Efficiency of heat unit and accumulative growing degree-day phonological stages and their relation with grain yield of wheat genotypes

This research in three independent experiments each as split plots using complete randomized block design with three replications was conducted in 2010-2011 cropping year under Ahvaz climate conditions. Each experiment consisted of three planting dates as main factor and six genotypes (Chamran cultivar as control and five selected lines and cultivars from different groups of early maturity) as sub factor. First planting date in the first ,second and third experiment was Oct.27, Nov. 16 and Dec.16 and 10 days interval between the second and third plantings date with first planting date in first and third experiments and 15 days interval in the second experiment were assigned. Grain yield was determined and accumulative growing degree-day amount from planting to some phonological stages and heat unit efficiency index from equation for genotypes were calculated. Results showed that planting date, genotypes difference and interaction genotype x planting date were significant for duration of different phonological stages duration. The average of day and accumulative growing degree-days from planting through phonological stages were decreased in response to planting delaying in which reduction intensity was higher in mid maturity genotypes due to delaying in planting. Correlation among grain yield with accumulative growing degree-day was not significant, while grain yield was significantly correlated and positive with heat unit efficiency. In comparison with accumulative growing degree-day index and regarding to its high accessibility due to planting date, that may bring about misleading results, according to the results of this research it seems that heat efficiency index has higher efficiency for wheat genotypes responsiveness explanation.