Assessment of population genetics of brown plant hopper Nilaparvata lugens Stal from India

Abstract

The brown planthopper, Nilaparvata lugens (Stål.), wreaks havoc in Asian rice fields, demanding a good understanding of its genetic diversity, identification of new resistance sources and resistance mechanisms to insecticides. In the present study, 268 rice genotypes were screened against N. lugens during 2020-2021. Initial screening identified 12 resistant (score 1) and 18 moderately resistant (score 3) rice genotypes. Further, 96 genotypes were selected for phenotypic and molecular characterization using 93 molecular markers linked to 26 N. lugens resistant genes. Resistant genotypes exhibited lower plant damage, nymphal survival and honeydew excretion compared to susceptible genotypes, which ranged from 4.60% to 8.90%, 11.50% to 22.00% and 3.43 to 6.37 cm2, respectively. Yet, resistant genotypes displayed higher feeding marks (16.03-32.00 numbers plant-1). Genetic analysis revealed that, the mean genetic diversity was 0.275 and polymorphic information content (PIC) was 0.240. Genetic grouping through cluster and population structure differentiated the 96 genotypes into three genetic groups with resistant genotypes grouped in a separate cluster. Principal co-ordinate analysis (PCoA) confirmed this separation. Analysis of molecular variance (AMOVA) showed 8% variation among population and 92% within population. Marker trait association unveiled five markers (RM19291, RM28472, RM28449, RM7 and RM5633) linked to three N. lugens resistant genes (Bph30, Bph18, Bph17) and 2 QTLs (Qbph3 and Qbph4.4) were significantly associated with phenotypic parameters. Further, the resistance of N. lugens to five insecticides viz. imidacloprid, triflumezopyrim, buprofezin, dinotefuran and pymetrozine was evaluated over five generations. In F5 generation, highest LC50 of 2.896 mg/l was detected against imidacloprid whereas, lowest of 0.018 mg/l was recorded against triflumezopyrim. Detoxifying enzymes (GST and CYP) showed greater activity in F5 individuals of N. lugens than F0. The RT-PCR result revealed that, four P450 genes (CYP6