Rice Genetics IV - IRRI books - International Rice Research Institute

in the response to daylength in rice? Other factors whose expression is affected bydaylength change might be involved downstream of Hd1 in the genetic control pathway.The identification of other QTLs by map-based cloning is progressing. This simultaneousapproach to identifying QTLs controlling photoperiod sensitivity willcontribute to elucidating the genetic control pathway for photoperiod response in rice.Plant materials for the analysis of quantitative traitsTo facilitate the genetic analysis of complex traits in rice, permanent mapping populationsbased on japonica × indica or japonica × japonica crosses are being constructed.Recombinant inbred lines (RILs), backcross inbred lines (BILs), and doubled-haploidlines have been developed and framework linkage maps for permanent use arebeing constructed (Table 1, Tsunematsu et al 1996, Lin et al 1998, M. Yano and S.Y.Lin, unpublished data). These permanent mapping populations will facilitate the detectionof naturally occurring allelic variations for target traits. However, these materialsare not enough to allow us to proceed with further analysis, such as fine mappingand characterization of target QTLs. Secondary mapping populations, such as chromosomalsubstitution lines or NILs, will be required to facilitate more comprehensiveanalysis of target QTLs. To this end, we have been developing chromosomal substitutionlines derived from crosses between Nipponbare and Kasalath and betweenKoshihikari (japonica) and Kasalath (Table 1).The construction of a series of intraspecific substitution lines of rice with overlappingchromosomal segments is progressing by marker-assisted selection (Table 1). InTable 1. Permanent mapping populations for the analysis of naturally occurring allelic variations.Cross combination Population Generation No. Genotype Institution involved cstructure a of lines data bNipponbare/Kasalath BIL BC 1 F 10 98 245 RFLPs NIAR, STAFF,Hokuriku NAESNipponbare/Kasalath SL BC 3 F 7 /BC 4 F 6 115 125 RFLPs NIAR, STAFF,Hokuriku NAESAsominori/IR24 RIL F 12 71 375 RFLPs Kyushu University,NIAR, STAFFKoshihikari/Akihikari DH A 4 214 108 RFLPs Ishikawa Agricultural48 RAPDs College, NIAR, STAFFSasanishiki/Habataki BIL BC 2 F 6 85 238 RFLPs Hokuriku NAES, NIAR,STAFFKoshihikari/Kasalath BIL BC 1 F 7 183 135 RFLPs NIAR, STAFFKoshihikari/Kasalath SL BC 3 F 2 /BC 4 F 1 Under NIAR, STAFFdevelopmentaRIL = recombinant inbred line, BIL = backcross inbred line, SL = chromosome segment substitutionline, DH = doubled-haploid line. b RFLPs = restriction fragment length polymorphisms, RAPDs = randomlyamplified polymorphic DNAs. c NIAR = National Institute of Agrobiological Resources, STAFF = Instituteof Society for Techno-innovation for Agriculture, Forestry and Fisheries, Hokuriku NAES = Hokuriku NationalAgricultural Experiment Station.Naturally occurring allelic variations as a new resource . . . 235