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CROP ECOLOGY, MANAGEMENT & QUALITY

Planting Systems on Lodging Behavior, Yield Components, and Yield of Irrigated Spring Bread Wheat

^a Directorate of Wheat Research (DWR), Agronomy, PB No. 158, Karnal, Haryana, India
^b Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT), Apdo. #370, P.O. Box 60326, Houston, TX 77205
^c Punjab Agricultural Univ., Dep. of Agronomy, Ludhiana, India

^* Corresponding author (k.sayre{at}cgiar.org)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Lodging control of irrigated spring wheat (Triticum aestivum L.) through both crop management practices and cultivar improvement is needed to increase yield and grain quality in farmer fields, especially in developing countries where wheat production under irrigation predominates. The objectives of this research were to: (i) determine how different planting systems combined with cultivar choice can alter lodging incidence; (ii) provide a better understanding of planting system x genotype interactions to identify improved management alternatives for farmers facing chronic wheat crop lodging; and (iii) assess potential lodging consequences that may be associated with the translocation containing the Lr19 gene which has been shown to contribute to increased grain yield potential. Lodging behavior and yield potential were studied for 16 spring wheat genotypes under disease free, irrigated conditions at the CIMMYT (Centro Internacional de Mejoramiento de Maíz y Trigo) experiment station near Ciudad Obregon, Sonora, Mexico, during the 1997–1998 and 1998–1999 crop cycles. Among the genotypes tested were SUPER SERI, which carries the Lr19 gene, and Seri 82, which is a near isogenic cultivar lacking the gene. Comparisons were made between the widely used, flat planting system with flood irrigation versus an innovative bed planting system with furrow irrigation that has been widely adopted by many farmers in northwest Mexico. An additional treatment using support nets to eliminate lodging for the flat planting system was included to estimate yield losses attributable to lodging. There were yield differences among planting systems and genotypes and their interactions were significant for yield and most other traits. Bed planted genotypes demonstrated over 50% less lodging compared with flat planting providing evidence that bed planting irrigated spring wheat may be beneficial where chronic lodging occurs. Although SUPER SERI significantly out-yielded Seri 82, it also exhibited significantly more lodging.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
THE ADVENT of semidwarf wheat cultivars occurred through incorporation of dwarfing genes, mainly from Norin 10, which can limit lodging with high levels of inputs, especially N fertilizer and irrigation. This lodging resistance, resulting from shorter and stiffer straw, is markedly expressed at high levels of N fertility (Pinthus, 1973; Fischer and Wall, 1976; Stapper and Fischer, 1990a, 1990b). Cultivars with improved lodging resistance increase yield largely by permitting greater doses of fertilizer. However, some spring wheat cultivars carrying one or even two major dwarfing genes (Rht1, Rht2) have been observed to lodge in Mexico and Australia (Fischer and Stapper, 1987) and in India (Narang et al., 1994). Crook and Ennos (1995) found that stem strength decreased by 20% as N fertilizer rate increased from 160 to 240 kg ha^–1. Similarly, application of N at 200 kg ha^–1 decreased breaking strength of the second stem internode, leading to increased lodging (Garg et al., 1973). Ali (1993) and Kheiralla et al. (1993) reported 19.9 and 7.2% less grain yield in Egypt caused by lodging at 225 and 275 kg N ha^–1 compared with lower N rates between 150 and 175 kg N ha^–1.

Lodging is most common with intensively managed crops and usually occurs near or after anthesis, mainly the result of wind during or soon after irrigation or rainstorm events. To avoid lodging, many farmers in south Asia forego the last irrigation, which may be crucial for grain filling and can ultimately limit grain yield (Hobbs et al., 1998). 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 which can lead to extended, saturated soil moisture conditions following irrigation that are conducive to crop lodging; and (iii) the lack of acceptable cultivars that are lodging tolerant at higher N rates (>180 kg ha^–1).

