Erratic weather patterns associated with increased temperatures and decreasing rainfall pose unique challenges for wheat breeders playing a key part in the fight to ensure global food security. Within rain fed winter wheat areas of Turkey and Iran, unusual weather patterns may prevent attaining maximum potential increases in winter wheat genetic gains. This is primarily related to the fact that the yield ranking of tested genotypes may change from one year to the next. Changing weather patterns may interfere with the decisions breeders make about the ideotype(s) they should aim for during selection. To inform breeding decisions, this study aimed to optimize major traits by modeling different combinations of environments (locations and years) and by defining a probabilistic range of trait variations [phenology and plant height (PH)] that maximized grain yields (GYs; one wheat line with optimal heading and height is suggested for use as a testing line to aid selection calibration decisions). Research revealed that optimal phenology was highly related to the temperature and to rainfall at which winter wheat genotypes were exposed around heading time (20 days before and after heading). Specifically, later winter wheat genotypes were exposed to higher temperatures both before and after heading, increased rainfall at the vegetative stage, and reduced rainfall during grain filling compared to early genotypes. These variations in exposure to weather conditions resulted in shorter grain filling duration and lower GYs in long-duration genotypes. This research tested if diversity within species may increase resilience to erratic weather patterns. For the study, calculated production of a selection of five high yielding genotypes (if grown in five plots) was tested against monoculture (if only a single genotype grown in the same area) and revealed that a set of diverse genotypes with different phenologies and PHs was not beneficial. New strategies of progeny selection are discussed: narrow range of variation for phenology in families may facilitate the discovery and selection of new drought-resistant and avoidant wheat lines targeting specific locations.

. 2005. Regulation of low-temperature tolerance in barley under field conditions in northwest Iran. Can. J. Plant Sci. 85: 587-592. Low-temperature (LT) stress is a major factor limiting the over-winter survival of barley (Hordeum vulgare L.). The objective of this study was to determine the relationship between vegetative/reproductive transition and expression of LT tolerance in barley cultivars acclimated under field conditions. Three cultivars with different vernalization response and photoperiod sensitivity were planted in the field at the Maragheh Dryland Agricultural Research Station (37°15′N, 46°15′E; 1720m) in Iran in the autumns of 2002 and 2003. LT tolerance, as measured by LT 50 , and stage of phenological development, as estimated from final leaf number (FLN) and shoot apex developmental morphology, were determined during the autumn and winter seasons. The short-day insensitive spring-habit cultivar Rihane-03 had a limited ability to acclimate to LT and it reached its maximum level of LT tolerance very quickly. The winter-habit cultivar Dobrinya reached its maximum LT tolerance at the point of vernalization saturation. The very short-day (SD) sensitive spring-habit cultivar Dicktoo entered the double ridge (DR) stage at about the same time as the winter-habit Dobrinya. The delay in the phenological development of both Dobrinya and Dicktoo was accompanied by increased expression of LT tolerance confirming that the length of the vegetative phase determines a plant's ability to maintain a high level of cold-tolerance gene expression when temperatures are in the acclimation range. These observations suggest that more detailed studies should be initiated to establish the importance of interactions between photoperiod sensitivity and vernalization requirement with the objective of identifying genetic combinations and management systems that extend the vegetative stage and provide longer-term protection from LT stress in regions with long mild winters like those normally experienced in north-west Iran. (37°15′N, 46°15′E, 1 720 m), en Iran. Ils ont mesuré la tolérance au froid (exprimée par le SF 50 ) et estimé le stade phénologique (d'après le nombre final de feuilles et la morphologie de l'extrémité des pousses) à l'automne et en hiver. Le cultivar de printemps Rihane-03, insensible à la brièveté de la photopériode, s'acclimate mal au froid et atteint très vite son seuil de tolérance maximal. Le cultivar d'hiver Dobrinya atteint son seuil de tolérance maximal au froid au point de saturation de la vernalisation. Le cultivar de printemps Dicktoo, très sensible aux jours courts, entre dans le stade double ride à peu près au même moment que le cultivar d'hiver Dobrinya. Ce retard dans le développement phénologique de Dobrinya et de Dicktoo s'accompagne d'une plus forte expression de la tolérance au froid, signe que la durée de la phase végétative détermine bien l'aptitude de la plante à maintenir une forte expression du gène de tolérance au froid quand les températures se situent dans la fourchette de l'accli...

Genotype × environment (G × E) interaction analysis was investigated on grain yield of 20 winter wheat genotypes grown in 24 environments in cold winter areas of Iran during 3 yr. Cluster and biplot analyses were applied to separate testing environments into groups with the same top‐yielding genotypes. Environment followed by G × E interaction effects accounted for the greatest proportion of the variability of grain yield of winter wheat genotypes. Cluster analysis divided both genotypes and environments into three groups, which accounted for 64.4% of the G × E sum of squares (SS). Biplot analysis confirmed the classification analysis and showed that different environment groups tend to discriminate genotype groups in dissimilar fashions. The genotype group G‐I with the highest yielding performance had the best adaptation to environment groups with the highest (E‐I) and the lowest (E‐III) yield potential. Genotype group G‐II was adapted to environment group E‐II with average yield potential, while the genotype group G‐III appeared to have the poorest adaptation to environment groups. The environmental PC1 leads to noncrossover G × E interactions, while PC2 represents a disproportional genotype response across locations, explaining crossover G × E interactions. The testing environments involved in E‐I and E‐III with large PC1 scores and low PC2 scores were the best for genotype discrimination. Results show that the highest yielding genotypes G4, G10, and G17 with the lowest changes in grain yields across environments were the most stable and are consequently good candidates for commercial release in cold winter areas of Iran.

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