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This paper reviews the results of published and unpublished experiments over 30 years looking at the effect on yield of planting density and row spacing, and of raised bed planting, of modern irrigated short wheat cultivars under the favourable climatic conditions of northwest Mexico. With optimum planting dates (mid Nov. to mid Dec.), regardless of row spacing, wheat yield was remarkably insensitive to planting density within the range normally studied (80–400 plants/m2). However yield was sensitive to row spacing: the most sensitive cultivars (erect dwarf cultivars) lost yield at spacing 30 cm and greater, while the least sensitive (some taller vigorous semidwarf cultivars) tolerated spacing up to at least 50cm without yield loss. Yield sensitivity to wide spacing was unaffected by density but varied between years, being less in favourable cooler years, and was markedly greater with later plantings (Jan.). The response to yield on narrow raised beds (2–3 rows per bed, 75–90 cm between bed centres), which have many agronomic advantages, could be explained by the aforementioned yield responses to spacing, in this case the furrow gap or distance between rows on adjacent beds being critical. Yield testing with a furrow gap of 44–50 cm appeared to select cultivars more suited to this system, but it wasn’t clear whether such cultivars represented the best option under normal 20 cm row spacing in the absence of raised beds. When testing was extended to very low plant densities, yield was remarkably insensitive (maximum yield often achieved with only 16/m2), provided the planting date was normal and the planting arrangement did not deviate greatly from a square grid, with the honeycomb design giving an additional small yield advantage. These yield responses reflect the great plasticity in wheat imparted especially by tillering, and appear to be reasonably well explained by the notion that maximum yield requires close to full light interception no later than just before flag leaf emergence, being the onset of dry weight accumulation in growing spikes. Greater leaf greenness and probably higher radiation use efficiency with very low densities (and wide gaps), and associated delays in 50% flowering, may also assist in compensation for gaps. In contrast to much conventional wisdom, it is suggested that a worthwhile breeding objective would be selection for high per spaced-plant yield, with a view to achieving normal (or better) commercial yields at very low plant densities (

Smale, M., Singh, R. P., Sayre, K., Pinga li, P., Rajaram, S., and Dubin, H. J. 1998. Estimating the economic impact of breeding nonspecific resistance to leaf rust in modern bread wheats. Plant Dis. 82:1055-1061. Breeding for resistance to rust diseases in wheat is an example of productivity maintenance research. Productivity maintenance research is n ecessary to avoid contractions in the wheat supply curve that result from changes in the biological or physical environment. In this study, the benefits of incorporating nonspecific resistance to leaf rust caused by Puccinia recondita into modern bread wheats (Triticum aestivum) have been estimated using data on resistance genes identified in cultivars, trial data, and area sown to cultivar in the Yaqui Valley, Sonora State, Mexico. In the most pessimistic scenario, the gross benefits generated in the Yaqui Valley from 1970 to 1990 were 17 million U.S. dollars (in 1994 real terms). Even when costs were overstated and benefits were understated, the internal rate of return on capital invested was 13%, well within the range recommended for use in project evaluations by the World Bank. Substantial economic benefits likely are associated with deployment of nonspecific resistance in many wheat-producing areas of developing countries where farmers change cultivars slowly because of delays in cultivar release, incomplete seed markets, and ec onomic factors related to adoption or where disease pressure is heavy and the costs of treating disease outbreaks is high.

a b s t r a c t Mismanagement of irrigation water and the ensuing secondary salinization are threatening the sus- tainability of irrigated agriculture especially in many dryland regions. The permanent raised-bed/furrow system, a water-wise conservation agriculture-based practice, is gaining importance for row- and high value-crops in irrigated agriculture. However, because of additional surface exposure and elevation, raised beds may be more prone to salt accumulation especially under shallow water table conditions. A field study was carried out in 2008 and 2009 in the Khorezm region, Central Asia, to investigate the effect of three furrow irrigation methods on salt dynamics of the soil and the performance of the cot- ton crop on the raised bed-furrow system. The irrigation methods compared included (i) Conventional furrow irrigation wherein every furrow was irrigated (EFI) at each irrigation event; (ii) Alternate skip furrow irrigation (ASFI where one of two neighbouring furrows were alternately irrigated during con- secutive irrigations events; and (iii) Permanent skip furrow irrigation (PSFI) during which irrigation was permanently skipped in one of the two neighbouring furrows during all irrigation events. For salinity management with PSFI a 'managed salt accumulation and effective leaching' approach was pursued. The EFI method increased salt accumulation on the top of the raised beds. In contrast, the PSFI method allowed an effective salt leaching from the top of the raised beds. After leaching, salinity on top of the beds under PSFI was reduced to

Aerobic rice (Oryza sativa L.) cultivation is considered an alternative production system to combat increased water scarcity and arsenic (As) contamination in the food chain. Pot experiments were conducted at the Wheat Research Centre, Dinajpur, Bangladesh to examine the role of water management (WM), As and phosphorus (P) on yield and yield attributes of boro (variety BRRI dhan 29) and aman (variety BRRI dhan 32) rice. A total of 18 treatment combinations of the three levels of As (0, 20 and 40 mg/kg) and P (0, 12.5 and 25.0 mg/kg) and two WM strategies (aerobic and anaerobic) were investigated. Yield attributes were significantly affected by increasing As levels. Grain yields of BRRI dhan 29 and BRRI dhan 32 were reduced from 63.0 to 7.7 and 35.0 to 16.5 g/pot with increasing As application, respectively, indicating a greater sensitivity of BRRI dhan 29 than BRRI dhan 32. Moreover, As toxicity was reduced with aerobic compared to anaerobic WM for all P levels. During early growth stages, phytotoxic symptoms appeared on BRRI dhan 29 and BRRI dhan 32 rice stems with increasing As levels without applying P under anaerobic WM. Under anaerobic and As-contaminated conditions, BRRI dhan 29 was highly susceptible to straighthead, which dramatically reduced grain yields. There were significant relationships between the number of effective tillers per pot and root dry weight, grain yield, and number of fertile and unfertile grains per pot for both BRRI dhan 29 and BRRI dhan 32 (P

