Study On The Factors Of Affecting The Germination Of Bacillus Thuringiensis Spores

Strains of Bacillus thuringiensis(Bt) HB-2 and BtHBF-1 were isolated in Biological Control Laboratory of Institute of Plant Protection, Hebei Agricultural and Forestry Sciences, and strain HD-1 was obtained from Wuhan Bt Research Institute. The morphology, biochemical properties and insecticidal efficiency of the HD-1, HB-2 and HBF-1 strains, especially the factors affecting Bt spore germination were studied.The results indicated that HB-2 was a highly effective strain against Lepidoptera insects, especially against Spodoptera exigua and Helicoverpa armigera, and HBF-1 was a highly effective strain against Scarabaeidea insects.There are many factors that can affect spores germination. The influence of different physical, chemical and nutritional factors on Bt spore germination were evaluated under the laboratory condition. The physical factors tested include temperature, inoculum, aeration and ultraviolet; the chemical factors tested include pH and osmotic pressure; the nutritional factors tested include twenty amino acids.The results showed that when the suspension of HD-1 > HB-2 and HBF-1 strains were treated by 70, 75 and 80℃ for 15 min, germination rate of spores beyond 98%; while treated by 100℃ for 15min, the germination rate was lower than 20%. When spores were treated with different temperature for different time, the germination rate was different. Under 60℃ for 30 min, the rate of germination was the highest. While treated higher than 70℃ for 15 min, the rate of germination was the highest. When the suspension of HD-1, HB-2 and HBF-1 strains were treated with high temperature and low temperature alternatively, the rate of germination was different significantly. The 1% of inoculum was optimal concentration in a flask with 30ml medium. When treated with ultraviolet, the rate of germination declined, but the germination was quicker than untreated.The initial pH value range for germination of HD-1, HB-2 and HBF-1 strains was 5.5-8.5, 6.0-8.5 and 6.5~8.5 respectively. The osmotic pressure, which could be changed by adjusting the concentration of sodium chloride, was also a factor affecting spores germination. The results showed that the HB-2, HD-1 and HBF-1 strains had the highest germination rate with the sodium chloride amounts of 0.7%> 1.0% and 0.9% respectively.By the orthogonal test, the incubation conditions for high rate of germination were selected. The optimal incubation conditions for spore germination were selected by the orthogonal test Lg (34) . Based on the results from the orthogonal test, the temperature was the key factor for spores germination of HD-1 and HBF-1, and initial pH was for HB-2.Finally, the author studied the effects of amino acid on the germination of Bt spores. The spores of three Bt strains could not germinate in BM medium, but they germinated after adding amino acids to the medium. Alanine was an obligate amino acid for HD-1 and HB-2 spore germination, while valine was an obligate amino acid for HBF-1. The results also showed the germination rate of spores were different in different media of amino acid combination.