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Lodging behavior and yield potential of spring wheat (Triticum aestivum L.): effects of ethephon and genotypes
Field Crops Research 87 (2004) 207–220
Lodging behavior and yield potential of spring wheat (Triticum aestivum L.): effects of ethephon and genotypes S.C. Tripathia,*, K.D. Sayreb, J.N. Kaulc, R.S. Narangc a
b
Directorate of Wheat Research, Post Box No. 158, Karnal, 132 001, Haryana, India Wheat Programme, CIMMYT, Lisboa 27, Apartado Postal 6-641, 06600 Mexico, D.F., Mexico c PAU, Ludhiana, Punjab, India
Received 12 June 2003; received in revised form 10 October 2003; accepted 11 November 2003
Abstract Crop lodging is a chronic constraint, commonly limiting irrigated spring wheat yields. Cultivar selection and use of growth regulators are the two factors that can alter lodging incidence to a significant extent. In this study, lodging behavior and yield potential for 16 spring wheat (Triticum aestivum L.) genotypes were studied under disease-free, irrigated conditions at the CIMMYT (Centro Internacional de Mejoramiento de Maı´z y Trigo) experiment station near Ciudad Obregon, Sonora, Mexico, during 1997–1998 and 1998–1999. For the conventional planting system, two additional treatments were implemented, one using support nets to eliminate lodging and the other by applying the growth regulator, ethephon, to control lodging. In both years, lodging occurred late (25–30 days after anthesis) but significant grain yield reductions for lodging susceptible genotypes were observed. The Indian cultivar, HD 2329, and the Mexican advanced line, Super Seri, recorded maximum grain yield loss (7.6–8.9%) due to lodging. Ethephon (480 g ha1) application controlled lodging by reducing plant height but also decreased average grain yield by 8.3%, which was primarily associated with a significant reduction in number of kernels per spike. Interaction between management practices (with and without ethephon) and genotypes was significant for grain yield, HI, kernel weight and kernels per spike but non-significant for biomass and spikes per square meter. Super Seri produced the highest yield across all management practices. This genotype possesses the translocation carrying the Lr19 gene, which likely contributed to its higher grain yield (10–12%) when compared to the near isogenic cultivar, Seri 82, which is devoid of the Lr19 gene. Therefore, the incorporation of this gene into other high yielding semi-dwarf wheat genotypes may enhance wheat yield in addition to providing resistance to leaf rust. # 2003 Elsevier B.V. All rights reserved. Keywords: Spring wheat; Lodging behavior; Netting; Yield; Ethephon; Growth regulator; Lr19 gene
1. Introduction The advent of semi-dwarf wheat cultivars occurred through incorporation of dwarfing genes mainly from Norin 10, which can limit lodging under moderate levels of inputs, especially fertilizer and irrigation. *
Corresponding author.
This lodging resistance, resulting from shorter and stiffer straw, is markedly expressed at moderate levels of N fertility (Pinthus, 1973; Fischer and Wall, 1976; Stapper and Fischer, 1990a,b). Improved lodging resistance increases yield largely by permitting greater doses of N fertilizer. Under certain agronomic conditions, however, even spring wheat cultivars carrying one or even two major, Norin 10 dwarfing genes (Rht1,
0378-4290/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2003.11.003
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Rht2) have been observed to lodge in Mexico, Australia (Fischer and Stapper, 1987) and in India (Narang et al., 1994). This form of lodging which is most common with well-managed crops, occurs near or after flowering and is primarily the result of wind during or soon after irrigation or rainstorms. Crook and Ennos (1995) advanced the view that stem strength was reduced by 20% as N fertilizer rate increased from 160 to 240 kg ha1. Similarly, application of N at 200 kg ha1 decreased breaking strength of the 2nd internode, leading to increased lodging (Garg et al., 1973). To avoid lodging, many farmers in South Asia forego the last irrigation (Hobbs et al., 1998), which may be crucial for grain filling and can ultimately limit grain yield. This practice is common in India for the following reasons: (i) occurrence of frequent high winds during grain filling; (ii) the wide use of flat planting and flood irrigation; and (iii) the lack of acceptable cultivars that are lodging tolerant at higher N rates (180–200 kg ha1). Fischer and Stapper (1987) reported that increasing the N fertility beyond a certain limit induced lodging and ultimately decreased grain yield and its components. The reduction in grain yield caused by culm lodging ranged from 7 to 35% with greatest effect when lodging occurred within the first 20 days after anthesis. Stapper and Fischer (1990b) concluded that higher yields under irrigated condition could be achieved consistently and efficiently only with the genotypes that can resist lodging. Ali (1993) and Kheiralla et al. (1993) reported 19.9 and 7.2% reductions in grain yield in Egypt caused by lodging at 225 and 275 kg N ha1 compared with 150 and 175 kg N ha1 applications, respectively. Recently, in a study of winter wheat, it was observed that lodging occurred in patches, usually after rain, and was most common in early sown, high seed rate, high residual nitrogen treatments (Berry et al., 2000). Lodging, a serious problem under irrigated and high input N fertility conditions, interferes with water and nutrient uptake, reduces effective light interception, decreases grain fill, provides a more conducive environment for disease and increases harvesting costs and losses. Yield reductions associated with harvesting losses caused by lodging are usually greater where combine harvesting is a common practice, but may be less in developing countries where
hand harvesting instead of combine harvesting is commonly practiced by many small farmers. The nature and extent of lodging are closely related to culm characteristics, which can be modified by application of growth inhibitors (Pinthus, 1973). Application of growth inhibitors, like ethephon (2chloro ethyl phosphonic acid) or CCC (chlormequat chloride), was reported to be useful in decreasing plant height and subsequently reducing lodging (Pinthus, 1973; Knapp et al., 1987; Ali, 1993; Crook and Ennos, 1995). However, in another study it was observed that ethephon did not provide complete lodging control but increased grain yields by 5–21% depending upon the genotype and lodging severity (Webster and Jackson, 1993). To quantify the effect of lodging on grain yield and to estimate the yield potential of different high yielding genotypes requires a thorough study. Wheat genotypes should be grown with and without artificial lodging protection (support nets) and protected from other prevalent diseases. At the same time, it may also be helpful in understanding the lodging behavior of high yielding wheat genotypes with the use of growth retardant like ethephon. Fischer and Stapper (1987) conducted artificial lodging experiments in northwest Mexico, where the crop was forced to lodge at varying angles at different stages of crop development. However, lodging at a specified angle at a given time does not occur normally under most field conditions. Thus, it seems that yield losses from lodging in this study might have been over estimated. The mechanics of lodging in winter wheat (single genotype) was studied by Berry et al. (2000) and they calculated wind speed at which a shoot’s leverage would exceed the strength of stem base (stem lodging), and at which the leverage of all the shoots on a plant would exceed its anchorage strength (root lodging). This phenomenon in spring wheat, however, might be different as crop suffers high temperature coupled with moderate to high wind speed during grain filling period. Severity of lodging at Yaqui Valley (Obregon) was observed in a recurring socioeconomic survey (80 farmers field each year, 1981–1991) where all farmers experienced lodging, ranging from 18 to 40% (Dagoberto Flores, CIMMYT Economist, personnel communication). In our study, high yielding spring wheat cultivars (16) were grown under high N fertility using flat planting with
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flood/basin irrigation, with and without support nets, and with ethephon application. Other biotic and abiotic factors were not yield limiting at any stage of crop development. Thus, a favorable situation was achieved to maximize yield potential and assess yield loss due to natural lodging. Our objectives, therefore, were to: (1) estimate yield potential and losses caused by lodging for different genotypes; (2) ascertain the effect of applying ethephon to control lodging for flat seeded, flood irrigated conditions; and (3) assess the interaction between management practices and genotype on yield and other traits.
2. Materials and methods The experiment was conducted in 1997–1998 and 1998–1999 at the CIMMYT experiment station near Ciudad Obregon, Sonora, Mexico (27.330 N latitude, 109.090 W longitude and 38 m above sea level). The soil type was coarse sandy clay (mixed montmorillonitic typic calciorthid), low in NO3-N (29.5 mg kg1) and NH4 þ -N (6.1 mg kg1) and organic matter (0.89%), medium in available P (7.7 mg kg1), high in K (557 mg kg1) and alkaline ðpH ¼ 8:0Þ in nature. There was more rainfall after planting in 1997–1998 but minimum temperatures in November–January and March were lower in 1998–1999 as compared to 1997–1998 providing more favorable conditions for growth and development (Table 1). This type of macro-environment for wheat in this location is classified as an irrigated area having a rather dry climate, high solar radiation, cool nights, and moderate daytime temperatures during the growing season.
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The present study included 16 genotypes, including eleven cultivars/advanced lines from Mexico and five cultivars from India (Table 2), which represented a range of both era of development and contrast in plant morphology. All genotypes were semi-dwarf carrying at least one dwarfing gene (Rht1 or Rht2). One Mexican cultivar, Oasis 86, has both Rht1 and Rht2. Another CIMMYT advanced line, ‘‘Super Seri’’, which carries the translocation conveying the Lr19 leaf rust resistance gene, was included in this trial, and is a near isogenic line of the cultivar, ‘‘Seri 82’’. These two near isogenic lines were included to quantify the effect of this translocation/gene on yield and other features under different management practices where leaf rust was not present. Singh et al. (1998), using comparisons of several sets of near isogenic lines (with and without Lr19), found consistently higher yields for the lines with the translocation carrying Lr19. The genotypes included in the trials were divided into two categories, tolerant and susceptible to lodging, on the basis of past experience in India and Mexico. A relatively large number of different genotypes was included in the study to provide adequate diversity in plant type and to insure that more reliable information could be generated. Each year the experiment was conducted as a randomized complete block design with three replications using a split plot treatment arrangement. Main plots consisted of the following three management practices: (i) seeding on the flat with flood irrigation without support nets; (ii) seeding on the flat with support nets for protection against lodging; and (iii) seeding on the flat with ethephon applied (480 g ha1) at DC 38 (Zadoks et al., 1974). The stage (DC 38) of
Table 1 Monthly mean maximum and minimum temperature and rainfall during wheat growing cycle (1997–1998 and 1998–1999) at CIMMYT, Cd Obregon, Sonora, Mexico Months
Temperature (8C)
Rainfall (mm)
1997–1998
November December January February March April
1998–1999
Maximum
Minimum
Maximum
Minimum
29.7 23.3 26.1 24.6 27.7 30.4
13.4 8.6 7.1 7.1 9.4 9.8
30.3 25.2 26.7 27.2 27.9 29.9
12.8 7.7 5.5 7.1 8.9 11.3
1997–1998
1998–1999
38.5 33.4 0.0 11.8 1.9 0.0
1.1 1.0 0.0 0.0 3.4 0.0
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Table 2 List of genotypes, pedigree, source, lodging rating and ethephon application (days before anthesis) No.
