| The entomopathogenic fungi, Verticillium lecanii(Zimm.) Viegas, is one of the most promising fungal species which is used to control greenhouse aphids and other sucking insect pests. In recent years, different commercial formulations have been registered in many countries. In order to develop mass production and application of this fungus in China, its biological characteristics, biochemical and physiological factors, diphasic fermentation, conidium drying techniques, nutrient metabolism during storage, and field trial against greenhouse aphids. were studied in this thesis.Biological characters of 11 strains of V. lecanii isolated from different regions were investigated. At the same time, Bioassay was carried out against the 2~3th instar Myzus persicae larvae with the 11 strains. The most virulent strain was screened out after evaluated by the indices of mortality, infection rate and the median lethal time (LT50). The result showed that VL07 was the most virulent strain which caused mortality soon after 3 days, followed by VL18. The mortality reached 100% and 93.83%, with infection rate at 93.0% and 84.44%, LT50 at 3.30d and 4.02d, respectively. The optimum temperature for V. lecanii infection on M. persicae was 25℃. LD50 of VL07 reached 533 conidia per aphid.The mycelial biomass and the production of conidia of V. lecanii were studied at different temperatures. The result showed that all strains grew at 10℃ to 30℃, but 25℃ was the optimum temperature for mycelium growth and conidium production. The mycelia biomass of VL07, VL09 and VL18 was compazatively high at 25℃ after 14d. These diameters of colonies reached 4.69cm, 4.72cm and 4.98cm, respectively, obviously higher than other strains. The differentce of conidia production was significant between different strains at different temperature. For VL07, VL18, conidia production reached 5.83 X 109/cm2 and 4.64 X 109/cm2. The result of germination test of conidia showed that the conidia germinated rapidly and uniformly. The germination rates all reached 100% at RH 100%. The germination rates of all strains except for VL07, VL18 declined to 20% as RHdecreased down to below 75%, and grew very slowly.Some non-hazard insecticides were tested for their effection on conidial germina -tion of V. lecanii. The result showed that they made some effect at high concentration, but the effect was hight at low concentration. 25% flowable colloid of diflubenzuron induced little effect on the germination of the virulent strain VL07. The inhibition rate reached only 1.66% at a concentration of 2 ×104 times.Some physiological and biochemical factors of V. lecanii were tested. The result showed that the total amount of esterases and the frontier band esterase number were significantly correlated to the virulence, with r=0.9198 and r=0.8820, respectively, and the virulence was poorly correlated to extracellular protease production level and oxalic acid production level.A series experiments were conducted including screening of carbon and nitrogen resources, inorganic salt, initial value of pH, and initial inoculum by an orthogonal test. The optimum liquid medium for industrial fermentation production of the strain VL07 was determined by comparison of biomass of dry mycelia. Its main components were as follows: soybean powder 4%, white sugar 4%, KH2PO4 0.02%, MgSO4 . 7H2O 0.01%, FeSO4 . 7H2O 0.05%, Vb2 0.05%, Vc 0.05%, with pH value of 6.89. The initial inoculum ranged from 10% to 15%. 21.25mg/ml dry mycelial biomass was acquired after 72h cultivation with inoculum at 3.69-5.50mg/ml. The solid fermentation medium was screened for industrial production of strain VL07 by a L9 (34) orthogonal experiment. The optimum medium determined included bran 42%, rice shell 28%, maize powder 20% and soybean powder 10%. As the initial ratio of water content in the medium was 50%, conidiation reached the highest at 1.05 × 1010 conidia per gram.In an attempt to develop a drying method of the conidia of V. lecanii produced in diphasic fermentation, several drying methods... |