Fischer and Stapper (1987) reported that increasing N fertility beyond a threshold induced lodging and ultimately decreased grain yield and yield components. The reduction in grain yield caused by stem lodging ranged from 7 to 35% with greatest effect when lodging occurred within the first 20 d after anthesis. Stapper and Fischer (1990b) concluded that higher yields with irrigation could be achieved consistently and efficiently only with genotypes that resist lodging. Lodging, therefore, is a serious problem associated with irrigation and high N levels and interferes with water and nutrient uptake, reduces effective light interception, decreases grain fill, provides a more conducive environment for disease, increases both harvesting costs, and losses and reduces grain quality. Yield reductions associated with harvesting losses caused by lodging, however, may be less in developing countries where hand harvesting instead of combine harvesting is commonly used by many small farmers.

In the Yaqui Valley of Sonora, Mexico, striking progress has been made in increasing spring wheat yield potential for cultivars that have been released during the past 50 yr but with a concurrent intensification in lodging as a yield constraint (Sayre et al., 1997). To increase wheat genetic yield potential further, Singh et al. (1998) compared several sets of near isogenic lines (with and without the translocation that carries the Lr19 gene for leaf rust resistance) and demonstrated higher yield potential for lines carrying the Lr19 translocation. However, little is known concerning how lodging incidence may be affected by this translocation, especially for different planting systems.

At present, most farmers in this region of Mexico have adopted bed planting with two or three rows of wheat seeded on top of beds 70 to 80 cm wide (furrow to furrow) with furrow irrigation as opposed to the traditional planting system of flat planting in solid stands and flood irrigation. The adoption of this new planting configuration has reduced irrigation water requirement by 25%, provided new opportunities for mechanical weed control and afforded new opportunities to reduce tillage in addition to dramatically reducing the incidence of lodging (Sayre and Moreno Ramos, 1997). In contrast, immense areas of wheat in India are flood irrigated, which results in lodging when even moderate levels of N fertilizer are applied. Consequently, the realizable, potential irrigated wheat yields in farmers' fields in northwest India remain about 4 to 5 Mg ha^–1 (Narang et al., 1994), whereas average yield over farmer fields with bed planting in the Yaqui Valley of northwest Mexico often exceeds 6 Mg ha ^–1 (Aquino, 1998). The change in recent years from traditional flat planting wheat with flood irrigation to furrow irrigated bed planting wheat has conferred many advantages, including reduced lodging (Sayre and Moreno Ramos, 1997). It is therefore speculated that bed planting may provide a more expedient planting system.

The objectives of this research, therefore, were to determine how different planting systems and appropriate cultivar selection can alter lodging incidence and subsequent yield expression, to understand better planting system x genotype interactions to provide better alternative management practices to farmers facing chronic crop lodging, and to assess the potential lodging implications associated with the use of the translocation that carries the Lr19 gene for resistance to leaf rust as a possible new genetic source for increasing grain yield potential.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The experiments were conducted during the fall–winter crop cycles of 1997–1998 and 1998–1999 at the CIMMYT experiment station near Ciudad Obregon, Sonora, Mexico (lat. 27.33' N, long. 109.09' W and 38 m above sea level). The soil type was a coarse, sandy clay (mixed montmorillonitic Typic Calciorthid). The upper 60-cm soil profile was high in total N (450 mg kg^–1), low in organic matter (8.9 g kg^–1), medium in Olsen-P (7.7 mg kg^–1), high in K (557 mg kg^–1 determined by 1 N ammonium acetate extraction), and alkaline (pH = 8.0) in nature.

To quantify the effect of lodging on grain yield and to estimate the yield potential, different wheat genotypes were grown with and without artificial lodging protection (support nets) and with protection from other prevalent, yield-reducing factors. In our study, high yielding spring wheat cultivars were grown with the same high N fertility for both the flat planting system (with and without support nets) and the bed planting system. Other biotic and abiotic factors were not yield limiting at any stage of crop development. Thus, a favorable situation was achieved to attain a lodging expression for the different genotypes to better assess possible crop management measures to reduce lodging and maximize yield.

Sixteen genotypes were used consisting of 11 cultivars or advanced lines from Mexico and five cultivars from India (Table 1) representing both a historical range in development and an array of contrasting plant morphologies. All genotypes were semidwarf carrying at least one dwarfing gene (Rht1 or Rht2). One Mexican cultivar, Oasis 86, carries both Rht1 and Rht2. The genotypes consisted of both lodging tolerant and susceptible lines, which were chosen mainly on the basis of experiences by farmers and researchers in India and Mexico. The CIMMYT advanced line, SUPER SERI containing the translocation conveying the Lr19 leaf rust resistance gene, was included along with its near isogenic line, the cultivar Seri 82. These two near isogenic lines were included to quantify the effect of this translocation/gene on yield and lodging under the different planting systems where leaf rust was not present.

