| The brown planthopper (BPH), Nilaparvata lugens (Stal), is one of the most destructive pests of rice-growing areas in Asia. Resistant rice varieties have been used as the preferential method in the control of this pest for its safety, economy and efficiency. However, the BPH biotypes, which can "overcome" the resistance of rice varieties with different major resistance genes, occurs soon after the release of resistant rice varieties, and this has become a serious problem for resistant rice breeding and pest controlling.Extensive studies have been made on the biology, morphology, cytology, biochemistry and genetics of different BPH biotypes, the monitoring method of biotypes in the field, and the resistance mechanism of rice varieties to this pest, et al. Valuable data accumulated and it has greatly deepened our knowledge about the BPH biotypes. However, due to the extra complex of this problem and the limitation in the former research measures, some key problems, such as the genetic basis and hereditary characters of the biotype virulence, the occurrence and variation mechanism of biotypes, the interaction between BPH biotypes and rice varieties, are still waiting for clarification. In addition, although many methods are applicable for the identification of biotype populations, it has been a pressing task to establish some rapid, convenient and accurate means for the identification of individuals. Resolution of all these problems would be most important for the progress in resistant rice breeding and pest controlling.To clarify the key questions about the BPH biotypes, it would be most helpful to study the biochemical and molecular variation between different biotypes. Yet up to now, limited research has been done on this aspect. Anyway, some research results indicated from recent studies that the virulence of BPH biotypes seems to be controlled by multiple genes. Thus, the variation in different BPH biotypes is probably correlated to differential expression of many genes in quality or quantity. To identify the genes correlated with the virulence of BPH biotypes, we established the individual virulence indexes of BPH females to Mudgo (a rice variety with Bph1 resistance gene) in the first. According to the index, females with typical virulence were selected respectively from the purified biotype 1 and biotype 2family line. Then a newly-developed molecular technique -suppression subtract!ve hybridization (SSH), was used to separate differentially expressed genes between biotype 1 and biotype 2 females. Also, considering the importance of metabolizing enzymes in the adaptation of insects to their host plants, the influence of resistant rice varieties on some metabolizing enzymes in BPH was also investigated. The results are summed as follows:(1) Influence on Esterase (ESTs), glutathione S-transferases (GSTs) and mixed function oxidases (MFOs) in BPH was studied with one susceptible (TN1) and three resistant rice varieties (Mudgo, ASD7, and Ruthu Heenati). It was showed that one-generation feeding on resistant varieties did not make any significant difference in esterase activity. However, females feeding on Mudgo and ASD7 had significantly different esterase activity. Feeding on Mudgo made the Km of esterase in males increase as high as 2.78 times, and on Ruthu Heenati 2.58 times when compared with hoppers feeding on TN1. Esterase activity showed also some changes between different BPH biotypes. Study on distribution of individual esterase activity in biotype 1 and biotype 2 BPH populations indicated that esterase activity in BPH biotype 2, both male and females, was much lower than that of biotype 1. GSTs activity increased significantly after the hoppers feeding on ASD7 or Ruthu Heenati for one generation, but no changes was found in this enzyme when hpoppers were reared on Mudgo. For MFOs, no significant difference in the activity of microsomal O-demethylase was detected among various treatments. Finally, a conclusion was drown that the influence of host plant varieties on metabolizing enz... |
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