Importance of over-dominance as the genetic basis of heterosis in rice

In populations derived from commercial hybrid rice combination Shanyou 10, F-1 heterosis and F-2 inbreeding depression were observed on grain yield (G YD) and number of panicles (NP). Using marker loci evenly distributed on th e linkage map as fixing factors, the F-2 population was divided into sub-po pulations. In a large number of sub-populations, significant correlations w ere observed between heterozygosity and GYD, and between heterozygosity and NP. This was especially true in type III sub-populations in which the geno type of a fixing factor was heterozygotes. In type III sub-populations, 15 QTL for GYD and 13 QTL for NP were detected, of which the majority exhibite d over-dominance effects for increasing the trait values. This study showed that over-dominance played an important role in the genetic control of het erosis in rice.