Genotypes a
1 2 3 4 5 6 7 8 9 10 11 12
PBW 343 UP 2338a Baviacora 92a Seri 82a Starb Munia/Kauzb Pastorb Super Serib Weaverb WH 542a CPAN 3004a HD 2329a
13 14 15 16
Pavon 76a Rayon 89a Bacanora 88a Oasis 86a a b
Pedigree
Lodging rating
Origin
Ethephon application
ND/VG9144//KAL/BB/3/YACO/4/VEE#5 UP368/VL421//UP262 BOW/NAC//VEE/3/BJY/COC KVZ/BUHO//KAL/BB LFN/SDY//PVN JUN/BOW//VEE#5/BUC PFAU/SERI//BOW Seri5//Aga/6Yr HAHN2/PRL JUP/BJY//URES GLL/AUSTII61.157//CNO/NO/3/VEE SLSib/NP852/4/PjSib/P14//Kt54B/3/K65/5/ Ska/6/UP262 VCM//CNO/7C/3/KAL/BB URES2/PRL JUP/BJY//URES AGA/3YR
Tolerant Tolerant Tolerant Tolerant Tolerant Tolerant Susceptible Susceptible Tolerant Susceptible Susceptible Susceptible
India India CIMMYT CIMMYT CIMMYT CIMMYT CIMMYT CIMMYT CIMMYT India India India
21 21 20 22 17 16 20 23 17 20 21 17
Susceptible Susceptible Susceptible Susceptible
CIMMYT CIMMYT CIMMYT CIMMYT
17 20 20 22
Mexican or Indian cultivars. CIMMYT advanced lines.
ethephon application was in the line of literature (Thomson, 1995; Sayre, 1996). The support net treatment was installed soon after the first irrigation at the level of the current crop height at that time to facilitate the growth of the young plants through the 20 cm 20 cm net holes. As the crop grew, the height of the net was adjusted so that it was maintained 15–20 cm below the full height of the wheat plants. Sub-plots consisted of the 16 genotypes. The sub-plots for the three flat seeded, flood irrigated main plot treatments were 5.5 m long with eight rows per plot, 20 cm apart, providing a plot area of 8.8 m2. In both years, the experiments were planted with a plot drill in the last week of November into dry soil at a rate of 300 viable seeds m2 followed by irrigation. Prior to planting, a summer green manure crop (Sesbania aculeata), which contained approximately 80 kg N ha1 in the biomass, was incorporated into the soil by cultivation. At the time of planting 100 kg N ha1 was applied as urea and 20 kg ha1 P as triple super phosphate. Potassium was not applied due to inherent high soil content. The remaining N fertilizer was top dressed as urea at the 1st node stage (DC 31) followed by irrigation. Irrigation was applied by basin flooding when available water in the top 60 cm approached 50% depletion. Fungicides were applied at 15-day intervals from head-
ing to mid-grain filling stage to prevent prevalent diseases, which facilitated an unbiased estimate of yield. Clodinafop-propargyl at 250 ml ha1 for grass weed control and bromoxinil at 1.5 l ha1 tank-mixed with thiofensulfuron at 25 g ha1 for broad leaf weed control were applied at recommended times using a back-pack motorized sprayer. Ethephon (2-chloro ethyl phosphonic acid) was applied at 480 g ha1 at DC 38 by a carbon dioxide, pressure sprayer, using a flat nozzle. This growth retardant was applied as and when genotypes attained DC 38 stage. Varieties like Star, Munia Kauz, Weaver, HD 2329 and Pavon 76 reached DC 38 stage 16–17 days before anthesis whereas others between 20 and 23 days before anthesis (Table 2). Lodging was scored with the formula ((% plot area lodged angle of lodging from the vertical)/90), as described by Fischer and Stapper (1987). Occurrence of lodging was recorded in each plot in relation to days after anthesis. Dates of 75% seedling emergence, anthesis (50% of spikes with at least one anther extruded) and physiological maturity (loss of spike and peduncle color in at least 75% of the plot) were recorded via frequent visits. Duration from emergence to anthesis and maturity was considered to be days to anthesis and maturity, respectively, for the different genotypes. A 3 m length per plot of the center six rows was manually harvested approximately 7–10 days after
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physiological maturity for each experiment, leaving approximately 1 m border on each plot end. At the time of harvest, a sub-sample of 100 culms from each plot was taken at random and its fresh weight was recorded. The sample was then dried at 75 8C for 48 h, weighed and used to determine the dry matter content of biomass for calculating total biomass production, harvest index (HI) and number of spikes per square meter. The remaining harvested plot material was weighed fresh at harvest, threshed after 1–2 weeks of sun drying and then the grain weight was recorded. A sub-sample of kernels was taken and weighed (fresh and dry) to adjust grain yield to t ha1 at the standard 120 g kg1 moisture content, which is used for grain yield designation throughout. The same grain subsample was also used to provide 400 random kernels to estimate kernel weight. Biomass production rate (BPR) was calculated as biomass divided by duration from seedling emergence to physiological maturity and similarly grain production rate (GPR) as grain yield divided by duration from anthesis to physiological maturity. The methodology, outlined above, to estimate biomass and grain yield, HI, BPR, GPR and yield components is as per the procedure described by Bell and Fischer (1994). Analysis of variance was carried out on yearly and data combined over years for the split plot design by using MSTATC (Michigan State University). Whereas, lodging %, lodging angle and lodging score were analyzed as completely randomized block design by excluding two main plots, due to no lodging in ethephon applied and netting, artificially lodging protected plot. Significance of each source was determined by an F-test. Least significance difference (LSD) tests were performed to determine significant differences between individual means. Phenotypic correlations (r) were calculated using genotype means (across replications, main plots and years) between all recorded traits vs grain yield.
3. Results 3.1. MSS and F-test of growth, yield, yield components and lodging behavior Tables 3 and 4 represent the analysis of variance summary for biomass, grain yield, yield components,
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days to anthesis and maturity, plant height, biomass and grain production rate, lodging %, angle and lodging score. Lodging behavior parameters were not significant for year but were significant for genotype and year genotype. Significant main plot effect differences for year, management practice were detected for all factors except kernel weight, spikes per square meter, height and maturity for years, and kernel weight and spikes per square meter were for management practices, which were non-significant. The year management practice interaction was significant for grain yield, HI, kernels per square meter, anthesis and GPR. Cultivar main effect and the year cultivar were significant for all the factors. The management practices cultivar interactions were significant for all factors except biomass, spikes per square meter, anthesis and BPR, whereas, the three-way interaction was significant for HI only. These significant interactions with genotype clearly illustrated the necessity and benefit of including a relatively large number of divergent advanced lines/ cultivars rather than the limited number that is normally used for agronomic experiments that are aimed at comparing contrasting crop management practices. This approach can also help in insuring a thorough understanding of potential crop management cultivars interactions, which should lead to a more efficient identification of the type of cultivar that needs to be selected for defined crop management practices. 3.2. Effect of lodging From combined analysis over the years and cultivars, it was observed that flat planting with support nets, which completely eliminated lodging, resulted in significantly higher biomass yield and grain yield as compared to the treatment without nets (Table 5). The difference in grain yield between flat planting with support nets (8.89 t ha1) vs flat planting without support nets (8.59 t ha1) provided an estimate of average grain yield loss as a consequence of lodging (0.3 t ha1 or 3.4% yield loss), ranging from many genotypes showing no significant lodging or yield loss without the support nets to cultivars like HD 2329 which recorded a 8.9% grain yield loss (and a lodging score of 75.4) without the support nets (Tables 5 and 6). The lodging protection by nets resulted in higher
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Source
Mean squares d.f.a
Year (Y) 1 Error a 4 Management (M) 2 YM 2 Error b 8 Genotype (G) 15 YG 15 MG 30 YMG 30 Error c 180 CV (error c, %) a
Degrees of freedom. Values 103. c Values 106 . * F-test at P ¼ 0:05. ** F-test at P ¼ 0:01. b
Biomassb (t ha1)
Yieldb (t ha1)
HI
Kernel weight (mg)
Spikes per square meter
Kernels per spike
BPR (kg ha1 GPR (kg ha1 Gram of kernels Kernels per square meterc per day) per day) per spike
81.913** 6.687 11.944** 6.588 2.182 8.811** 1.920** 0.941 0.721 0.841 5.2
90.950** 0.902 26.775** 2.902** 0.169 4.858** 0.826** 0.481** 0.179 0.149 4.6
0.067** 0.001 0.052** 0.004** 0.001 0.014** 0.001** 0.001** 0.001* 0.000 4.1
1.69 11.05 0.49 4.93 3.93 331.18** 6.53** 2.74** 1.97 1.29 2.8
1,554 2,439 15,130 314 3,740 94,410** 4,045** 2,143 1,801 1,627 8.2
1872** 22 718** 53 15 500** 25** 17** 12 9 8.0
476.08** 117.697 118.312** 22.632** 1.972 107.315** 6.429** 1.743** 1.194 0.956 5.3
4860** 307 1190** 256 100 202** 142** 44 43 46 5.1
57252** 443 18394** 1034* 59 4960** 644** 215** 104 73 4.9
2.89** 0.02 1.30** 0.04 0.02 0.98** 0.05** 0.04** 0.02 0.01 7.6
S.C. Tripathi et al. / Field Crops Research 87 (2004) 207–220
Table 3 Analysis of variance summary, across years, for biomass and grain yield, harvest index (HI), kernel weight, spikes per square meter, kernels per square meter, kernels per spike, BPR, GPR and gram of kernels per spike
S.C. Tripathi et al. / Field Crops Research 87 (2004) 207–220
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Table 4 Analysis of variance summary, across years, for plant height (Ht), days to anthesis and maturity, lodging %, angle and lodging score Sources
Mean squares a
Year (Y) Error a Management (M) YM Error b Genotype (G) YG MG YMG Error c CV (error c, %)
Sources
d.f.
