, H., Njue, C., 1996. Evaluation of selected nonlinear regression models in quantifying seedling emergence rate of spring wheat. Crop Sci. 36, 165–168. Gomes, L.F., Chandler, J.M., Vaughan, C.E., 1978. Aspects of germination, emergence and seed production of three Ipomoea taxa. Weed Sci. 26, 245–248. Gomez, R., Naranjo, E.M., Garzon, O., Castillo, J.M., Luque, T., Figueroa, M.E., 2008. Effects of salinity on germination and seedling establishment of endangered Limoniumem arginatum (Wild.) Kuntze. Coast. Res. 24, 201–205. Grubben, G.J., 1978. Ipomoea Eriocarpa R.Br. in: Vegetable Seeds for the Tropics. Koninklijk Instituutvoor de Tropen, p. 336. Hardcastle, W.S., 1978. Influence of temperature and acid scarification duration on scarlet morning glory (Ipomoea coccinea) seed germination. Weed Sci. 26, 261–263. Horak, H.J., Wax, L.M., 1991. Germination and seedling development of big root morningglory (Ipomoea pandurata). Weed Sci. 39, 390–396. Hoveland, C.S., Buchanan, G.A., 1973. Weed seed germination under simulated drought. Weed Sci. 21, 322–324. Ikeda, F.S., Carmona, R., Mitja, D., Guimaraes, R.M., 2008. Light and KNO3 on Tridax procumbens seed germination at constant and alternating temperatures. Planta Daninha 26, 751–756. Marwat, K.B., Hashim, S., Ali, H., 2010. Weed management: a case study from north-west Pakistan. Pak. J. Bot. 42, 341–353. Michel, B.E., Kaufmann, M.R., 1973. The osmotic potential of polyethylene glycol 6000. Plant Physiol. 51, 914–916. Niaz, A., Ranjha, A.M., Rahmatullah, A.H., Waqas, M., 2007. Boron status of soils as affected by different soil characteristics–pH, CaCO3, organic matter and clay contents. Pak. J. Agric. Sci. 44, 428–435. Oliveira, M.J., Norsworthy, J.K., 2006. Pitted morningglory (Ipomoea lacunosa) germination and emergence as affected by environmental factors and seeding depth. Weed Sci. 54, 910–916. Romo, J., Eddleman, L., 1985. Germination response of greasewood (Sarcobatus vermiclatus) to temperature. Water potential and specific ions. Range Manag. 38, 117–120. SAS (Statistical Analysis Systems), 2002. SAS Procedures Guide. Statistical Analysis Systems Institute, Cary, NC, Version 9. Sekar, K.C., Manikandan, R., Srivastava, S.K., 2012. Invasive alien plants of uttarakhand Himalaya. Proc. Natl. Acad. Sci. India Sect. B Biol. Sci. 82, 375–383. Shaw, D.R., Smith, H.R., Cole, A.W., Snipes, C.E., 1987. Influence of environmental factors on small flower morningglory (Jacquemontia tamnifolia) germination and growth. Weed Sci. 35, 519–523. Singh, M., Ramirez, A.H., Sharma, S.D., Jhala, A.J., 2012. Factors affecting the germination of tall morningglory (Ipomoea purpurea). Weed Sci. 60, 64–68. Smith, P.T., Comb, B.G., 1991. Physiological and enzymatic activity of pepper seeds (Capsicum annuum) during priming. Plant Physiol. 82, 71–78. Steel, R.G.D., Torrie, J.H., Dickey, D., 1997. Principles and Procedures of Statistics. A Biometrical Approach, third ed. McGraw Hill Book Co. Inc., New York, pp. 352–358. Suwanketnikom, R., Julakasewee, A., 2004. Hard seededness and germination of small white flower morning glory. Kasetsart. Nat. Sci. 38, 425–433. Tanveer, A., Arshad, M., Abbas, R.N., Tahir, M., Javaid, M.M., Ikram, R.M., 2012. Germination response of weeds to different sources and concentrations of N and P. Role of Agronomy in National Food Security, p. 36. Ungar, I., 1991. Ecophysiology of Vascular Halophytes. CRC Press, Boca Raton, FL, p. 209. Webster, T.M., MacDonald, G.E., 2001. A surveys of weeds in various crops in Georgia. Weed Technol. 15, 771–790. Younis, S.A., Shahatha, H.A., Hagop, P.G., Al-Rawi, F.I., 1991. Effect of Salinity on the Viability of Rice Seeds. Plant Growth, Drought and Salinity in the Arab Region, pp. 235–244.