Management practices may influence yield and nitrogen (N) use efficiency of irrigated cotton (Gossypium hirsutum L.) in irrigated arid lands such as those of the Aral Sea basin. A field experiment was conducted to compare the effects of conservation tillage (permanent raised beds; PB) with conventional plow tillage (CT) under three different N application rates (0, 125 and 250 kg ha−1) on cotton growth, yield, N use efficiency and N balance in irrigated arid lands of Uzbekistan for two years. Raw cotton yield and yield components were not affected by tillage methods in both years. However, yield and yield components significantly increased when N fertilizer rate was increased from zero to 125 kg ha−1 N application. When the N rate was doubled from 125 to 250 kg ha−1, a relatively much lower increment was observed in both tillage methods. The groundwater nitrate concentration was reduced considerably, while efficiency of applied N was increased in 2009, i.e., after introduction of the cover crop in the cotton mono cropping system, compared to 2008. The efficiency of the applied N decreased with increased N application rate. Tillage method did not affect agronomic N use efficiency in both years. However, in the 2nd year, apparent N recovery efficiency was higher in PB than in CT, while physiological N use efficiency with N-250 was 54% lower in PB than in CT. The apparent system N balance was negative with N-0 and N-125, but positive (N loss) with high N application (250 kg ha−1) with both tillage methods. A significant interaction effect between tillage and N level was observed; with N-0, CT had a 32% higher negative N balance than PB. With N-250, CT had a significantly higher positive N balance (N loss), more than twice as high (66 kg ha−1) as for PB. Thus, cotton cultivation in PB with proper N application and the introduction of a winter cover crop can be considered a viable alternative to the present unsustainable CT cotton mono-cropping system in irrigated arid lands, assuming the patterns are confirmed in the long-run.

Intensive soil tillage and mismanagement of irrigation water and fertilizers are increasing production costs, reducing soil fertility and crop water productivity and threatening the sustainability of crop production systems in the irrigated arid lands of Uzbekistan, Central Asia. Conservation agriculture (CA) practices combined with optimum nitrogen (N) management can counterbalance some of these adverse effects. Most work has been done in rainfed areas so there is less information available for irrigated production systems. This study compared the effects of tillage, crop residue management and N rates on yield and water productivity for irrigated cotton, winter wheat and maize grown in a two-year rotational sequence in Uzbekistan under CA practices vs. current conventional farmer practices. Permanently raised beds (PB) and conventional tillage (CT) were compared under two crop residue levels (retained residue – RR and removed residue – RH), and three N levels (zero, medium and high, with actual rates depending on the crops) on a sandy loam to loam soil. Raw cotton yield, yield components and water productivity were not affected by tillage methods. However, the following crops, wheat and maize, produced 12 and 42% higher grain yields, respectively, under PB than under CT. Under PB, water productivity increased in wheat by 27% and in maize by 84%, while 11% less water was applied during wheat and 23% during maize production, compared to CT. All three crops showed a considerable increment in yield and water productivity when N fertilizer levels were increased from zero to medium N application, and a relatively much lower increment when the N rate was doubled from medium to high N, for both tillage methods. In maize, the response to applied N was more pronounced with PB than with CT. Irrespective of tillage method, RR increased the grain yield of wheat by 5% compared to RH. In maize, RR in PB increased grain yields by 15% compared to RH. RR had no effect for CT. The positive effect of PB and RR on yield and water productivity of wheat and maize and the lack of negative effects on cotton yield reflect that PB with RR and proper N application may be viable alternatives to the present, unsustainable conventional agriculture practices in these irrigated arid lands, assuming the patterns are confirmed in the long-run.

Increasing water shortage and low water productivity in the irrigated drylands of Central Asia are compelling farmers to adopt resource conservation technologies, such as dry seeded, non-flooded rice. Alternate wet and dry (AWD) water management combined with alternative establishment methods, e.g., zero tillage planting in bed and flat layouts, and residue retention, may substantially reduce rice irrigation water requirement. Field experiments were conducted in a rice–wheat cropping system to evaluate these technologies and to identify the underlying processes responsible for possible reductions in rice yield. Zero till dry seeded rice (DSR) on the flat (DSRF) and on raised beds (DSRB), combined with three levels of wheat and rice straw residue retention – none (R0), 50% (R50) and 100% (R100) were therefore evaluated during the 2008 and 2009 growing seasons, using AWD water management. These treatments were compared with water seeded rice (WSR) grown with conventional tillage (dry tillage) on the flat under continuous flood irrigation (WSRF-R0-FI) or alternate wet and dry irrigation (WSRF-R0-AWD). The use of AWD reduced irrigation amount to only 30% of the amount of water applied to continuously flooded rice. However, yield of residue removed AWD treatments was lower than yield of the continuously flooded treatment by 27% in 2008 and by 40% in 2009. The significant reduction in rice yield in all treatments with AWD was caused by reduced growth rate, resulting in lower biomass, leaf area, panicle density, number of florets panicle−1 and floret fertility, with significant differences in the second year. In 2008, this appeared to be due to water deficit stress in the AWD treatments. In 2009, the reduction in growth and yield with AWD was greater, and more so as the level of residue retention increased. Residue retention reduced rice yield by 59% in 2009 with R100 compared to the R0. By far the biggest cause was a reduction in floret fertility. The reduction in fertility with AWD in 2009 appeared to be due to cold damage, whereas the continuously flooded rice appeared to have been protected from cold damage by the floodwater. The weather during the period from panicle initiation (PI) to flowering in 2009 was very cold, with 20 days with minimum temperature less than 15 °C. About 1 in 10 years experience such low temperatures in this region. Therefore, the development of varieties with greater cold and water deficit stress tolerance is needed if non-flooded rice culture and surface residue retention are to be adopted in this region.

Crop residue mulching combined with zero tillage and crop rotation, known as conservation agriculture (CA), is being promoted as an alternative system to revert soil degradation in maize-based farming in the central highlands of Mexico. The goal of this paper was to determine the effects of CA vs. conventional tillage systems on soil quality, with a special focus on the role of earthworms in affecting the soil structure morphology, and on crop yield. For the conventional tillage system, the effect of crop residue retention (CONV + RES) was also compared to the conventional farmers’ practice (residues removed; CONV). CA resulted in four times higher earthworm abundance when compared to CONV. Residue retention per se (CONV + RES) did not favor earthworm abundance. In all cases the earthworm community was dominated by exotic species. CA increased total N and soil organic C concentrations relative to CONV, but only at 0–5 cm soil depth. Nevertheless, the more pronounced vertical stratification of soil organic carbon content under CA favored soil surface aggregation and aggregate stability as expressed by the aggregate mean weight diameter after dry sieving (MWDds = 2.6 mm for CA and 1.6 mm for CONV) and wet sieving (MWDws = 0.9 mm and 0.6 mm, respectively). Also, CA improved topsoil water stable macroaggregation (WSA = 415 mg g−1) when compared to CONV (251 mg g−1). Residue retention within conventional tillage (CONV + RES) led to small increases in topsoil aggregate stability (i.e. MWDds and WSA). Soil structural improvements were accompanied by a higher direct surface water infiltration. Micromorphological analysis of thin sections indicated a loose and highly biogenic soil microstructure in CA, whereas CONV was characterized by a physicogenic microstructure, despite similar soil bulk densities (SBD). SBD is thus a poor indicator of soil physical quality when comparing different tillage systems. Redundancy analysis illustrated that CA resulted in improvement in most parameters related to soil quality, especially at the soil surface, but significant yield increases were recorded only in 2004. CONV + RES lead to marginal improvements in soil quality with no yield increases.

