Rice Genetics IV - IRRI books - International Rice Research Institute

Table 2. A summary of the significant (P ≤0.01) interactions identified in1994 and 1995 in the F 2:3population by searching all possible two-locuscombinations (adapted from Yu et al 1997).Trait Interaction 1994 1995 CommonYield Positive pairs a 105 165 10AA 60 91 8AD (DA) 51 73 3DD 4 18 0Tillers plant –1 Positive pairs a 105 141 17AA 79 105 17AD (DA) 28 42 1DD 10 6 0Grains panicle –1 Positive pairs a 99 160 15AA 52 80 9AD (DA) 56 74 10DD 4 16 0Grain weight Positive pairs a 125 164 49AA 84 102 27AD (DA) 47 71 19DD 15 16 9Number of tests b 7,585 7,681aNumber of two-locus combinations showing significant interactions (P ≤0.01).bNumber of possible two-locus combinations tested.interactions. The proportion of common interactions was the largest for grain weight.They made up approximately 40% and 30% of the significant interactions detected in1994 and 1995, respectively. Common interactions ranged from 6% to 17% of the significantinteractions for the remaining three traits in the two years (Table 2).The number of three different types of interaction (AA, AD/DA, and DD) determinedusing the orthogonal contrast test is also given in Table 2. All three types ofinteraction were found in all the traits and the types of interaction were also very consistentbetween the two years. The loci involved in the interactions, as indicated by the molecularmarkers, were distributed in all 12 chromosomes. Overall, AA interactions werethe most frequent and DD interactions were the least frequent. In general, each ofthe interactions had only a small effect on the trait by explaining on average 3.0%of the genotypic variation of the trait. In some cases, two different types of interactionwere detected for the same two-locus pairs. In other cases, the same two-locuspair showed interaction effects on two or more traits, which may be referred to asthe pleiotropic effect of epistasis.The effects of epistasis on single-locus QTLsInteractions between QTLs were detected in grains per panicle and grain weight in1994 and in yield and grains per panicle in 1995 (Table 1). The most noteworthycase was that of grain weight in 1994, in which significant interactions were detectedin four pairs of QTLs. Interactions of QTLs with loci in the rest of the genomewere also detected using markers flanking the QTLs and markers located inGenetic and molecular basis of heterosis in rice 177