5. Conclusion The germination and seedling emergence of I. eriocarpa is influenced by the various ecological elements of temperature, salinity, drought, pH, and sowing depth. Our results explain that I. eriocarpa can survive under subtropical and semi-arid conditions, which are characterized by hot summers and mild to cool winters, moderate moisture, and welldrained, slightly acidic soil conditions. This weed has the potential to germinate and emerge to varying degrees under a variety of ecological conditions. Our study will be supportive in describing an environment conducive to the germination of this weed for the purpose of its effective management. Furthermore, the results of this study will contribute to wards the efficient management of this weed species not only in agro nomic crops but also in pastures. Author contributions Asif Tanveer: Supervision, Supervised the overall research, Mujahid Abbas Khan: Data curation, Experimental execution and data handling, Hafiz Haider Ali: Formed paper structure, Muhammad Mansoor Javaid: Formal analysis, Data analysed, Ali Raza: Graphics and tabulation of data, Bhagirath Singh Chauhan: Supervised the overall research and reviewed the paper. Declaration of competing InterestCOI No potential conflict of interest was reported by the authors. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.cropro.2019.105070. References Association of Official Seed Analysts, 1983. Rules for testing seeds. Seed Technol. 16, 1–113. Burkill, H.M., 1985. The Useful Plants of West Tropical Africa, second ed., vol. 1. Families A–D. Royal Botanic Gardens, Kew, United Kingdom, p. 960. Canossa, R.S., Oliveira, J.R., Constantin, R.S., Braccini, J., Biffe, A.L., Alonso, D.F., Blainski, D.G., 2008. Effect of temperature and light on joyweed (Alternanthera tenella) seed germination. Planta Daninha 26, 745–750. Chandler, J.M., Munson, R., Land Vaughan, C.E., 1977. Purple moonflower: emergence, growth and reproduction. Weed Sci. 25, 163–167. Chauhan, B.S., Gill, G., Preston, C., 2006. African mustard (Brassica tournefortii) germination in southern Australia. Weed Sci. 54, 891–897. Chauhan, B.S., Gill, G., Preston, C., 2006. Tillage system effects on weed ecology, herbicide activity and persistence: a review. Anim. Prod. Sci. 46, 1557–1570. Chauhan, B.S., Johnson, D.E., 2010. The role of seed ecology in improving weed management strategies in the tropics. Adv. Agron. 105, 221–262. Chauhan, B.S., Abugho, S.B., 2012. Threelobe morningglory (Ipomoea triloba) germination and response to herbicides. Weed Sci. 60, 199–204.
6
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Influence of different environmental factors on the germination and seedling emergence of Ipomoea eriocarpa R. Br. Asif Tanveer a, Mujahid Abbas Khan a, Hafiz Haider Ali b, *, Muhammad Mansoor Javaid b, Ali Raza b, Bhagirath Singh Chauhan c a b c
Department of Agronomy, University of Agriculture, Faisalabad, Pakistan Department of Agronomy, College of Agriculture, University of Sargodha, Sargodha, Punjab, Pakistan The Centre for Crop Science, Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Gatton, Queensland, 4343, Australia
A R T I C L E I N F O
A B S T R A C T
Keywords: Germination Temperature Salinity Drought stress pH Sowing depth
Ipomoea eriocarpa R. Br., an annual prostrate plant, is a troublesome weed species in the tropical and sub-tropical regions of Asia, Africa, and Australia. For a better understanding of the plant’s ecology, a seed germination study was conducted in order to predict the weed’s ability to increase its global distribution, as well as presenting suitable management strategies for combating its spread. Germination and emergence of I. eriocarpa were examined in order to investigate the impact of abiotic factors such as temperature, salinity, moisture, soil pH, and burial depth on seeds. Germination and growth experiments were conducted under a completely randomized design with four replications. Maximum germination (77.5%) of I. eriocarpa occurred at 25 � C, decreasing ac cording to an increase in temperature. A decrease in germination from 77.5 to 27.5% was observed where salinity increased from 0 to 200 mM of sodium chloride (NaCl). Germination of I. eriocarpa was 75% in no-water stress conditions; however, it gradually decreased with increasing water stress, with 32.5% germination at 0.8 MPa osmotic potential and no germination at 0.1 MPa osmotic potential. Germination was similar (74–76%) at pH levels ranging from 5 to 8 and decreased to 38% at pH 10. Optimal sowing depths ranged from 2 to 6 cm. Emergence decreased to 37.5% and 12.5% at burial depths of 8 and 10 cm, respectively. Our results suggest that I. eriocarpa has the potential to germinate, emerge and survive under different ecological conditions. Soil solarisation, organic manure application, and deep ploughing all respectively assist in altering the soil tem perature, soil pH, and seed burial depths of I. eriocarpa, contributing towards the effective management of this weed species.
1. Introduction Ipomoea eriocarpa R. Br., a member of the Convolvulaceae family, is an annual, aggressive and invasive herb in cropping systems. It is a vigorous climber, tolerant to drought and cold snaps that prefers well-drained, moist and rich alluvial and sandy loam soils (Tanveer et al., 2012; Webster and MacDonald, 2001). It is widely distributed across tropical Africa, extending from Egypt to South Africa, including Madagascar (Firehun and Tamado, 2006; Grubben, 1978). It occurs as a weed in maize (Zea mays. L) and cotton (Gossypium hirsutum L.) production across Pakistan, India and northern Australia (Marwat et al., 2010; Sekar et al., 2012; Webster and MacDonald, 2001). Ipomoea eriocarpa is also a common weed in sugarcane (Saccharum officinarum L.), pearl millet (Pennisetum americanum (L.) Leeke), and guar (Cyamopsis tetragonoloba
(L.) Tauber) (Burkill, 1985; Firehun and Tamado, 2006). Ipomoea erio carpa was introduced to Pakistan as an ornamental and is commonly found in warm climates of the northwest region of the country (Marwat et al., 2010). In the life cycle of a plant, germination and emergence are consid ered significant stages in determining the successful survival and effi cient utilization of plant-available nutrients and water (Gan et al., 1996). They are the key phenological stages of plant survival in an agro-environment and are generally affected by environmental factors such as temperature, soil salinity, soil pH and soil moisture (Canossa et al., 2008; Chauhan et al., 2006a, 2006b; Chauhan and Johnson, 2010; Ikeda et al., 2008). There exists a wide body of research into the seed ecology of different Ipomoea species. Oliveira and Norsworthy (2006) found a closely related species, Ipomoea lacunosa L., successfully
* Corresponding author. Department of Agronomy, College of Agriculture, University of Sargodha, Sargodha, Pakistan. E-mail addresses: [email protected], [email protected] (H.H. Ali). https://doi.org/10.1016/j.cropro.2019.105070 Received 18 April 2018; Received in revised form 15 December 2019; Accepted 21 December 2019 Available online 24 December 2019 0261-2194/© 2019 Elsevier Ltd. All rights reserved.