An individual genotype comprised each subplot, which for flat planting consisted of eight rows spaced 20 cm apart and for bed planting consisted of two beds 80 cm wide (furrow to furrow) with three rows of wheat per bed spaced 20 cm apart, planted on the top of the bed. Subplot dimensions were 5.5 m long by 1.6 m wide (8.8 m²) for both planting systems. In both years, the experiments were planted with a plot drill in the last week of November into dry soil at 300 viable seeds m^–2 followed by irrigation.

The support nets for the flat-planted treatment were installed as soon as possible following the seeding irrigation as the crop was emerging and well before the tillering stage at a level below the existing crop height to facilitate the rapid growth of the young plants through the 20- by 20-cm mesh. The crop rapidly grew through the nets resulting in insignificant shading effects. As the crop grew, the level of the net was regularly adjusted upward but was always maintained 15 to 20 cm below the full height of the wheat plants and the main expanded leaf area.

A summer green manure crop of dhaincha [Sesbania aculeate (Willd. Peir.)] was incorporated into the soil during normal tillage before planting. The incorporated biomass contained approximately 80 kg N ha^–1. Immediately before planting, 100 kg N ha^–1 as urea and 20 kg P ha^–1 as triple super phosphate were broadcast and incorporated. An additional 200 kg N ha^–1 was top dressed as urea at the first node stage followed by immediate irrigation The high total applied N rate used (over 300 kg N ha^–1) was to ensure that N was not limiting in this high yield environment and to provide conditions prone to lodging. N rates applied to wheat by farmers in the Yaqui Valley have averaged approximately 275 kg N ha^–1 (Aquino, 1998). Potassium was not applied because of inherent high soil content.

Irrigation was applied by basin flooding for planting on the flat and in furrows for bed planted plots when available water in the top 60 cm approached 50% depletion as determined by frequent gravimetric sampling. Fungicides were applied at 15-d intervals from heading to mid-grain fill to prevent diseases, which facilitated an unbiased estimate of yield. Clodinafop-propargyl {prop-2-ynyl (R)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)phenoxy]propionate} at 250 mL ha^–1 for grass weed control and bromoxinil (3,5-dibromo-4-hydroxibenzonitrilo) at 1500 mL ha^–1 tank-mixed with thiofensulfuron (3-(4-methoxy-6-methyl-1,3,5-triazin-2-ylcarbamoylsulfamoyl)thiophene-2-carboxylic acid) at 25 g ha^–1 for broad leaf weed control were applied at recommended times using a back-pack, motorized sprayer. Lodging was scored with the formula, lodging score = [(% plot area lodged) x (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 emergence (75% seedlings emerged), anthesis (50% of spikes with at least one anther extruded) and physiological maturity (loss of spike and peduncle green color in at least 75% of the plot) were recorded for each plot via frequent visits. Duration from emergence to anthesis and maturity was considered to be days to anthesis and maturity, respectively, for the different genotypes.

Approximately 7 to 10 d after physiological maturity, a 3-m section of the central six rows was harvested by hand at ground level from each flat-planted plot providing a harvest area of 3.6 m². The two outside rows for each flat planted plot were not included to ensure an unbiased yield sample. For each bed planted sub-plot, a similar 3-m central section of all six rows from the two beds were harvested providing a harvested area of 4.8 m². The three rows on each bed composed the normal, repeating harvest unit for this planting system. It was deemed more relevant for the harvesting operation to maintain a similar harvest length for each planting system while, at the same time, also harvesting the largest number of natural repeating, unbiased harvest units for both planting system to maximize harvested area. All weighed parameters from both planting systems were converted to a standard kilogram per hectare.