Ht (cm)
Anthesis (days)
Maturity (days)
1 4 2 2 8 15 15 30 30 180
60.3 30.5 2873.4** 115.6 30.4 1041.2** 32.6** 10.9** 7.9 5.2 2.6
116.3** 5.6 54.7** 2.2* 0.4 392.3** 32.1** 0.7 0.9 0.5 0.8
1.68 5.33 225.27** 13.44 4.05 167.85** 13.38** 2.36** 1.32 1.3 0.9
Year (Y) Error a Genotype (G) YG Error b
Mean squares d.f.a
Lodging %
Lodging angle
Lodging score
1 4 15 15 60
3939 1370 7642** 1311** 439
1066 844 4838** 928** 294
5104 1737 5285** 937* 400
a
Degrees of freedom. F-test at P ¼ 0:05. ** F-test at P ¼ 0:01. *
biomass and grain yield that was associated with significantly higher kernels per square meter than without nets (Table 5). It is of interest to note that even though many genotypes lodged more than 90% (Table 6) at dough stage, yield losses were 2–4% only. 3.3. Effect of ethephon Application of ethephon at DC 38 significantly reduced the plant height (9.8%), grain yield (8.3%), HI (9.0%), kernels per square meter (8.0%), kernels per spike (12.5%), kernel weight per spike (12.9%) and grain production rate (10.9%) despite controlling lodging as compared to the treatment without ethephon (Table 5). This yield reduction was largely associated with the decrease in number of kernels per spike while biomass, kernels weight, spikes per square meter and BPR were non-significant. Durations from emergence to anthesis and maturity were delayed by 1–2 days by ethephon application (Table 5). Ethephon acts as an anti-auxin and thereby retards growth, biomass and yield when compared with the lodging protected treatment. Interestingly, the ethephon application did not result significant difference in kernel weight. It indicated that ethephon acted in more to reduce kernel number rather than its weight.
3.4. Management genotypes The results presented in Fig. 1 revealed significant interactions between management practice and genotype for grain yield, HI, kernel weight and kernels per spike but were non-significant for biomass and spikes per square meter (Table 2). Many genotypes exhibited significantly lower grain yield when treated with ethephon as compared to the control. Grain yield reduction by ethephon application led to a significant decreases in HI for all the genotypes except Super Seri and Star. The reduction in grain yield was characterized by significant decreases in number of kernels per spike for many genotypes. Ethephon application reduced kernels per spike for some genotypes (such as Baviacora 92) but not for other genotypes (such as Weaver). Although kernel weight of most genotypes was not affected by ethephon application, it was increased for Pavon 76 and decreased for PBW 343. Phenotypic correlations between plant height and the lodging parameters were all non-significant ðr < 0:06Þ. These results tend to negate the conventional wisdom that taller genotypes are inclined to lodge more than shorter ones. In this study, the tallest cultivar (Baviacora 92) showed almost no lodging while the shortest cultivar (Oasis 86) exhibited an intermediate level for all lodging indicators.
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Table 5 Effect of ethephon and netting on average biomass, grain yield, HI, yield components, plant height, days to anthesis and maturity across varieties (in yearly and combined analysis) Parameters
Management practices Years 1
Biomass (t ha )
nets
þ nets
þ ethephon
LSD (5%)
1997–1998 1998–1999 Combined
17.07 17.54 17.31
17.33 18.62 17.98
16.73 18.17 17.45
ns
Grain yield (t ha1)
1997–1998 1998–1999 Combined
8.17 9.01 8.59
8.39 9.41 8.89
7.11 8.62 7.87
0.31 0.11 0.14
HI
1997–1998 1998–1999 Combined
0.42 0.45 0.44
0.43 0.45 0.44
0.38 0.42 0.40
0.01 0.01 0.01
Kernel weight (mg)
1997–1998 1998–1999 Combined
40.68 41.05 40.86
41.08 40.72 40.89
40.99 40.53 40.76
0.46 0.49
0.76 ns ns
Spikes per square meter
1997–1998 1998–1999 Combined
475 478 477
498 500 499
494 503 498
Kernels per square meter
1997–1998 1998–1999 Combined
17896 19561 18728
18160 20614 19387
15424 19019 17221
673 902 467
Kernels per spike
1997–1998 1998–1999 Combined
38 42 40
37 42 39
32 38 35
2 2 1
Gram of kernels per spike
1997–1998 1998–1999 Combined
Anthesis (days)
1997–1998 1998–1999 Combined
89 89 89
89 90 89
90 91 91
0.4 0.3 0.3
Maturity (days)
1997–1998 1998–1999 Combined
132 131 132
131 132 132
134 134 134
1.2 1.0 0.7
Plant height (cm)
1997–1998 1998–1999 Combined
91.9 88.9 90.4
92.1 90.8 91.5
80.8 82.2 81.5
2.9 3.4 1.8
BPR (kg ha1 per day)
1997–1998 1998–1999 Combined
129.1 133.6 131.3
131.9 141.3 136.6
124.5 135.3 129.8
7.5 2.8 3.3
GPR (kg ha1 per day)
1997–1998 1998–1999 Combined
166.8 191.6 179.1
174.4 198.4 186.4
141.7 177.5 159.6
4.8 3.9 2.6
1.54 1.72 1.63
In contrast, Weaver, the second shortest genotype did not lodge at all but Pastor, the second tallest genotype, was fairly lodging susceptible (Table 6).
1.52 1.69 1.61
1.56 1.71 1.42
ns ns ns
0.06 0.09 0.04
This again illustrates the value for agronomists to study a relatively large number of diverse genotypes, whenever possible to better understand management
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Table 6 Genotypic differences in lodging behavior, grain yield loss, height and spikes per square meter across years Parameters
Grain yield (t ha1)
Genotypes PBW 343 UP 2338 Baviacora 92 Seri 82 Star Munia Kauz Pastor Super Seri Weaver WH 542 CPAN 3004 HD 2329 Pavon 76 Rayon 89 Bacanora 88 Oasis 86
nets 8.56 8.98 8.99 8.73 8.08 8.98 7.97 9.21 9.16 8.63 8.22 7.93 7.68 8.11 8.81 9.37
LSD (5%) Correlationb with yield a b
þ nets 8.85 9.10 9.14 9.03 8.49 8.89 8.36 9.97 9.08 9.19 8.60 8.71 8.06 8.26 9.07 9.55
% loss in yield
Lodging %
Lodging angle
Lodging score
Time of lodginga
Plant height (cm)
Spikes per square meter
3.3 1.3 1.6 3.3 4.8 1.0 4.7 7.6 0.8 6.1 4.4 8.9 4.7 1.8 2.8 1.9
0 0 5.0 12.5 16.7 16.7 66.7 58.3 0 76.7 41.7 90.8 84.2 95.0 50.0 76.7
0 0 5.0 12.5 15.8 22.5 50.0 55.8 0 62.5 39.5 74.2 70.0 77.5 39.2 57.5
0 0 1.7 4.9 8.8 8.9 47.2 43.4 0 63.7 31.8 75.4 67.0 82.8 34.8 50.7
– – A A A A A A – A A A A A A A
90.8 87.3 99.5 89.4 82.4 87.5 98.7 90.9 75.0 83.5 91.6 82.9 94.5 95.0 82.8 73.0
441 424 406 424 545 462 469 445 672 519 396 526 543 527 501 567
28.7 0.27
23.2 0.24
28.2 0.30
þ þ þ þ þ þ
25 24 21 31 25 21
þ þ þ þ þ þ þ
25 31 24 31 30 24 31
1.5 0.58
27 0.11
A denotes duration from emergence to anthesis (days). d:f: ¼ 14; r > 0:497 and 0.623 for P < 0:05 and 0.01, respectively.
and genotype interactions. The genotypes in this study were initially selected to include two main categories, namely lodging tolerant and lodging susceptible. Beyond that, height, maturity and morphological characteristic differences were not specifically scrutinized but geographical and the developmental time-frame were considered, in order to insure broad diversity. Generally, genotypes categorized as lodging tolerant did not show much lodging while those categorized as susceptible lodged in both years (Tables 2 and 6). Maximum lodging % and lodging angle were observed for Rayon 89 and HD 2329, respectively (Table 6). The combined effect of these two factors led to the highest lodging score for Rayon 89 followed by HD 2329, both classified as lodging susceptible, whereas, genotypes like PBW 343, UP 2338, Baviacora 92, Seri 82, Star, Munia Kauz and Weaver either did not lodge or showed a lodging score of less than a 10, which confirmed their classification as lodging tolerant. The phenotypic correlations between yield and lodging %, lodging angle and lodging score were non-significant (Table 6). Most severe lodging each year occurred at the time of last irrigation (25–30 days
after anthesis), this again confirms the findings of Fischer and Stapper (1987). 3.5. Effect of Lr19 Data presented in Table 7 provides simple comparisons for several parameters for two genotypes and for the three management practices. From the analysis of the 16 genotypes across main plots and years (data not reported), it was observed that Super Seri exhibited significantly higher biomass, yield, kernels per square meter, kernels per spike and lodging score than the near isogenic cultivar, Seri 82, which did, however, demonstrate a significantly higher kernel weight. Super Seri (with Lr19), averaged 5–12% higher biomass and grain yield (Table 7) across the management practices as compared to Seri 82 (without Lr19). The higher yields for Super Seri were related to a larger number of spikes per square meter for flat planting with and without nets and a higher number of kernels per spike with ethephon application. Ethephon application drastically reduced kernels per spike for Seri 82. Kernel weight was consistently less for
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Kernels/spike
50 45 40 35 30 25 20
Kernel wt (mg)
50 45 40 35 30 25
0.60
HI
0.50 0.40 0.30 0.20
Without ethephon
With ethephon
9.5 8.5 7.5 6.5 5.5 PB W 3 U 43 P B av 23 3 ia co 8 ra Se 92 ri 82 M S un ta ia r K au Pa z Su st p e or rS W eri ea v W er H C PA 54 N 2 30 0 H D 4 23 Pa 29 vo R n7 ay 6 B ac on an 89 or a 8 O as 8 is 86
Yield (t/ha)
10.5
Genotypes Fig. 1. Ethephon and genotype interaction on yield, HI, kernel weight and kernels per spike.
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Table 7 Comparison of Super Seri (with Lr19) vs Seri 82 (without Lr19) yields and other traits for three management treatments averaged across years Parameters
Biomass (t ha1) Yield (t ha1) % Yield increase over Kernel weight (mg) Spikes per square meter Kernels per square meter Kernels per spike Anthesis (days) Maturity (days) Height (cm) Lodging score
Varieties
Seri 82 Super Seri Seri 82 Super Seri Seri 82 Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri
Super Seri although a higher number of kernels per square meter was always associated with higher grain yield for Super Seri. Super Seri was slightly later than Seri 82 for both anthesis and maturity (1–2 days) and plant height was about 3 cm more. The lodging score for Super Seri for flat planting without support nets, however, was nearly 10 times more than Seri 82. There could be some association between the translocation carrying the Lr19 gene and the apparent greater lodging tendency for Super Seri or the higher lodging for Super Seri may simply be related to its markedly higher biomass and grain yields per se.
