STUDIES ON COMBINING ABILITY AND HETEROSIS FOR SOME TRAITS OF ROOT AND YIELD CHARACTERS OF SOME RICE GENOTYPES UNDER NORMAL AND WATER DEFICIT CONDITIONS

 Rice, root traits, physiological characters, combining ability, heterosis.

        Eight genotypes cultivars of rice were crossed to obtain 15 F₁ crosses, through line x tester mating design was employed for this purpose. The experiment was carried out using line x tester mating design, during 2021 and 2022 rice growing seasons at the experimental farm of Sakha Research Station, Sakha, Kafr El-Sheikh, Egypt. Both GCA and SCA variances were found to be significant or highly significant for all studied traits.  The estimates of GCA effects indicated that, the parent IR 12 G 3222 was a good general combiner for root length, number of roots/plant, and flag leaf area under both conditions. In addition, GZ 1368 was a good combiner for root volume under both conditions. While the line IR 69432 was a good combiner for root/shoot ratio under water deficit condition.  The line 11 L 236 for chlorophyll content, number of filled grains/panicle, grain yield/plant and the tester Giza 178 for relative water content and grain yield/plant were good combiners under both conditions. On the other hand, the cross combinations, IR 69432 X GZ 1368 was found to be the best specific combinations for root length, number of roots/plant, root volume and root/shoot ratio under two conditions. The cross combination, IR 12 G 3213 XGiza 178  was the best specific combinations for relative water content, flag leaf area and chlorophyll content under both conditions . The cross combination, IR 12 G 3222 XGiza 178 was the best specific combination for 1000-grain weight and fertility % under both conditions.  In addition, the cross combination, IR 69432 X GZ 1368 under normal and IR 69432 X Nerica 7 under water deficit were the best specific combinations for grain yield/plant. On the other hand, the crosses, IR 69432 X GZ 1368, IR 6500-127 XNerica 7, IR 12 G 3222 X GZ 1368, 11 L 236 X GZ 1368 and11 L 236 X Nerica 7 exhibited highly significant positive estimates of heterosis as a deviation from mid and better parent for most of the studied traits under normal and water deficit condition.

Conclusively,from these results it could be concluded that IR 12 G 3222, GZ 1368, 11 L 236 and Giza 178 were the best general combiners and the crosses IR 69432 × GZ 1368 and IR12G3222 × GZ1368 were the best crosses for estimates of SCA and heterosis effects relative to the mid- and better- parents for most of the studied traits under water deficit and normal conditions.