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germinated across temperatures ranging from 7.5 to 52.5 � C with opti mum germination occurring between 20 and 25 � C; Ipomoea coccinea L. germinated best at 20–30 � C (Hardcastle, 1978); Ipomoea hederacea L. var. hederacea, I. lacunosa, and Ipomoea hederacea (L.) var. integriuscula Gray germinated at constant temperatures of 20, 25, 35, and 40 � C (Gomes et al., 1978). Germination of the scarified seeds of Ipomoea tri loba L. was similar (96–99%) at different day/night temperature ranges of 25/15, 30/20 and 35/25 � C (Chauhan and Abugho, 2012). However, such information is not available for I. eriocarpa. Different species of Ipomoea were found to have varying levels of tolerance to osmotic stress. Ipomoea lacunosa presented greater tolerance to osmotic stress than Jacquemontia tamnifolia L. (Oliveira and Nors worthy, 2006; Shaw et al., 1987). Non-stressed seeds (0 MPa osmotic potential) in Ipomoea obscura L. were observed to have the greatest germination rate after 2 days (Hoveland and Buchanan, 1973). The maximum germination of I. obscura occurred at 0.2 MPa after 4 days, at 0.4 MPa after 6 days and at 0.6 and 0.8 MPa after 8 days. The maximum emergence of three Ipomoea species, I. hederacea, I. lacunosa, and I. hederacea occurred at burial depths ranging from 1.3 to 2.5 cm (Gomes et al., 1978). There was no significant effect of the tested burial depths (1–10 cm) on seedling emergence of Ipomoea asarifolia (Desr.) Roem. & Schult (Dias-Filho, 1996). Minimal emergence (five percent germination) was observed for seeds placed on the soil surface, possibly due to low seed and soil interaction, as well as desiccation. It is reported that various Ipomoea species have the potential to germinate and emerge at relatively significant depths (Suwanketnikom and Jula kasewee, 2004). Seedling emergence of I. obscura has been shown to gradually decrease when sowing depth exceeds 1 cm. Only 7% of seedlings emerged when sown at a depth of 8 cm, with no germination occurring at 12 cm depth. The germination of I. lacunosa occurred at a pH range of 3–10, with optimum germination occurring at pH 6 to 8 (Oliveira and Norsworthy, 2006). Ipomoea pandurata L. germinated best in soils ranging from 6 to 8.5 pH, levels commonly present in agricul tural systems (Horak and Wax, 1991). No such information is available for I. eriocarpa. While the germination ecology of several Ipomoea species have already been studied, no work has been done on the germination ecol ogy of I. eriocarpa. To better understand the agro-ecological threats presented by this emerging and problematic weed species, it is essential to acquire information related to its seed germination in response to environmental conditions. The aims of this study were to evaluate the germination and growth of I. eriocarpa in response to the ecological factors of temperature, salinity, drought, soil pH and burial depth.
above) were placed in incubators at five constant temperatures (25, 30, 35, 40 and 45 � C). Each Petri dish was first rinsed with 5 ml of distilled water. Subsequent water was added if necessary to avoid drought. 2.3. Salt stress The salinity levels utilized to observe the impact of salt stress on germination were 0, 25, 50, 75, 100, 125, 150, 175, and 200 mM sodium chloride (NaCl). Each Petri dish received an initial application of 5 ml of saline solution to dampen the filter paper, as well as subsequent appli cations to maintain moisture. Petri dishes were stored in an incubator at 25 � C. 2.4. Drought stress Ipomoea eriocarpa seeds were checked for germination in aqueous solutions having osmotic potential of 0, -0.2, 0.4, 0.6, 0.8, and 1.0 MPa, Polyethylene glycol 6000 (PEG, Sigma Aldrich Co., Spruce St., MO, 63103, USA) was dissolved in distilled water to develop solu tions for osmotic potential. From the known concentration levels of PEG 6000, the undersigning equation (Michel and Kaufmann, 1973) was used to observe water potentials. Water potential ¼ - (1.18 � 10 2) C - (1.18 � 10 4) C2 þ (2.67 � 10 4) 18CT þ (8.39 � 10 7) C2T where C represents the concentration levels of PEG (g per kg of distilled water) and T shows temperature (� C). Petri dishes were stored in an incubator at 25 � C. 2.5. pH A 2-mM solution of MES [2-(N-morpholino) ethanesulfonic acid] was used to prepare the pH of 5 and 6 with an aqueous form of 1 N NaOH. Similarly, a 2 mM solution of HEPES [N-(2-hydroxymethyl) piperazineN-(2-ethane sulfonic acid)] was fixed for the pH of 7 and 8 with one N NaOH. The pH solutions from 9 to 10 were prepared with 2-mM tricine [N-tris (hydroxymethyl) methyl glycine] and fixed with 1 N NaOH. The seeds of I. eriocarpa were prepared according to the method described for preceding tests. Aqueous solutions of pH 5, 6, 7, 8, 9, and 10 were added to each Petri dish individually. An additional solution of pH was used on demand. Petri dishes were stored in an incubator at 25 � C. 2.6. Sowing depth
