QTL Mapping And Genetic Analysis For Rice Quality Traits

The demand for superior grain quality is increasingly becoming a priority for international export markets in all of the cultivated rice-producing areas worldwide.The primary components of rice grain quality include appearance,eating,cooking,and milling quality,and nutritional qualities,all values that are determined by their physical-chemical properties and other socio-cultural factors.Among these quality properties,consumers pay more attention to the fine appearance,high eating and nutritional quality.Therefore,these are major goals in rice quality improvement.In order to characterized the genetic components,including additive effects,epistasis,and QTL-by-environment interaction,that are involved in the control of grain quality,data were collected from replicated tests of a recombinant inbred line population derived from the cross between Koshihikari,a top elite japonica variety with superior grain quality,and Nanjing11,a high-yield indica variety with poor grain quality,in two successive years.The results are as follows:1.The RIL population showed bimodal segregations for amylase content,indicating the involvement of a major gene for it;whereas,normal distributions of the others,indicating qualititative-inherited.A total of 27 QTL were identified with significant additive effects on nine chromosomes except chromosomes 7,9,10 and 11.Although only qAC-6 for amylase content had the largest effects.Epistasis analysis detected 16 significant additive-by-additive interactions on the traits.For grain length(GL),grain width(GW),grain length-width ratio(GLWR),grain length of rice seed of brown rice(MGL),grain width of rice seed of brown rice(BRW),grain length-width ratio of brown rice(LWRBR), thousand-seed weight(TSW),percentage of grains with chalkiness(PGWC),rice fat content(RFC),amylose content(AC).Only one additive QTL,qRPC-4,interacted with the environments for rice protein content(RPC).Compared with QTL previously reported for these traits,eleven additive QTL,namely qGL-3,qGL-4,qGL-6,qGL-12 qGW-1,qGW-2,qGW-5,qLWR-2,qLWR-3,qBRL-3-1,qBRL-3-9,qBRL-4,qBRW-1,qLWRBR-2-11,qLWRBR-4,qTSW-4,qTSW-5,qPGWC-6 and qRFC-12,are novel loci.Interestingly,the QTL qRFC-6a for RFC with the highest LOD score was located in the interval RM190-RM588 on chromosome 6,which corresponded to the waxy gene region.2.Based on the dissection of genetic basis in controlling grain quality,it revealed that grain length of rice seed of milled rice,grain width of rice seed of brown rice and fat content were mainly determined by additive QTL;additive effect and epistatic effect were the main genetic components for length-width ratio and thousand-seed weight rice;and amylose content was controlled by Wx and multiple minor loci.3.QTL multipurpose is normal in this research.We found 6 pairs QTLs there are locate the same place as follows:grain length and grain width of rice seed of brown rice each has the QTL of chromosome 1;grain width,grain width of rice seed of brown rice and grain length-width ratio of brown rice all have the same QTL of chromosome 2;grain length-width ratio,grain width of rice seed of brown rice and grain length-width ratio of brown rice all have the same chromosome 2 QTL;there is the same QTL of chromosome 3 for grain length and grain length of rice seed of brown rice;the same QTL is found in chromosome 3 for grain length-width ratio and grain length of rice seed of brown rice;in those QTLs,the same QTL is in the chromosome 4,and they are grain length,grain length of rice seed of brown rice,grain length-width ratio of brown rice and thousand-seed weight; and the last same QTL is in chromosome 6,the owner are grain length,percentage of grains with chalkiness and amylose content.