Progress and perspectives of distant heterosis in rice

Abstract

Heterosis, or hybrid vigor, represents one of the greatest contributions of genetics to the improvement of major crops such as maize and rice, which is intensively studied and exploited by breeders and seed companies worldwide. The exploitation of distant heterosis is a promising way to further raise the yield potential of crops. This review describes aspects of the genetic basis for heterosis, diversification of rice and its related species, principles and methodologies for exploiting distant heterosis in hybrid rice breeding. Both promises and constraints are discussed for understanding the importance and difficulties of distant heterosis utilization. Progress of distant heterosis is demonstrated by the intersubspecific heterosis between two subspecies of Asian rice (Oryza sativa L.), ssp. indica and ssp. japonica, and the interspecific heterosis between two cultivated species, Asian rice and African rice (O. glaberrima Steud.). Strategies of using the doubled haploid method and molecular genetics approaches are suggested for accelerating distant heterosis breeding, eliminating sterility loci to overcome the hybrid sterility of distant crosses, and identifying and pyramiding QTLs of distant heterotic loci and favorable genes to develop a more typical intersubspecific hybrid rice with higher ratio of indica/ japonica heterozygotic loci, and to create a more adaptive and productive partial interspecific hybrid rice incorporating sativa/glaberrima heterozygotic loci and favorable genes from the two cultivated species.