The Effect of Phosphate Solubilizing Bacteria on the Reaction of Bread Wheat Cultivars to Late-Season Heat Stress

In order to investigate the possibility of reducing the negative effects of late-season heat stress using phosphate-solubilizing bacteria, this experiment is carried out as split factorial based on a complete randomized block design with three replications in a farm located in Haftkol city under the supervision of Ramhormoz Islamic Azad University, during the growing season 2016-2017. The main factor consists of planting date in two levels (22 November and 2 January) and the sub factors as a factorial consisted of five bread wheat cultivars (Chamran2, Mehregan, Sirvan, Shush and Barat) and of two levels application of phosphate solubilizing bacteria (inoculation and without inoculation). The results show that with a delay in planting and occurrence of heat stress in grain filling period, grain yield, biological yield, harvest index, and effective grain filling period are decreased and grain filling rate is increased. Also, the reaction intensity has varied depending on the cultivar. Mehregan cultivar has high yield in both planting dates and in the delayed planting date with the highest increase in grain filling rate and the lowest decrease in number of seeds per spike, had the highest grain yield and harvest index. By inoculating the seeds with bacteria, on both planting dates, on average, the number of seeds per spike is increased by 4.6%, grain yield by 7.6%, and biological yield by 7%, but the interaction effect between planting date, cultivar and bacteria on yield and its related traits is not significant. Therefore, the effect of phosphate solubilizing bacteria on mitigating the effect of heat stress is not proven and the positive effect of bacteria is the same on both planting dates. Overall, in this study, higher ability to increase grain filling speed and maintain more grain number per spike are identified as two important traits for achieving higher grain yield under late-season heat stress conditions.