effect of planting date on grain filling trend and grain yield of bread wheat genotypes using multivariate analysis method under dryland conditions

in order to evaluate the relationship between grain yield and agronomic characteristics in bread wheat genotypes in different planting dates under rainfed conditions, a factorial experiment was conducted based on rcbd with four replications at gonbad-e qabus region, iran, during 2012-2014 growing seasons. number of spikes per unit area, grain filling rate, effective grain filling period, number of grain per spike, 1000kw, grain weight, grain yield, biological yield and harvest index were measured. planting dates including dec. 2nd, dec. 21st, jan. 9th, jan. 28th and feb. 17th were considered as first and five wheat genotypes: gonbad, karim, koohdasht, line 7 and line 16, as second factor, respectively. combined analysis of variance revealed that the mean grain yield decreased from 4956 in the first year to 2833 kg.ha-1 in the second year (43% reduction). grain yield had the highest and positive significant correlation with biological yield (r= 0.97**) and grain filling duration (r= 0.97**). the stepwise regression analysis showed that biological yield and harvest index justified more than 99% of grain yield variation, indicating their considerable importance in grain yield. grain filling duration was the first variable to enter to the model and showed more important role in grain yield justification. the grain filling duration and biological yield had effective role in grain yield that could be used for selecting the suitable genotypes of wheat for rainfed conditions.