Analysis On The Heterosis And Drought Tolerance Of Japonica/Japonica And Indica/Japonica Hybrids Between Irrigated And Upland Rice

4 Japonica and 1 wide compatible Indica photoperiod/temperature sensitive genetic male sterile (P/TGMS ) lines were used as female parents to cross with 8 Japonica upland rice varieties according 5×8 NCII mating design. The 40 Japonica/Japonica and Indica/Japonica 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 including, leaf water potential, relative water content, and electric conductivity etc were tested during the drought stressed period. And agronomic characteristics including plant height, growth duration, panicle length, panicle number, grain yield and yield components were evaluated after harvest. Analysis 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 and regression between yield and yield components; and the relationships between the physiologic traits and drought tolerance. The main results are as follows:1. The average yield of the 40 F₁ hybrids was 522.15 g/m², ranging from 219.62 g/m² to 999.38 g/m² under well irrigated. While the average yield of the F₁ hybrids reduced to 88.38 g/m², ranging from zero to 293.08 g/m² under drought stressed condition. There was a drastically yield loss due to the drought stress in the field experiments.2. The average yield heterobeltiosis over the male parents of the 40 hybrids was 45.02%, ranging from -40.63%²97.94%; And the average competitive heterosis over the CK was 17.45%, ranging from -49.23% to 124.78% under well irrigated condition. The average yield heterobeltiosis was 140.38%, ranging from -100%¹325.14%; And the average competitive heterosis reached 181.74%, ranging from -100%²93.08% under drought stressed condition. The Indica/Japonica inter-subspecies hybrids showed relatively stronger heterosis in yield performance under well irrigated field but lower seed setting rate under drought stressed environment.3. Significant correlation was found between grain yield of F₁ and the sum of GCA ofthe parents as well as between Fi and SCA of the combinations under both well irrigated and drought stressed fields. In well irrigated field, correlation coefficient between the grain yield of hybrid and the sum of parents' GCA was r=0.826** and that between hybrid yield and SCA effect was r=0.488*. While under drought stress, the correlation coefficients between the grain hybrid yield and GCA was r=0.754*\ and that between hybrid yield and SCA effect was r=0.657**.4. Established the multianalysis regression equation according to four important yield components factor. The equation was y=-1672.559+ 739.193x,+ 65.178x2+ 3.081x3+24.976x4 under well irrigated, the independent x( x2 x3 X4 refer to full grain percentage per panicle, number of valid panicles per plant, number of spikelets per panicle and 1000-grain weight respectively. The equation was y=-279.426 +19.503xi +0.69 Ix2+ 222.381x3+ 6.177x4 under the drought stressed environment, independent xi x2 x3 X4 refer to number of valid panicles per plant, number of spikelets per panicle, full grain percentage per panicle and 1000-grain weight respectively.5. The data of leaf water potential, leaf relative water content and electric conductivity were more erratic despite of they had a comparatively little correlation with drought resistance, so they were unsuitable as a reliable physiologic trait alone for thescreening of drought tolerance.