Factors affecting application of Verticillim lecanii for insect control

• Main Authors: Yung-Sheng Tsai, 蔡勇勝
• Other Authors: Wen-Shi Wu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/48834641677644791750

博士 === 國立臺灣大學 === 植物病理與微生物學研究所 === 92 === The optimal temperature for mycelial growth of various Verticillium lecanii isolates was 24�aC except 20�aC for isolate F168. V. lecanii isolates were sensitive to higher temperature. Most isolates could not grow at 32�aC, but they grew well between 16~28�aC. On water agar, V. lecanii isolate F168 germinated significantly slower than other isolates which germination rate reached to 98% after 16 hr of incubation at 24�aC. There was hundred-fold difference in the amount of spore production among tested isolates when they were incubated at 24�aC for 9 days. APIZYM test revealed that most isolates had alkaline phosphatase, arylamidase, esterase/lipase, leucine N-acetyl-��-glucosaminidase, acid phosphatase, ��-glucosidase, ��-galactosidase, naphthol-AS-BI-phosphohydrolase activity. Each isolate showed different chitinase activity on the colloidal chitin-amended medium. Molecular techniques such as AFLP and RAPD of genomic DNA, RFLP of IGS and 18S rRNA and PCR of ITS were used to analyze the relationships among different V. lecanii isolates. The dendrogram produced from the RAPD data in this study divided the 10 tested isolates into 2 groups. Four local isolates were grouped in the same cluster. The AFLP analysis method provided a lot of information on polymorphism between isolates. AFLP and RAPD techniques could not differentiate between Acremonium charticola from V. lecanii isolates. The V. lecanii isolates could not be distinguished by IGS-RFLP and ITS sequence. Conidia of V. lecanii isolates germinated when the relative humidity was more than 94%. Conidial germination was affected by transient desiccation and high temperature. Conidia of V. lecanii isolates germinated and penetrated directly into Myzus persicae without producing appresorium. Most conidia could be found around setae. Bioassays in laboratory showed that V. lecanii at a concentration of 1x 107 conidia /ml were highly virulent to Lipaphis erysimi, Myzus persicae and Thrips palmi. It caused 60% mortality of T. palmi after 5 days of treatment. The mortality of L. erysimi was 90% when F091, F096 F168, VL578 or VL615 was treated. In contrast, V. lecanii was not pathogenic to A. gossypii. A strong deleterious effect of UV irradiations on conidial germination of V. lecanii isolates was observed. Exposure to UV-B irradiation (310 nm, 540 μW cm-2) or UV-C (254 nm, 120 μW cm-2) for 2 minutes postponed the germination of three isolates tested (F096, VL159 and VL578). This delayed effect did not occur when conidia exposed under UV-A irradiation (360 nm, 540 μW cm-2) for 90 minutes. A UV-induced dimer, cyclobutane pyrimidine dimer could be detected by using T4 endonuclease digestion method. Among 10 UV protectants tested, uric acid, folic acid, active carbon and xanthine provided significantly UV-protective effect for V. lecanii. Active carbon was the best UV protectant among them. Molasses or plumbago also possessed the UV-protective effect for the conidia of V. lecanii. Increasing the concentration of molasses in the conidial suspension enhanced the protective effect. The feasibility of V. lecanii isolates to control aphid on cabbage was investigated. Field trial showed that weekly spray of indigenous V. lecanii isolates could control aphid when the population density was below 20 aphids per leaf.