Rice Genetics IV - IRRI books - International Rice Research Institute

(genetic/statistical models and corresponding software). Recently, the mixed linearmodel approaches with inclusion of digenic epistasis and QE interactions and comprehensivecontrol of background genetic variation developed by Wang et al (1999)and by Kao et al (1999) have allowed more accurate detection and quantification ofepistasis affecting complex quantitative traits.Table 3 shows the relative contributions of M-QTLs and E-QTLs to total phenotypicvariation of some quantitative traits detected in five related rice mapping populationsfrom the cross between Lemont (japonica) and Teqing (indica). These includea set of recombinant inbred lines (RILs), two BCF 1 (the RILs × the parents, Lemontand Teqing), and two testcross F 1 populations (the RILs × two testers, Zhong413 andIR64) (Li et al 2001a, Luo et al 2001). Both M-QTLs and E-QTLs affecting severalagronomic traits were mapped. Obviously, E-QTLs account for a much greater portionof the total phenotypic variation than M-QTLs for all traits except grains perpanicle. Similar results were obtained in the IR64/Azucena doubled-haploid (DH)population (Li et al 2001b) except for plant height, in which the segregation of amajor gene, sd-1 (for semidwarf plant stature), accounted for more than 30% of thetotal trait variation. The relative importance of E-QTLs versus M-QTLs is furthersupported by the magnitude of epistatic effects of E-QTLs versus the main effects ofM-QTLs estimated in these mapping populations (Table 4). Again, for complex grainyield and its components, the mean epistatic effects of the identified E-QTLs areequivalent to the M-QTL main effects.Phenotypic value(cm or d)105Main-effect QTLsEpistatic QTL pairs0–5–10–15AAaaQTLs affecting plant heightQTLs affecting heading dateAABB aabb AAbb aaBBGenotypesFig. 1. Comparison between two main-effect QTLs, QPh2 (plant height) and QHd3a(heading date), and two epistatic QTL pairs, between RG13 (chromosome 5) andRG103 (chromosome 11) (plant height), and between Pgi1 (chromosome 3) andRZ66 (chromosome 8) (heading date). A is the Lemont (japonica) allele and arepresents the Teqing (indica) allele.QTL mapping in rice: . . . 157