Identification of interspecific heterotic loci associated with agronomic traits in rice introgression lines carrying genomic fragments of Oryza glaberrima

In the present study, a set of 79 rice introgression lines (ILs) carrying variant introgressed segments of African rice (Oryza glaberrima Stued.) was used to identify quantitative trait loci (QTL) and heterotic loci (HL) associated with 7 agronomic traits. A total of 180 polymorphic markers between the donor and recurrent parents were found and 115 markers were used to identify the segregation of the introgression fragments. Based on the genotypic data of the ILs and test variety GZ63S as well as the phenotypic data of the IL and PIH, QTLs and HLs can be mapped on introgressed chromosome segments. One representative marker on each specific introgressed segment was defined as a QTL or a HL. 24 QTLs associated with six agronomic traits were mapped on 9 chromosomes and 23 interspecific HLs for seven agronomic traits were identified on 10 chromosomes in 2 years. Among them, 22 QTLs and 19 HLs were found to be associated with 5 yield-related traits respectively. The PIH (F1) testcross population showed superiority in most yield-related traits and was characterized by a high frequency of overdominant interspecific HLs. In addition, the pleiotropism was found in 5 marker loci for 11 QTLs associated with five agronomic traits and 4 marker loci for ten interspecific HLs for all the seven traits. This study is the first attempt for the identification of interspecific HLs between the two cultivated rice species, Asian rice (Oryza sativa L.) and African rice (O. glaberrima Steud.). Therefore, our results may help to lay the foundation for exploring the genetic mechanism of interspecific heterosis in rice.