Preliminary Study On Biocontrol Bacteria Paenibacillus Polymyxa Y25 Against Green Mould Of Citrus

Nowdays, people have paid more and more attention to health and environment protection. People also paid increasingly attention to the chemical fungicide which caused a series of problems to the nature. So it is becoming more and more urgent to find a kind of environmentally friendly way that can be alternative to chemical fungicide to prevent and control of fruit decay. As a kind of emerging technology, biological control which conforms to the concept of sustainable development has attracted many researchers’ attention. In this research, it found that Y25 had obvious inhibitory effect to Penicillium digitatum, which showed a good application prospect in the prevention of green mildew of citrus fruits. The main results are as follows:1.Our laboratory separated and obtained a kind of bacteria from the soil of citrus root which had antagonistic effect on citrus green mildew. After morphological identification, physiological and biochemical identification and 16S rDNA sequence homology analysis, it was proved to belong to Paenibacillus polymyxa, and we named it strain Y25.2. Using three types of culture medium, which respectively were LB culture, beef extract peptone and YEPD culture, to cultivate Paenibacillus polymyxa Y25 and study the inhibitory effect of its fermentation broth’s active substance on Penicillium digitatum. The results showed that in the LB culture the inhibitory effect was the best. After using uniform design test to optimize its fermentation medium, we got the best fermentation culture mediun formula:yeast power 5.7g/L, peptone 10.8g/L, NaCl 4.8g, and the best fermentation condition:fermentention time 48h, inoculum size 1%, fermentation temperature 32℃, Liquid loading quantity 50mL/250mL, the initial pH 7.5, rotate speed 180r/min.3.Using plate confrontation method and oxford cup method to test the inhibitory effect of 6 plants pathogenic fungi and 5 bacteria. The result showed that strain Y25 had good inhibitory effect on 3 plants pathogenic fungi(Fusarium oxysporum, Rhizoctonia solani and Geotrichum candidum) and 2 bacteria(Staphyloccocus aureus and Escherichia coli). So it suggests that the spectrum antibiotic of strain Y25 has certain broad spectrum properties.4. We preliminary studied the effect on the growth of Penicillium digitatum inhibited by Y25’s fermention broth. It showed that Y25’s fermention broth could effectively restrain the spore’s germimation. Compared to the control group, the hyphae in the experimental group appeared to melt and fracture, and its branches twisted. It indicated that Y25’s fermentation broth has good inhibitory effect on hyphae’s growth and spore’s germimation of penicillium digitatum.