Studying the relationship between agronomy traits of rice under flooding and drought stress conditions

In order to determine the relationship between agronomic traits of rice genotypes (6 drought tolerant and one native cultivars) under flooding and drought stress conditions, two separate experiments were conducted as split- plot in randomized block design with tree replications at the research farm of Gonbad Kavous University during spring 2010. The main plots were weed control in three levels (controlling weeds until maximum tillering stage, weed control from maximum tillering till maturity and un-weeded) and sub plots consisted of rice genotypes (Shiroudi, Domsiah, IR70358-84-1-1, IR70358-84-1-2, WAB56-125, IR83752-B-B-12-3 and KORAL). Yield and yield components of cultivars showed significant differences under flooding and drought stress conditions (p<0.05). Moreover, each cultivar had significantly different yield and yield components under the two environments (p<0.05). Considering the correlation coefficients among traits under flooding and drought environments showed that in either of different moisture conditions grain yield had significant and positive correlation with straw yield, harvest index, filled grain number and fertile tiller number. Results of step wise regression showed that under flooding condition, straw yield and harvest index traits and under the drought stress condition, harvest index and straw yield entered the final multiple regression model as important characteristics and effective traits on grain yield (93.4%), respectively. Evaluation of direct and indirect effects of each of the yield components on grain yield via path analysis showed that in each of the different moisture conditions, number of filled grains due to positive and high direct effect and number of fertile tillers due to indirect effect via number of filled grains can be considered as the most important traits for increasing the grain yield.