At the time of harvest, a subsample of 100 culms was taken at random from the culms from the harvested area. Its fresh weight was recorded and it was dried at 75°C for 48 h, weighed and used for the calculation of total biomass, harvest index (HI), and number of spikes per square meter. The remaining culms from the harvested area were also immediately weighed to determine their fresh weight, were threshed after 1 to 2 wk of sun drying and their grain weight was recorded. A subsample of kernels was taken after threshing and weighed to determine fresh weight and then oven dried at 75°C to adjust grain yield to megagrams per hectare at the standard 120 g kg^–1 moisture content as used in Mexico. This same grain subsample was also used to estimate mean kernel weight. Harvesting followed the procedure described by Bell and Fischer (1994).

The data of biomass, grain yield, yield components, and other traits including lodging scores were subjected to analysis of variance using a mixed model where year (crop cycle) and cultivar effects were considered random and the planting system effect was fixed. Significance of each source of variation was determined by application of the F test. Least significance difference (LSD) tests were performed to determine the significant differences between individual means at the 0.05 level of probability. Statistical analyses were preformed by MSTATC (Crops and Soil Sciences Department, Michigan State University, Version 2.0, 1991).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Effects of Year, Planting Method, and Genotype
The macroenvironment for wheat in this location is classified as an irrigated region having a dry climate, high solar radiation, cool nights, and moderate daytime temperatures during the growing season. During the 1997–1998 crop cycle, there was more rainfall (86 mm) as compared with the 1998–1999 crop cycle (6 mm) but minimum temperatures in November, December, January and March were lower in 1998–1999 than in 1997–1998, providing more favorable conditions for growth and development.

Table 2 presents the analysis of variance summary for biomass yield, grain yield, and yield components. The significant interactions with genotype illustrate the importance of including a relatively large number of elite, high-yielding, yet divergent genotypes to ensure a more thorough understanding of potential planting system x cultivar interactions, which should lead to a more efficient identification of the optimum cultivars suited for specific crop management practices.

Biomass and Grain Yield and Yield Components
Tables 4 and 5 present the planting system x genotype interaction means for biomass and grain yield, HI and yield components. The inclusion of flat planting with support nets allowed an estimate of yield potential for the different genotypes in the absence of lodging and provided a basis to compare each genotype's relative performance under the other planting systems. Close comparison of genotype performance for either bed planting or flat planting without support nets to flat planting with support nets provided useful information to determine the suitability of genotypes for these two planting systems. For example, UP2338, Seri 82, STAR, SUPER SERI, and WEAVER exhibited significantly smaller biomass yields for bed planting when compared with flat planting with support nets and these same genotypes plus HD 2329, Pavon 76, and Bacanora 88 also had smaller grain yields (Table 4). It is probable that the reduced biomass and grain yields for bed planted SUPER SERI, HD2329, Pavon 76, and Bacanora 88 compared with flat planting with support nets were associated with their modest lodging levels for bed planting but, since UP2338, Seri 82, STAR, and WEAVER did not lodge with bed planting, they may be unsuitable for bed planting (Table 6).

Biomass and grain yield comparisons between the flat planting system without nets and the bed planting system are more relevant in terms of identifying appropriate cultivars for planting systems applicable to farmers. Only WH542 and HD2329 had greater biomass yields with bed planting compared with flat planting without support nets (Table 4), and these yield differences were related to more lodging with flat planting (Table 6). All other genotypes had similar biomass yields for both flat planting without support nets and bed planting but UP2338, WEAVER, Pavon 76, and Oasis 86 did have significantly smaller grain yields with bed planting compared with flat planting without support nets. The smaller bed planting grain yields for genotypes like UP2338 and Weaver, which did not lodge, and for both Pavon 76 and Oasis 86, which had markedly more lodging with flat planting (Tables 4 and 6), again indicated that such lines are likely not suitable for bed planting. The poor performance by both WEAVER and Oasis 86, which were the shortest genotypes included in the study (Table 6), supported the observations by Sayre and Moreno Ramos (1997) that short genotypes tend to yield less in bed planting systems than in conventional planting on the flat. In addition, both UP2338 and WEAVER are characterized by very upright, compact growth habits which likely contributed to their poor performance with bed planting even in the absence of lodging (Table 6). In a study at the same location, Sayre and Moreno Ramos (1997) further concluded from comparing a large number of randomly chosen advanced lines planted on the flat and on beds, that the average grain yield for the lines planted on the flat was 5% more then in bed planting. The authors, however, further noted that, while it was common to observe genotypes that performed well under flat planting but did not perform well with bed planting, it was rare to find the reverse, lines that performed well on beds but did poorly on the flat, unless markedly differential lodging was involved. This study reinforces their results.

