Effects Of Factors On Germination And Storage Survival Of Conidia Of Verticillium Lecanii

Verticillium lecanii is an important entomologic fungus that is compatible with sustainable agriculture in the 21st century. The effect of temperatures, nutrients and harvesting time on the germination and virulence of conidia of V. lecanii was examined in the laboratory. The effect of different temperatures and carriers on the storage and virulence of conidia of V. lecanii was also researched, the ultrastructure of conidia reared under different conditions.Germination of conidia was influenced by the type of nutrient solution used to rear the conidia. The germination rate and germ-length of conidia were examined on microscope slides. Conidia grown in a glucose solution had highest germination, reaching 95.48% after 16h, and displayed higher virulence to Trialeurodes vaporariorum, reaching 35.56% at a dose of 1× 106conidia/ml and 75.00% at a dose of 1× 108conidia/ml. Germination of conidia was also influenced by temperature and harvest time. Of the 4 temperatures were used in the experiment, 23℃ was found to give the highest germination of V. lecanii (the length of germ tube reached 50 um after 10h), which is consistent with previous studies. Germination was also highest with younger conidia cultured for 5ds or 15ds (89.76% and 94.98% respectively after 16h) than older conidia, cultured for 30ds, which had only 6.12% germination. Older conidia may have lesser germination because of the accumulation of products.excreted by the conidia themselves. The results of the bioassay against T. vaporariorum were similar to those for the germinations, the percentage infection of younger conidia was higher (31.59% and 40.00% at a dose of 1× 106conidia/ml, 83.40% and 74.44% at a dose of 7× 106conidia/ml than with older conidia (only 10.20% and 8.76% at doses of 1×106 conidia/ml and 7× 106 conidia/ml). While with conidia cultured on PDA media, it was the younger that gave the highest infections, with conidia cultured on rice it was older conidia, harvested at 20ds, that gave the highest infection. Further studies on the reasons for such differences are required.Storage of conidia of V. lecanii was affected by temperature and carrier type. Storage of conidia was better at lower temperatures. Those stored at 30℃ for 6 months had almost no germination and had very low virulence to whiteflies. Ultrastructure studies showed that conidia stored at 30℃ had most of their organelles disrupted. The type of carrier also affected the storage of conidia, with clay, charcoal and silica gel being the best. While silica gel might be expected to enhance survival by keeping the conidia dry, the mechanisms of enhanced survival for the other carriers is uncertain. These studies on V. lecanii are an important step in developing this pest as a method of biological control of vegetable pests.