2. Materials and methods
Twenty-five seeds of I. eriocarpa were sown at depths of 0 (surface), 2, 4, 6, 8, and 10 cm in plastic pots (14 cm diameter and 15 cm height). A sandy loam soil of 0.7% organic carbon and a pH of 7.2 was collected from a nearby field, and used for this study. In each pot, 100 ml of distilled water was applied at sowing, with additional water added to avoid drought stress. These pots were subjected to a minimum and maximum temperature of 25 and 29 � C, respectively. Seedlings at the soil surface were considered to have emerged when cotyledons were visible. Time for 50% germinating or emergence (T50 or E50) was based on Coolbear et al. (1984): � � N=2 ni ðtj ti T50 ¼ nj ni
2.1. Seed description and germination tests Mature I. eriocarpa seeds were collected from several consenting farmers’ fields in the Bhakkar District of Punjab Province, Pakistan (31� N, 71� E) during the start of the winter season of 2014. After har vesting, seeds were properly threshed, cleaned, and dried in the shade at room temperature for seven days prior to being stored in paper bags. Seeds damaged by insects or pathogens were discarded. Before the establishment of each experiment, seeds were soaked in a 10% sodium hypochlorite solution for 5 min to sterilize the seed coat and then rinsed with distilled water. For each treatment, 25 seeds were placed in 9 cm diameter Petri dishes with Whatman No. 10 filter paper for germination. Petri dishes were sealed with a strip of parafilm to reduce water loss. Seeds with radicles of 2 mm were counted as germi nated and removed daily over the course of three weeks.
where N is the total number of germinated seeds or emerged seedlings, nj and ni represent the cumulative number of germinated seeds by adjacent sampling dates, day tj, and ti, respectively, when ni is less than N/2, but N/2 is less than nj. Mean germination or emergence time (MGT or MET) is a measure of the rate and time-spread of germination and was calculated using Ellis and Roberts (1981) equation:
2.2. Temperature In order to evaluate the impact of temperature on seed germination and the emergence of I. eriocarpa, Petri dishes (prepared as explained 2
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MGT / MET ¼
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P
(Dn) /
P
n
where n shows the number of germinated seeds on day D and Dn in dicates the number of days from the beginning of germination/emer gence. The germination or emergence index (GI or EI) is the sum of the ratios of the un-germinated seeds from the day of first count until the final counting day and was recorded as defined by the Association of Official Seed Analysts (1983) applying the undersigning formula. GI ¼ EI ¼
No:of germinated seeds þ Days of first count No:of germinated seeds þ Days of final count
2.7. Statistical analyses All experiments were conducted in a completely randomized design with four replications. All trials were repeated within 20 days of termination of the first run. From the repeated tests, data was subjected to one-way analysis of variance (ANOVA) followed by the use of least significant difference (LSD) at p ¼ 0.05 (Steel et al., 1997), by using SAS (Statistical Analysis Systems), (2002). Nonlinear regression analysis was applied to calculate the effect of NaCl concentration, osmotic/water stress, or soil depth on germination or emergence. At various levels of NaCl and osmotic stress, the germi nation value (%) was fixed to a functional model of three-parameter logistics using SigmaPlot 11.0 software (Systat Software, Inc., Point Richmond, CA, 94801, USA) for analysis:
Fig. 1. Effect of temperature on seed germination of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and the dotted lines show 95% confidence intervals. Vertical bars represent � standard error of the mean. Table 1 Effect of temperature on germination traits of Ipomoea eriocarpa.
Y ¼ A / [1 þ (x/x50)B] where Y is the percentage (%) of germination or emergence at NaCl or osmotic potential x, A is the maximum germination or emergence (%), x50 is the NaCl or osmotic potential concentration required for 50% suppression, and B shows the slope.
Temperature � C
Time to start germination (days)
T50 (days)
MGT (days)
GI
25 30 35 40 45 LSD ¼ 0.05
1.00 1.00 1.00 1.25 1.25 NS
1.48 1.61 1.72 1.65 1.68 NS
4.22 4.17 4.16 4.27 4.45 NS
16.57 16.34 12.78 9.17 3.95 2.95
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index, NS ¼ non-significant.
