Studies On The Heterosis And Drought Tolerance Of Indica Hybrids Between Paddy And Upland Rice

5 Indica photoperiod/temperature sensitive genetic male sterile (P/TGMS) lines were used as female parents to cross with 8 Indica upland rice varieties according a 5×8 NCII mating design. The 40 F₁ hybrids, their male parents and CK were tested in 3 replications with randomized complete-block design in well-irrigated and artificially induced drought stressed conditions during reproductive and grain filling stage respectively. Drought related physiologic traits were tested during the drought stressed period. And agronomic characteristics, grain yield and yield components were evaluated after harvest. Studies were made on the grain yield heterosis of the paddy/upland rice hybrids; general combining ability (GCA) and special combining ability (SCA) of the parents and the correlations between heterosis and GCA, SCA; heritability of the agronomic characters; correlation between yield and agronomic traits; and the relationships between the physiologic traits and drought tolerance. The main results are as follows:1. Under well irrigation, 21 hybrids (52.25% out of all hybrids) had yields greater than that of CK. The average heterobeltiosis of hybrids over male parents was 35.7%, ranging from -19.19% to 142.78%. Average competitive heterosis over CK was 4.18%, ranging from -95.53% to 97.21%. The hybrids with highest yields were W9593S×Super upland rice, PA64SxWenhui3/ E260-F5 and 1103Sx super upland rice, the achieved yields were 1290.85g/m², 1229.82g/m² and 1211.15g/m² respectively.The decline of yield was significant between the well irrigated and drought stressed conditions, the average yield loss due to drought was 569.62 g/m², ranging from 20.21 g/ m² to 1078.84 g/m²; The average rate of yield reduction was 75.54%, ranging from 32.27% to 99.12%.Under drought stressed condition, 16 hybrids (40% out of all hybrids) got greater yields over the CK. The average heterobeltiosis of hybrids was 118.16%, ranging from -94.86% to 1308.07%. The average competitive heterosis over CK was 1.35%, ranging from -96.24% to 151.47%. The hybrids with highest yields were Guangzhan63-4SxKMP34, 1103Sx IRGA318, Guangzhna63-4SxIRGA346, the value was 415.33g/m% 398.96g/mJ and 384.34g/nf respectively.2. The full grain percentage per panicle of PA64S* Zhenshan97B/Zhonghan 5, PA64SxRR-272-17 and Guangzhan63-4S*KMP34 raised slightly under drought stressed condition. For example, the spikelets per panicle and the full grain per panicle of GuangZhan63-4SxKMP34 were 175.41 and 84.31 respectively under well irrigated condition, while in the drought condition they were 71.93 and 138.77, and the rate of decline was 20.89% and 14.68% respectively, which raised slightly the full grain percentage per panicle. The impacts of drought stress on the spikelets formation was bigger than that on grain filling in this type of hybrids.3. Significant correlations were found between grain yield of Fl and 7 agronomic traits under well irrigated condition. The correlation coefficients between grain yield and the full grain per panicle, the number of panicles per plant and the length of panicle were 0.721, 0.723, 0.706 and 0.639 respectively. The coefficient between yield and the number of spikelets per panicle and full grain percentage increased to 0.874 and 0.854 under drought stressed condition, which indicated that the number of full grain per panicle and full grain percentage became more important yield components under drought stress.4. The parents showed higher GCA under normal irrigation tended to have higher GCA under drought stress. For example, IRGA318> Wenhui3/E260-F5 and Super upland rice had GCA values of 17.65, 20.79, 17.54 and 400.67, 380.23 and 333.95 in well irrigated and drought stressed conditions respectively. And almost all the hybrids derived from these parents showed positive competitive heterosis over CK under well irrigated fields.5. The rank of heritability of agronomic traits was plant height ( 0.949 ) > the length of panicle (0.892) >1000-grain weigh (0.836) > grain yield (0.801) > the full grain percentage (0.761) > the number of full grains per panicle (0.755) > the number of spikelets per panicle (0.574) > the number of panicles per plant (0.545) under well irrigated condition; While under drought stressed condition it was plant height (0.841) >1000-grain weigh (0.816) > the number offull grains per panicle (0.738) >grain yield(0.736) > the full grain percentage (0.728) >the number of panicles per plant (0.692)> the length of panicle(0.611 )> the number of spikelets per panicle(0.229). Plant height and 1000-grain weigh have high heritability values under both drought stressed and well irrigated conditions, which means the environment has little effect on their heritability.6. The leaf water potential, leaf relative chlorophyll content, electric conductivity and the canopy temperature represented different aspects of the drought-resistant capacity to certain extent. However, little correlation has been found between the yield under stress and the data of the physiologic traits. The correlation coefficients were 0.044, -0.115, -0.03 and 0.034 respectively. Further investigation had to be done to determine if any of these traits could be used as a target secondary trait to evaluate the drought resistance in rice.