| Nowdays there are primary four types of Bemisia tabaci reported in China and B. tabaci biotype non-B in Zhejiang province was Chinese native biologistic types. They were not attached more because of its minority parasitics plants and unseriously harmfulness. However, B. tabaci (Gennadius) biotype B (B. tabaci-B) has become the world's most damaging white fly pest species. It is proved that silverleaf is associated with B. tabaci-B. B. tabaci-B originated in the Middle East/Asia Minor region and is one of the most devastating tropical and sub-tropical agricultural pests, affecting the yield of a broad range of agricultural, fiber, vegetable and ornamental crops. Former researches mainly concentrated on the life history, host plants, population dynamics, host selectivity and emergency control of B. tabaci, as well as the symptomatic description of silverleaf, while we investigated the photosynthesis and chlorophyll fluorescence characteristic of the plants under disease adversity combined with the physiology content change in order to research the harmfulness of B. tabaci on Cucurbita pepo in different point of view, which give some proof to the mechanism of silverleaf. The results are as follows:1) The effects of B. tabaci B biotype and non-B bitotype on C. pepo were compared by investigating the photosynthesis, chlorophyll fluorescence characteristic and physiological and biochemistry indexes of C. pepo leaves. The results showed that squash leaves infected by B. tabaci-B became silvering obviously, while the appearance of leaves infected by B. tabaci non-B biotype had no significant difference with CK. The areas of leaves infected by B. tabaci-B were different with that of the CK significantly. Areas of leaves infected by B biotype were much smaller than that of CK. And there was no significant difference between biomass of non-B infected leaves and the control, especially in leaf length and leaf perimeter. Similarly, soluble protein contents and chlorophyll content of leaves infected by B. tabaci-B were smaller than that of CK and non-B. Measurements of photosynthesis indicated that Pn of leaves infected by B. tabaci non-B was lower than other treatments. Parameters of chlorophyll fluorescence showed that, effective yield of photochemical energy conversion (Yield), apparent electron transport rate (ETR), photochemical (qP) and non-photochemical (qN) quenching of leaves infected by B. tabaci-B was significantly lower than CK. Photosynthesis and chlorophyll fluorescence of leaves infected by B. tabaci non-B biotype was lower than CK which suggested that photosynthesis system was destroyed by non-B, although silvered leaf was not appeared.2) Results of the photosynthesis and chlorophyll fluorescence characteristic and leaf morphological characteristics showed that Net photosynthetic rate (Pn), chlorophyll fluorescence, chlorophyll content, soluble protein, soluble sugar and MDA decreased with the increased disease severity. There is significantly difference of fresh weight between the leaves of different disease severity. Fresh weight of 0 grade leaf was higher than others. The water ratio of 0 and 1 grade diseased leaf was significantly higher than the leaf under other treatments. The result of leaf morphological characteristics showed that pongy tissue thickness was loose and cell was decreased with increased disease severity. Spongy tissue thickness and the leaf thick ness increased significantly with the increase of disease severity, while percent of palisade tissue thickness decreased.3) The effects of B. tabaci-B density on squash demonstrated that squash with parasitic density of 10 and 20 had no symptom of silvering after 20 days, and squash with parasitic density of 30 and 50 appeared silvered after 10 and 7 days, respectively. After 3 days, chlorophyll fluororescence parameters of squash with parasitic density of 10,20 and 30 had no significant difference with those of CK, while F0 of squash with parasitic density of 50 were higher than that of the control, while Fv/Fm, Fm/F0, Fv/F0, ETR, qP and Yield were much lower than CK. With the increasing of parasitic time, parameters of chlorophyll fluorescence changed significantly. After 10 days, F0 of squash with parasitic density of 30 was significantly lower than that with parasitic density of 10 and CK while the Fm of that was higher. Fv/Fm of squash was decreased with the increasing of the density. After 20 days, F0 of squash with parasitic density of 10 was significantly lower than that with parasitic density of 50. Results of Fm showed that Fm was decreased with the increasing of the parasitic density. Results indicated that although parasitic density was lower, squash silverleaf can be induced by B. tabaci-B for longer time. More than 30 B. tabaci-B can induced squash silverleaf easily while it happened more difficult when parasitic density was fewer than 20.4) The result of CK on the silverleaf showed that foliar spray showed fast and higher efficacy than irrigation. After spraying 0.5g/L concentration solution, the efficacy can reached 91.14% and after spraying 0.3g/L and 0.5g/L concentration solution the efficacy can last 10 days. However, irrigation performed lower control efficacy. After irrigate the solution, the maximum control efficacy reached 80.14%. And it kept higher efficacy even in 20 days. The results of nosography showed that the silverleaf nosography was lowest under 0.3g/L concentration solution. The optimum spraying and irrigation concentration solution was 0.3g/L and its efficacy can kept 10 days and 20 days respectively. Efficacy of lower concentration solution may keep shorter tiem and higher concentration solution can increased the insect drug resistance, which were all not adviced.
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