Although no genotype produced significantly more grain yield with bed planting (Table 4), many genotypes like Baviacora 92, PASTOR, SUPER SERI, WH 542, CPAN 3004, and HD 2329 did have similar yields when planted on beds (Table 4) and with consistently less lodging (Table 6). Baviacora 92 had essentially no lodging for either planting system and produced consistent, superior grain yields over all planting systems. It may characterize a plant type that combines the traits essential to select genotypes with superior and stable performance across differing management systems. It was the tallest genotype but combined lodging tolerance with an intermediate to large values of all yield components (Tables 4, 5, and 6). Furthermore, the superior bed planting yields for lines PASTOR, SUPER SERI, WH 542, CPAN 3004, and HD 2329 (Table 4) clearly demonstrated that this planting system can also provide farmers with an opportunity to utilize promising, high yield yet moderately, lodging-prone genotypes like SUPER SERI (Table 6), with a markedly lower risk level of sustaining yield and grain quality losses from lodging. This is supported by a yield survey conducted in the Yaqui Valley in 1994 which found that, although all farmers planted a similar spectrum of wheat cultivars regardless of planting system, the average yield for farmers planting on beds was 5.62 Mg ha^–1, whereas farmers planting wheat on the flat had a lower average yield of 4.92 Mg ha^–1 which was associated with more apparent lodging for flat planting (Aquino, 1998). Similar results were reported from a study conducted at PAU, Ludhiana in India in 1994–1995, which found an average grain yield of 6.15 Mg ha^–1 under bed planting with furrow irrigation and 5.82 Mg ha^–1 for conventional flat planting with flood irrigation with lower incidences of lodging for bed planting (Hobbs et al., 1998).

There were very few differences in harvest index for the genotypes between the different planting systems. Where differences did occur, they generally involved larger HI with flat planting without support nets compared with bed planting such as for HD2329 (Table 4). Although the planting system x genotype interaction for kernel weight was significant, the differences were very small and not associated with the observed grain yield or lodging differences (Table 5). Fischer and Stapper (1987) also reported that when lodging occurred during mid-to-late grain fill (as happened in the experiments reported here), it had little effect on kernel weight.

Differences in spikes per square meter for the three planting systems were small (Table 5). Seri 82, STAR, and WH 542 had significantly fewer number of spikes per square meter for flat planting without nets as compared with flat planting with support nets. Similarly, Seri 82, STAR, SUPER SERI, WEAVER, and Pavon 76 exhibited fewer spikes per square meter with bed planting compared with flat planting with support nets. It is likely that these differences in spike numbers were associated with the differences in lodging incidences but were not found to be associated with grain yield differences. However, there were no significant genotypic differences for spikes per square meter between flat planting without nets and bed planting (Table 5).

The planting system x genotype interaction for kernels per spike was largely related to a few subtle differences. CPAN 3004, for example, had more kernels per spike with bed planting compared with the other planting systems while Oasis 86 had significantly fewer kernels per spike for bed planting compared with flat planting with and without support nets (Table 5). Compensations involving the different yield components that occurred between the different genotypes or over the different planting systems conditioned similar yield levels with markedly different yield component expression. The comparison of MUNIA/KAUZ and Oasis 86 for bed planting illustrates this since both had very similar bed planting yields even though Oasis 86 had substantially more spikes per square meter yet considerably fewer kernels per spike (Tables 4 and 5).

Plant Height and Lodging Traits
Among these semidwarf wheat genotypes, Baviacora 92 and PASTOR were the tallest and Oasis 86, the only double dwarf, and WEAVER were the shortest (Table 6). There was no significant relationship between plant height and yield nor was there a significant association between plant height and lodging which counters the conventional wisdom that taller genotypes tend to lodge more than shorter ones. In this study Baviacora 92, the tallest cultivar, had almost no lodging, while the shortest cultivar, Oasis 86, exhibited an intermediate level. In contrast, WEAVER, the second shortest genotype did not lodge, but PASTOR, the second tallest genotype, was lodging susceptible (Table 6).

