Screening Of Germplasm Adaptable To Direct Seeding And Discovery Of Favorable Alleles For Seed Vigor And Seedling Anoxic Tolerance In Rice (Oryza Sativa L.)

Direct seeding in rice (Oryza sativa L.) is a cultivation pattern of light-labor, high effect and water-saving. It is widely adopted in America, Europe and other developed countries. With the rapid development of national economy in our country, and more and more labor force moving from countryside to city, the areas of direct sowing in rice is increasing year after year. Whether the cultivation of direct seeding in rice is successful is first determined by the situation of seedling establishment in the field. Anoxic stress and lower temperature stress are the main factors affecting seedling establishment in direct seeding rice field. Breeding rice cultivars with anoxic tolerance and high vigor is one of the ways to improve seedling establishment in direct sowing field. Rice has been widely cultivated in the Taihu lake region, Jiangsu Province, and maintained broad genetic diversity during the long history of rice cultivation. In order to discovery favorable alleles for seed vigor and seedling tolerance to anoxia, we conducted following studies. Firstly, genetic variation of seed vigor and seedling tolerance to anoxia, and the correlations between the traits mentioned above with seedling establishment index were studied by using 297 accessions of rice in Tai lake region. Secondly, QTL mapping was carried out for the traits of seed vigor and seedling tolerance to anoxia by using a BIL population (98 lines) made from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare and a RIL population (247 lines) made from a cross between Xiushui 79 (japonica cultivar) and C Bao(japonica restorer). Thirdly, association mapping was conducted for the traits of seed vigor and seedling tolerance to anoxia by using a natural population composed of 94 accessions from Taihu lake region. The main results were obtained as follows:1. Genetic coefficient of variation was 19.5% for seed vigor and 15.2% for tolerance to anoxia among the 297 accessions(belong to five ecotypes). The genetic variations of the two traits were mainly existed in early maturity late japonica rice ecotype. Highly significant positive correlations were found between the two traits respectively with 14-day-seedling height and seedling establishment index. Seven accessions with high seed vigor and high tolerance to anoxia were screened out from early maturity late japonica rice ecotype. They were Bodao3, Yingtoujing, Sanbailitou, Dadaotou, Wujinxiangnuo, Huangsanshi4, Wanbagetou. They could be utilized as parents in breeding programs which aim to develop varieties suitable for direct seeding technology.2. For trait of seed vigor, six favorable alleles in Kasalath and one favorable allele in Nipponbare were detected in BIL population, and eight favorable alleles in C-Bao and one favorable allele in Xiushui79 were detected in RIL population. Forty-two favorable alleles for seed vigor trait were explored in the natural population.In BIL population, Kasalath carried two favorable alleles for root length which located on 1 and 7 chromosomes tightly linked to RFLP marker C813 and R3089, two favorable alleles for shoot height which located on 7 and 8 chromosomes tightly linked to RFLP marker C847 and C166, and two favorable alleles for seedling dry weight which located on 7 and 8 chromosomes tightly linked to RFLP marker R3089 and C166. Nipponbare only carried one favorable allele for seedling dry weight which located on 1 chromosomes tightly linked to RFLP marker C122.In RIL population, C-Bao carried two favorable alleles, RM486-112bp and RM48-240bp, controlling root length which located on 1 and 7 chromosomes. Four favorable alleles, RM48-240bp, RM545-220bp, RM6948-116bp and RM206-165bp, controlling shoot height which located on 2,3,8 and 11 chromosomes, and two favorable alleles, RM2127-175bp and RM454-170bp, controlling seedling dry weight which located on 2 and 6 chromosomes. Xiushui79 only carried one favorable allele RM525-143bp controlling seedling dry weight which located on 2 chromosomes.In the natural population, totally 42 favorable alleles were detected for the traits of seed vigor. Among them, seventeen favorable alleles were for root length, thirteen were for shoot height, and twelve were for seedling dry weight. The favorable allele, RM486-112bp, detected on chromosome 1, for root length, and the favorable allele RM6948-116bp, detected on chromosome 8, for shoot height, were also detected in the RIL population.3. For seedling anoxic tolerance, Kasalath and Nipponbare both carried three favorable alleles in BIL population. All favorable alleles for the trait came from C-Bao in RIL population. Six favorable alleles for seedling anoxic tolerance were explored in the natural population.In BIL population, Nipponbare carried three favorable alleles controlling seedling anoxic tolerance which located on chromosomes 2,3 and 9, tightly linked to RFLP marker C747, C1488 and R2272. Kasalath carried three favorable alleles controlling seedling anoxic tolerance which located on chromosomes 5,8 and 12, tightly linked to RFLP marker R830, C1121 and R642.In RIL population, two favorable alleles, RM525-140bp and RM418-250bp, were detected on chromosome 2 and chromosome 7 in C-Bao for seedling anoxic tolerance.Six favorable alleles for seedling anoxia tolerance detected in natural population were RM112-127bp, RM317-164bp, RM317-157bp, RM311-176bp, RM311-170bp and RM20-205bp.4. Torty-two accessions carring favorable alleles for seed vigor and 6 accessions carring favorable alleles for seedling anoxic tolerance were discovered.Among the 42 accessions discovered in the natural population, Diantun 502 xuan zao, Yangdao 6 hao and Nannongjing62401 carried positive allele with larger effect for root length. Kaiqing and Huixian429 carried positive allele with larger effect for shoot height. Diantun 502 xuan zao and C-Bao carried positive allele with larger effect for seedling dry weight. Some materials carried favorable alleles for two seed vigor traits such as Yangdao6hao (root length and shoot height), Kongqueqing(root length and dry weight), Huixian429(shoot height and dry weight). On the other hand, some materials carried more than two favorable alleles for one seed vigor traits such as Yangguang2000 (root length), Ebushinuodao(dry weight), shujing4hao(dry weight) and shuijingbaidao(dry weight). Some materials carried two favorable alleles for two seed vigor traits as well as two favorable alleles for one seed vigor traits such as Diantun 502 xuan zao(two for root length and one for dry weight) and Kaiqing(two for shoot height and root length).Six varieties possessing favorable alleles for anoxic tolerance discovered in natural population were Kaiqing, Baimangdao, Zhendao88, Youmangzaodao, cuganhuangdao and C-Bao. Zhendao88 carried positive allele with the largest effect for anoxic tolerance.Kaiqing, Zhendao88 and C-Bao which carried favorable alleles not only for seed vigor but also for anoxic tolerance could be utilized as parents in breeding programs which aim to develop varieties suitable for direct seeding technology.