Response of Wheat Genotypes to Temperature and Photoperiod in Natural Conditions

Abstract

Floral initiation in wheat (Triticum aestivum L.) depends on complex interactions between temperature and photoperiod. The aim of this study was to analyze genetic variation in the response to combined variations of changing and often suboptimal photoperiods and temperatures as they occur in natural environments. Twelve genotypes were analyzed in the field, using vernalized and nonvernalized seeds, for times of floral initiation, anthesis, and beginning of stem elongation. Climate was varied by changing sowing date, year, and site. This resulted in large variations in the date of achievement of all stages. However, these variations could be expressed by a unique curve for each genotype when dates were characterized by the combination of the thermal time from seedling emergence (K) and of the daylength (P) on the date considered. The curve was specific to a stage and to a genotype. The curves obtained for the different genotypes were variants of the same general curve, which allowed definition and quantitative assessment of three characteristics for describing the developmental response of a genotype to climate: vernalization requirements, photothermal sensitivity, and intrinsic earliness. These three components, which are confounded in the common notion of earliness, showed large variations among genotypes, especially at the lemma stage. They were largely independent. Our results also show that, compared to differences in the sensitivity to photoperiod and temperature, differences in vernalization requirements are of secondary importance in choosing a genotype in temperate areas, even for a very late spring sowing.