The genotypes in this study were initially selected to include both lodging tolerant and lodging susceptible lines based on general researcher and farmer perceptions. Beyond that, height, maturity, and morphological characteristic differences were not specifically used as criteria for inclusion except to ensure that a fairly diverse set of well-adapted, contrasting lines were considered. Generally, genotypes that had been categorized as lodging tolerant did not demonstrate much lodging while those classified as susceptible lodged in both years (Tables 1 and 6). Although the planting system x genotype interaction was significant for lodging, maximum lodging occurred for flat planting with a consistent, markedly lower incidence for bed planting. Lodging-prone genotypes like Rayon 89 and HD 2329 consistently lodged whereas genotypes like PBW 343, UP 2338, Baviacora 92, Seri 82, STAR, MUNIA/KAUZ, and WEAVER either did not lodge or had a lodging scores of less than 10 for the flat planting system, which confirmed their classification as lodging tolerant (Table 6). The consistently low level of lodging for bed planting even considering the significant planting system x genotype interaction for lodging illustrate the importance of bed planting as a management practice to reduce lodging and the significance of identifying appropriate cultivars for this planting system.

Effect of Lr19
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, even in the absence of leaf rust. Table 7 provides simple comparisons for several parameters for these two genotypes for the three planting systems.

SUPER SERI was slightly later for both anthesis and maturity (1–2 d) and plant height was about 3 cm taller. The lodging score for SUPER SERI for flat planting without support nets was nearly 10 times more than Seri 82 and this may be of some concern related to the use of this translocation to enhance yield. There may be some association between the plant height and lodging scores for SUPER SERI with the Lr19 translocation as compared with Seri 82, or the greater incidence of lodging may simply be related to the markedly higher grain yield potential of SUPER SERI per se. However, the lodging score for SUPER SERI was reduced nearly threefold with bed planting (Table 7) which perhaps provided the clearest evidence of the utility of the bed planting system to dramatically reduce lodging for irrigated production systems as compared with the widely used flat planting system with flood irrigation, especially for high yielding, yet lodging-prone cultivars.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Crop lodging was more extensive for flat planting with flood irrigation without support nets, which is the most common production system used by farmers who grow irrigated wheat, especially in developing countries. Comparisons between flat planting both with and without support nets provided estimates of grain yield loss which ranged from nil for lines with no lodging up to nearly 10% for lodging-prone genotypes even though lodging occurred well after anthesis during both crop cycles. Wheat bed planting with furrow irrigation, which is a new production system now commonly used for irrigated wheat in the Yaqui Valley of Sonora, Mexico, produced dramatic reductions in crop lodging for all lodging-prone genotypes and appears to be an extremely attractive technology for irrigated wheat producers, especially where crop lodging is a major production constraint.

Close scrutiny of the 16 genotypes identified those whose yields were at par or better with bed planting compared with flat planting and in most cases these lines also demonstrated less lodging with bed planting. Other genotypes were observed that yielded more when planted on the flat when compared with bed planting even in cases where more sever lodging occurred with flat planting. This clearly demonstrated that some genotypes were not appropriate for bed planting. Genotypes that were unsuitable for bed planting could generally be characterized as being unduly short and/or possessing an extreme upright, compact growth habit. However, several genotypes were identified that had similar, high yields for both bed and flat planting combined with consistent, lower incidences of lodging for bed planting. Genotypes, which demonstrated superior performance across the different planting systems, exemplified a more "farmer friendly" choice and characterized the plant type that plant breeders should strive to develop.

The translocation that carries the Lr19 gene for leaf rust resistance appears to carry other yield enhancing mechanisms as observed for the comparison here between SUPER SERI (+Lr19) and Seri 82 (–Lr19), although the much higher incidence of lodging observed for SUPER SERI is of some concern

	ACKNOWLEDGMENTS

 
The authors greatly acknowledge the assistance provided by the team of workers, Jaime Cruz, Saul Sánchez, Manuel Cano, and Beatriz Martínez at Cd. Obregon. The senior author is greatly thankful to Dr. S. Rajaram, previous Director, Wheat Program (CIMMYT), Mexico and Dr. S. Nagarajan, previous Project Director (Wheat), Karnal, India for providing the fellowship and opportunity to do research work at CIMMYT, Mexico.

Received for publication July 15, 2003.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS 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.
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