Genetic Identification Of A Maize Male Sterile Mutant Induced By Irradiation

The plant male sterile materials are valuable resources for genetic research and breeding utilization, which has been widely used in the major food crops, oil crops and vegetable crops. Using male sterile line to produce hybrid seeds, not only can save a lot of artificial emasculation labour, decrease the cost of seed production, but also can improve the seed genetic purity, give full play to the role of heterosis. A lot of former studies have been reported on male sterile mutants through natural or artificial mutation, including 2 kind of types cytoplasmic and genie male sterility. K305 male sterile mutant was obtained from dry seeds of widely used maize inbred line K305 exposed to 60Co-y rays. The research showed that, there were no significant differences in combining ability and heterosis of major characteristics between the mutant and wild-type K305, and the traits of mutant were uniform in sibling population. Therefore, the further study of the mutant is of great significance.In the present research, the sibling population of maize K305 male sterile mutant induced by 60Co-y-irradiation were planted in different years, seasons and locations, to identify the genetic stability of male sterility by using interior microscopic examination of pollen and the field investigation. To determine the genetic pattern of the male sterility, the nucleus effects were analyzed according to the sister crosses, test crosses, and their selfing and backcross progenies with the sterile plants as females; and the cytoplasm effects were analyzed through the reciprocal F1 and F2 with normal inbred lines as females, and the fertility fully recovered test-crosses and fertile sibling as males, respectively. Locating the male sterile gene by using SSR-BSA method to make a preliminary determination of its position on chromosome and provide the basis for gene fine mapping and cloning. The main results were as follows:1. The results of fertility identification showed that the tassel of the fertile plants in sibling population grew normally, pollination was good with exserted anther, the six anthers were plump with golden color, and the pollen grains showed obvious round shape by staining anther tablet with 1%I2-KI. Compared to the fertile plants, the sterile mutants showed similar tassel size, but with no anther exsertion, and the anther were degenerated and shrivelled with yellowish colour, and no pollen grains in chamber, indicated that the mutant was a typical pollen-less type male sterility. The male sterility performed stability with no effects by photoperiod and temperature change in different years, places and seasons,.2. Genetic analysis showed that the gene of male sterility did not express in the heterozygous, which was recessive heredity. The fertility segregation ratio of fertile to sterile plants was 1:1 in sister cross and backcross progenies, while 3:1 in self-crossed progenies of the fertile sibling and the reciprocal testcrosses, showed a single gene inheritance, it was a typical Mendelian inheritance. The male sterility can be inherited to offspring from not only the female parents, but also the male parents; The male sterile gene expressed not only in cytoplasmic background of male sterile mutant itself, but also in that of other inbred lines including K169, K318,21-ES and R08, indicated that the heredity of the male sterility was not associated with the varied cytoplasm. The results demonstrated that the male sterility was controlled by a single recessive nuclear gene. The male sterile mutant was named as K305ms and the sterile gene as ms305 temporarily.3. The male sterile gene mapping was conducted in F2 population of A×156.7 pairs of SSR primers with polymorphism between both parents and two gene pools, were screened from 649 SSR primers by SSR-BSA method, and the results were verified in F2 and BC populations. Then, DNA amplication of the 68 recessive sterile individuals in F2 population were performed through SSR-PCR method, the sterile gene ms305 was preliminarily located on long arm of chromosome 2 between bnlg469b and bnlg1940, and the genetic distance were 2.9 cM and 7.4 cM, respectively, close to gene ms32, but the homology and fine mapping need further study. The strategy of fine mapping including expand the mapping population and develop better markers, or use SNPs to narrow gene segments. In short, identification of the target gene could lay the foundation of sterile gene cloning and its practical application.