New crop rotation and adequate fertilizer management are needed to maintain productivity of high input irrigated wheat (Triticum aestivum L.) systems. This study was initiated in 1998 in northwest Mexico. The objective was to examine the effects of two straw managements (incorporated or burned), three crop rotations [wheat-sesbania (Sesbania spp.), wheat-maize (Zea mays L.), or wheat-fallow], and the application for wheat of three N fertilizer sources (urea, chicken [Gallus gallus] manure, or a mixture of both) at two rates (0 and 200 kg N ha⁻¹) on soil properties. Soil microbial biomass C and N, soil N, P, K concentrations, pH, sodium absorption ratio, electrical conductivity, aggregate size distiribution and stability were evaluated in 2001, 2002, and 2005 during the wheat cropping seasons. Straw management had no consistent effect on the amount of carbon mineralized from the soil microbial biomass (SMB C). Planting sesbania as a summer crop after harvesting wheat in the spring enhanced both SMB C and N. The effect of straw management and crop rotation on aggregate size distribution was minimal. Chicken manure application increased the soil N, P, and K concentration. Potassium was accumulated after burning residues. Enhancing rotation complexity and reducing fallow by including summer maize or sesbania increased the soil organic matter. To enhance the measured soil attributes wheat should be followed by a crop like sesbania in the summer and the use of organic manure should be combined with an inorganic N source allowing a balanced application of nutrients as required by the crop.

Nitrogen fertilizer management from different sources and annual crop rotations are important components of wheat (Triticum aestivum L.) production systems, especially where air and soil quality issues have prompted a search for alternatives to wheat straw burning. This study examined the effects of two different wheat straw management options (burning and incorporation by tillage), three crop rotations [wheat-sesbania (Sesbania spp.), wheat–maize (Zea mays L.), and wheat-clean fallow] and three N sources (urea, chicken manure, and urea plus chicken manure) on wheat grain yield and N use efficiency. The experiment was conducted as split–split plot treatment arrangement with three replications for eight wheat cropping seasons in the state of Sonora, Mexico. Results indicated that both wheat grain yield and N use efficiency were higher with burning than incorporation of wheat straw and with fertilization with urea or urea plus chicken manure than chicken manure alone. As shown by the crop rotation-by-straw management interaction, planting sesbania following incorporation of the straw by tillage produced comparable grain yields to straw burning treatment. In contrast, wheat in annual rotation with maize produced the lowest wheat grain yield and N use efficiency irrespective of the wheat straw management and N source applied.

Climate change could strongly affect the wheat crop that accounts for 21% of food and 200 million hectares of farmland worldwide. This article reviews some of the approaches for addressing the expected effects that climate change may likely inflict on wheat in some of the most important wheat growing areas, namely germplasm adaptation, system management, and mitigation. Future climate scenarios suggest that global warming may be beneficial for the wheat crop in some regions, but could reduce productivity in zones where optimal temperatures already exist. For example, by 2050, as a result of possible climate shifts in the Indo-Gangetic Plains (IGPs) – currently part of the favorable, high potential, irrigated, low rainfall mega-environment, which accounts for 15% of global wheat production – as much as 51% of its area might be reclassified as a heat-stressed, irrigated, short-season production mega-environment. This shift would also represent a significant reduction in wheat yields, unless appropriate cultivars and crop management practices were offered to and adopted by South Asian farmers. Under the same climate scenarios, the area covered by the cool, temperate wheat mega-environment could expand as far as 65°N in both North America and Eurasia. To adapt and mitigate the climate change effects on wheat supplies for the poor, germplasm scientists and agronomists are developing heat-tolerant wheat germplasm, as well as cultivars better adapted to conservation agriculture. Encouraging results include identifying sources of alleles for heat tolerance and their introgression into breeding populations through conventional methods and biotechnology. Likewise, agronomists and extension agents are aiming to cut CO2 emissions by reducing tillage and the burning of crop residues. Mitigation research promises to reduce emissions of nitrous oxide by using infrared sensors and the normalized differential vegetative index (NDVI) that determines the right times and correct amounts of fertilizer to apply. Wheat geneticists and physiologists are also assessing wild relatives of wheat as potential sources of genes with inhibitory effects on soil nitrification. Through the existing global and regional research-for-development networks featuring wheat, technology and knowledge can flow to allow farmers to face the risks associated with climate change.

Two experiments were conducted in 2003 – 2005 at Hennessey and Lake Carl Blackwell, Oklahoma, to determine the effect of row configuration in bed and flat planting systems in dryland winter wheat. In the bed and flat systems, 8 and 12 treatments were evaluated that included a factorial combination of 2-varieties (“Jagalene” and “2174”), 2-N rates (0 and 100 kg ha−1) and row configurations. The row configurations were 2- and 3-row on a 75 cm bed. With 2- and 3-row per bed, 30 and 15 cm row spacing were used, respectively. In addition the traditional configuration of a solid stand with 15 cm row spacing was evaluated in the flat system. In four of six site years, bed wheat (either 2- or 3-row per bed) resulted in yields equal to flat planted wheat (15 cm row spacing). No differences in wheat grain yield were found when planting either 2- or 3-row per bed, or on the flat. However, both 2- and 3-row per bed resulted in increased yields when compared to 2- and 3-row configurations without beds. This s...

This article describes the global wheat mega-environments and consequently need for different types of wheat germplasm. The breeding programs worldwide have targeted yield potential gains as one of their major objectives. The yield gains have been variable, but consistently increasing until the end of the last century. However, in general, there has been a large benefit (estimated between 2 to 6 billion US$ based on year 2000 parity) to the agricultural economy in developing countries due to international and national partnerships in wheat breeding. The production and productivity of wheat in India has begun to show stagnation, primarily due to natural resource base decline. The research results indicate that this can be reversed by practicing zero tillage and timely planting in the Gangetic Plains. The dryland wheat based agriculture is also declining, especially in WANA (West Asia and North Africa). However, the results pertaining to minimum tillage, timely sowing and lentil/vetch rotation with...

The Green Revolution era focused on enhancing the production and productivity of rice and wheat. New challenges demand that the issues of efficient resource use and resource conservation receive high priority to ensure that past gains can be sustained and further enhanced to meet the emerging needs. Extending some of the resource-conserving interventions developed for wheat to rice culture is a major challenge for researchers and farmers alike. The present paper shares recent research experiences on resource conservation technologies involving tillage and crop establishment options and associated agronomic practices which enable farmers in reducing production costs, increase profitability and help them move forward in the direction of adopting conservation agriculture.

