Biotypes of the brown planthopper Nilaparvata lugens (Stål) and strategies in deployment of host plant resistance

Abstract

Resistant rice varieties have proved to be highly effective against the brown planthopper Nilaparvata lugens (Stal), but their long-term stability is threatened because of the evolution of prolific biotypes. At present, identification of biotypes is based principally on the differential reactions of host rice varieties to pest in greenhouse screenings and in field plantings of test nurseries at many locations. So far, three N. lugens biotypes that attack different rice varieties have been identified in the Philippines. Biotype 1 can survive on and damage only those varieties that do not carry any genes for resistance. Biotype 2 can thrive on varieties carrying Bph 1 resistance gene and on those susceptible to biotype 1. Biotype 3 can infest and destroy varieties having bph 2 resistance gene and those susceptible to biotype 1. However, none of these biotypes is capable of damaging varieties with Bph 3 and bph 4 genes for resistance, and the variety Ptb 33 carrying two unidentified genes is resistant to almost all known biotypes. Recently, a population of N. lugens was found thriving on the common weed grass Leersia hexandra Swartz on the IRRI farm and in some locations in Luzon, Philippines, This biotype does not survive on rice.Several varieties which are resistant in the Philippines are susceptible in India and Sri Lanka because the South Asian biotypes of N. lugens are more virulent than the Southeast Asian biotypes. To monitor the pest biotypes in different geographical regions and to identify new sources of resistance, an International Rice Brown Planthopper Nursery (IRBPHN) has been established in many cooperating Asian countries.Biotypes can also be differentiated by studying their behavioural and physiological responses to plants of known genotypes. Distinctive differences can be observed in insect feeding, growth, longevity, fecundity, oviposition and population increase on differential varieties and relative susceptibility or tolerance for hosts' allelochemics. Recent investigations of the existence of subtle morphological, cytological, and electrophoretic differences among N. lugens biotypes and results of hybridization experiments strongly complement other methods of biotype identification.The evolution of biotypes is a complex process that is governed by the interactions of the genetic and other biological characteristics of the pest populations and the genetic makeup of cultivated varieties. While the strategy of sequential release of varieties with major resistance genes has been fairly successful, the monogenic nature of those varieties makes them vulnerable to the development of virulent pest biotypes. Therefore, present breeding endeavors envisage use of both major and minor resistance genes for effective pest suppression.

Interpopulation Crosses, Inheritance Study, and Genetic Variability in the Brown Planthopper Complex, Nilaparvata lugens (Homoptera: Delphacidae)

“…This result corroborates the findings of Tan et al (1995), Latif et al (2008), and Claridge et al (1985a, b). Saxena and Barrion (1985) also reported that karyotypes, idiograms, nuclear organelles, and chromosomes within the nucleolus-organizing region (site of RNA synthesis) showed clear differences between rice-and Leersiainfesting populations of N. lugens. Despite their morphological similarities, a distinct cytological incongruity and a certain degree of genetic isolation between the two populations was inferred.…”

Allozyme variation among biotypes of the brown planthopperNilaparvata lugens in the Philippines

“…host-mediated behavioral and physiological responses, morphological differences, cytological behavior, and crossability differences (Saxena and Barrion, 1985). Accumulation of host-adapted gene complexes in the pest may have led to differentiation of populations on rice varieties with genes for resistance and on the nonrice host, L. hexandra.…”

“…Differentiation of the two species may have resulted from single-gene substitutions or chromosomal rearrangements, provided that these changes act to interrupt the gene flow between populations (Bush, 1975). Similar genetic events may have led to the evolution of N. lugens biotypes which were observed to have considerable differences in cytological behavior and crossability (Saxena and Barrion, 1985). In another study, we have analyzed the allozyme variation ofN.…”

“…Studies conducted at IRRI in the Philippines have demonstrated the existence of three rice-infesting biotypes based on differential varietal reactions. Biotype 1 damages and survives on varieties without any genes for resistance to N. lugens, biotype 2 thrives on varieties carrying the Bph 1 resistance gene and on those susceptible to biotype 1, and biotype 3 can multiply on varieties having the bph 2 resistance gene and on those susceptible to biotype 1 (Seshu and Kaufman, 1980;Saxena and Barrion, 1985). Biotypes 1, 2, and 3 do not attack rice varieties with resistance genes Bph 3 and bph 4 and Ptb 33 carrying two resistance genes.…”

“…Studies of hybridization between N. lugens biotypes showed differences in crossability (Saxena and Barrion, 1985).…”