A new gene for gall midge resistance in rice variety MR 1523

The Asian rice gall midge Orseolia oryzae (Wood-Manson) is a serious pest of rice in certain regions of south, central and east India causing significant yield loss mainly during kharif season. Breeding rice varieties with pest resistance has been a viable, ecologically acceptable approach for the management of the gall midge. However, rapid development of virulent biotypes capable of overcoming the host plant resistance has been posing problem in recent years. Systematic germplasm evaluation has led to the identification of important sources of resistance like Eswarakora, Ptb18, Ptb21, Siam29, Leuang152 etc. (see, Bentur et al., 2003) which have been extensively used in breeding resistant varieties. Genetic studies have identified, so far, 10 major genes conferring resistance (Kumar et al., 2005). Most of the 60 plus gall midge resistant rice varieties developed to date contain one of the three major genes viz., Gm1, Gm2 and an unidentified gene(s) in Ptb21 conferring immune level of resistance. Seven distinct gall midge biotypes have been characterized so far (Vijaya Lakshmi et al., 2006), some of them being selected as direct consequence of extensive cultivation of these varieties. In most of the studies, resistance to gall midge has been found to be conferred by a single dominant or (as in case of gm3) a recessive gene (Kumar et al., 2005). Exceptionally, sources deriving resistance from Ptb18 and Ptb21 have displayed complex pattern of inheritance of resistance (Kalode and Bentur, 1989). The rice variety MR1523 derives its gall midge resistance from Ptb18 & Ptb21 which have contributed resistance in 25% of the released varieties. But genetics of resistance in this breeding line has not been studied. This paper attempts to note inheritance of gall midge resistance in MR1523 and we note that possibly a new gene present in this variety confers resistance against gall midge biotype 4.