This study examines the utility of resistant varieties and their associated resistance genes against brown planthopper, Nilaparvata lugens (Stål), populations from South and South East Asia. A collection of 39 rice accessions that included resistant, tolerant and susceptible varieties and breeding lines were examined for performance against populations of N. lugens from India (4), Bangladesh (1), Myanmar (1), Vietnam (1), Indonesia (1), China (1), Taiwan (1), and the Philippines (2). Planthopper virulence varied between regions; however only 6 varieties were generally less damaged than the susceptible check Taichung Native 1 (TN1) among ≥50% of the test populations. Each of these 6 varieties contained multiple resistance genes. One further variety, also with multiple resistance genes, and a modern cultivar (possibly with the Bph3 gene) were moderately effective against the South Asian populations, whereas a traditional variety with the Bph6 gene was effective against South East Asian populations. Bph1, bph2, bph5, bph7, bph8, Bph9, Bph10 and Bph18 were ineffective against most planthopper populations. Bph20, Bph21, and Bph17 have potential to be used in resistance breeding in both South and South East Asia, whereas BPH25 and BPH26 have potential for use in South Asia. The results indicate that only a few of the currently available resistance genes will be effective in monogenic rice lines; but that pyramiding of two or more genes with strong to weak resistance could improve resistance strength and durability as apparent with the most resistant, traditional varieties. Strategies to avoid planthopper adaptation to resistant rice varieties are discussed.

This study examines aspects of virulence to resistant rice varieties among planthoppers and leafhoppers. Using a series of resistant varieties, brown planthopper, Nilaparvata lugens, virulence was assessed in seedlings and early-tillering plants at seven research centers in South and East Asia. Virulence of the whitebacked planthopper, Sogatella furcifera, in Taiwan and the Philippines was also assessed. Phylogenetic analysis of the varieties using single-nucleotide polymorphisms (SNPs) indicated a clade of highly resistant varieties from South Asia with two further South Asian clades of moderate resistance. Greenhouse bioassays indicated that planthoppers can develop virulence against multiple resistance genes including genes introgressed from wild rice species. Nilaparvata lugens populations from Punjab (India) and the Mekong Delta (Vietnam) were highly virulent to a range of key resistance donors irrespective of variety origin. Sogatella furcifera populations were less virulent to donors than N. lugens; however, several genes for resistance to S. furcifera are now ineffective in East Asia. A clade of International Rice Research Institute (IRRI)-bred varieties and breeding lines, without identified leafhopper-resistance genes, were highly resistant to the green leafhopper, Nephotettix virescens. Routine phenotyping during breeding programs likely maintains high levels of

A BPH-resistant locus designated as Bph34 identified in Oryza nivara acc. IRGC104646 on long arm of chromosome 4 using high-resolution mapping with 50 K SNP chip. BPH resistance contributed by locus showed dominant inheritance in F and F. The Bph34 locus is 91 kb in size and contains 11 candidate genes. In addition to SNP markers, SSR markers, RM16994 and RM17007 co-segregated with the BPH resistance. These two SSR markers can facilitate marker-assisted transfer of the Bph34 locus into elite rice cultivars in all labs. Brown planthopper (BPH, Nilaparvata lugen Stål) is one of the most destructive insects of rice (Oryza sativa L.) causing significant yield losses annually. Exploiting host plant resistance to BPH and incorporating resistant genes in susceptible commercial cultivars is economical and environmentally friendly approach to manage this pest. Here, we report high-resolution mapping of a novel genetic locus for resistance to BPH, designated as Bph34 on long arm of rice chromosome 4. The locus was mapped using an interspecific F population derived from a cross between susceptible indica cultivar PR122 and BPH-resistant wild species, O. nivara acc. IRGC104646. Inheritance studies performed using F and F populations revealed the presence of single dominant gene. Construction of high-density linkage map using 50 K SNP chip (OsSNPnks) followed by QTL mapping identified single major locus at 28.8 LOD score between SNP markers, AX-95952039 and AX-95921548. The major locus contributing resistance to BPH designated as Bph34 and explained 68.3% of total phenotypic variance. The Bph34 locus is 91 Kb in size on Nipponbare reference genome-IRGSP-1.0 and contains 11 candidate genes. In addition to associated SNP markers, two SSR markers, RM16994 and RM17007, also co-segregated with the Bph34 which can be used efficiently for markers assisted transfer into elite rice cultivars across the labs.

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