So far, 38 genetic loci have been identified for BPH resistance from cultivated and wild species of Oryza and assigned to different rice chromosomes. Till now, very few genes are available that confer resistance against all the four biotypes of BPH. Genes such as bph5, Bph6 and bph7 confer resistance to biotype 4 only, but not against biotype 1, 2 and 3 (Khush & Brar, 1991). A new variety IR36 carrying the bph2 gene conferring resistance to biotypes 1 and 2 was released in 1976 by IRRI, but the resistance of bph2 was broken by the resurgence of new biotype (Biotype 3). IR26 became susceptible due to the emergence of biotype 2. The first BPH resistant variety IR26 containing the Bph1 gene derived from a cross between IR24 and TKM6 was released in 1973 by International Rice Research Institute (IRRI), Philippines (Khush, 1979). The resurgence of new BPH biotypes was experimentally demonstrated in 1969 (Pathak, Cheng, & Fortuno, 1969). The BPH biotype 4 is widespread in the Indian subcontinent and considered as the most destructive pest among all BPH biotypes. Biotypes 1 and 2 are mainly found in Southeast and East Asia whereas biotype 3 was developed by rearing the insects on the resistant variety carrying the bph2 gene in the laboratory. In general, there are four predominant BPH biotypes found across the major rice-growing countries. BPH outbreaks have been frequently reported in many countries due to the rapid evolution of new BPH biotype. Subsequently, BPH evolved as a monophagous insect, which selectively feeds on rice plants (Jing et al., 2017 Zhao et al., 2016).
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The BPH is believed to undergo the host shift from Leersia plants to rice about 0.25 million years ago (Jones, Gacesa, & Butlin, 1996). Therefore, utilization of natural host-plant resistance is considered as one of the most economical and effective ways to manage BPH. Chemical controls are the most common method for managing BPH infestation, but are costly and potentially harmful to the environment and human health. BPH also causes indirect damage to the rice crop by transmitting rice grassy stunt virus and ragged stunt virus (Fujita, Kohli, & Horgan, 2013 Jena & Kim, 2010 Sarao et al., 2016). Severe BPH infestation induces a complex wound response represented by gross discoloration and dehydration of the rice plant known as “hopper burn” (Backus, Serrano, & Ranger, 2005). It is a sap-sucking insect that damages the rice crop by feeding the phloem sap resulting in reduction of growth, vigor and numbers of productive tillers. Among the biotic stresses, brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most devastating insects of rice causing loss of millions of dollars, every year (Kumar et al., 2018 Liu et al., 2015). Various biotic and abiotic stresses impair the productivity of rice in most of the rice-growing countries.
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To meet the demand for food grain, 40% more rice needs to be grown by 2030, and 70% by 2050 (Khush, 2001, 2005, 2013). The world's population was estimated to increase from 6 billion in 2000 to 9.6 billion by 2050. Worldwide, more than three billion people depend on rice for 20%–80% of their daily calories.
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Rice ( Oryza sativa L.) is one of the most important staple food crops. We also discuss the potential utility of the cutting-edge genomics tools for breeding BPH resistance cultivars. In this review, we comprehensively updated the advances made in the identification of the BPH resistance genes and their functional validation to understand the molecular basis of host–BPH interaction. The comparative gene expression profiling, transcriptomics, proteomics and metabolomics studies have also accelerated the resistance breeding programme. Numerous other genes including WRKY, MYB, DELLA, OsGID1, CYP71A1, mitogen-activated protein kinase and micro RNAs have been functionally characterized that mediate resistance response to BPH. The Bph3 encodes a cluster of three Lectin Receptor Kinase genes ( OsLecRK1-3) that confer broad-spectrum resistance. Four genes ( Bph14, Bph26, Bph18 and Bph9) encode a typical CC-NBS-LRR domain-containing protein. Of 38 resistance genes, eight genes ( Bph14, Bph3, Bph26, bph29, Bph18, Bph6, Bph32 and Bph9) were positionally cloned. Till to date, 38 BPH resistance loci have been mapped from cultivated and wild species of rice. Brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most destructive insects that impair rice productivity per year.