4. Discussion Lodging significantly reduced grain yield (Table 5), although, the relatively low yield losses (Table 6) associated with lodging that are reported here support the findings of Fischer and Stapper (1987) that 7–35% loss in grain yield was observed when lodging occurred in the first 20 days after anthesis but following that, lodging resulted in a smaller, detrimental
Management practices nets
þ nets
þ ethephon
16.74 18.17 8.73 9.21 5.4 42.05 39.69 392 451 18283 20433 47 46 92 94 132 134 92 93 4.8 43.4
18.12 18.98 9.03 9.97 10.4 41.05 40.84 448 455 19405 21512 43 47 92 93 132 134 93 94 0 0
16.81 17.32 7.95 8.90 12.0 41.17 40.42 431 429 17003 19215 39 45 94 95 134 137 83 86 0 0
effect on grain yield. These authors conducted artificial lodging experiments at same location as the experiments reported here, where the crop was forced to lodge at varying angles at different stages of crop development. However, lodging at a specified angle at a given time does not arise normally under most field conditions. Thus, it seems that yield losses from lodging in their study might have been over estimated. The low range of yield losses that are described here are most likely related to the late onset of lodging events in the trials (Table 6) combined with the use of hand harvesting with its overall lower harvesting losses for lodged wheat as compared to combine harvesting. Berry et al. (2000) observed that a cultivar yielding 10 t ha1 and having 500 shoots m2 with 50 cm height would lodge (stem failure) at a gust speed of 28 m s1. Whereas, in our study the height of most of cultivars was 90 5 cm under high N level (300 kg ha1). So, it appears that a much lower wind, gust speed would be required to lodge the plants having almost double the height with similar production levels. Lodging in wheat is a serious problem under high fertility, in this case 300 kg N ha1 over and above green manuring, and irrigated conditions.
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Significantly higher lodging in wheat was also reported with 195 kg N ha1 (Mohammad et al., 1987), 275 kg N ha1 (Kheiralla et al., 1993), 180 kg N ha1 (Narang et al., 1994), and with 225 kg N ha1 (Hobbs et al., 1998). In a plant cell, ethephon acts by releasing ethylene (Crook and Randall, 1969), which is a natural hormone for growth inhibition (Burg, 1973). Therefore, application of ethephon to a crop can retard the growth and development processes, which is evident from Table 5, where ethephon application significantly reduced biomass, grain yield, plant height with a major reduction in one of the important yield attributing characters, number of kernels per spike. Simmon et al. (1988) determined that the effect of ethephon on grain yield varied from a 13% reduction to 12% increase and was dependent upon how much loss in grain yield occurred by lodging. In winter wheat, application of ethephon at 0.56 kg ha1 decreased grain yield by 6% (Nafziger et al., 1986). However, Ali (1993) found a 15–20% increase in grain yield by ethephon (250 g ha1) application at boot stage. At CIMMYT, Sayre (1996) observed reduction in lodging by using ethephon (480 g ha1) at DC 37–39. Increases in grain yield after ethephon application were encountered by various other researchers (Pinthus, 1973; Nafziger et al., 1986; Wiersma et al., 1986; Knapp et al., 1987; Webster and Jackson, 1993; El Debaby et al., 1994). Application of this growth inhibitor significantly reduced plant height and simultaneously produced equal biomass and spikes per square meter as compared to no application (Table 5). This suggests that the application of ethephon might have produced thicker stem, which ultimately controlled the lodging but since the timing of the lodging events was late in the crop cycle reducing lodging-related yield losses, the potential beneficial effects of ethephon were not expressed. Recently, in a companion study at the same site with 12 of the same genotypes (Tripathi et al., 2003), ethephon application increased the stem wall thickness for the 1st (4.3%), 2nd (6.3%) and 3rd (8.1%) internodes and peduncle (3.6%) when compared at same N level (300 kg N ha1) without ethephon. Genotypic differences for all the traits under study were significant. Generally, taller varieties lodge more than shorter varieties. However, in this study, Baviacora 92, tallest genotype, showed nil lodging
compared to the shortest variety, Oasis 86, which exhibited 76.7% lodging despite having two dwarfing genes (Rht1 and Rht2). Many researchers (Hobbs et al., 1998; Sayre and Moreno Ramos, 1997) recorded similar observations at this site. Therefore, plant height is not the only criterion for lodging resistance. Lodging susceptible varieties produced more spikes per square meter than lodging resistant varieties with few exceptions (Table 6). Varietal differences in lodging were observed by various workers (Pinthus, 1973; Luthra et al., 1981; Knapp et al., 1987; Crook and Ennos, 1995; Sayre, 1996) and are influenced by sowing time and density (Stapper and Fischer, 1990b). Under Egyptian conditions, Salem et al. (1992a,b) reported 72% lodging by variety Giza 155 and no lodging by Giza 157. Various workers (Mohammad et al., 1987; Swati et al., 1987; Kheiralla et al., 1993) also had opined similar findings by using different varieties. Plant height correlated significantly and negatively (Table 6) with grain yield but lodging parameters did not correlate with yield (Table 6). In this study, ethephon did not increase grain yield for any of the 16 cultivars, regardless of the extent of lodging with flat planting without support nets, but this again was likely due to late onset of lodging in the experiments. Therefore, application of this growth inhibitor might be more useful where occurrence of heavy loss in grain yield due to lodging and mechanized harvesting is a common phenomenon. The two near isogenic lines, Super Seri (with Lr19) and Seri 82 (without Lr19), were included to attempt to corroborate previously reported results by Singh et al. (1998) that the translocation containing Lr19 can impart significant improvements in grain yield and other factors. Super Seri recorded up to 12% increase in grain yield (Table 7), and it can be assumed that the translocation carrying the Lr19 gene, in addition to providing a source of resistance to leaf rust, can also enhance grain yield, at least under irrigated, high production potential conditions.
5. Conclusions The results of this study indicated that lodging occurring even at the end of crop cycle significantly decreased the grain yield for lodging-prone genotypes. Ethephon application controlled lodging by
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significantly reducing plant height but also reduced yield as well as resulting from a marked decrease in kernels per spike. Application of this growth hormone would be pertinent where conditions leading to chronic and severe lodging causing severe losses in yield occur. The disease-free as well as lodging protection conditions managed in these experiments provided a conducive environment to achieve the potential yield of different high yielding cultivars. Consequently Super Seri, one of the higher yielding genotypes, yielded almost 10 t ha1. Furthermore, significant management genotype interaction was encountered for yield, as well as for some other traits studied. The translocation that carries the Lr19 gene for leaf rust resistance appears to carry other yield enhancing mechanisms as seen for the comparison here between Super Seri (þLr19) and Seri 82 (Lr19), which gave 10–12% higher grain yield for Super Seri under no lodging condition. Therefore, incorporation of this gene into semi-dwarf wheat cultivars might result in higher yield potential.
Acknowledgements The authors greatly acknowledge the assistance provided by the team of workers, Jaime Cruz, Saul Sa´ nchez, Manuel Cano, and Beatriz Martı´nez at Cd. Obregon. The senior author is greatly thankful to Dr. S. Rajaram, Director, Wheat Program (CIMMYT), Mexico and Dr. S. Nagarajan, former Project Director, DWR, Karnal, India for providing the financial and technical support to complete research work at CIMMYT, Mexico.
References Ali, A.A., 1993. Effect of nitrogen nutrition and ethephon on lodging and yield of wheat (Triticum aestivum L.). Menofiya J. Agric. Res. 18, 2225–2234. Bell, M.A., Fischer, R.A., 1994. Guide to plant and crop sampling: measurements and observations for agronomic and physiological research in small grain cereals. Wheat Program Special Report No. 32. CIMMYT, Mexico, D.F. Berry, P.M., Griffin, J.M., Sylvester-Bradley, R., Scott, R.K., Spink, J.H., Baker, C.J., Clare, R.W., 2000. Controlling plant form through husbandry to minimize lodging in wheat. Field Crops Res. 67, 59–81.
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Burg, S.P., 1973. Ethylene in plant growth. Proc. Natl. Acad. Sci. USA 70, 591–597. Crook, M.J., Ennos, A.R., 1995. The effect of nitrogen and growth regulators on stem and root characteristics associated with lodging in two cultivars of winter wheat. J. Exp. Bot. 46, 931–938. Crook, A.R., Randall, D.I., 1969. 2-Halo-ethanephosphonic acid as ethylene—releasing agent for induction to flowering in pine apple. Nature (London) 218, 974–975. El Debaby, A.E., Ibrahim, K.E., Saad, A.M.M., El Salhy, T.S., 1994. Wheat lodging and growth characters as affected by some agricultural practices. Ann. Agric. Sci. 32, 1325–1337. Fischer, R.A., Stapper, M., 1987. Lodging effects on high yielding crops of irrigated semi-dwarf wheat. Field Crops Res. 17, 245– 258. Fischer, R.A., Wall, P.C., 1976. Wheat breeding in Mexico and yield increases. J. Aust. Inst. Agric. Sci. 42, 139–148. Garg, O.K., Singh, R.H., Tiwari, B., 1973. Physiological significance of nitrogen nutrition in relation to lodging in wheat. Field Crop Abst. (India) 26, 1527. Hobbs, P.R., Sayre, K.D., Ortı´z-Monasterio, I., 1998. Increasing wheat yields through agronomic means. In: Nagarajan, S., Singh, G., Tyagi, B.S. (Eds.), Wheat Research Beyond 2000 AD. Proceedings of the International Group Meeting on Research Needs Beyond 2000 AD, Karnal, August 12–24, 1997. Narosa Publishing House, New Delhi, India. Kheiralla, K.A., Mehdi, E.E., Dawood, R.A., 1993. Evaluation of some wheat cultivars for traits related to lodging resistance under different levels of nitrogen. Assiut. J. Agric. Sci. 24, 257–271. Knapp, J.S., Harms, C.L., Volence, J.J., 1987. Growth regulator effects on wheat culm non structural and structural carbohydrates and lignin. Crop Sci. 27, 1201–1205. Luthra, O.P., Paroda, R.S., Srivastava, R.B., 1981. Combining ability of characters related to lodging in wheat. Indian J. Agric. Sci. 51, 367–371. Mohammad, T., Anwar Shah, S., Hasan, S., 1987. Effect of different combinations of N and P on some agronomic characters of wheat mutants. Pakistan J. Sci. Ind. Res. 30, 841–845. Nafziger, E.D., Wax, L.M., Brown, C.M., 1986. Response of five winter wheat cultivars to growth regulators and increased nitrogen. Crop Sci. 26, 767–770. Narang, R.S., Tiwana, U.S., Dev, G., 1994. Maximum yield research studies in rice wheat system and soil productivity. The Indian experience. In: Proceedings of the Transactions of 15th World Congress of Soil Science, Satellite Symposium ID-5 Research for Maximum Yield in Harmony with Nature, Acapulco, Mexico, pp. 46–57. Pinthus, M.J., 1973. Lodging in wheat, barley and oats: the phenomenon, its causes, and preventive measures. Adv. Agron. 25, 209–263. Salem, A.H., Rabie, H.A., Nigam, S.A., Awaad, H.A., 1992a. Studies on morphological characters associated with lodging resistance in wheat. Zagazig J. Agric. Res. 19, 1589–1609. Salem, A.H., Rabie, H.A., Nigam, S.A., Awaad, H.A., 1992b. Mean performance, heritability, genetic advance from selection and correlations for lodging measurement in wheat (Triticum aestivum L.). Zagazig J. Agric. Res. 19, 1611–1623.
