| Nilaparvata lugens Stal, the brown planthopper (BPH), is one of the most destructive phloem-feeding insect pests of rice (Oryza sativa L.) throughout Asia. It attaches by preference to the stem, from where it penetrates the phloem through its stylet. BPH feeding interferes with the translocation of assimilate, thereby damaging plant growth and development. Where a large number of BPH individuals feed on a single plant, a common outcome is leaf desiccation and stem wilting, a condition called hopper-burn. BPH is also a carrier of two viruses, one responsible for the disease rice grassy stunt, and the other rugged stunt. Chemical control of BPH is commonly practiced, but is both costly and harmful to the environment. The use of genetically resistant cultivars has proven to be a more economical, efficient and environmentally friendly means to control this pest.Non-durability of many of the major resistance genes due to changes in the pest biotype remains a problem. IR26, released in 1973, was the first cultivar specifically bred for BPH resistance. It harbors Bphl, a gene that was overcome within two years of the widespread use of the variety. This pattern of rapid breakdown of resistance was repeated by cultivars harboring bph2 or Bph3. The frequency damaged on rice production by BPH infestation, has driven the search for new sources of genetic resistance. It has been suggested that quantitative resistance may be more durable than that determined by major genes, but these genes are more difficult to handle in a breeding program. Fine mapping is the key step for mapping based cloning, and the development of resistance gene closed linked molecular marks would provid the useful tools for the application of resistance gene.The identification and cloning of insect resistance is not only helpful for elucidating the molecular mechanism, and also can speed up the application in breeding program. Even a gene has been fine mapped, but there would still be a number of candidate genes. However, if the mechanism of the gene has been clear, it would be able to provide a basis for cloning of the target gene and also can improve the efficiency in production.The activation of insect resistant mechanism often involves a series of molecular signals in the network. The previous studies have shown that systemin, jasmonic acid, salicylic acid, ABA, ethylene and some peroxides, may be as signal molecules associated with plant insect response.In this study, we evaluated the feeding behavior of BPH on several rice varieties with different BPH resistant genes, fine mapped a brown planthopper resistance gene BPH20, analysis the genetic base of an Vietnamese landrace YA resistance against brown planthopper; investigated the effect of BPH feeding on some defense-related enzymes and found NO may be as an important signal molecular participated in BPH resistant response.1 The Feeding Behaviors of Brown Planthopper on some Resistance Rice VarietiesThe feeding behavior of BPH was evaluated on twelve rice varieties with several BPH resistant genes from the plant three basic resistanc mechanisms:antibiosis, antixosis, and tolerance. RH and Balamawee scored very well in antibiosis and antixosis tests, but had relatively low levels of tolerance compared to the other verities tested. Kaharamana, Balamawee and Pokkali contain the same dominant resistance gene designated as Bph9 in previous reports, but the feeding behaviors of BPH on Balamawee significantly differed from the other two varieties. A strong toxic resistance in Col.5 was found in tiller stage, but not in seedling stage, the BPH resistance is development regulated. We divided the tested varieties’seedling resistance into four types. The results showed that RH and Balamawee belonged to the antixenosis/antibiosis type; DV85, Pokkali, Karhamana, Col.5, Col.11, Chin Saba perform strong tolerance instead; other varieties showed moderate levels of antixenosis, antibiosis and tolerance.2 Fine mapping of a brown planthopper (BPH) Nilaparvata lugens Stal tolerance gene, BPH20 in riceBrown planthopper (BPH), Nilaparvata lugens Sta1, is one of the most destructive insect pests of rice (Oryza sativa L.) throughout the Asian rice-growing countries. DV85 is one of BPH resistance indica cultivar. A single dominance gene dominated the resistance in DV85 and was mapped on the long arm of chromosome 11, here designated as BPH20. The results of evaluation on BPH resistance mechanism indicate that DV85 perform tolerance instead of antixenosis and antibiosis, when infested by BPH. In order to fine map and positional clone of the tolerance gene against BPH, we have developed a high-resolution genetic map of BPH20 in the target chromosomal region. Mapping was based on a PCR-based screening of the recombinant plants of two F2 populations derived from two crosses between DV85 and a susceptible japonica cultivar (cv.), Kinmaze and another susceptible indica cultivar (cv.) 9311, which include 4025 and 5926 individuals respectively. The gene locus was delimited an interval between two InDel markers Indel59 and Indel66. The BPH20 locus was physically defined to an interval of about 20 kb.3 SSR mapping of rice brown planthopper resistance gene in Vietnamese landrace YAGYAW (YA)To explore new sources for BPH resistance breeding, an F2 mapping population was created from the cross between a BPH resistant Vietnamese landrace Yagyaw and the susceptible cultivar Cpslo17. Four quantitative trait loci (QTL) of BPH resistance were mapped to chromosomes 2,4,7 and 11. The individual QTL accounted for between 8.7% and 16.5% of the phenotypic variance, with the resistant alleles provided by Yagyaw.4 Changes of Some Defensive Enzyme Activity Induced by the Piercinging-Sucking of Brown Planthopper in RiceThe effects of brown planthopper on the activities of some key enzymes involved in defense response and the H2O2 content were investigated in rice. From the fact that after piercing-sucking of brown planthopper, malondialdehyde (MDA) content of rice plant was increased rapidly, one can conclude that it induced lipid peroxidation; Lipoxygenase(LOX), hydroperoxide lyase(HPL) and phenylalanine ammonia-lyase(PAL) activities were increased significantly in plants of resistant and susceptible varieties by piercing-sucking of brown planthopper; whereas the catalase activity and the H2O2 content were significantly different between resistant and susceptible plants by piercing-sucking of brown planthopper, the former being decreased and the latter increased in resistance plants of variety RH, while the reverse was true in the susceptible plants of variety TN1. The effect of brown planthopper on the PAL activity and the H2O2 content were systemic, but the effect on the LOX activity occured only in stem the organ which brown planthopper sucking. The transgentic plants the key enzymes in JA, SA and ET biosynthesis, AOS, PAL, ACC silenced by RNAi were obtained. The transgenetic plants provide the useful materials for studying the JA, S A and ET pathway in brown planthopper resistance response.5 Nitric oxide production is associated with the tolerance of rice to brown planthopper infestationNilaparvata lugens Stal, the brown planthopper (BPH), is one of the most destructive phloem-feeding insects of rice (Oryza sativa L.) throughout Asia. Here, we show that BPH feeding increased the level of endogenous nitric oxide (NO) in the leaf and sheath of both a resistant and a susceptible rice cultivar. However, in the roots, the NO level increased in the resistant cultivar, but decreased in the susceptible one. A burst in NO production occurred in the sheath within one hour of infestation with BPH. The production of NO in response to BPH feeding appears to be partially dependent on the activity of nitric oxide synthase, but not dependent on nitrate reductase, and other pathway may be also participated in the release of NO. NO reduced plant water loss by its effect on both stomatal opening and root architecture. It also stimulated the expression of certain drought stress related genes, reduced plant height and delayed leaf senescence. Over the short term, NO supplementation attenuated the seedling mortality caused by BPH feeding. We suggest that NO signalling plays a role in genetic tolerance to BPH feeding in rice. |
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