Breeding for stem borer and gall midge resistance in rice

Abstract

Breeding for insect-resistant varieties has been central to the integrated pest management as it offers a viable and ecologically acceptable approach. Status of progress made in breeding and adoption of resistant varieties against stem borers versus gall midge presents two contrasting scenarios. The conventional resistance breeding for yellow stem borer has not gained much impetus due to the lack of resistance sources in cultivated rice (Oryza sativa and O. glaberrima) gene pool, want of efficient insect rearing and varietal screening protocols, and inherently complex genetics of resistance. Hence, alternative approaches like wide hybridization to introgress resistance from other species of Oryza, transgenic approach to deploy Bt cry and other insecticidal genes and RNAi approach are being actively pursued. In contrast, high level of gall midge resistance is available in the crossable gene pool, insect rearing and greenhouse screening methods are well developed, genetics of resistance are well studied, molecular markers linked to R genes are developed, and many resistant rice varieties have been released for commercial cultivation and well adopted by farmers. To date 7 gall midge biotypes and 11 plant resistance genes have been reported. Nonetheless, the diversity in insect pest populations and continuous selection of virulent biotypes necessitate supplementation of conventional breeding techniques with molecular and transgenic approaches. Recent advances in the molecular breeding techniques and transgenic rice biotechnology present a great scope for enhanced varietal tolerance to biotic stresses. Status and prospects in this field are presented in this chapter.