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Sayre, K.D., 1996. Effect of cerone on grain yield of wheat, Personal communication. Sayre, K.D., Moreno Ramos, O.H., 1997. Application of raised bed planting system to wheat. Wheat Program Special Report No. 31. CIMMYT, Mexico, D.F. Simmon, S.R., Olke, E.A., Wiersma, J.V., Lueschen, W.E., Warnes, D.D., 1988. Spring wheat and barley responses to ethephon. Agron. J. 80, 829–834. Singh, R.P., Espino, J.H., Rajaram, S., Crossa, J., 1998. Agronomic effects from chromosome translocations 7DL.7Ag and 1BL.1Rs in spring wheat. Crop Sci. 38, 27–33. Stapper, M., Fischer, R.A., 1990a. Genotype, sowing date and plant spacing influence on high yielding irrigated wheat in Southern new South Wales. II. Growth, yield and nitrogen use. Aust. J. Agric. Res. 41, 1021–1041. Stapper, M., Fischer, R.A., 1990b. Genotype, sowing date and plant spacing influence on high yielding irrigated wheat in Southern new South Wales. III. Potential yields and optimum flowering dates. Aust. J. Agric. Res. 41, 1043–1056.
Swati, M.S., Swati, U., Ahmad, K., 1987. The response of wheat genotypes towards fertilizer based on lodging, grain yield and other relevant characters. Sarhad J. Agric. 3, 365–373. Thomson, W.T., 1995. Agricultural Chemical Books, vol. III, Miscellaneous Agricultural Chemicals. Thomson Publications, Fresno, CA, USA, p. 53. Tripathi, S.C., Sayre, K.D., Kaul, J.N., Narang, R.S., 2003. Growth and morphology of spring wheat culm and their association with lodging: effects of genotype, N levels and ethephon. Field Crops Res. 84, 271–290. Webster, J.R., Jackson, L.F., 1993. Management practices to reduce lodging and maximize grain yield and protein content of fallsown irrigated hard red spring wheat. Field Crops Res. 33, 249– 259. Wiersma, D.W., Oplinger, E.S., Guy, S.O., 1986. Environment and cultivar effects on winter wheat response to ethephon plant growth regulator. Agron. J. 78, 761–764. Zadoks, J.C., Chang, T.T., Konzak, C.F., 1974. A decimal code for growth stages of cereals. Weed Res. 14, 415–421.
Lodging behavior and yield potential of spring wheat (Triticum aestivum L.): effects of ethephon and genotypes S.C. Tripathia,*, K.D. Sayreb, J.N. Kaulc, R.S. Narangc a
b
Directorate of Wheat Research, Post Box No. 158, Karnal, 132 001, Haryana, India Wheat Programme, CIMMYT, Lisboa 27, Apartado Postal 6-641, 06600 Mexico, D.F., Mexico c PAU, Ludhiana, Punjab, India
Received 12 June 2003; received in revised form 10 October 2003; accepted 11 November 2003
Abstract Crop lodging is a chronic constraint, commonly limiting irrigated spring wheat yields. Cultivar selection and use of growth regulators are the two factors that can alter lodging incidence to a significant extent. In this study, lodging behavior and yield potential for 16 spring wheat (Triticum aestivum L.) genotypes were studied under disease-free, irrigated conditions at the CIMMYT (Centro Internacional de Mejoramiento de Maı´z y Trigo) experiment station near Ciudad Obregon, Sonora, Mexico, during 1997–1998 and 1998–1999. For the conventional planting system, two additional treatments were implemented, one using support nets to eliminate lodging and the other by applying the growth regulator, ethephon, to control lodging. In both years, lodging occurred late (25–30 days after anthesis) but significant grain yield reductions for lodging susceptible genotypes were observed. The Indian cultivar, HD 2329, and the Mexican advanced line, Super Seri, recorded maximum grain yield loss (7.6–8.9%) due to lodging. Ethephon (480 g ha1) application controlled lodging by reducing plant height but also decreased average grain yield by 8.3%, which was primarily associated with a significant reduction in number of kernels per spike. Interaction between management practices (with and without ethephon) and genotypes was significant for grain yield, HI, kernel weight and kernels per spike but non-significant for biomass and spikes per square meter. Super Seri produced the highest yield across all management practices. This genotype possesses the translocation carrying the Lr19 gene, which likely contributed to its higher grain yield (10–12%) when compared to the near isogenic cultivar, Seri 82, which is devoid of the Lr19 gene. Therefore, the incorporation of this gene into other high yielding semi-dwarf wheat genotypes may enhance wheat yield in addition to providing resistance to leaf rust. # 2003 Elsevier B.V. All rights reserved. Keywords: Spring wheat; Lodging behavior; Netting; Yield; Ethephon; Growth regulator; Lr19 gene
1. Introduction The advent of semi-dwarf wheat cultivars occurred through incorporation of dwarfing genes mainly from Norin 10, which can limit lodging under moderate levels of inputs, especially fertilizer and irrigation. *
Corresponding author.
This lodging resistance, resulting from shorter and stiffer straw, is markedly expressed at moderate levels of N fertility (Pinthus, 1973; Fischer and Wall, 1976; Stapper and Fischer, 1990a,b). Improved lodging resistance increases yield largely by permitting greater doses of N fertilizer. Under certain agronomic conditions, however, even spring wheat cultivars carrying one or even two major, Norin 10 dwarfing genes (Rht1,
0378-4290/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2003.11.003
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Rht2) have been observed to lodge in Mexico, Australia (Fischer and Stapper, 1987) and in India (Narang et al., 1994). This form of lodging which is most common with well-managed crops, occurs near or after flowering and is primarily the result of wind during or soon after irrigation or rainstorms. Crook and Ennos (1995) advanced the view that stem strength was reduced by 20% as N fertilizer rate increased from 160 to 240 kg ha1. Similarly, application of N at 200 kg ha1 decreased breaking strength of the 2nd internode, leading to increased lodging (Garg et al., 1973). To avoid lodging, many farmers in South Asia forego the last irrigation (Hobbs et al., 1998), which may be crucial for grain filling and can ultimately limit grain yield. This practice is common in India for the following reasons: (i) occurrence of frequent high winds during grain filling; (ii) the wide use of flat planting and flood irrigation; and (iii) the lack of acceptable cultivars that are lodging tolerant at higher N rates (180–200 kg ha1). Fischer and Stapper (1987) reported that increasing the N fertility beyond a certain limit induced lodging and ultimately decreased grain yield and its components. The reduction in grain yield caused by culm lodging ranged from 7 to 35% with greatest effect when lodging occurred within the first 20 days after anthesis. Stapper and Fischer (1990b) concluded that higher yields under irrigated condition could be achieved consistently and efficiently only with the genotypes that can resist lodging. Ali (1993) and Kheiralla et al. (1993) reported 19.9 and 7.2% reductions in grain yield in Egypt caused by lodging at 225 and 275 kg N ha1 compared with 150 and 175 kg N ha1 applications, respectively. Recently, in a study of winter wheat, it was observed that lodging occurred in patches, usually after rain, and was most common in early sown, high seed rate, high residual nitrogen treatments (Berry et al., 2000). Lodging, a serious problem under irrigated and high input N fertility conditions, interferes with water and nutrient uptake, reduces effective light interception, decreases grain fill, provides a more conducive environment for disease and increases harvesting costs and losses. Yield reductions associated with harvesting losses caused by lodging are usually greater where combine harvesting is a common practice, but may be less in developing countries where
hand harvesting instead of combine harvesting is commonly practiced by many small farmers. The nature and extent of lodging are closely related to culm characteristics, which can be modified by application of growth inhibitors (Pinthus, 1973). Application of growth inhibitors, like ethephon (2chloro ethyl phosphonic acid) or CCC (chlormequat chloride), was reported to be useful in decreasing plant height and subsequently reducing lodging (Pinthus, 1973; Knapp et al., 1987; Ali, 1993; Crook and Ennos, 1995). However, in another study it was observed that ethephon did not provide complete lodging control but increased grain yields by 5–21% depending upon the genotype and lodging severity (Webster and Jackson, 1993). To quantify the effect of lodging on grain yield and to estimate the yield potential of different high yielding genotypes requires a thorough study. Wheat genotypes should be grown with and without artificial lodging protection (support nets) and protected from other prevalent diseases. At the same time, it may also be helpful in understanding the lodging behavior of high yielding wheat genotypes with the use of growth retardant like ethephon. Fischer and Stapper (1987) conducted artificial lodging experiments in northwest Mexico, where the crop was forced to lodge at varying angles at different stages of crop development. However, lodging at a specified angle at a given time does not occur normally under most field conditions. Thus, it seems that yield losses from lodging in this study might have been over estimated. The mechanics of lodging in winter wheat (single genotype) was studied by Berry et al. (2000) and they calculated wind speed at which a shoot’s leverage would exceed the strength of stem base (stem lodging), and at which the leverage of all the shoots on a plant would exceed its anchorage strength (root lodging). This phenomenon in spring wheat, however, might be different as crop suffers high temperature coupled with moderate to high wind speed during grain filling period. Severity of lodging at Yaqui Valley (Obregon) was observed in a recurring socioeconomic survey (80 farmers field each year, 1981–1991) where all farmers experienced lodging, ranging from 18 to 40% (Dagoberto Flores, CIMMYT Economist, personnel communication). In our study, high yielding spring wheat cultivars (16) were grown under high N fertility using flat planting with
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flood/basin irrigation, with and without support nets, and with ethephon application. Other biotic and abiotic factors were not yield limiting at any stage of crop development. Thus, a favorable situation was achieved to maximize yield potential and assess yield loss due to natural lodging. Our objectives, therefore, were to: (1) estimate yield potential and losses caused by lodging for different genotypes; (2) ascertain the effect of applying ethephon to control lodging for flat seeded, flood irrigated conditions; and (3) assess the interaction between management practices and genotype on yield and other traits.
