Environments for Selecting Widely Adapted Spring Wheat

Abstract

Breeding widely adapted wheat (Triticum aestivum L.) genotypes with stable and high yields across environments is particularly important for developing countries since yield stabilizing inputs are often limited or not available. To evaluate the screening ability of locations for identification of such genotypes, data collected for 19 yr by the International Spring Wheat Yield Nursery (ISWYN) were analyzed; 1221 trials at 268 locations in 69 countries were involved. To compare single‐experiment parameters, i.e., genotypic variance (σ̂2g)k, error variance (σ̂2e)k, heritability (h2)k, and coefficient of variation (CV)k, trials without major biotic stresses were divided into three groups according to mean grain yield. Genotypic variance, error variance, and heritability increased and (CV)k decreased with yield. Group means for the four parameters were significantly (P = 0.01) different. A fourth group containing trials with major biotic stresses had the highest, but not significantly higher, average estimates for (σ̂2g)k, (h2)k, and (CV)k. The screening ability for each location was calculated as the correlation, rk, between mean grain yield of genotypes at each location and mean yield across locations. The screening ability was highest for locations with no major abiotic and biotic stress factors apart from leaf rust (Puccinia recondita Roberge ex Desmaz. f. sp. tritici) and stem rust (P. graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.). CIMMYT's principal test site, Ciudad Obrégon, Sonora, Mexico, was most suitable for screening, with an average rk of 0.77. Sensitivity to photoperiod, cold tolerance, need for late maturity, tolerance to problem soils, and resistance to diseases other than rusts were the main adaptation‐limiting and location‐specific factors.

The Impact of Drought Stress on some Morpho-Physiological Traits and RAPD Markers in Wheat Genotypes

“…This latter result may be a contributing reason to the fact that unfavorable environments tend to be more useful than favorable ones for the selection of wheat genotypes aimed at identifying material that performs well across environments with different stress levels in the region (Ceccarelli et al, 1991). The choice between favorable and unfavorable test sites, sometimes addressed especially for target regions where a relatively low yearto-year climatic variation and/or the adoption of sitespecific agronomic practices (e.g., irrigation) make the difference between locations rather constant in the time (e.g., Braun et al, 1992;Cooper et al, 1995), can be considered of lesser importance in the current target region, in which the same location may act as a favorable or unfavorable environment for selection depending on the year. Association between grain yield and other tolerance indices The indices GMP, MP and YS were very similar to the selection based on Y is and Y s .…”

Combining ability analysis for grain filling duration and yield traits in spring wheat (Triticum aestivum L. em. Thell.)

“…However, due to the domination of long duration rice varieties such as MTU 7029, late transplanting, water stagnation and other related factors it is unlikely that, in the near future, the sowing of wheat will be advanced in the NEPZ region by more than two to three weeks. The warm and humid NEPZ region, classified as a Mega Environment 5 by Braun et al (1992), best supports wheat varieties that are heat tolerant or display rapid grain filling. Grain filling duration is an important factor when wheat is grown under conditions of high temperature and water stress and it has been suggested (Wiegand and Cuellar, 1981) that for such environments wheat lines should be developed with a shorter grain filling duration.…”

Gains from Selection for High Grain Yield under Contrasting N Environments in F2 Populations of Wheat Diallel Crosses

“…Braun et al (1992) has argued for this approach, citing results from 17 years of CIMMYT winter performance trails.…”