Genetic mapping of host plant resistance genes against rice planthopper species and monitoring the breakdown of the host plant resistance in rice

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The brown planthopper (BPH), Nilaparvata lugens Sal. is one of the most serious and destructive pests of rice that can be found throughout the rice growing areas in Asia. In the present study, we report a genetic basis of high resistance to BPH derived from an Indian rice cultivar, ADR52. An F_2 population derived from a cross between ADR52 and a susceptible cultivar, Taichung 65 was used for quantitative trait loci (QTL) analysis. The result showed that multiple loci controlled the high resistance to BPH in this F_2 population. Further linkage analysis using nearly isogenic populations, which carry resistance genes transferred from ADR52,revealed that a new BPH resistance gene, bph20(t) was mapped on distal end of the short arm of chromosome 6 and another one, Bph21(t) was mapped on the long arm of chromosome 12.Rice ovicidal response to whitebacked planthopper (WBPH) is characterized by the formation of watery lesions which result in the death of the eggs at the ovipositional sites. … More We revealed that the expression of benzyl alcohol benzoyl transferase (BEBT) increased three hours after oviposition of the WBPH on NILs carrying ovicidal QTLs in addition to the ovicidal gene. In addition to the expression of BEBT, cinnamic acid-4-hydroxylase(C4H) was also accumulated in the rice plant after oviposition of the WBPH.Long-term monitoring of the virulence of the brown planthopper (BPH), Nilaparvata lugens (Stal.) strains was carried out using differential cultivars and NILs carrying the BPH resistance genes. The BPH strains collected between 1966 and 2005 in Japan were evaluated using nine differential cultivars carrying different resistance genes against the BPH. The results showed that the1989-BPH, the 1999-BPH and the 2005-BPH strains were virulent to Mudgo (carrying Bph1) and the1999-BPH and the 2005-BPH strains were virulent to ASD7 (carrying bph2). It is appeared that the resistance genes, Bphl and bph2 had been broken down before 1989 and 1999, respectively. In addition, we revealed that the 1999-BPH and the 2005-BPH were virulent to either bph2C(t) or Bph21(t), but not against the combined line of bph20(t) and Bph21(t) based on the adult survivorship and oviposition of the BPH. Less