Net work of quantitative trait loci responsible for evolutionary change in rice

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Wide and cultivated rices differ in many quantitative characters responsible for yielding capacity and propagation method. The objective of this study is to identify loci of those quantitative traits (QTL) and elucidate their network on rice genome using a cross between cultivated rice and a strain of wild rice.1) QTL analysisOne-hundred forty molecular markers were found to be polymorphic between two parents. Segregation of those markers were surveyed among 125 R_6 Recombinant Inbred Lines (RILs) derived from the above cross, and linkage map was constructed. More than 30 quantitative traits were measured in respective RILs, and cosegregation of molecular markers and quantitative traits were analyzed by qGENE.A total of 176 QTLs for 22 traits were detected. QTLs controlling a given trait were widely scattered on different chromosomes. QTLs for different traits tended to cluster on several specific regions of 12 chromosomes. Such clusters were found near the markers which showed signifi … More cant excess of cultivar-derived alleles.2) Selection experiment on seed shatteringTwo hybrid populations of the above cross were established by propagating after F_3 in bulk as follows. One is shattering group (S) in which seeds shattered on the ground were collected and used for raising next generation. The other is non-shattering group (NS) in which seeds remaining on the panicles were harvested and used for raising next generation. Two F_7 populations thus established were examined regarding 80 RFLP markers and various quantitative traits. Lines of S group showed later heading, stronger seed dormancy, stronger regenerating ability than those of NS group. Allele frequencies of some RFLP showed significant difference between S and NS groups. They are mostly linked with QTLs responsible for seed shattering.The above results suggest possible genetic mechanisms of domestication in rice. "Cultivation" defined by seeding and harvesting by man must have worked as strong natural selection favoring non-shattering plants. Further, linkage or gene cluster of QTLs also contributed to forming adaptive association of characters in domestication process. Less