Summary As farmers increasingly adopt resource conserving farming practices, there is a need for wheat cultivars that better adapt to the changing environment and the nutritional needs of people, particularly those living in developing countries. Improved adaptation to zero and minimum tillage, better water use efficiency, improved root health, durable resistance to foliar diseases and enhanced nutritional value of the grain are key selection criteria for plant breeders. Significant responses to selection for these constraints have been achieved at the International Maize and Wheat Improvement Center (CIMMYT), by selecting segregating populations and advanced lines in carefully managed tillage, moisture deficit and heat stressed environments, that correlate with key spring wheat growing environments globally. Root health has been improved through a combination of marker assisted selection and disease bioassays, and the nutritional value of wheat grain has been enhanced using genetic variation for high Fe and Zn grain content found among tetraploid wheat ancestral species.

Six greenhouse and three field experiments were conducted at the International Center for Improvement of Maize and Wheat (CIM-MYT), Mexico, on bread wheat (Triticum aestivum L.) genotypes to ascertain the role of osmotic adjustment (OA) in sustaining grain yield and its stability under water deficit conditions. Under simulated water deficit conditions of the greenhouse and field, the genotypes differed considerably regarding OA, ranging from 0.31 to 0.86 MPa and from 0.60 to 0.99 MPa, respectively. When the mean values of OA across the six greenhouse experiments were regressed against those of grain yield obtained at different moisture levels of the line source, the correlation coefficient value increased with the increase in moisture stress, turning positively significant (P < 0.001) at the highest water deficit level. Similarly, osmotic potential at full turgor (OP100) and turgor potential (TP), measured in the greenhouse, were positively correlated (P < 0.05) with grain yield at the highest line source water deficit level. Osmotic adjustment and grain yield, both measured in the simulated water deficit condition in the field, were also positively correlated (P < 0.05). Besides, OA maintained yield stability through maintenance of turgor under water deficit during reproductive period of crop growth. The heritability of OA, OP100, and TP, computed by pooled analysis of variance across the six greenhouse experiments, was 0.74, 0.73, and 0.79, respectively. The results indicated that OA, as well as OP100 and TP, could be used as screening tools for drought-resistant bread wheat genotypes in the greenhouse. This study also demonstrated the appropriate greenhouse screening methodology in this regard.

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 × 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 Lrl9 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 Maiz 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 Lrl9 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.

The cropping systems simulation model APSIM-Nwheat was tested against detailed field measurements representing possible growing conditions under future climate change scenarios. Increasing average temperatures by 1.7 °C observed over several seasons at Obregon, Mexico reduced the time to flowering by 11 days and resulted in a decline of total biomass and grain yield. These effects were reproduced by the model, except when the observed total biomass inexplicably rose again in the fourth and fifth year, despite higher temperature and a much shorter growing time. In a water stress experiment, the effects of different timing and duration of water deficit on crop growth and yield were reproduced with the model for a rain-shelter experiment at Lincoln, New Zealand where observed grain yields were reduced from 10 to 4 t ha −1 due to increased water deficit. In experiments from Western Australia, reduced growth and yields due to extreme terminal water deficit were also reproduced with the model where measured yields fall below 0.5 t ha −1 . In the Maricopa Free Air Carbon-Dioxide Enrichment (FACE) experiment in Arizona, USA, the largest yield increase occurred with elevated CO 2 in the dry and high N treatments, whereas little or no response was observed in the wet and low N supply treatments, as simulated with the model. Combining elevated CO 2 with increased temperature in a sensitivity analysis, two levels of water supply and a range of N applications indicated a positive effect of elevated CO 2 on yield as long as N was not limiting growth. Increased temperature and reduced water supply reduced yields and the yield response to N supply under ambient and elevated CO 2 . Grain protein concentrations were reduced under elevated CO 2 , but the difference was minor with ample N fertiliser. Evapotranspiration was reduced under elevated CO 2 . Higher temperatures increased evapotranspiration with low N input, but reduced it with ample N fertiliser, resulting in a reduction and an increase, respectively, in drainage below the root zone. In the Mediterranean environment of Western Australia the impact of elevated CO 2 and increased temperature on grain yield was in average positive, but varied with seasonal rainfall distribution. Based on the range of model testing experiments and the sensitivity analysis, APSIM-Nwheat was found suitable for studies on directional impacts of future climate change on wheat production. Due to some large discrepancies between simulated and observed data, field experiments representing only a limited range of possible climate change scenarios and the large possible range of factorial interactions not tested, simulated quantitative effects with the model should be interpreted cautiously.

Lodging behavior and morphological characters of 12 spring wheat ( Triticum aestivum L.) genotypes (four Indian cultivars and eight Mexican cultivars/CIMMYT advanced lines) were studied under disease free condition with different N rates (180, 240 and 300 kg ha −1 ), and at 300 N, with ethephon (480 g ha −1 ) application at CIMMYT (Centro Internacional de Mejoramiento de Maiz y Trigo), near Ciudad Obregon, Sonora, Mexico, during 1997–1998 and 1998–1999. In both years, the crop lodged, mainly by buckling or bending of the culms, 25–30 days after anthesis. Ethephon application at DC 38 prevented lodging and was associated with reduction in plant height (10.2%), peduncle length (14.2%), length of third internode (8.6%). It also simultaneously increased tillers m −2 (9.1%), stem wall thickness for the first (4.3%), second (6.3%) and third (8.1%) internodes and peduncle (3.6%) when compared at the same N level. Varietal differences in lodging behavior were significant during both years. The lodging tolerant genotype, Baviacora 92, had 31.9, 34.0, 40.7 and 34.1% larger diameter for the first, second, third internodes and peduncle, respectively, when compared to HD 2329, one of the most lodging susceptible genotypes. Furthermore, Baviacora 92 had first, second, third internode and peduncle stem walls that were also 31.7, 33.5, 35.4 and 37.1% greater, respectively, than Pavon 76, which had the thinnest stem walls. Genotypic correlations were better than phenotypic correlations, which suggested that environmental effects did not reinforce the genotypic effects rather they weakened them. Tillers m −2 correlated ( r =0.89, P −2 . Simple linear regression explained that 79% of the variation in lodging score could be due to tillers m −2 and 49–65% due to diameter of different internodes. The best sub-set of the regression showed that number of tillers m −2 and/or stem diameter of internodes were the key variables when deciding two or three important characters for selecting for varieties with lodging resistance. Three variables such as stem diameter of first, second internode and length of first internode or tillers m −2 , height and length of stem or tillers m −2 , stem diameter of first, second internode together explained about 89–91% of the variation in lodging score. Therefore, it was suggested that selection for lodging resistant cultivars should emphasize larger stem diameter and wall thickness of basal internodes and fewer tillers per unit area with heavy spikes.

