MOLECULAR DISSECTION OF BIOTYPE EVOLUTION IN RICE GALL MIDGE (ORSEOLIA ORYZAE): INTEGRATING CLASSICAL EVIDENCE WITH MULTI-OMICS INSIGHTS FROM TELANGANA AND INDIA

Abstract

Rice gall midge, Orseolia oryzae (Wood-Mason, 1889), is an important insect pest of rice in India, which is highly evolutionarily adaptable to the long-term selection pressure of its host plants. A brief summary of the historical emergence, biotype diversification, molecular evolution and resistance breeding of rice gall midge populations in India is provided. Early research found that these biotypes could be separated in different reaction patterns to the resistant rice varieties that contain rice gall midge resistance genes (Gm). The repeated occurrence of virulent biotypes (e.g. GMB4, GMB5, GMB6 and GMB4M) indicated an increasing virulence spectrum and also indicated a rapid breakdown of resistance under high levels of cultivation of resistant cultivars. A large number of germplasm screening programmes found a number of important resistance donors, including Eswarakora, PTB-series lines, Siam 29, Leuang 152 and wild Oryza species and major resistance genes were identified, including Gm1, Gm2, Gm3, Gm4 and Gm8. Both RAPD and ISSR molecular analysis, SSR, mitochondrial DNA and SNP-based analysis showed a significant amount of genetic divergence, phylogeographic structuring and localized adaptation among the populations of Indian gall midges. In addition, transcriptomic and effector biology studies further showed that virulent populations regulate host defence pathways by detoxification genes and stress-response proteins and defence suppressors. It was emphasized that interaction between rice gall midge (RGM) and rice was an arms race which needs to involve multiple resistance sources, molecular surveillance, gene pyramiding and genomic breeding strategies to achieve durable and sustainable management of RGM in changing agro-climatic conditions.