| Peach Fruit Moth, Carposina sasakii (Matsmura) is an important fruit pest in north of China. The chemical pesticides have not work well for control this pest because the larvae of the insect bored inside fruit or under the surface soil in a majority of life time. Applying entomogenous fungi in biological control against Carposina sasakii is significant. The purpose of this study is to select some higher virulent pathogens for this pest biological control. The content are as follows, (1) The fungual isolation, morphological observation and identification. (2) Strain filtration for control C. sasakii larvae with high virulent and with strong adaptability to the northern climate with lower temperature and humidity.in north of China. (3) The role of the extracellular enzyme of the fungus BbTST05 during infecting the host insect.Results:(1) The five strains of entomopathogenic fungi were obtained by isolating from the naturally infected larvae of Carposina sasakii (Matsmura). These strains were designated numbers as NO.TSL01, NO.TSL02, NO.TSL03, No.TSL04 and No.TST05 and they are proved to be the pathogens of Carposina sasakii larvae by re-inoculation test on the host insect. The culture character and morphological characteristics observation showed that the strains TSL01, TSL03 and TSL04 grew white mycelium, formed a big colony and could secrete some snuffcolored or orchid pigment. They produced two kinds of conidiophores, macroconidia and microconidia, in which, the macroconidia were crescent or falciform with separators, while the microconidia were oblong or kidney-shaped and grew as cephalosporium. Their hyphae also possessed separators. The strain TSL02 possessed a relatively small colony and unconspicuous pigment. Its conidiophores were shaped as columniform or spindly and arranged in a chain. The peduncles of the conidiophores shaped in a "Y" form. The TST05 had a smaller colony with white myceliume at the early and yellow myceliume at the later during growth. Its conidiophores were yellow and globoid with tubular conidiophore peduncle. According to these characteristics, the strain TSL01, TSL03 and TSL04 were identified to the species Fusarium oxysporum in the genus Fusarium. The strain TSL02 was identified to the species Paecilomyces farinosus in the genus Paecilomyces. The strain TST05 was identified to the species Beauveria bassiana in the gens Beauveria. Of which, two species, Paecilomyces farinosus and Fusarium oxysporum are new pathogens of C. sasakii(2) Some important characteristics of the isolated five strains were examined on their biology, ecological adaptability, virulence and extracellular enzyme. In comparison, BbTST05 and PfTSL02 caused the highest host mortality that reached 89.28% and 72.22%, respectively. Mealwhile, their median lethal times (LT50) were 5.48d and 7.09d, respectively, which were the smallest. The two strains produced more spores that germinated in a higher rate under the experiment conditions with different temperature and humidity. The spore numbers produced by the two strains were as 6 to 11 times as that produced by the three strains of Fusarium oxysporum. Their spore germination rate were above 93%; Even under the condition of 15℃arid RH 30%, the two strains still kept a higher level in spore production and spore germination rate. BbTST05's spore production was the biggest,1.93×108spore /cm2, while PfTSL02 followed to 1.63×108spore/cm2. Spore germination rate of the two strains all reached 30% or above.To evaluate the virulence of the five strains the fungal extracellular enzymes activity were comparison, BbTST05 showed the highest activity and the earliest emergence of the maximum activities of the subtilisin-like protease, chitinase and lipase, while PfTSL02 was ranked on the second place. The relationship between the host insect mortality infected by the five strains and the enzymatic activities of the subtilisin-like protease, chitinase and lipase was positive lineal relativity and their coefficients were 0.9213, 0.8922,0.8008, respectively. Theses results provide some significant evidence for developing theses pathogenic fungi as an effective agent in the biological control of C. sasakii.At last, two strains Paecilomyces farinosus PfTSL02 and Beauveria bassiana BbTST05 were selected as higher virulent pathogens for C. sasakii biological control.(3) The strain BbTST05 was cultured on the culture mediun prepared with cuticle material of C. sasakii larvae. The results showed that the subtilisin-like protease activity kept rising continuously during the first 3 days and the activity values were higher than that on the late 4 days. On the 3rd day, the protease activity reached the maximum value 12.43±0.69U/g, then it decreased. Meanwhile, the chitinase activity raised fast during the first 3 days, then it kept rise slowly in the last 4 days, finally, its activity reached the maximum value,1.467±0.108U/g at 8th day. It indicated that the protease of the fungus played an important role in the early phase in decomposing protein within the insect cuticle. With the protein degrading, the chitinase was induced and chitin in the cuticle was subsequently decomposed. The lipase activity gradually increased in the first 6 days and the maximum value 2.654±0.163U/g emerged on the 6th day, then the activity decreased. It indicated that the fungal lipase could play a better role on the wax layer decomposition in the early phase than in the latter phase during BbTST05 infected the insect. By culturing this strain on the insect material medium, as the culture time goes by, the content of trehalose in the medium was continuously reduced, and its reduction rates was greater in the first 3 days. At the same time, the trehalase activity in the medium was rise at the first 2 days, and the maximum value was 3.622±0.185mU/mg, after that the activity decreased. It suggested that the strain BbTST05 was albe to produce trehalase to decompose trehalose in the insect body as the nutrition for its development during the insect infection. This result revealed the pathogenic mechanism of the Beauveria bassiana BbTST05 infecting C. sasakii larvae based on the role of extracellular enzyme and trehalase. |
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