Present study involved 12 lodging tolerant/ susceptible spring wheat (Triticum aestivum L.) genotypes grown at 180, 300 kg N/ha and 480 g/ha ethephon application in latter N rate at CIMMYT (Centra Internacional de Mejoramiento de Maiz y Trigo), Mexico during 1997-98 and 1998-99 under disease free and irrigated condition. During both the years, crop lodged 25 to 30 days after anthesis in varying degrees at different N levels whereas, ethephon application at DC 38 prevented lodging and decreased the ADF (acid detergent fibre), cellulose and lignin content by 8.47, 8.81 and 5.56 %, respectively in the basal internode and increased K content of 2nd intemode by 9.6 % as compared to without its application. However, increasing N rates from 180 to 300 kg/ha determined non-significant difference for ADF, cellulose, lignin and K concentrations in the 2nd and 3rd internodes. ADF and cellulose concentrations of 3rd internode were higher by 3.2-3.8 % and 4.7-5.3 %, respectively when compared with 2nd internode whereas 2nd internode determined 1.9-4.2 % higher lignin and 12.3-13.4 % more potassium contents than the 3rd internode at different N levels. Pooled analysis indicated that genotypic differences for ADF, cellulose, lignin and K contents were significant for both the internodes. ADF, cellulose and lignin contents for the 2nd and the 3rd internodes were negatively correlated with lodging score and in combined analysis of 3rd internode its phenotypic correlation was - 0.53, - 0.57 and - 0.61 with lodging score, respectively. Also, from multiple correlations study it was observed that ADF, cellulose and lignin contents had a positive impact among themselves and their cumulative effect in turn might be preventing lodging. Therefore, it could be said that higher ADF, cellulose and lignin content of basal internode were important parameters in developing a lodging resistant cultivar under irrigated and high N conditions.

Wheat cultivars often show highly significant genotype by environment interaction (G×E) for yield, even when comparing different years within a relatively stable location. This study attempts to explain some of the physiological bases of G×E in two experiments: (i) historic yield potential trials (HYPTs) of bread wheat ( Triticum aestivum L.), durum ( T. durum Desf.) and triticale (X Triticosecale Wittmack) cultivars grown under agronomically optimal conditions; (ii) an elite spring wheat yield trial (ESWYT) of 30 bread wheat genotypes cultivated at 27 international locations. For the HYPT, the main objectives were to determine the environmental variables during different phenological stages associated with: (i) G×E among the three crop species, (ii) G×E within each species, and (iii) underlying physiological causes of G×E. For ESWYT, meteorological data were not available and so mean site values of certain crop parameters were used as proxy environmental data to determine whether conditions either pre- or post-anthesis were more influential in determining G×E. Partial least-squares analysis and factorial regression models were used to identify the environmental factors best explaining G×E independent of the main effects. Of the three crops, durums were shown to be the most sensitive to conditions pre-anthesis, requiring higher radiation and cooler average temperatures in order to set high grain number. Triticale, despite having the highest average yield and biomass, performed relatively poor when conditions from spike growth stage onwards were sunny and warm. Bread wheat appeared to be the most robust of the three species. Considering yield, biomass, and yield components, it was apparent that the spike primordia growth stage was generally the most sensitive to environmental factors causing G×E. Results for the ESWYT suggested that conditions post-anthesis were more influential on G×E than conditions pre-anthesis. Implications for how such analysis may assist with both conventional and molecular approaches to breeding are discussed.

In the Yaqui valley, northwest Mexico, wheat ( Triticum aestivum L.) is grown as a winter crop followed by maize ( Zea mays L.) as a summer crop both planted on beds. Straw of both crops is usually burned to facilitate seedbed preparation for the succeeding crop. Soil physical and biological attributes were determined from 1996 to 2000 from a study initiated in 1992 at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station. The objective was to compare five treatments: (1) conventional tilled bed (CTB)-straw incorporated, and permanent bed (PB) with (2) straw removed, (3) straw partly removed, (4) straw retained, and (5) straw burned — on soil strength, soil structure, and soil microbial biomass carbon (SMB). Seven N treatments were applied to wheat, but for the purpose of this study we chose a subset of three N treatments (0, 150 and 300 kg N ha −1 ) for measurements. Maize received a uniform application of 150 kg N ha −1 each year. Soil strength decreased as the amount of crop residues applied for each tillage-straw treatment increased. Permanent beds-straw burned treatment had the highest soil strength and CTB-straw incorporated the lowest. The largest soil aggregate fractionation, evaluated with a fractal dimension parameter ( D ), corresponded to PB-straw burned treatment and the lowest to PB-straw retained treatment. SMB was greater at 0–7 cm than at 7–15 cm depth. As the amount of crop residues increased in each tillage PB-straw treatment, the SMB generally increased. The largest amount of SMB occurred most often on either CTB-straw incorporated or PB-straw retained and the lowest in PB-straw burned treatment. The practice of retaining crop residues as stubble should be adopted in the Yaqui valley since changes resulting from burning crop residues showed the tendency to decrease productivity and soil quality as shown by increased soil strength and soil fractionation, and reduced SMB.

Wheat (Triticum aestivum L.) in the Yaqui Valley, northwest Mexico, is planted as a winter crop using a raised-bed, furrow-irrigated system and high fertilizer N rates. Wheat residues are usually burned before planting maize (Zea mays L.) as a summer crop. The N use of wheat planted following conventional tillage using a raised-bed system (CTB) incorporating both wheat and maize residues was compared with wheat planted using permanent raised beds (PB) under four residue management treatments: all straw (wheat and maize) left as stubble, straw partly removed (maize residues removed; wheat residues retained), all straw removed, and all straw burned. Each wheat plot was split into seven N fertilizer (N t ) treatments: five applied at planting (0, 75, 150, 225, and 300 kg ha 1 ) and two at the 1st node stage (150 and 300 kg ha -1 ). Maize received a uniform N f application of 150 kg ha -1 . The N use efficiency of wheat with 150 kg N f ha -1 at the 1st node stage was superior to basal applications at the same rate. Permanent bed-all straw left as stubble and PB-all straw burned had the highest average wheat grain yields (5.57 and 5.52 Mg ha 1 , respectively), N use efficiency (28.2 and 29.1 kg grain kg -1 of N supply, respectively), and total N uptake (133 and 137 kg ha -1 , respectively). Total N uptake for 150 and 300 kg N f ha -1 at the 1st node stage was 14 and 8% greater, respectively than at planting. In most tillage-straw treatments, 21% of the difference in wheat grain yields was due to the N supply component at low N rates; at high N rates, 97% was due to N use efficiency.

