Effect Of Nilaparvata Lugens Infestation Levels On Preference And Performance Of Anagrus Nilaparvatae And Screening Of Rice Lines With Antisense Inhibition Of A Defense-related Gene 9-LOX

Previous studies have shown that the degree of attraction of the parasitoid Anagrus nilaparvatae and the Nilaparvata lugens infestation level did not fit a dose related positive relationship: a maximum for attraction appeared at intermediate infestation levels, but no attraction at low or very high infestations. And we also found that N. lugens and Chilo.suppressalia infestation up-regulated the expression levels of a gene 9-LOX in rice plants. In order to elucidate the biological mechanism of the behavior response of A. nilaparvatae to the volatiles emitted from plants with defferent N. lugens infestation level, we determined the effect of N. lugens infestation level on the host preference and performance of A. nilaparvatae. We also set up rice lines with antisense inhibition of the gene 9-LOX by using an Agrobacterium-mediated transformation system, which is the first step to determine the function of the gene 9-LOX in defense response of rice plants. The main results are as follows:1) Host preference tests showed that the parasitism rates of N. lugens eggs by A. nilaparvatae on the plants that had been infested with 10 gravid N. lugens females for 1 d were significantly higher than those on the plants that had been infested with 10 gravid N. lugens females for 2 or 3 d. Parasitism rates of N. lugens eggs by A. nilaparvatae was the highest on plants that had been infested with 20 gravid N. lugens females, followed by that on plants that had been infested with 10 or 40 gravid females, and the lowest on plants that had been infested with 5 or 80 gravid females. In performance assays, when the N. lugens infestation time was the same as the parasitoid introduced, significantly lower survival rates in immature stage, female ratios, fecundities and ICPI (index of capacity for population increase), and longer developmental durations in immature stage were observed in the parasitoid emerged from plants that were individually infested with 80 gravid N. lugens femlaes, compared to those from plants that were individually infested with 5, 10, 20 or 40 gravid females; there was no significant difference in all tested biological parameters except for fecundity of the parasitoid emerged from plants that had been individually infested with 5, 10, 20 or 40 gravid females: the fecundity is the highest from plants that had been individually infested with 20 gravid females, followed by from plants individually infested with 5 or 10 gravid females, and the lowest from plants individually infested with 40 gravid females. When the N. lugens infestation time was one day earlier than the parasitoid introduced, the parasitoid emerged from N. lugens eggs on plants individually infested with 40 N. lugens females had longer developmental durations and lower survival rates, female ratios and ICPI than those on plants that had been infested with 20 gravid females. These suggest that N. lugens infestation levels influence the host preference and performance of the parasitoid. Based on this result together with our previous data on behavioral responses of the parasitoid to rice volatiles and chemical analysis for rice volatiles induced by N. lugens, we concluded that the host preference of A. nilaparvatae is mainly influenced by rice volatiles, by which the parasitoid perceive the existence, the quantity, and the suitability of the host, and finally prefer the suitable host.2) According to the published sequence, a fragment of the rice gene 9-LOX-was PCR amplified and cloned in pMD19-T vector. After digestion with BamHI and Sad, the 950bp resulting fragment was cloned in pCambia1301, yielding the transformation vector pCambia1301-9LOX that contained the hygromycin resistance gene hpt as a selectable marker. On the T-DNA of the resulting binary plant transformation vector, the 9-LOX gene fragment was present in an antisense orientation downstream from 35S promoter and upstream of terminators, thus enabling the transcription of 9-LOX antisense RNA. By using Agrobacterium-mediated transformation system, rice lines with antisense inhibition of the gene 9-LOX were set up, which lays a foundation for elucidating the function of the gene 9-LOX in the defense responses of rice plants.