2. Materials and methods The experiment was conducted in 1997–1998 and 1998–1999 at the CIMMYT experiment station near Ciudad Obregon, Sonora, Mexico (27.330 N latitude, 109.090 W longitude and 38 m above sea level). The soil type was coarse sandy clay (mixed montmorillonitic typic calciorthid), low in NO3-N (29.5 mg kg1) and NH4 þ -N (6.1 mg kg1) and organic matter (0.89%), medium in available P (7.7 mg kg1), high in K (557 mg kg1) and alkaline ðpH ¼ 8:0Þ in nature. There was more rainfall after planting in 1997–1998 but minimum temperatures in November–January and March were lower in 1998–1999 as compared to 1997–1998 providing more favorable conditions for growth and development (Table 1). This type of macro-environment for wheat in this location is classified as an irrigated area having a rather dry climate, high solar radiation, cool nights, and moderate daytime temperatures during the growing season.
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The present study included 16 genotypes, including eleven cultivars/advanced lines from Mexico and five cultivars from India (Table 2), which represented a range of both era of development and contrast in plant morphology. All genotypes were semi-dwarf carrying at least one dwarfing gene (Rht1 or Rht2). One Mexican cultivar, Oasis 86, has both Rht1 and Rht2. Another CIMMYT advanced line, ‘‘Super Seri’’, which carries the translocation conveying the Lr19 leaf rust resistance gene, was included in this trial, and is a near isogenic line of the cultivar, ‘‘Seri 82’’. These two near isogenic lines were included to quantify the effect of this translocation/gene on yield and other features under different management practices where leaf rust was not present. Singh et al. (1998), using comparisons of several sets of near isogenic lines (with and without Lr19), found consistently higher yields for the lines with the translocation carrying Lr19. The genotypes included in the trials were divided into two categories, tolerant and susceptible to lodging, on the basis of past experience in India and Mexico. A relatively large number of different genotypes was included in the study to provide adequate diversity in plant type and to insure that more reliable information could be generated. Each year the experiment was conducted as a randomized complete block design with three replications using a split plot treatment arrangement. Main plots consisted of the following three management practices: (i) seeding on the flat with flood irrigation without support nets; (ii) seeding on the flat with support nets for protection against lodging; and (iii) seeding on the flat with ethephon applied (480 g ha1) at DC 38 (Zadoks et al., 1974). The stage (DC 38) of
Table 1 Monthly mean maximum and minimum temperature and rainfall during wheat growing cycle (1997–1998 and 1998–1999) at CIMMYT, Cd Obregon, Sonora, Mexico Months
Temperature (8C)
Rainfall (mm)
1997–1998
November December January February March April
1998–1999
Maximum
Minimum
Maximum
Minimum
29.7 23.3 26.1 24.6 27.7 30.4
13.4 8.6 7.1 7.1 9.4 9.8
30.3 25.2 26.7 27.2 27.9 29.9
12.8 7.7 5.5 7.1 8.9 11.3
1997–1998
1998–1999
38.5 33.4 0.0 11.8 1.9 0.0
1.1 1.0 0.0 0.0 3.4 0.0
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Table 2 List of genotypes, pedigree, source, lodging rating and ethephon application (days before anthesis) No.
Genotypes a
1 2 3 4 5 6 7 8 9 10 11 12
PBW 343 UP 2338a Baviacora 92a Seri 82a Starb Munia/Kauzb Pastorb Super Serib Weaverb WH 542a CPAN 3004a HD 2329a
13 14 15 16
Pavon 76a Rayon 89a Bacanora 88a Oasis 86a a b
Pedigree
Lodging rating
Origin
Ethephon application
ND/VG9144//KAL/BB/3/YACO/4/VEE#5 UP368/VL421//UP262 BOW/NAC//VEE/3/BJY/COC KVZ/BUHO//KAL/BB LFN/SDY//PVN JUN/BOW//VEE#5/BUC PFAU/SERI//BOW Seri5//Aga/6Yr HAHN2/PRL JUP/BJY//URES GLL/AUSTII61.157//CNO/NO/3/VEE SLSib/NP852/4/PjSib/P14//Kt54B/3/K65/5/ Ska/6/UP262 VCM//CNO/7C/3/KAL/BB URES2/PRL JUP/BJY//URES AGA/3YR
Tolerant Tolerant Tolerant Tolerant Tolerant Tolerant Susceptible Susceptible Tolerant Susceptible Susceptible Susceptible
India India CIMMYT CIMMYT CIMMYT CIMMYT CIMMYT CIMMYT CIMMYT India India India
21 21 20 22 17 16 20 23 17 20 21 17
Susceptible Susceptible Susceptible Susceptible
CIMMYT CIMMYT CIMMYT CIMMYT
17 20 20 22
Mexican or Indian cultivars. CIMMYT advanced lines.
ethephon application was in the line of literature (Thomson, 1995; Sayre, 1996). The support net treatment was installed soon after the first irrigation at the level of the current crop height at that time to facilitate the growth of the young plants through the 20 cm 20 cm net holes. As the crop grew, the height of the net was adjusted so that it was maintained 15–20 cm below the full height of the wheat plants. Sub-plots consisted of the 16 genotypes. The sub-plots for the three flat seeded, flood irrigated main plot treatments were 5.5 m long with eight rows per plot, 20 cm apart, providing a plot area of 8.8 m2. In both years, the experiments were planted with a plot drill in the last week of November into dry soil at a rate of 300 viable seeds m2 followed by irrigation. Prior to planting, a summer green manure crop (Sesbania aculeata), which contained approximately 80 kg N ha1 in the biomass, was incorporated into the soil by cultivation. At the time of planting 100 kg N ha1 was applied as urea and 20 kg ha1 P as triple super phosphate. Potassium was not applied due to inherent high soil content. The remaining N fertilizer was top dressed as urea at the 1st node stage (DC 31) followed by irrigation. Irrigation was applied by basin flooding when available water in the top 60 cm approached 50% depletion. Fungicides were applied at 15-day intervals from head-
ing to mid-grain filling stage to prevent prevalent diseases, which facilitated an unbiased estimate of yield. Clodinafop-propargyl at 250 ml ha1 for grass weed control and bromoxinil at 1.5 l ha1 tank-mixed with thiofensulfuron at 25 g ha1 for broad leaf weed control were applied at recommended times using a back-pack motorized sprayer. Ethephon (2-chloro ethyl phosphonic acid) was applied at 480 g ha1 at DC 38 by a carbon dioxide, pressure sprayer, using a flat nozzle. This growth retardant was applied as and when genotypes attained DC 38 stage. Varieties like Star, Munia Kauz, Weaver, HD 2329 and Pavon 76 reached DC 38 stage 16–17 days before anthesis whereas others between 20 and 23 days before anthesis (Table 2). Lodging was scored with the formula ((% plot area lodged angle of lodging from the vertical)/90), as described by Fischer and Stapper (1987). Occurrence of lodging was recorded in each plot in relation to days after anthesis. Dates of 75% seedling emergence, anthesis (50% of spikes with at least one anther extruded) and physiological maturity (loss of spike and peduncle color in at least 75% of the plot) were recorded via frequent visits. Duration from emergence to anthesis and maturity was considered to be days to anthesis and maturity, respectively, for the different genotypes. A 3 m length per plot of the center six rows was manually harvested approximately 7–10 days after
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physiological maturity for each experiment, leaving approximately 1 m border on each plot end. At the time of harvest, a sub-sample of 100 culms from each plot was taken at random and its fresh weight was recorded. The sample was then dried at 75 8C for 48 h, weighed and used to determine the dry matter content of biomass for calculating total biomass production, harvest index (HI) and number of spikes per square meter. The remaining harvested plot material was weighed fresh at harvest, threshed after 1–2 weeks of sun drying and then the grain weight was recorded. A sub-sample of kernels was taken and weighed (fresh and dry) to adjust grain yield to t ha1 at the standard 120 g kg1 moisture content, which is used for grain yield designation throughout. The same grain subsample was also used to provide 400 random kernels to estimate kernel weight. Biomass production rate (BPR) was calculated as biomass divided by duration from seedling emergence to physiological maturity and similarly grain production rate (GPR) as grain yield divided by duration from anthesis to physiological maturity. The methodology, outlined above, to estimate biomass and grain yield, HI, BPR, GPR and yield components is as per the procedure described by Bell and Fischer (1994). Analysis of variance was carried out on yearly and data combined over years for the split plot design by using MSTATC (Michigan State University). Whereas, lodging %, lodging angle and lodging score were analyzed as completely randomized block design by excluding two main plots, due to no lodging in ethephon applied and netting, artificially lodging protected plot. Significance of each source was determined by an F-test. Least significance difference (LSD) tests were performed to determine significant differences between individual means. Phenotypic correlations (r) were calculated using genotype means (across replications, main plots and years) between all recorded traits vs grain yield.