In the Yaqui Valley, northwest Mexico, the crop sequence that is becoming more common consists of planting wheat (Triticum aestivum L.) as a winter crop on a raised bed followed by maize (Zea mays L.) as a summer crop. In this area, straw of both winter and summer crops is commonly burned. The consequences of burning crop residues on crop yields in the Yaqui Valley have not previously been documented, and alternative practices have not been proposed. A 5-yr study was conducted at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico, to compare the effects of burning with other straw management strategies on wheat and maize yields. We tested two tillage systems (conventional-tilled bed, CTB, and permanent bed, PB), five straw management treatments (incorporated with CTB and straw as stubble, partly removed, removed, or burned with PB), and seven N treatments, five applied preplant (0, 75, 150, 225, and 300 kg N ha -1 ) and two at the 1st node stage (150 and 300 kg N ha -1 ) of wheat. Maize following wheat received a uniform application of 150 kg N ha -1 . The combination of PB and straw as stubble produced superior maize and wheat grain yields in high-yielding environments; in low-yielding environments, PB-straw burned produced greater wheat grain yields. Nitrogen fertilizer application of 150 and 300 kg N ha -1 at the 1st node stage of wheat increased grain yields compared with preplant N fertilizer applications. Permanent beds combined with retaining all crop residues in the soil as stubble have the potential to increase both wheat and maize yields in the Yaqui Valley.

Partial least squares (PLS) and factorial regression (FR) are statistical models that incorporate external environmental and/or cultivar variables for studying and interpreting genotype × environment interaction (GEl). The Additive Main effect and Multiplicative Interaction (AMMI) model uses only the phenotypic response variable of interest; however, if information on external environmental (or genotypic) variables is available, this can be regressed on the environmental (or genotypic) scores estimated from AMMI and superimposed on the AMMI biplot. The objectives of this study with two wheat [Triticum turgidum (L.) var. durum] field trials were (i) to compare the results of PLS, FR, and AMMI on the basis of external environmental (and cultivar) variables, (ii) to examine whether procedures based PLS, FR, and AMMI identify the same or a different subset of cultivar and/or environmental covariables that influence GEI for grain yield, and (iii) to find multiple FR models that include environmental and cultivar covariables and their cross products that explain a large proportion of GEI with relatively few degrees of freedom. Results for the first trial showed that AMMI, PLS, and FR identified similar cultivar and environmental variables that explained a large proportion of the cultivar × year interaction. Results for the second wheat trial showed good correspondence between PLS and FR for 23 environmental covariables. For both trials, PLS and FR complement each other and the AMMI and PLS biplots offered similar interpretations of the GEl. The FR analysis can be used to confirm these results and to obtain even more parsimonious descriptions of the GEL

Leaf rust, caused by Puccinia recondita Roberge ex Desmaz., is an important disease of wheat (Triticum aestivum L.) worldwide. To estimate the genetic progress in reducing grain yield losses through breeding for resistance to leaf rust, replicated trials including 15 popular CIMMYT germplasm-derived wheat cultivars released between 1966 and 1988 in northwestern Mexico were sown in that same area; normal and late planting dates were used for four and two seasons, respectively. Leaf rust epidemics were established by inoculating spreader rows planted adjacent to plots of the cultivars which were not protected by fungicide. Average losses in grain yields of the cultivars due to leaf rust ranged between 6.6 and 62.7% and were highly correlated with final disease severity (r = 0.898, P < 0.01) and relative area under the disease progress curve (r = 0.917, P < 0.01). The losses in grain yield were mostly due to reductions in kernel weight, kernels per square meter, and grain fill rate. Grain yield losses (7.7-10.4%) in slow rusting cultivars Cocoraque 75, Nacozari 76, Opata 85, and Bacanora 88 were similar to those observed in the immune 'Oasis 86' (6.6%) or resistant 'Ciano 79' (10.2%). The average annual progress in grain yield potential achieved through breeding averaged over the six trials was estimated to be 0.48% (r 2 = 0.38, P < 0.01) for fungicide protected and 2.21% (r 2 = 0.47, P< 0.01) when not protected by fungicide. We conclude that while the grain yield potential of CIMMYT-derived cultivars has increased significantly over the years, progress in protecting this yield potential through the incorporation of genes that confer slow rusting resistance has been more dramatic.

Germplasm from the spring wheat (Trificum oesfivum L.) breeding program at the International Center for Improvement of Maize and Wheat (CIMMYT has had a major impact on the yield of irrigated spring wheats in most developing countries in the past 30 yr. The rate and nature of yield potential progress in this germplasm was measured cornparing eight outstanding short cultivars released in northwest Mexico between 1962 and 1988. They were grown under irrigation and optimal management, including disease and lodging protection, in each of six winter growing seasons (1989-1990 to 1994-1995) at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico. There were highly significant effects of cultivar on grain yield, and, although cultivar x year interaction was significant, there were few significant crossover interactions between pairs of genotypes and years in the grain yield data set. Yield averaged across the 6 yr increased linearly from 6680 kg ha -l for the earliest cultivar, Pitic 62, to 8475 kg ha -l for Bacanora 88, the latest. The rate of progress against year of release was 67 kg ha -1 yr -1 (r = 0.99, P< 0.001), or 0.88% per year. Grain yield progress was correlated with kernel number per square meter (r = 0.84, P < 0.01) and harvest index (r = 0.81, P < 0.02), but not with total biomass production, kernel weight, days to anthesis, spikes per square meter, or kernels per spike. Thus linear progress in yield within short germplasm has continued at least until the late 1980s, and the yield components studied did not indicate any clear direction for future progress, apart from that suggested by the strong relationships between grain yield and harvest index and grain yield and kernels per square meter, as has been seen in most studies of yield progress in cereals.

