Effect of indol acetic acid and kinetin on morphological traits, yield and yield components of rice varieties under drought stress conditions

To assess the effects of indol acetic acid (IAA) and kinetin regulators on morphological، yield and yield components of rice (Oryza sativa L.) varieties under early and terminal drought stress conditions a pot experiment under farm condition was carried out as factorial experiment based on completely randomized design with three replications in Faculty of Agricultural Science، University of Guilan in 2013. The experimental factors were four rice varieties (Gharib، Khazar، Sepidrood and Upland rice، IR 83750-131-1)، drought stress in three levels (non-stress، early season stress from stage 1 to stage 4 of Vergara coding system and terminal season stress from stage 4 to end of the stage 9) and growth regulators in three levels (non-regulator and 5×10-5 M of IAA and kinetin as spraying on whole plant). Results indicated that main effects of the all factors on all measured traits were significant، but the interaction effect of variety×stress×growth regulator was significant only on total grain number، grain number per panicle، panicle length and 1000-grain weight. Under early season stress، reduction of tiller number leads to a reduction in grain yield in all studied varieties. Generally، application of both growth regulators، IAA and kinetin، increased grain yield more than 50 percent under both early and terminal season drought stress، but under terminal drought stress، the role of kinetin was more than IAA. The highest value of stress tolerance index (STI) with average of 1. 01 was observed in Sepidrood. Drought stress index (DSI) also indicated that all measured traits decreased under terminal season stress compared to non-stress condition and the highest decrease with average of 71. 45 percent was observed in grain yield. In total، results of this research indicated that exogenous application of these two regulators had the effective role in the improvement of morphological traits، grain yield and yield component in both early and terminal season drought stress.