3. Results 3.1. MSS and F-test of growth, yield, yield components and lodging behavior Tables 3 and 4 represent the analysis of variance summary for biomass, grain yield, yield components,
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days to anthesis and maturity, plant height, biomass and grain production rate, lodging %, angle and lodging score. Lodging behavior parameters were not significant for year but were significant for genotype and year genotype. Significant main plot effect differences for year, management practice were detected for all factors except kernel weight, spikes per square meter, height and maturity for years, and kernel weight and spikes per square meter were for management practices, which were non-significant. The year management practice interaction was significant for grain yield, HI, kernels per square meter, anthesis and GPR. Cultivar main effect and the year cultivar were significant for all the factors. The management practices cultivar interactions were significant for all factors except biomass, spikes per square meter, anthesis and BPR, whereas, the three-way interaction was significant for HI only. These significant interactions with genotype clearly illustrated the necessity and benefit of including a relatively large number of divergent advanced lines/ cultivars rather than the limited number that is normally used for agronomic experiments that are aimed at comparing contrasting crop management practices. This approach can also help in insuring a thorough understanding of potential crop management cultivars interactions, which should lead to a more efficient identification of the type of cultivar that needs to be selected for defined crop management practices. 3.2. Effect of lodging From combined analysis over the years and cultivars, it was observed that flat planting with support nets, which completely eliminated lodging, resulted in significantly higher biomass yield and grain yield as compared to the treatment without nets (Table 5). The difference in grain yield between flat planting with support nets (8.89 t ha1) vs flat planting without support nets (8.59 t ha1) provided an estimate of average grain yield loss as a consequence of lodging (0.3 t ha1 or 3.4% yield loss), ranging from many genotypes showing no significant lodging or yield loss without the support nets to cultivars like HD 2329 which recorded a 8.9% grain yield loss (and a lodging score of 75.4) without the support nets (Tables 5 and 6). The lodging protection by nets resulted in higher
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Source
Mean squares d.f.a
Year (Y) 1 Error a 4 Management (M) 2 YM 2 Error b 8 Genotype (G) 15 YG 15 MG 30 YMG 30 Error c 180 CV (error c, %) a
Degrees of freedom. Values 103. c Values 106 . * F-test at P ¼ 0:05. ** F-test at P ¼ 0:01. b
Biomassb (t ha1)
Yieldb (t ha1)
HI
Kernel weight (mg)
Spikes per square meter
Kernels per spike
BPR (kg ha1 GPR (kg ha1 Gram of kernels Kernels per square meterc per day) per day) per spike
81.913** 6.687 11.944** 6.588 2.182 8.811** 1.920** 0.941 0.721 0.841 5.2
90.950** 0.902 26.775** 2.902** 0.169 4.858** 0.826** 0.481** 0.179 0.149 4.6
0.067** 0.001 0.052** 0.004** 0.001 0.014** 0.001** 0.001** 0.001* 0.000 4.1
1.69 11.05 0.49 4.93 3.93 331.18** 6.53** 2.74** 1.97 1.29 2.8
1,554 2,439 15,130 314 3,740 94,410** 4,045** 2,143 1,801 1,627 8.2
1872** 22 718** 53 15 500** 25** 17** 12 9 8.0
476.08** 117.697 118.312** 22.632** 1.972 107.315** 6.429** 1.743** 1.194 0.956 5.3
4860** 307 1190** 256 100 202** 142** 44 43 46 5.1
57252** 443 18394** 1034* 59 4960** 644** 215** 104 73 4.9
2.89** 0.02 1.30** 0.04 0.02 0.98** 0.05** 0.04** 0.02 0.01 7.6
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Table 3 Analysis of variance summary, across years, for biomass and grain yield, harvest index (HI), kernel weight, spikes per square meter, kernels per square meter, kernels per spike, BPR, GPR and gram of kernels per spike
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Table 4 Analysis of variance summary, across years, for plant height (Ht), days to anthesis and maturity, lodging %, angle and lodging score Sources
Mean squares a
Year (Y) Error a Management (M) YM Error b Genotype (G) YG MG YMG Error c CV (error c, %)
Sources
d.f.
Ht (cm)
Anthesis (days)
Maturity (days)
1 4 2 2 8 15 15 30 30 180
60.3 30.5 2873.4** 115.6 30.4 1041.2** 32.6** 10.9** 7.9 5.2 2.6
116.3** 5.6 54.7** 2.2* 0.4 392.3** 32.1** 0.7 0.9 0.5 0.8
1.68 5.33 225.27** 13.44 4.05 167.85** 13.38** 2.36** 1.32 1.3 0.9
Year (Y) Error a Genotype (G) YG Error b
Mean squares d.f.a
Lodging %
Lodging angle
Lodging score
1 4 15 15 60
3939 1370 7642** 1311** 439
1066 844 4838** 928** 294
5104 1737 5285** 937* 400
a
Degrees of freedom. F-test at P ¼ 0:05. ** F-test at P ¼ 0:01. *
biomass and grain yield that was associated with significantly higher kernels per square meter than without nets (Table 5). It is of interest to note that even though many genotypes lodged more than 90% (Table 6) at dough stage, yield losses were 2–4% only. 3.3. Effect of ethephon Application of ethephon at DC 38 significantly reduced the plant height (9.8%), grain yield (8.3%), HI (9.0%), kernels per square meter (8.0%), kernels per spike (12.5%), kernel weight per spike (12.9%) and grain production rate (10.9%) despite controlling lodging as compared to the treatment without ethephon (Table 5). This yield reduction was largely associated with the decrease in number of kernels per spike while biomass, kernels weight, spikes per square meter and BPR were non-significant. Durations from emergence to anthesis and maturity were delayed by 1–2 days by ethephon application (Table 5). Ethephon acts as an anti-auxin and thereby retards growth, biomass and yield when compared with the lodging protected treatment. Interestingly, the ethephon application did not result significant difference in kernel weight. It indicated that ethephon acted in more to reduce kernel number rather than its weight.
3.4. Management genotypes The results presented in Fig. 1 revealed significant interactions between management practice and genotype for grain yield, HI, kernel weight and kernels per spike but were non-significant for biomass and spikes per square meter (Table 2). Many genotypes exhibited significantly lower grain yield when treated with ethephon as compared to the control. Grain yield reduction by ethephon application led to a significant decreases in HI for all the genotypes except Super Seri and Star. The reduction in grain yield was characterized by significant decreases in number of kernels per spike for many genotypes. Ethephon application reduced kernels per spike for some genotypes (such as Baviacora 92) but not for other genotypes (such as Weaver). Although kernel weight of most genotypes was not affected by ethephon application, it was increased for Pavon 76 and decreased for PBW 343. Phenotypic correlations between plant height and the lodging parameters were all non-significant ðr < 0:06Þ. These results tend to negate the conventional wisdom that taller genotypes are inclined to lodge more than shorter ones. In this study, the tallest cultivar (Baviacora 92) showed almost no lodging while the shortest cultivar (Oasis 86) exhibited an intermediate level for all lodging indicators.
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Table 5 Effect of ethephon and netting on average biomass, grain yield, HI, yield components, plant height, days to anthesis and maturity across varieties (in yearly and combined analysis) Parameters
Management practices Years 1
Biomass (t ha )
nets
þ nets
þ ethephon
LSD (5%)
1997–1998 1998–1999 Combined
17.07 17.54 17.31
17.33 18.62 17.98
16.73 18.17 17.45
ns
Grain yield (t ha1)
1997–1998 1998–1999 Combined
8.17 9.01 8.59
8.39 9.41 8.89
7.11 8.62 7.87
0.31 0.11 0.14
HI
1997–1998 1998–1999 Combined
0.42 0.45 0.44
0.43 0.45 0.44
0.38 0.42 0.40
0.01 0.01 0.01
Kernel weight (mg)
1997–1998 1998–1999 Combined
40.68 41.05 40.86
41.08 40.72 40.89
40.99 40.53 40.76
0.46 0.49
0.76 ns ns
Spikes per square meter
1997–1998 1998–1999 Combined
475 478 477
498 500 499
494 503 498
Kernels per square meter
1997–1998 1998–1999 Combined
17896 19561 18728
18160 20614 19387
15424 19019 17221
673 902 467
Kernels per spike
1997–1998 1998–1999 Combined
38 42 40
37 42 39
32 38 35
2 2 1
Gram of kernels per spike
1997–1998 1998–1999 Combined
Anthesis (days)
1997–1998 1998–1999 Combined
89 89 89
89 90 89
90 91 91
0.4 0.3 0.3
Maturity (days)
1997–1998 1998–1999 Combined
132 131 132
131 132 132
134 134 134
1.2 1.0 0.7
Plant height (cm)
1997–1998 1998–1999 Combined
91.9 88.9 90.4
92.1 90.8 91.5
80.8 82.2 81.5
2.9 3.4 1.8
BPR (kg ha1 per day)
1997–1998 1998–1999 Combined
129.1 133.6 131.3
131.9 141.3 136.6
124.5 135.3 129.8
7.5 2.8 3.3
GPR (kg ha1 per day)
1997–1998 1998–1999 Combined
166.8 191.6 179.1
174.4 198.4 186.4
141.7 177.5 159.6
4.8 3.9 2.6
1.54 1.72 1.63
In contrast, Weaver, the second shortest genotype did not lodge at all but Pastor, the second tallest genotype, was fairly lodging susceptible (Table 6).
1.52 1.69 1.61
1.56 1.71 1.42
ns ns ns
0.06 0.09 0.04
This again illustrates the value for agronomists to study a relatively large number of diverse genotypes, whenever possible to better understand management
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Table 6 Genotypic differences in lodging behavior, grain yield loss, height and spikes per square meter across years Parameters
Grain yield (t ha1)
Genotypes PBW 343 UP 2338 Baviacora 92 Seri 82 Star Munia Kauz Pastor Super Seri Weaver WH 542 CPAN 3004 HD 2329 Pavon 76 Rayon 89 Bacanora 88 Oasis 86
nets 8.56 8.98 8.99 8.73 8.08 8.98 7.97 9.21 9.16 8.63 8.22 7.93 7.68 8.11 8.81 9.37
LSD (5%) Correlationb with yield a b
þ nets 8.85 9.10 9.14 9.03 8.49 8.89 8.36 9.97 9.08 9.19 8.60 8.71 8.06 8.26 9.07 9.55
% loss in yield
Lodging %
Lodging angle
Lodging score
Time of lodginga
Plant height (cm)
Spikes per square meter
3.3 1.3 1.6 3.3 4.8 1.0 4.7 7.6 0.8 6.1 4.4 8.9 4.7 1.8 2.8 1.9
0 0 5.0 12.5 16.7 16.7 66.7 58.3 0 76.7 41.7 90.8 84.2 95.0 50.0 76.7
0 0 5.0 12.5 15.8 22.5 50.0 55.8 0 62.5 39.5 74.2 70.0 77.5 39.2 57.5
0 0 1.7 4.9 8.8 8.9 47.2 43.4 0 63.7 31.8 75.4 67.0 82.8 34.8 50.7
– – A A A A A A – A A A A A A A
90.8 87.3 99.5 89.4 82.4 87.5 98.7 90.9 75.0 83.5 91.6 82.9 94.5 95.0 82.8 73.0
441 424 406 424 545 462 469 445 672 519 396 526 543 527 501 567
28.7 0.27
23.2 0.24
28.2 0.30
þ þ þ þ þ þ
25 24 21 31 25 21
þ þ þ þ þ þ þ
25 31 24 31 30 24 31
1.5 0.58
27 0.11
A denotes duration from emergence to anthesis (days). d:f: ¼ 14; r > 0:497 and 0.623 for P < 0:05 and 0.01, respectively.