3. Results 3.1. Temperature A logistic model of three-parameters {G (%) ¼ 79.6/[1 þ (x/ 40.5)7.9], R2 ¼ 0.97} was fixed to check the germination (%) of I. eriocarpa obtained at different temperature ranges (Fig. 1). Germina tion of I. eriocarpa seeds occurred between 25 and 45 � C. Maximum germination (77.5%) was recorded at 25 � C followed by 30 � C (75%). Germination significantly decreased with the increase of temperature. Minimum germination (22.5%) was attained at the highest temperature (45 � C). A 50% reduction from the maximum germination rate (x50) at a temperature of 40.5 � C was observed. The germination index (GI) of I. eriocarpa was maximum (16.57) at 25 � C, which was statistically similar to those at 30 � C. While minimum GI (3.95) was observed at 45 � C (Table 1). 3.2. Salt stress A three-parameter logistic model {G (%) ¼ 68.9/[1 þ (x/190)4.5], R2 ¼ 0.88} was used to model the ability of I. eriocarpa to germinate at various NaCl concentrations (Fig. 2). Salinity tolerance was observed in I. eriocarpa seeds up to a concentration of 125 mM NaCl, with germi nation steadily decreasing according to an increase in salinity. Ipomoea eriocarpa germination was 67.5% at 75 mM NaCl, and low germination (27.50%) followed at 200 mM NaCl. A 50% reduction from the maximum germination rate was achieved at 190 mM of NaCl (Fig. 2). The outset of I. eriocarpa germination was significantly affected by salinity (Table 2). Maximum time to start germination (2.8 days) and T50 (3.5 days) of I. eriocarpa was recorded at 200 mM NaCl followed by 175
Fig. 2. Effect of sodium chloride concentration on seed germination of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and the dotted lines show 95% confidence intervals. Vertical bars represent � standard error of the mean.
mM NaCl (Table 2). The minimum starting time for germination (1.0 day) and T50 (1.6 days) was observed at 0 mM NaCl. The highest germination time for the mean (5.3 days) of I. eriocarpa was noted at 200 mM NaCl, followed by 175 mM NaCl. The lowest mean germination time (3.9 days) was recorded at 0 mM (distilled water), which remained 3
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Table 2 Effect of salinity levels on germination traits of Ipomoea eriocarpa.
Table 3 Effect of drought stress on germination traits of Ipomoea eriocarpa.
NaCl concentration (mM)
Time to start germination (days)
T50 (days)
MGT (days)
GI
Osmotic potential (MPa)
Time to start germination (days)
T50 (days)
MGT (days)
GI
0 (control) 25 50 75 100 125 150 175 200 LSD ¼ 0.05
1.00 1.00 1.00 1.00 1.00 1.00 1.25 2.25 2.75 0.70
1.60 1.62 1.88 1.66 1.91 2.22 2.32 2.79 3.50 0.730
3.93 4.08 4.12 4.16 4.12 4.19 4.42 4.87 5.28 0.30
17.84 15.47 15.62 15.12 13.93 13.33 9.00 5.75 2.52 2.67
0 (control) 0.2 0.4 0.6 0.8 1.0 LSD ¼ 0.05
1.00 1.00 1.25 2.25 3.00 NG 0.73
1.94 2.04 2.27 2.92 3.02 NG 1.00
3.36 3.89 4.50 4.53 5.31 NG NS
16.69 14.04 9.89 6.25 3.0 NG 1.96
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index, NG ¼ no germination; NS ¼ non-significant.
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index.
3.4. Effect of pH Seeds of I. eriocarpa germinated under a range of pH conditions, with maximum germination (77.5%) observed at pH 7 followed by 75% at pH 5 and 6 (Fig. 4). Minimum germination (40%) was calculated at pH 10. At different pH levels, the GI was efficiently affected (Table 4). The maximum GI of I. eriocarpa (17.59) was recorded at pH 7, while the minimum GI (4.37) occurred at pH 10.
similarly consistent up to 125 mM NaCl. The maximum GI (17.84) was recorded at 0 mM, which was similar to those observed at 25 and 50 mM (Table 2). The lowest GI (2.52) was recorded at 200 mM NaCl. 3.3. Osmotic stress A three-parameter logistic model {G (%) ¼ 67.29/[1 þ x/-0.75]7.0, R2 ¼ 0.90} revealed a 50% reduction from maximum germination at 0.75 MPa (Fig. 3). Germination was reduced from 75 to 32% as os motic stress increased from 0 to 0.8 MPa. Similar levels of germination were observed in I. eriorcarpa up to 0.4 MPa, with germination pro gressively decreasing according to an increase in stress. At 1.0 MPa, seed germination was completely suppressed (Fig. 3). The minimum starting time for germination (1 day) of I. eriocarpa was achieved in the control treatment (0 MPa) and at 0.2 MPa (Table 3). At 0.8 MPa, the beginning of germination was delayed to three days. The maximum time for 50% germination was observed at 0.8 MPa (3 days), while minimum time was observed at 0 MPa (1.9 days), being similar to 0.2, 0.4 and 0.6 MPa. The maximum time for mean germination was observed at a maximum of 0.8 MPa (5.3 days) which was followed by 4.5 days at 0.6 and 0.4 MPa. The minimum time for germination was observed at 0 MPa (3.4 days). In the control treatment, the maximum GI was recorded (16.7) while minimum GI (3) was observed at 0.8 MPa (Table 3).
