Study On Inheritance And Gene Location Of Purple Leaf Character Of Rice (Oryza Sativa L.)

Purple leaf of rice is a significant mark and could be recognized in its whole life. Purple leaf rice is a special type of rice germplasm. The purple leaf character has important value in genetic study and breeding practice as well as taxonomy due to its stability and not greatly affected by environment. By use of purple leafed male sterile line is the most effective way to solve seed purity problems in hybrid rice seed production and parental line multiplication, and the fast and simple way to identify the purity of F₁ seed. This study is to conduct genetic analysis and gene locating, to understand the rule of inheritance, and to know the number of expression and control gene (s), the gene location on chromosome, and interaction of the genes of purple leaf character and its effects on the photosynthetic and senescence physiology of male sterile lines during the late stages of growth and development, and its effects on the consequence of growth, development, seed filling and yield of the hybrid F₁ plants by use of purple leafed rice germplasm introduced from the International Rice Research Institute (IRRI) to explore the possibility of using purple leafed rice in hybrid rice breeding, and provide theoretical and practical bases for purple leaf character of rice in breeding program. The major results are shown as follows:1. Hybridization was made between purple leafed line IR1552 and 22 green leaf varieties with different genetic backgrounds and restoring-maintaining relationship, and investigation and genetic analysis were done for leaf color segregation on F₁, F₂, BCF₁ and BCF₂ populations. The results showed that the purple leaf character from IR1552 was controlled by a pair of recessive gene (pl-pl) and a pair of dominant gene (Ipl-Ipl), while also affected by the purple regulation gene (Ci-Ci). The amount of regulation gene is related to the gene number difference between the two parents, i.e. related to their genetic backgrounds. It was concluded that the inheritance model of the purple pigment was plplIplIplCiCi.2. The purple gene and control gene were mapped in the BCF₂ population of Xianhong A and Guanghui 128 found by using SSR molecular markers. The result showed as follows: the purple gene was flanked by SSR markers RM587 and RM584 on the short arm of chromosome 6 with a genetic distance of 3.1 cM and 2.2 cM, respectively, while the purple control gene was flanked by RM9 and RM488 on the long arm of chromosome 1 with a distance of 1.2 cM and 0.8 cM, respectively. The two pairs of genes were tentatively named pl₁ and Ipl₁.3. Studies on physiological indexes of leaf photosynthesis and aging in the late stage of growth of purple leafed male sterile line and its F₁ hybrids were done and showed that the chlorophylls contents, photosynthetic rate, soluble protein and activity of SOD of flag leaf in the late growth stage of purple leafed male sterile lines Xiahong A, Zhihong A and Guizhi-1S were higher than the controls Bo A and GD-1S, while MDA content and activity of POD were lower than the controls. The chlorophyll contents, photosynthetic rate, soluble protein content, MDA content, activity of SOD and POD in the flag leaf during the late growth stage of F₁ hybrids by use of purple leafed male sterile lines were similar to those of CK Boyou 253, not significantly different. All the results showed that the leaf function of purple leafed male sterile lines Xianhong A, Zhihong A, Guizhi-1S and their F₁ hybrids is normal with good photosynthesis, no early aging, and there is no negative effect on the agronomic traits and yield of IR1552 and derived male sterile lines and F₁ hybrids. It is a good donor of purple leaf mark for rice breeding practice and has important use value.4. Through hybridization between purple leafed IR1552 and different indica three-line sterile maintainers, two-line sterile lines, the ideal purple leaf mark was introduced into three-line and two-line male sterile lines. The results showed that the purple leaf character not only could be introduced into indica type of three and two lines sterile lines, but also could be used to develop breeding goals' purple leafed three and two lines sterile lines with good transferring results. So far five purple leafed three and two line sterile lines have been developed, among which both Xianhong A and Zhihong A have passed the experts' evaluation organized by Guangxi Crop Variety Registration Committee (GCVRC) in August, 2007, and ready for commercial use.5. Indica type purple leafed three-line male sterile lines Xianhong A and Zhihong A are the first wild abortion (WA) type three-line male sterile lines bred in Guangxi with significant purple leaf mark, vigorous plant, high stigma exertion ratio, easy to be restored, strong general combining ability (GCA), good plant type and strong heterosis. It is promising for use of their hybrids.6. The results of test crosses of different R lines with three-line Xianhong A and two-line Guizhi-1S, respectively, showed that the sterility could be restored in all F₁ hybrids, but there were differences in the agronomic traits and yield among the hybrids. The agronomic traits and yield components of some hybrids are better than the CK Teyou 63, and the highest yield increased by 8.61%, showing significant heterosis. This suggested that, through adding WC gene (s) and japonica rice germplasm, combining disease resistances and wide adaptability, widening genetic distance of the parental lines, enhancing R line improvement, widely test crossing and screening, it is possible to develop hybrid rice with very strong heterosis for commercial production.