Trait Evolution And Cenome-wide Association Study Of Late-maturity Medium Japonica Varieties In Jiangsu Province

Late-maturity medium japonica varieties are the main ecological type for rice production in Jiangsu province,and research on the breeding status of such type varieties is of great importance for rice production in Jiangsu province.During 2012 to 2013 years,we performed researches on 44 late-maturity medium japonica varieties of Jiangsu Province approved in the latest 30 years in Yangzhou,Jiangsu province.According to the change trend of yield gained from regional trial,44 late-maturity medium japonica varieties were divided into 4 groups,based on which the traits of these varieties were collected and analyzed for understanding the change trend of late-maturity medium japonica varieties.Then,genome-wide association study(GWAS)of important traits in 105 germplasm resources consisting of late maturity japonica rice varieties and their parents was performed to provide a reference frame for breeding and improvement of varieties.The main results were as follows:(1)In recent 30 years,there were three development phases of the grain yield per 667m2 of late-maturity medium japonica varieties in Jiangsu province:from the average of 520kg/667m2 in the early 80's,to 570 kg/667m2 at the beginning of the century and the end of last century.Yield of varieties bred after 2005 was fluctuated around 550kg/667m2.The change trend of yield degree was consistent with the regional trial results,but the improvement of yield degree was not obvious.(2)The panicle number per plant of late-maturity medium japonica varieties was gradually reducing,but secondary branch number,the number of grains per panicle and 1000 grain weight were increasing,which indicated that the yield of early-stage varieties depended on panicle number but the number of panicle and grain or heavy panicle in the recent years.(3)The improvement of plant type of late-maturity medium japonica varieties was key factor for the increasing yield per unit area.The flag leaf angle,length of top third leaves,distance between flag leaf and panicle and panicle length of varieties declined and grain density increased gradually,which resulted in the semi-erect or erect panicle type and optimizing canopy light transmission.With the increasing thickness of basel culm,the lodging resistance of varieties had been improved significantly.(4)The appearance quality of late-maturity medium japonica varieties had been improved on the decreasing percentage of chalkiness grain but the chalkiness degree.The gel consistency and amylose content of varieties could meet the first level of National quality rice standard,but there were a few varieties having the good taste quality of Wuyujing3 bred in 1992.(5)Analysis of population structure revealed that 105 germplasm resources consisting of 44 late-maturity medium japonica varieties and their parents might derived from 9 ancestors.(6)GWAS had been performed for 15 yield traits,12 agronomic traits and 9 quality traits based on 38,323 SNPs which had been developed by sequencing 105 varieties including late-maturity medium japonica varieties and their ancestors.19 SNPs were acquired only in seed-setting and total grain number on main stem among 15 yield traits.For 12 agronomic traits,50 SNPs were acquired only in the plant height,flag leaf angle,flag leaf length,leaf length of 2nd and 3rd leaf.Among 9 quality traits,7 traits including brown rice rate,head milled rice,chalkiness degree,gel consistency,gelatinization temperature,protein content and rice taste quality were identified to associate with 83 SNPs,and 86 SNPs were identified to associate with the characteristic values of RVA.