3.5. Sowing depth A three-parameter logistic model {E (%) ¼ 68.20/[1þ(x/8.6)7.9, R2 ¼ 0.82} was fixed for the observation of the seedling emergence data of I. eriocarpa (Fig. 5). Seeds of I. eriocarpa placed at the soil surface pro duced lower rates of germination compared to those buried at 2 cm depth. Seed germination and emergence increased from 55 to 75% as the depth of seed burial increased from 0 to 2 cm. Seedling emergence was 17.5% at 10 cm. According to the model values, suppression of 50% would be achieved at 8.6 cm (Fig. 5). Emergence started earlier at 2 cm (one DAS), similar to 0, 4, 6 and 8 cm, while the beginning of seedling emergence at 10 cm was delayed to 4.3 DAS. Minimum time to 50% emergence (1.4 days) and time to mean emergence (3.0 days) of I. eriocarpa was recorded at the sowing depth of 2 cm while the highest time to 50% emergence (5.1 days) and time to mean emergence (6.6 days) of I. eriocarpa was observed at a sowing depth of 10 cm. This was statistically equivalent to that of 0 cm of sowing depth (Table 5). The maximum EI of I. eriocarpa was calculated at 2 cm sowing depth, while the minimum EI (0.92) was recorded at 10 cm sowing depth. Generally, the EI reduced with increased sowing depth.
Fig. 3. Effect of osmotic potential (MPa) on seed germination of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and the dotted lines show 95% confidence intervals. Vertical bars represent � standard error of the mean.
Fig. 4. Effect of pH on seed germination of Ipomoea eriocarpa. Vertical lines on the top of bars represent � standard error of the mean. 4
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Generally, germination is delayed under critical concentrations of salt (Ungar, 1991). The level of critical concentration which affects germination varies according to species, biotype, ecological conditions, osmotic potential and specific ions present. (Gomez et al., 2008). Our results also suggest that as salt concentration increased, the time to start germination, T50, and the MGT of I. eriocarpa was delayed. The GI and germination percentage of I. eriocarpa were reduced with an increasing rate of salt solution. Significant decreases in the rate and percentage of germination in response to salinity in other Ipomoea spp. were confirmed earlier by Horak and Wax (1991), Oliveira and Norsworthy (2006), Shaw et al. (1987) and Singh et al. (2012). Salinity may also affect germination due to reduced water uptake during imbibition; through high toxicity due to poor ion selectivity or decreased nutrient absorption as a result of ionic imbalance (Romo and Eddleman, 1985). This decrease in germination might be due to an increase in the absorption of toxic substances with water at maximum concentrations of salt (Smith and Comb, 1991; Younis et al., 1991). Similarly, our study suggests that time start to germination, T50, germination index, and MGT of I. eriocarpa increased according to the level of drought stress, while the percentage of germination and GI of I. eriocarpa decreased. In 1978, Gomes et al. reported that I. lacunosa showed 3% germination at 1.0 MPa drought stress. This could be attributed to species-specific behaviour. The literature revealed that some species of Ipomoea have different levels of tolerance to osmotic stress (Hoveland and Buchanan, 1973; Suwanketnikom and Julaka sewee, 2004). In previous studies, germination was delayed due to os motic stress and was faster at 0 MPa in different I. eriocarpa species, including I. purpurea, I. hederacea, I. lacunosa, I. hederacea, J. tamnifolia, and I. obscura (Crowley and Buchanan, 1980; Hoveland and Buchanan, Oliveira and Norsworthy, 2006, 1973; Shaw et al., 1987; Suwanketni kom and Julakasewee, 2004). This study also demonstrated that I. eriocarpa seeds can germinate under variable soil moisture conditions in sub-tropical areas of Pakistan. The survival and germination of I. eriocarpa under a wide pH range indicates that this could not be considered a restrictive factor in the germination and emergence of the weed under varying soil conditions in Pakistan. Ipomoea eriocarpa showed similar results to those reported for I. pandurata, which germinated well in the soil at a pH of 6–8.5 (Horak and Wax, 1991). Ipomoea lacunosa germinated at a pH range from 3 to 10, but optimal germination was recorded at 6–8 pH (Oliveira and Norsworthy, 2006). Pakistani soils are generally alkaline in nature and have low amounts of organic matter, especially in irrigated areas near canals and tubewells (Niaz et al., 2007). The results of this study indicate that seed germination and emer gence increased as sowing depth increased from 0 to 2 cm, whilst it decreased as burial increased towards a maximum sowing depth of 10 cm. Similarly, at a sowing depth of 10 cm, I. eriocarpa seedling emer gence was delayed. The minimum starting time to emergence, T50 for emergence and MGT for this species were observed at a burial depth of 2 cm. Similarly, the EI was reduced by increasing sowing depth. The germination and emergence of various species of Ipomoea have been observed from greater soil depths (Suwanketnikom and Julakasewee, 2004). When the seed burial depth increased from 1.3 to 5 cm in the soil, the seedling emergence of I. purpurea was delayed (Cole, 1976). Ipomoea hederacea, I. lacunosa, and I. hederacea (all closely related to I. eriocarpa) had maximum emergence at sowing depths between 1.3 and 2.5 cm (Gomes et al., 1978). The seedling emergence of I. obscura was also low (5%) at the soil surface. The highest emergence of I. lacunosa was 87% for the seeds planted at a depth of 1 cm (Suwanketnikom and Julaka sewee, 2004). The emergence of Ipomoea tricolor Cav. was greatest for sowing depths between 2.5 and 7.5 cm (Chandler et al., 1977). Greater emergence at shallow depths indicates that zero-tillage farming prac tices can improve the germination and survival of this weed under field conditions. Our results also suggest that the placement of seeds on the soil surface may decay faster because of increased predation activity and variations in temperature and moisture conditions (Chauhan and
Table 4 Effect of pH on germination traits of Ipomoea eriocarpa. pH
Time to start germination (days)
T50 (days)
MGT (days)
GI
5 6 7 8 9 10 LSD ¼ 0.05
1.00 1.00 1.00 1.25 1.25 1.25 NS
1.75 1.70 1.73 1.80 1.74 2.20 NS
4.16 4.13 4.14 4.26 4.42 4.37 NS
16.94 17.07 17.59 14.35 9.52 7.37 2.64
T50 ¼ time to obtain 50% germination, MGT ¼ mean germination time, GI ¼ germination index, NS ¼ non-significant.