and genotype interactions. The genotypes in this study were initially selected to include two main categories, namely lodging tolerant and lodging susceptible. Beyond that, height, maturity and morphological characteristic differences were not specifically scrutinized but geographical and the developmental time-frame were considered, in order to insure broad diversity. Generally, genotypes categorized as lodging tolerant did not show much lodging while those categorized as susceptible lodged in both years (Tables 2 and 6). Maximum lodging % and lodging angle were observed for Rayon 89 and HD 2329, respectively (Table 6). The combined effect of these two factors led to the highest lodging score for Rayon 89 followed by HD 2329, both classified as lodging susceptible, whereas, genotypes like PBW 343, UP 2338, Baviacora 92, Seri 82, Star, Munia Kauz and Weaver either did not lodge or showed a lodging score of less than a 10, which confirmed their classification as lodging tolerant. The phenotypic correlations between yield and lodging %, lodging angle and lodging score were non-significant (Table 6). Most severe lodging each year occurred at the time of last irrigation (25–30 days
after anthesis), this again confirms the findings of Fischer and Stapper (1987). 3.5. Effect of Lr19 Data presented in Table 7 provides simple comparisons for several parameters for two genotypes and for the three management practices. From the analysis of the 16 genotypes across main plots and years (data not reported), it was observed that Super Seri exhibited significantly higher biomass, yield, kernels per square meter, kernels per spike and lodging score than the near isogenic cultivar, Seri 82, which did, however, demonstrate a significantly higher kernel weight. Super Seri (with Lr19), averaged 5–12% higher biomass and grain yield (Table 7) across the management practices as compared to Seri 82 (without Lr19). The higher yields for Super Seri were related to a larger number of spikes per square meter for flat planting with and without nets and a higher number of kernels per spike with ethephon application. Ethephon application drastically reduced kernels per spike for Seri 82. Kernel weight was consistently less for
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Kernels/spike
50 45 40 35 30 25 20
Kernel wt (mg)
50 45 40 35 30 25
0.60
HI
0.50 0.40 0.30 0.20
Without ethephon
With ethephon
9.5 8.5 7.5 6.5 5.5 PB W 3 U 43 P B av 23 3 ia co 8 ra Se 92 ri 82 M S un ta ia r K au Pa z Su st p e or rS W eri ea v W er H C PA 54 N 2 30 0 H D 4 23 Pa 29 vo R n7 ay 6 B ac on an 89 or a 8 O as 8 is 86
Yield (t/ha)
10.5
Genotypes Fig. 1. Ethephon and genotype interaction on yield, HI, kernel weight and kernels per spike.
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Table 7 Comparison of Super Seri (with Lr19) vs Seri 82 (without Lr19) yields and other traits for three management treatments averaged across years Parameters
Biomass (t ha1) Yield (t ha1) % Yield increase over Kernel weight (mg) Spikes per square meter Kernels per square meter Kernels per spike Anthesis (days) Maturity (days) Height (cm) Lodging score
Varieties
Seri 82 Super Seri Seri 82 Super Seri Seri 82 Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri Seri 82 Super Seri
Super Seri although a higher number of kernels per square meter was always associated with higher grain yield for Super Seri. Super Seri was slightly later than Seri 82 for both anthesis and maturity (1–2 days) and plant height was about 3 cm more. The lodging score for Super Seri for flat planting without support nets, however, was nearly 10 times more than Seri 82. There could be some association between the translocation carrying the Lr19 gene and the apparent greater lodging tendency for Super Seri or the higher lodging for Super Seri may simply be related to its markedly higher biomass and grain yields per se.
4. Discussion Lodging significantly reduced grain yield (Table 5), although, the relatively low yield losses (Table 6) associated with lodging that are reported here support the findings of Fischer and Stapper (1987) that 7–35% loss in grain yield was observed when lodging occurred in the first 20 days after anthesis but following that, lodging resulted in a smaller, detrimental
Management practices nets
þ nets
þ ethephon
16.74 18.17 8.73 9.21 5.4 42.05 39.69 392 451 18283 20433 47 46 92 94 132 134 92 93 4.8 43.4
18.12 18.98 9.03 9.97 10.4 41.05 40.84 448 455 19405 21512 43 47 92 93 132 134 93 94 0 0
16.81 17.32 7.95 8.90 12.0 41.17 40.42 431 429 17003 19215 39 45 94 95 134 137 83 86 0 0
effect on grain yield. These authors conducted artificial lodging experiments at same location as the experiments reported here, where the crop was forced to lodge at varying angles at different stages of crop development. However, lodging at a specified angle at a given time does not arise normally under most field conditions. Thus, it seems that yield losses from lodging in their study might have been over estimated. The low range of yield losses that are described here are most likely related to the late onset of lodging events in the trials (Table 6) combined with the use of hand harvesting with its overall lower harvesting losses for lodged wheat as compared to combine harvesting. Berry et al. (2000) observed that a cultivar yielding 10 t ha1 and having 500 shoots m2 with 50 cm height would lodge (stem failure) at a gust speed of 28 m s1. Whereas, in our study the height of most of cultivars was 90 5 cm under high N level (300 kg ha1). So, it appears that a much lower wind, gust speed would be required to lodge the plants having almost double the height with similar production levels. Lodging in wheat is a serious problem under high fertility, in this case 300 kg N ha1 over and above green manuring, and irrigated conditions.
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Significantly higher lodging in wheat was also reported with 195 kg N ha1 (Mohammad et al., 1987), 275 kg N ha1 (Kheiralla et al., 1993), 180 kg N ha1 (Narang et al., 1994), and with 225 kg N ha1 (Hobbs et al., 1998). In a plant cell, ethephon acts by releasing ethylene (Crook and Randall, 1969), which is a natural hormone for growth inhibition (Burg, 1973). Therefore, application of ethephon to a crop can retard the growth and development processes, which is evident from Table 5, where ethephon application significantly reduced biomass, grain yield, plant height with a major reduction in one of the important yield attributing characters, number of kernels per spike. Simmon et al. (1988) determined that the effect of ethephon on grain yield varied from a 13% reduction to 12% increase and was dependent upon how much loss in grain yield occurred by lodging. In winter wheat, application of ethephon at 0.56 kg ha1 decreased grain yield by 6% (Nafziger et al., 1986). However, Ali (1993) found a 15–20% increase in grain yield by ethephon (250 g ha1) application at boot stage. At CIMMYT, Sayre (1996) observed reduction in lodging by using ethephon (480 g ha1) at DC 37–39. Increases in grain yield after ethephon application were encountered by various other researchers (Pinthus, 1973; Nafziger et al., 1986; Wiersma et al., 1986; Knapp et al., 1987; Webster and Jackson, 1993; El Debaby et al., 1994). Application of this growth inhibitor significantly reduced plant height and simultaneously produced equal biomass and spikes per square meter as compared to no application (Table 5). This suggests that the application of ethephon might have produced thicker stem, which ultimately controlled the lodging but since the timing of the lodging events was late in the crop cycle reducing lodging-related yield losses, the potential beneficial effects of ethephon were not expressed. Recently, in a companion study at the same site with 12 of the same genotypes (Tripathi et al., 2003), ethephon application increased the stem wall thickness for the 1st (4.3%), 2nd (6.3%) and 3rd (8.1%) internodes and peduncle (3.6%) when compared at same N level (300 kg N ha1) without ethephon. Genotypic differences for all the traits under study were significant. Generally, taller varieties lodge more than shorter varieties. However, in this study, Baviacora 92, tallest genotype, showed nil lodging
compared to the shortest variety, Oasis 86, which exhibited 76.7% lodging despite having two dwarfing genes (Rht1 and Rht2). Many researchers (Hobbs et al., 1998; Sayre and Moreno Ramos, 1997) recorded similar observations at this site. Therefore, plant height is not the only criterion for lodging resistance. Lodging susceptible varieties produced more spikes per square meter than lodging resistant varieties with few exceptions (Table 6). Varietal differences in lodging were observed by various workers (Pinthus, 1973; Luthra et al., 1981; Knapp et al., 1987; Crook and Ennos, 1995; Sayre, 1996) and are influenced by sowing time and density (Stapper and Fischer, 1990b). Under Egyptian conditions, Salem et al. (1992a,b) reported 72% lodging by variety Giza 155 and no lodging by Giza 157. Various workers (Mohammad et al., 1987; Swati et al., 1987; Kheiralla et al., 1993) also had opined similar findings by using different varieties. Plant height correlated significantly and negatively (Table 6) with grain yield but lodging parameters did not correlate with yield (Table 6). In this study, ethephon did not increase grain yield for any of the 16 cultivars, regardless of the extent of lodging with flat planting without support nets, but this again was likely due to late onset of lodging in the experiments. Therefore, application of this growth inhibitor might be more useful where occurrence of heavy loss in grain yield due to lodging and mechanized harvesting is a common phenomenon. The two near isogenic lines, Super Seri (with Lr19) and Seri 82 (without Lr19), were included to attempt to corroborate previously reported results by Singh et al. (1998) that the translocation containing Lr19 can impart significant improvements in grain yield and other factors. Super Seri recorded up to 12% increase in grain yield (Table 7), and it can be assumed that the translocation carrying the Lr19 gene, in addition to providing a source of resistance to leaf rust, can also enhance grain yield, at least under irrigated, high production potential conditions.
5. Conclusions The results of this study indicated that lodging occurring even at the end of crop cycle significantly decreased the grain yield for lodging-prone genotypes. Ethephon application controlled lodging by
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significantly reducing plant height but also reduced yield as well as resulting from a marked decrease in kernels per spike. Application of this growth hormone would be pertinent where conditions leading to chronic and severe lodging causing severe losses in yield occur. The disease-free as well as lodging protection conditions managed in these experiments provided a conducive environment to achieve the potential yield of different high yielding cultivars. Consequently Super Seri, one of the higher yielding genotypes, yielded almost 10 t ha1. Furthermore, significant management genotype interaction was encountered for yield, as well as for some other traits studied. The translocation that carries the Lr19 gene for leaf rust resistance appears to carry other yield enhancing mechanisms as seen for the comparison here between Super Seri (þLr19) and Seri 82 (Lr19), which gave 10–12% higher grain yield for Super Seri under no lodging condition. Therefore, incorporation of this gene into semi-dwarf wheat cultivars might result in higher yield potential.
Acknowledgements The authors greatly acknowledge the assistance provided by the team of workers, Jaime Cruz, Saul Sa´ nchez, Manuel Cano, and Beatriz Martı´nez at Cd. Obregon. The senior author is greatly thankful to Dr. S. Rajaram, Director, Wheat Program (CIMMYT), Mexico and Dr. S. Nagarajan, former Project Director, DWR, Karnal, India for providing the financial and technical support to complete research work at CIMMYT, Mexico.
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