Study On Rice Germplasm Enhancement Based On Marker Assisted Selection(MAS) Of Grain Length

Rice is one of the most important food crops in the world. The development of high quality rice has become one of key issues for the vast number of consumers and rice breeders. The improvement of rice quality and yield are two major objectives in rice breeding programmes. Rice grain shape is closely related to both yield and appearance quality. Rice grain shape is defined as grain length, grain width and length/width ratio. Since the consumers from most regions in the world may prefer long grain rice, rice grain length has become a very important breeding objective. SAGC-4 is an elite rice line developed by our center from inter-cross of multiple parental introgression lines and screening of drought resistance and nutrient use efficiency. This line had outstanding performance in the tests in several countries conducted by the Green Super Rice Project supported by the Bill & Melinda Gates Foundation. The commercial release of this line was suspended because of its short grain length. This study is conducted to improve the grain length of this line using MAS technique.Selecting GS3 as a gene with larger effect than other cloned grain shape genes, genotyping of SF28 as a CAPs marker was conducted in a set of rice accessions and the recipient parent to select donor parents which had genotypic polymorphism and good performance in grain length trait. Donor parents were crossed and backcrossed to SAGC-4 by two times. The molecular marker SF28 was used to check the reality of of F1 plants and select the individuals with heterozygous genotype of GS3 in BC1F1 and BC2F1 generations. Chosen BC2F1 plants were selfed to collect BC2F2 seeds within 5 crosses. A total of 65 BC2F2 populations were grown in Hainan Experimental Station. Based on the observations on rice grain length, plant height, panicle size, plant/leaf type, rice blast and visual estimation of grain yield in the field, promising individuals were selected. Seed samples were collected from each plant with the BC2F2 population which had signnificant separations in grain length and measured for both grain length and width by using an image analysis system. The main results were as follows:1. After the procedure of PCR amplification, digestion by PstⅠ and eletrophoresis for 240 rice accessions and the recipient parent, SF28 has obvious polymorphism between 42 selected donors and the recipient parent. Two kinds of electrophoresis bands in the derived progenies, namely SAGC-4 type(C) and heterozygous type(H).2. The segregation on grain length were analyzed in BC2F2 populations from different BC2F1 plants in 5 crosses. The progenies from the backcrosses between SANLICUN, HAOBUKA and IAC1246 and SAGC-4 have similar patterns in separation of grain length. The frequency diagrams showed a typical biamodel distribution in accordance with the Mendelian segregation ratio of 3:1, which indicated that GS3 had effects like single major gene on the background of those backcross populations GS3 Typical Mendelian segregation was not observed in populations from crossed between JAPPENITUNGKUNGO, MIGA and SAGC-4, but having normal distributions, which could be the results of the influence from the background genetic effects togethter with the effect of GS3 gene.4. There were significant differences on plant height among backcross progenies. Most populations had no large ranges in growth durations although some variance could be observed in the field. The backcross progenies of the crosses between the donor parents and SAGC-4 generally had good performance in agronomic characters.5. From a total of 65 separation plots, those plots were dropped if the plots did not show obvious grain length separation, having all individuals with high plant height, blast lesions and poor agronomic traits. A total of 109 promising individuals were selected from 35 separation plots. Among them, the plant height varied from 80 cm to 117cm; the lowest panicle number is 4 and the maximum panicle numbe is 23 per plant; the average number of spikelets per panicle ranged from 49.1 to 222.7 while the grain number per panicle ranged from 41.4 to 174.7.6. Compared to the original recipient parent, the grain length increased from 8.8 mm to 10.1 mm in some of the selected individuals.