Fig. 5. Effect of sowing depth (cm) on seedling emergence of Ipomoea eriocarpa. The bold lines represent a three-parameter logistic model fitted to the data of I. eriocarpa and thin lines show 95% confidence intervals. Vertical bars repre sent � standard error of the mean. Table 5 Effect of sowing depth on emergence traits of Ipomoea eriocarpa. Sowing depth (cm)
Time to start germination (days)
E50 (days)
MET (days)
EI
0 2 4 6 8 10 LSD ¼ 0.05
1.25 1.00 1.00 1.25 1.50 4.25 0.942
4.06 1.43 1.53 3.08 3.22 5.12 1.145
5.72 2.95 3.43 4.53 4.59 6.63 1.185
4.75 17.19 14.29 10.71 6.43 0.92 1.883
E50 ¼ time to obtain 50% germination, MET ¼ mean germination time, EI ¼ germination index.
4. Discussion The results obtained from our study suggest that I. eriocarpa is able to germinate over a range of temperatures, allowing its emergence over the spring, summer, and autumn seasons in a majority of the sub-tropical areas of Pakistan. Such temperature adaptation may provide I. eriocarpa with competitive advantages under varying environmental conditions. Results also indicate that the GI of I. eriocarpa decreased as the temperature increased. Reduced germination with increasing tem perature has also been reported in other Ipomoea species (Cole and Coats, 1973; Horak and Wax, 1991; Oliveira and Norsworthy, 2006; Shaw et al., 1987). These studies reported maximum germination of I. pandurata at 20 � C, Ipomoea purpurea (L.) Roth. at 24 � C, I. lacunosa at 25 � C and finally J. tamnifolia at 35 � C. 5
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Johnson, 2010). Tillage determines the vertical spread of seed in the soil structure and this, in turn, affects seedling establishment through factors such as seed predation, dormancy, longevity, and potential of seedling emergence from a given depth (Chauhan et al., 2006b). The emergence of this weed can be suppressed at burial depths of 8–10 cm under deep tillage operations.
Cole, A.W., Coats, G.E., 1973. Tall morning glory germination response to herbicides and temperature. Weed Sci. 21, 443–446. Cole, A.W., 1976. Tall morning glory response to planting depth. Weed Sci. 24, 489–492. Coolbear, P., Francis, A., Grierson, D., 1984. The effect of low temperature pre- sowing treatment on the germination performance and membrane integrity of artificially aged tomato seeds. J. Exp. Bot. 35, 1609–1617. Crowley, R.H., Buchanan, G.A., 1980. Responses of Ipomoea spp and small flower morningglory (Jacquenontia tamnifolia) to temperature and osmotic stress. Weed Sci. 28, 87-82. Dias-Filho, M.B., 1996. Germination and emergence of Stachytarpheta cayennensis and Ipomoea asarifolia. Planta Daninha 14, 183–188. Ellis, R.A., Roberts, E.H., 1981. The quantification of ageing and survival in orthodox seeds. Seed Sci. Technol. 9, 373–409. Firehun, Y., Tamado, T., 2006. Weed flora in the Rift Valley sugarcane plantations of Ethiopia as influenced by soil types and agronomic practises. Weed Biol. Manag. 6, 139–150. Gan, Y.E., Stobbe, H., Njue, C., 1996. Evaluation of selected nonlinear regression models in quantifying seedling emergence rate of spring wheat. Crop Sci. 36, 165–168. Gomes, L.F., Chandler, J.M., Vaughan, C.E., 1978. Aspects of germination, emergence and seed production of three Ipomoea taxa. Weed Sci. 26, 245–248. Gomez, R., Naranjo, E.M., Garzon, O., Castillo, J.M., Luque, T., Figueroa, M.E., 2008. Effects of salinity on germination and seedling establishment of endangered Limoniumem arginatum (Wild.) Kuntze. Coast. Res. 24, 201–205. Grubben, G.J., 1978. Ipomoea Eriocarpa R.Br. in: Vegetable Seeds for the Tropics. Koninklijk Instituutvoor de Tropen, p. 336. Hardcastle, W.S., 1978. Influence of temperature and acid scarification duration on scarlet morning glory (Ipomoea coccinea) seed germination. Weed Sci. 26, 261–263. Horak, H.J., Wax, L.M., 1991. Germination and seedling development of big root morningglory (Ipomoea pandurata). Weed Sci. 39, 390–396. Hoveland, C.S., Buchanan, G.A., 1973. Weed seed germination under simulated drought. Weed Sci. 21, 322–324. Ikeda, F.S., Carmona, R., Mitja, D., Guimaraes, R.M., 2008. Light and KNO3 on Tridax procumbens seed germination at constant and alternating temperatures. Planta Daninha 26, 751–756. Marwat, K.B., Hashim, S., Ali, H., 2010. Weed management: a case study from north-west Pakistan. Pak. J. Bot. 42, 341–353. Michel, B.E., Kaufmann, M.R., 1973. The osmotic potential of polyethylene glycol 6000. Plant Physiol. 