Three advanced technologies to measure soil carbon (C) density (g C m(-2)) are deployed in the field and the results compared against those obtained by the dry combustion (DC) method. The advanced methods are: a) Laser Induced Breakdown Spectroscopy (LIBS), b) Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS), and c) Inelastic Neutron Scattering (INS). The measurements and soil samples were acquired at Beltsville, MD, USA and at Centro International para el Mejoramiento del Maíz y el Trigo (CIMMYT) at El Batán, Mexico. At Beltsville, soil samples were extracted at three depth intervals (0-5, 5-15, and 15-30 cm) and processed for analysis in the field with the LIBS and DRIFTS instruments. The INS instrument determined soil C density to a depth of 30 cm via scanning and stationary measurements. Subsequently, soil core samples were analyzed in the laboratory for soil bulk density (kg m(-3)), C concentration (g kg(-1)) by DC, and results reported as soil C density (kg m(-2)). Results from each technique were derived independently and contributed to a blind test against results from the reference (DC) method. A similar procedure was employed at CIMMYT in Mexico employing but only with the LIBS and DRIFTS instruments. Following conversion to common units, we found that the LIBS, DRIFTS, and INS results can be compared directly with those obtained by the DC method. The first two methods and the standard DC require soil sampling and need soil bulk density information to convert soil C concentrations to soil C densities while the INS method does not require soil sampling. We conclude that, in comparison with the DC method, the three instruments (a) showed acceptable performances although further work is needed to improve calibration techniques and (b) demonstrated their portability and their capacity to perform under field conditions.

Genetic and agronomic contributions to yield gains for wheat (Triticum aestivum L.) in the Yaqui Valley of northwest Mexico were estimated for the period from 1968–1990. Five problems associated with estimating sources of yield gains were considered, namely: (1) adjusting yield gains for variation in weather over the study period; (2) considering annual cultivar-by-weather interactions, which are potentially problematic when relative yields of cultivars are generated over only part of the study period; (3) overestimating relative yields of cultivars if the check cultivar(s) become susceptible to disease; (4) ensuring that yields as estimated from research station trials represent cultivar performance under farmers' conditions; and (5) allowing for cultivar-by-management interactions. With these factors considered, 28% of the weather-adjusted yield gain of 103 kg ha−1 y−1 was attributed to genetic gain (i.e., cultivar improvement). If the yield gains had not been adjusted for annual weather variation, genetic gain would have been overestimated at 50%. By contrast, 48% of the gain was attributed to increased use of N fertilizer, driven at least in part by a decline in N prices; no N-by-cultivar interactions were apparent. The remainder of the yield gap (24%) could not be attributed to specific factors, although P application rates increased over time, and negative deviations from linearity were associated with years having greater than normal rainfall in November and December (a phenomenon which can delay sowing and/or reduce crop stand). In addition to identifying factors contributing to yield gains, technologies that have contributed benefits not measured by yield are discussed.

Carbon isotope discrimination (Δ), yield and other characters were determined for 75 spring bread wheat cultivars and advanced breeding lines in which water availability was varied using a line-source irrigation system. The experiment was carried out in 1989/90 at CIMMYT-CIANO, Cd. Obregon, in northwest Mexico. Forty of the cultivars and advanced breeding lines came from CIMMYT-Mexico, twenty from ICARDA-Syria, and fifteen from CIMMYT's International Drought Trial (IDT). Considering all materials together, grain yield and Δ were markedly reduced by drought (yield declined from 4560 to 1090 kg ha −1 , Δ from 16.9 to 14.0‰, from least to most stressed, respectively). For each group of lines, grain yield was positively correlated with Δ in both the most stressed and least stressed parts of the trial (except for the CIMMYT lines under low stress where the correlation was nonsignificant). In addition, high yield under stress was associated with an early maturity score and with less reduction in mature plant height. Δ may be potentially used to augment selection for high yield based on yield itself, in both low- and high-stressed environments. In the latter environment, early maturity and minimal reduction in plant height should also be considered in a selection program especially under conditions of mid-season to terminal drought and/or heat stress.

SummaryTwo cereal cropping systems are described which, through the introduction of a leguminous intercrop, increased productivity, nitrogen output and ground cover of the systems in the absence of added nitrogen fertilizer. Nitrogen-fixing legumes were cultivated between rows of wheat or barley grown at low levels of soil nitrogen, and mostly under rainfed conditions, in Mexico between 1989 and 1992. None of the legumes tested reduced yields of the cereal crop in comparison to controls where cereal yields were in the range of 1–4 t/ha, while the extra total biomass from legumes in some cases more than doubled productivity. Different legume crops were tested to demonstrate the adaptability of the system to the varying needs of farmers. The intercropped legumes achieved dry biomass yields as high as 6·5 t/ha in the case of a sequentially cropped forage crop of hairy vetch, or 1·4 t/ha of dry beans plus 3·5 t/ha of green residue in the case of Vicia faba. Total biomass in the intercropped situation gave land equivalent ratios as high as 1·54. Light measurements inside the crop canopies indicated that the intercropped systems intercepted a higher proportion of the incident solar radiation than the cereal monocrop, presumably accounting for the large differences in total biomass produced. In addition, with leaf nitrogen levels of 3·8%, it is assumed that the intercropped legumes fixed considerably more nitrogen than was removed by the wheat crop. The potential of the system to stabilize erodible soils by increasing ground cover as well as by raising inputs of soil organic matteris discussed.

Field experiments were conducted with modern semidwarf spring wheat cultivars representing a range of yield potential in order to compare their adaptation to levels of interplant competition for resources. Levels of competition were altered, in both leaf canopy and underground, by manipulating rows of plants in eight-row yield plots. Competition for light was decreased by bending adjacent rows away from the central two rows thus permitting greater penetration of light to lower leaves of the central rows (light treatment). Reduced competition underground was realized, simultaneously with reduced competition for light, by uprooting the plants adjacent to the central two rows (root/light treatment). These treatments were implemented at the developmental stage of flag-leaf ligule emergence (FLLE), when interplant competition was assumed to become maximal. While the average yield responses were 25%, and 40% to the light and root/light treatments respectively, there was a significant interaction with genetic material. Low-yield-potential (LYP) lines responded more to reduced competition than high-yield-potential (HYP) lines suggesting that the greater efficiency of the HYP lines, reflected in their higher yield, is related to their better adaptation to interplant competition. Physiological bases for improved performance are examined and discussed in relation to ideas about crop ideotypes and possible implications to breeding. These data appear to support the idea that genes conferming yield potential through improved adaptation to the crop environment are associated with a less competitive phenotype.

