VARIATION IN DEVELOPMENTAL STAGES AND ITS RELATIONSHIP WITH YIELD AND YIELD COMPONENTS OF BREAD WHEAT CULTIVARS UNDER FIELD CONDITIONS:I. PHENOLOGY

Wheat crop development is defined as a sequence of phenological events controlled by environmental factors as well as genetics determining differentiation in plant morphology and functions of some organs. It commences with germination and terminates with physiological maturity in each crop life-cycle and can be divided into different distinguishable stages/phases. To study the phenology of bread wheat genotypes, 20 different cultivarsor promising lines adapted in four different agro-climatic (cold and temperate cold temperate southern warm and dry northern warm and humid) zones were studied, using a randomized complete block design with three replications, under field conditions in Karaj, during three successive cropping seasons (2000-2003). The results revealed that genotypes were significantly different in the duration of different phenological stages. Genotypes associated with cold and temperate cold zone were of longer crop life-cycle which was mainly due to differences in the duration of their vegetative phase (Sowing to Double Ridge). The results also indicated that in all four agro-climatic zones, developmental phases including Sowing to Double Ridge (S-DR), Double Ridge to Terminal Spikelets (DR-TS), Terminal Spikelets to Anthesis (TS-Anth) and Anthesis to Physiological Maturity explained 0.39%, 68%, 0.63% and 0.52% of variations in grain yield, respectively. Correlation studies between different developmental stages and yield components also indicated that, in all four agro-climatic zones, the number of spikes m-2 was positively correlated with the duration from Sowing to Terminal Spikelets, however, it was negatively correlated with the duration from Terminal Spikelets to Anthesis. The relationship between Thousand Kernel Weight (TKW) and the duration of S-DR and S-Anth was negative. It is concluded that phenlogical studies can be utilized to study the adaptation of different genotypes to different agro-ecological zones and to explain the variation in grain yield and its components.