51, 914–916. Niaz, A., Ranjha, A.M., Rahmatullah, A.H., Waqas, M., 2007. Boron status of soils as affected by different soil characteristics–pH, CaCO3, organic matter and clay contents. Pak. J. Agric. Sci. 44, 428–435. Oliveira, M.J., Norsworthy, J.K., 2006. Pitted morningglory (Ipomoea lacunosa) germination and emergence as affected by environmental factors and seeding depth. Weed Sci. 54, 910–916. Romo, J., Eddleman, L., 1985. Germination response of greasewood (Sarcobatus vermiclatus) to temperature. Water potential and specific ions. Range Manag. 38, 117–120. SAS (Statistical Analysis Systems), 2002. SAS Procedures Guide. Statistical Analysis Systems Institute, Cary, NC, Version 9. Sekar, K.C., Manikandan, R., Srivastava, S.K., 2012. Invasive alien plants of uttarakhand Himalaya. Proc. Natl. Acad. Sci. India Sect. B Biol. Sci. 82, 375–383. Shaw, D.R., Smith, H.R., Cole, A.W., Snipes, C.E., 1987. Influence of environmental factors on small flower morningglory (Jacquemontia tamnifolia) germination and growth. Weed Sci. 35, 519–523. Singh, M., Ramirez, A.H., Sharma, S.D., Jhala, A.J., 2012. Factors affecting the germination of tall morningglory (Ipomoea purpurea). Weed Sci. 60, 64–68. Smith, P.T., Comb, B.G., 1991. Physiological and enzymatic activity of pepper seeds (Capsicum annuum) during priming. Plant Physiol. 82, 71–78. Steel, R.G.D., Torrie, J.H., Dickey, D., 1997. Principles and Procedures of Statistics. A Biometrical Approach, third ed. McGraw Hill Book Co. Inc., New York, pp. 352–358. Suwanketnikom, R., Julakasewee, A., 2004. Hard seededness and germination of small white flower morning glory. Kasetsart. Nat. Sci. 38, 425–433. Tanveer, A., Arshad, M., Abbas, R.N., Tahir, M., Javaid, M.M., Ikram, R.M., 2012. Germination response of weeds to different sources and concentrations of N and P. Role of Agronomy in National Food Security, p. 36. Ungar, I., 1991. Ecophysiology of Vascular Halophytes. CRC Press, Boca Raton, FL, p. 209. Webster, T.M., MacDonald, G.E., 2001. A surveys of weeds in various crops in Georgia. Weed Technol. 15, 771–790. Younis, S.A., Shahatha, H.A., Hagop, P.G., Al-Rawi, F.I., 1991. Effect of Salinity on the Viability of Rice Seeds. Plant Growth, Drought and Salinity in the Arab Region, pp. 235–244.
5. Conclusion The germination and seedling emergence of I. eriocarpa is influenced by the various ecological elements of temperature, salinity, drought, pH, and sowing depth. Our results explain that I. eriocarpa can survive under subtropical and semi-arid conditions, which are characterized by hot summers and mild to cool winters, moderate moisture, and welldrained, slightly acidic soil conditions. This weed has the potential to germinate and emerge to varying degrees under a variety of ecological conditions. Our study will be supportive in describing an environment conducive to the germination of this weed for the purpose of its effective management. Furthermore, the results of this study will contribute to wards the efficient management of this weed species not only in agro nomic crops but also in pastures. Author contributions Asif Tanveer: Supervision, Supervised the overall research, Mujahid Abbas Khan: Data curation, Experimental execution and data handling, Hafiz Haider Ali: Formed paper structure, Muhammad Mansoor Javaid: Formal analysis, Data analysed, Ali Raza: Graphics and tabulation of data, Bhagirath Singh Chauhan: Supervised the overall research and reviewed the paper. Declaration of competing InterestCOI No potential conflict of interest was reported by the authors. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.cropro.2019.105070. References Association of Official Seed Analysts, 1983. Rules for testing seeds. Seed Technol. 16, 1–113. Burkill, H.M., 1985. The Useful Plants of West Tropical Africa, second ed., vol. 1. Families A–D. Royal Botanic Gardens, Kew, United Kingdom, p. 960. Canossa, R.S., Oliveira, J.R., Constantin, R.S., Braccini, J., Biffe, A.L., Alonso, D.F., Blainski, D.G., 2008. Effect of temperature and light on joyweed (Alternanthera tenella) seed germination. Planta Daninha 26, 745–750. Chandler, J.M., Munson, R., Land Vaughan, C.E., 1977. Purple moonflower: emergence, growth and reproduction. Weed Sci. 25, 163–167. Chauhan, B.S., Gill, G., Preston, C., 2006. African mustard (Brassica tournefortii) germination in southern Australia. Weed Sci. 54, 891–897. Chauhan, B.S., Gill, G., Preston, C., 2006. Tillage system effects on weed ecology, herbicide activity and persistence: a review. Anim. Prod. Sci. 46, 1557–1570. Chauhan, B.S., Johnson, D.E., 2010. The role of seed ecology in improving weed management strategies in the tropics. Adv. Agron. 105, 221–262. Chauhan, B.S., Abugho, S.B., 2012. Threelobe morningglory (Ipomoea triloba) germination and response to herbicides. Weed Sci. 60, 199–204.
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