| Bemisia tabaci (Gennadius) biotype B is a worldwide invasive pest. It has been a key pest of various vegetables and tobacco, and broke out in parts of tobacco-growing areas when it invades in China. Tobacco is an important model plant, with the invasive of B. tabaci biotype B, B. tabaci biotype B and Spodoptera litura are serious pests of tobacco and can occur simultaneously on the same plant. To determine the role of defense responses of tobacco plants induced by B. tabaci biotype B in interspecific competition between B. tabaci and S.litura and explored its possible mechanism, we chosed B. tabaci-tobacco-S. litura as research system, studied the effects of tobacco plants after infested by B. tabaci biotype B on host selection, feeding, growth, development and fecundity of S. litura and its temporal and spatial effect, We also investigated the temporal and spatial change of defense enzyme and PR proteins and nutrition content, discussed the relationship between SA signal pathway and the defense responses of tobacco plants induced by B. tabaci biotype B against S. litura. This research had important academic meaning for showing competitive replacement mechanism of B. tabaci to S. litura, and in-depth study of invasive mechanism of B. tabaci biotype B. Major results as follows:(1) The tobacco plants after infested by B. tabaci biotype B had negative effects on the adult oviposition and larvae feeding of S. litura. The treatment tobacco plants had great repellent effect to S. litura adult, the numbers of eggs of S. litura female adult oviposited on whitefly-infested tobacco plants decreased by 40.9% compared with the control. The damaged leaves preinfested by B. tabaci had great repellent effect on neonate larvae of S. litura, while the middle and systemic white-vein leaves attracted larvae to some extent. However, unexpanded leaves had no significant effect on host selection of larvae of S. litura. The leaves of infested tobacco plant had significant antifeedant activity on S. litura larvae, and the antifeedant activity of damaged leaves was more notable than of the systemic white-vein leaves. Compared with its control, the feeding times or percentage of feeding of S.litura larvae feeding on damaged leaves and systemic white-vein leaves of infested tobacco decreased during the observation time. Also, the start-feeding time was prolonged on the damaged leaves preinfested by B. tabaci, while the total feeding areas declined significantly.(2) Tobacco plants preinfested by B. tabaci B-biotype nymphs feeding had negative effect on growth, development and fecundity of S. litura, and had obvious temporal and spatial effects. S. litura larvae feeding on different leaf position of treated plants reacted differently, the sequence was the damaged leaves> the middle leaves> the white-vein leaves. There were significantly different between treatment and its control. The unexpanded leaves showed no significant effect on growth, development and fecundity of S. litura. Development duration of S. litura was 4.58d longer on whitefly-infested damaged leaves than on control leaves; survival was reduced by 28.0%; relative growth rate was reduced by 74.42%; fecundity was reduced by 47.30%, this proved the defense responses of tobacco plants preinfested by B. tabaci B-biotype nymphs to S. litura was systemic and can be transported through the plant. Tobacco plants preinfested by B. tabaci for 1d to 10 d had no significant effect on developmental and survival of 1st instar S. litura larvae, but after infestation by B. tabaci for 15d and 20 d, tobacco plants treated had a negative effect on developmental duration, survival and relative growth rate of 1st instar S. litura larvae, and the difference is significant. There were still some adverse effects on S. litura after infestation by B. tabaci for 25d, but the difference is not significant.(3) We investigated the temporal and spatial change of main defense enzyme activity and nutrition content, pre-infestation by B. tabaci led to the higher induction of related defense enzymes. Bioassay results indicated that the negative effect on S. litura may have positive correlation with chitinase,β-1,3-glucanase, PPO activity and TPI content, there were some correlation between POD activity, total sugar and C/N and the growth of S. litura, PAL activity may not be directly related to the tobacco defense response induced by B. tabaci biorype B against S. litura.(4) This research used transgenic NahG tobacco and Wild-type tobacco as experimental material, studying tobacco plants preinfestation by B. tabaci on growth of S. litura larvae. The results revealed that relative growth rate and feeding areas of S. litura was not affected by B. tabaci feeding on NahG tobacco plants, but compared with its control, relative growth rate of 3rd instar S. litura larvae was reduced by 33.22% and 19.04% respectively on the damaged leaves and the white-vein leaves of WT tobacco plants preinfested by B. tabaci B-biotype, feeding areas was reduced by 33.77% and 23.15% respectively. Application of exogenous 500 and 750μg/ml SA on NahG tobacco had no obvious effect on the growth and development of 3rd instar S. litura larvae, but treatment WT tobacco with 500 and 750μg/ml SA had disadvantaged influence on 3rd instar S. litura larvae. These results demonstrate that Salicylic acid signaling pathway was play an important role in tobacco-mediated defense response induced by B. tabaci to S. litura. |
PDF Full Text Request