Study On Screening Of Highly Virulent Fungal Strain Against Delia Antigua And Its Biological Characteristic

Delia Antigua is a worldwide pest which is harmful to the liliaceous vegetable, such as onions, garlic, leeks, spring onion and green chives. Most of time the pests were found in the soil and the period of pest damage is very long., which was well recognized as a pest difficult to control at home and abroad. Because of its operating quickly, the diversity of pest controlling methods, insecticidal spectrum and other advantages, the chemical pesticides were widely used in agriculture in the control of D. Antigua. However, there were also a long residual period, poor selectivity, environmental pollution and resistance to pests in chemical pesticides. With the enhancement of people’s awareness of environmental protection, as well as a variety of agricultural products, pesticide pollution problems, the use of chemical pesticides are limited. The biological control technology of pests has become the focus of the study because of its strong specificity, easy to produce resistance to pests, safety to human and animal and other advantages. In recent years, a variety of fungal pesticides have appeared and biological pesticides are continuously being developed and utilized, such as Beauveria bassiana, Metarhizium. However, highly virulent fungal strains against D. Antigua were very small.The purpose of this study were screening for highly virulent strains against D. Antigua using the existing microbial resources in the laboratory. The most suitable culture conditions and nutritional requirements of this strain in growth and spore production were studied. In the laboratory, the prevention of the strain against D. Antigua was preliminarily studied, which provided basic data for the large-scale fermentation and application in the field of the fungus.The main contents of the study included screening for high virulence fungi strains against D. Antigua, the virulence of the strains screened by the study against D. Antigua in the different periods. At the same time, the biological characteristics of the strain were studied, and its taxonomic status was determined. The most suitable culture conditions, nutritional requirements, and the composition of its culture were studied. The biological control effect of this strain was studied by pot experiment. The main research results were as follows:(1) Using various strains in the laboratory has successfully screened a high virulent strain CQBb119 against D. Antigua. Combining with the morphological characteristics, biological characteristics and the results of ITS sequence alignment, the strain was identified as Beauveria bassiana.(2) The virulence of B. bassiana CQBb119 against D. Antigua in different period using impregnation method. The results showed that the strain had a high toxicity against larvae, adults, pupae of D. Antigua.When treated with 1*109 spores/mL concentration of the spore suspension, the cumulative mortality rate of larvae, adults, pupae of reached 87.78%, 46.67% and 32.31% respectively. The LT50 of the larvae was 4.94 d and it could be used as the potential strains for killing D. Antigua.(3) The most suitable pH value was 6 using single factor experiment of CQBb119 strain in solid plates and the most suitable temperature was 25℃. The best carbon sources, nitrogen sources, trace elements were maltose, yeast powder, Mn2+. The orthogonal experiment was used to find the best culture medium and the cost was considered. The best medium composition of CQBb119 in solid culture was rice 10.0 g/L, potassium nitrate 2.5 g/L, calcium chloride 0.01 g/L, yeast 5.0 g/L, potassium chloride 0.5 g/L, magnesium sulfate heptahydrate 0.5 g/L, potassium dihydrogen phosphate 0.5 g/L, disodium hydrogen phosphate 0.65 g/L, agar 20.0 g/L.(4) Pot experiment results showed that using CQBb119 strain treatment could effectively control D. Antigua on the onion, leek and spring onion. The larvae reduction of the three host plants can reach more than 60% which indicated that the CQBb119 strains could play a good control effect on different host plants, and we can use CQBb119 strain to control D. Antigua.Conclusion: This experiment successfully screened B. bassiana strain CQBb119 with high virulence against D. Antigua. The toxicity of the strains against D. Antigua in different periods were studied. We explored the culture characteristics of the strain and preliminary studied its prevention effect. The results showed that the CQBb119 strain had good control effect on D. Antigua in different periods. The culture of this strain was good and the control effect was good in pot experiment. The strain could be used as a biological control strain in the field.