Rice consumption is one of the major pathways for As intake in populations that depend on a rice diet in several countries of South and South-east Asia. Pot experiments were undertaken to investigate the effects of water management (WM), arsenic (As) contaminated soil-water and Phosphorus (P) rates on As uptake in rice plants. There were 18 treatments comprising of three each of As rates (0, 20 and 40 mg kg(-1) soil) and P rates (0, 12.5 and 25 mg kg(-1) soil) and two WM (aerobic and anaerobic) strategies on winter (boro var. BRRI dhan 29) and monsoon (aman var. BRRI dhan 32) rice at the Wheat Research Center (WRC), Nashipur, Dinajpur, Bangladesh. Arsenic concentrations in rice grain and straw increased significantly (P ≤ 0.01) with the increasing As rates in the soil. Arsenic availability in soil pore-water solution was less (58%) under aerobic WM (redox potential-Eh=+135 to +138 mV; pH-6.50 at 24.3 °C) as compared to anaerobic WM (flooded: Eh=-41 to -76 mV; pH-6.43 at 23 °C). The highest total grain As content 2.23 ± 0.12 mg kg(-1) and 0.623 ± 0.006 mg kg(-1) was found in T(6) (P(12.5)As(40)-anaerobic) and T(9) (P(25)As(40)-anaerobic) in BRRI dhan 29 and BRRI dhan 32, respectively, which was significantly higher (41-45%) than in the same As and P treatments for pots under aerobic WM. The As content in rice straw (up to 24.7 ± 0.49 ppm in BRRI dhan 29, 17.3 ± 0.49 mg kg(-1) in BRRI dhan 32 with the highest As level) suggested that As can more easily be translocated to the shoots under anaerobic conditions than aerobic condition. BRRI dhan 29 was more sensitive to As than BRRI dhan 32. Under aerobic WM, P soil amendments reduced As uptake by rice plants. The study demonstrated that aerobic water management along with optimum P amendment and selection of arsenic inefficient rice varieties are appropriate options that can be applied to minimize As accumulation in rice which can reduce effects on human and cattle health risk as well as soil contamination.

In the next 20 years, it is estimated that global wheat production must increase by 40% to meet the ever increasing demand. “Increasing the intensity of production in those ecosystems that lend themselves to sustainable intensification, while decreasing intensity of production in the more fragile ecosystems” may be the only way for agriculture to keep pace with population (Borlaug and Dowswell, 1997). Hence, a greater reliance on maximizing production efficiency, or grain yield potential (GYP), under various agro-ecological scenarios will be required. Environmental, cultural, and political sustainability will define the focus of our research agenda. CIMMYT aims to contribute to this effort by protecting past achievements in yield potential and adaptation through continuing an aggressive program of incorporating resistance to abiotic and biotic stresses. This strategy capitalizes on newer empirical methods, advances in information technology, morphological and physiological markers, broadening the genetic resource base and the use of emerging biotechnologies. To date, high rates of progress in raising GYP have been achieved in spring durum and bread wheats.

Multienvironment trials are important in agronomy because the effects of agronomic treatments can change differentially in relation to environmental changes, producing a treatment × environment interaction (T × E). The aim of this study was to find a parsimonious description of the T × E existing in the 24 agronomic treatments evaluated during 10 consecutive years by (i) investigating the factorial structure of the treatments to reduce the number of treatment terms in the interaction and (ii) using quantitative year covariables to replace the qualitative variable year. Multiple factorial regression (MFR) for specific T × E terms was performed using standard forward selection procedures for finding year covariables that could replace the factor year in those T × E terms. Subsequently, we compared the results of the final MFR with those of a partial least squares based analysis to achieve extra insight in both the T × E and final MFR model. The MFR model with a stepwise procedure used in this study for describing the T × E showed that the most important interaction with year was that due to different N fertilizer levels and the most important environmental variables that explained year × N interaction were minimum temperatures in January, February, and March and maximum temperature in April. Evaporation in December and April were important covariables for describing year × tillage and year × summer crop interactions, whereas precipitation in December and sun hours in February were important for explaining the year × manure interaction. We also discuss the parallels with extended additive main effect and multiplicative interaction analysis. Biological interpretation of the results are provided.

Bread wheats (Triticum aestivum L.) were evaluated for plant characteristics contributing to grain yield and plant adaptation under various drought patterns. The usefulness of these traits as explicit selection criteria in developing drought tolerant wheat varieties was investigated in three experiments. Cultivars from four germ-plasm groups, representing the four relevant major and distinct global wheat growing environments, were grown under the respective simulated early, late, continuous and no drought conditions by manipulating irrigation in north western Mexico. Additionally, 560 advanced lines from the CIMMYT breeding program were grown under late drought conditions, and 16 randomly selected advanced genotypes were studied in more detail under late and no drought conditions. In these three studies, the association between yield in drought-stressed environments and yield in non drought-stressed environments was interpreted to reflect genotypic high yield potential, mainly by way of high biomass development. However, yield potential only partly explained the superior performance under drought. For each pattern of drought stress, particular and often different plant traits were identified that further contributed specific adaptation to the distinct drought stress conditions. Knowledge of these traits will be useful for developing CIMMYT germplasm for specific drought-stressed areas. Ultimately, these studies demonstrate that both yield potential and specific adaptation traits are useful criteria in breeding for drought environments, and should be combined to achieve optimum performance and adaptation to drought stress.

Three types of containers (125-ml Erlenmeyer flasks, 122×28mm glass centrifuge tubes, and 200×25mm glass screwcapped tubes) were compared as fermentation vessels for a modified Tilley and Terry two-stage in vitro artificial rumen procedure. This in vitro technique estimates true dry matter digestibility. Four forages (orchard-grass, alfalfa, bromegrass, and timothy) with wide differences in digestibility and three sample sizes (250, 375, and 500mg) were utilized for the comparison. Digestibilities were consistently low with the centrifuge tubes. Results with screw-capped tubes were comparable to those with Erlenmeyer flasks. Tubes utilize water bath space more efficiently and do not require a constant supply of CO 2 during fermentation to maintain an anaerobic condition. Small but significant differences in digestibility occurred between sample sizes.

Knowledge about the functioning of a crop system can be embedded in simulation models of crop growth and development. Such quantitative models have until now made extensive use of physiological knowledge, but modeling could benefit greatly by incorporating genetic information. Equally, because models can help resolve environmentally varying characteristics into stable characteristics that reflect groups of genes, genomics research could benefit from modeling efforts. The use of the model Cropsim to analyze wheat (Triticum aestivum L.) growth and development is demonstrated. Data on reproductive development were well fitted when the life cycle was divided into phases, although photoperiodic sensitivity varied between phases. Describing leaf appearance satisfactorily required introducing an effect of photoperiod. Understanding the need for a breakdown into phases of development, for varying photoperiodic sensitivities, and for photoperiodic control of leaf appearance, could be enhanced by genomic studies. Simulating growth of wheat over successive seasons required changing supposedly stable genotypic characteristics. Furthermore, growth of near inbred lines incorporating the Lrl9 chromosome translocation varied with genotypic background. These results also indicate that, given the variation in modeling outputs from year to year, care should be taken in the application of models to long-term problems, and that efforts should be devoted to model improvement. Further development of crop models will benefit from associating genomic analysis with field experiments and model analyses. Much could be gained from increased interaction among model developers, field experimenters, and genomics researchers.