| Two line hybrid rice is an important initiative of heterosis rice utilization with widespread promotion and remarkable achievements in China. But how to make breeding sterility express stability in the north japonica photo-thermo-sensitive genic male sterile (PTGMS) line and how to obtain the higher heterosis has plagued breeders, which greatly limits the development of two line hybrid rice in the north of China. To further investigate the male sterility conversion and heterosis characteristics, the fertility alteration of Japonica PTGMS lines, G317S, G321S, G326S and GB028S were studied under different low temperature, different light and different ecological conditions with upmost pulvinus interval (UPI) marker. The hybrid populations derived from a cross line between RIL (Akihikari×Qishanzhan) and GB028S were used to study the plant height, sword leaf width, yield heterosis and constitute factors. It was showed that:1. Three japonica PTGMS lines G317S, G321S and G326S were marked with UPI marker, such as the length of the pulvinus of the 2nd leaf recording young panicle differentiation stages under 20℃. It was showed that the pollen sterility of all three PTGMS lines was dramatically decreased under the 20℃ low temperature treated with 3 days, the average sterility of pollen and average seed-setting percentage of bagged was 50.06% and 60.42%, respectively, which indicating a distinct fertility alteration under -4～4cm of UPI. When the UPI was <-4 cm and >4 cm, the pollen sterility of lines remained over 99.95% without a significant decrease, indicating that the low temperature treatment at these developmental stages has no effect on fertility alteration. When the UPI was -4～-2 cm and 2-4 cm, the pollen sterility of spikelet at different panicle positions (upper, middle or low part of the panicle) do not vary very much. However, when the UPI was -2～2 cm, the pollen sterility of spikelets at different panicle positions was greatly different with an order that lower>middle> upper.2. The fertility alteration of GB028S, a japonica PTGMS line was treated with 20℃ low temperature for 1 d,3 d,5 d and 7 d. It was showed thatthe low temperature keeping heading stage lag for 2-8 d. The pollen sterility of 1 d and 3 d was more than 99.5%, which has no effect on fertility of GB028S. The pollen sterility of 5 d and 7 d was 98.33% and 94.33%, and the bagged seed set was 2.64% and 5.04%. The low temperature of 5 d and 7 d can not only decrease remarkably pollen sterility but also induce self fertility. The critical temperature is nearly 20℃ of GB028S, which the most sensitive stage of temperature on fertility alteration is-3-1 cm of UPI. Under different light conditions,11.5 h and 12.5 h were fertility, and it was sterility in 13.5 h and 14.5 h. Under the different light temperature combination conditions,11.5 h/24 ℃ of sterile lines fertility restoration and obtain higher self-seed setting rate, and the combination was suitable for sterile lines breeding.3. The effects of fertility alteration of japonica PTGMS lines were different in the different ecological areas (Panjin of Liaoning Province, Sanya of Hainan Province, and Lingshui). The two-line hybrid rice were combined, when the japonica PTGMS lines are sterility under day length (15 h) and high temperature (25 ℃) in Panjin. The japonica PTGMS lines could reproduce under short day (11-12 h) and low temperature (22-23 ℃) in Sanya and Lingshui.4. Heterosis analyse of japonica two line hybrid rice showed that the panicles per plant and 1000-grain weight of hybrid population have the middle parents heterosis and over male parent heterosis, and the grain per panicle has over the highest parents heterosis, and the seed setting rate has the middle parents heterosis. The panicles per plant, grain per panicle and seed setting rate were significantly positive correlation between the heterosis of yield and the heterosis. Genetic analysis on heterosis showed that 16 QTLs controlled F1 of yield and some character are detected,5 QTLs showed additive effects, others showed dominant effect. RM259-RM449 locus located on chromosome 1 gathered 9 QTLs related heterosis of yield, within the range of loci may be an important genetic basis for the formation of heterosis. Accordingly consider that two-line Japonica hybrid rice heterosis is the dominant effects, additive effect supplemented. Accordingly we consider that heterosis for yield of Japonica two-line hybrid rice is the dominant effects, and additive effect supplemented.5. Compared the Cheng’s index (Chi) based on morphology and partial japonica coefficient (Dj) analysis based on molecular marker, has a higher coefficient of consistency in indica/japonica classification. The results suggested that parents have higher uniformity in classification by Chi and Dj. Analysis of the relationship F1 yield and parent’s indica/japonica classification showed that the peak area of yield in F1 appears Dj between 0.55 and 0.70, and the peak area heterosis of yield in F1 appears Dj between 0.50 and 0.65. According to the female parent is GB028S japonica was sterile line (Chi:20.5, Dj:0.875), male parent’s Dj was between 0.55 and 0.65, relative production with higher yield of F1 and heterosis. Chr1, Chr12 were closely related with yield and heterosis of F1. The relationship among parent’s genetic distance, F1 yield and heterosis was not significant. |
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