Study On The Resistance Of Pepper Varieties To Bemisia Tabaci (Gennadius)

Bemisia tabaci(Gennadius) is a worldwide pest. Due to its wide distribution, host variety, short life span, high fecundity and excretion of honeydew which serves as media for sooty mold and virus diseases, B. tabaci is one of the most important pests of vegetable cultivation. Whitefly seriously affects the yield and quality of vegetables and cause great economic losses. The control of whitefly currently depends on chemical pesticides. However the use of chemical pesticides not only cause the environment pollution, but also induce the development of resistance to pesticides. Therefore, cultivation of pest-resistant plant varieties turns out to be one of the most effective ways to control whiteflies.In this study, different pepper varieties were used as test materials, whitefly as bio-stimulating factor, the mechanism of whitefly selection and antibiosis to different varieties of pepper, and herbivore-induced and methyl jasmonic acid induced has been systematically researched. The results will provide basis for screening the whitefly-resistant pepper varieties, and provide a new approach to the spread of the whitefly-resistant pepper varieties. The main findings are as follows:1、The whitefly host selection were studied on 10 pepper varieties. Pepper leaf physics properties and volatiles were analyzed to explore the resistance mechanism of pepper varieties to whiteflies. The results showed that whitefly host selection was significantly different, that is, xinsujiao No.5 and xinyidaisanyingjiao exhibited high resistance to whiteflies, and suj iao No.15, sujiao No.13 were the favourite strains for whitefly in tested varieties. Anti-insect variety had less surface fuzz density than susceptible variety, higher chlorophyll content and, deeper vascular bundle buried depth. Correlation analysis and multiple regression showed that the density of the leaf hairs of pepperr demonstrated significantly positive correlation with whitefly adult preference and oviposition, and vascular bundle burial depth and chlorophyll content showed significant negative correlation with that, and there was no obvious correlation between wax content and the adult preference and oviposition. And 72h later, there was no significant correlation between whiteflies adult numbers and chlorophyll content. Density of the leaf hairs plays the main role in the process of whiteflies host selection and oviposition. Through the determination of leaf volatiles of sujiao No.13, sujiao No.15, xinsujiao No.5 and xinyidaisanyingjiao, pepper leaf volatiles components were significantly different among different varieties. Anti-insect variety had less percentage of ketone volatiles and linalool, and higher percentage of aldehyde material and acetaldehyde.2、Content of soluble sugar, soluble protein and free proline, phenolic compounds and flavonoids were examined in the leaf of different pepper varieties. Contents of soluble sugar, phenolic compounds and flavonoids were higher than those in susceptible variety, soluble protein and free proline content was significantly lower than susceptible variety. Correlation analysis showed that, the whiteflies population trend index had significantly negative correlation with content of soluble sugar, phenolic compounds and flavonoids, and significantly positive correlation with content of soluble protein and free proline. Among them, soluble sugar content had the greatest effect on the index. Soluble sugar content increased by one unit, and the population trend index reduced by 1.754.3、Nutrient and secondary metabolites in leaves were detected after the peppers were fed by whiteflies to study the induced effect of insect damage. The results showed that, after damaged by whiteflies, the chlorophyll content increased. Chlorophyll content susceptible variety increased higher than that in anti-insect variety. Chlorophyll content decreased when the number of whitefly increased, but still higher than the control; the content of soluble sugar was decreased, anti-insect variety decreased more than susceptible variety, the greater the amount of whiteflies, the more obvious of change trend. As the rise of the population density, soluble protein content decreased and then increased, anti-insect variety rise above susceptible variety, phenols, flavonoids content increased, susceptible variety increased more than anti-insect variety, and the greater the amount of insect, the more obvious of the change trend. Thus, in the process of whitefly sucking period, the content changes was closely related to the pepper resistance, which can be used as an identification index of pepper resistance to whitefly.4、After application of exogenous methyl jasmonate on pepper leaf, determination of resistance-related substances, enzyme activity in different varieties of pepper leaf to study the induced insect resistant effect of exogenous methyl jasmonate. Results showed that, after the application of methyl jasmonic acid, different substances and enzyme activity changed to different degree. With the decrease of concentration of methyl jasmonic acid, the content of chlorophyll, soluble sugar, phenolic compounds and the activity of POD increased and then decreased, the content of soluble protein and the activity of PPO showed the trend of decrease after the increase.10-5mol/L methyl jasmonic exhibited the best effect resistance induction, the effect can last for 16 days.