The Colonization Of Endophytic Bacteria Strain BS-2 And TB2 In Lychnee And The Control Effects To Downy Mildew Disease

This paper reported the colonization dynamics in the different tissue sites of Lychnee by endogenous Bacillus subtilis BS-2 strain and Bacillus amyloliquefaciens TB2 strain, and their control effects and mechanisms on downy mildew disease of harvest fruit.The results showed that the endophytic bacteria could colonize in Lychnee leaves, flowers, unmature fruit and harvest fruit and could propagate in the host tissues. Moreover, with the changes of the seasons and the plant growth cycle, the colonization situation of the endophytic bacteria in Lychnee leaves would also be changed, such as the colonization time in leaves significantly longer in spring than that in fall. The colonization quantity of strain TB2 in fall was less than that in spring. The colonization conditions were also different in the different tissue sites of the host. After inoculation for 37d the target bacteria still could be isolated from Lychnee leaves, but could not be isolated from the flowers after inoculation for 15d. .In spring the most colonization quantities of strains BS-2 and TB2 in leaves were 5.64×104 cfu/g FW and 1.21×105 cfu/g FW respectively, but in fall they were 5.63×104 cfu/g FW and 3.36×104 cfu/g FW separately . In flowers they were only 1.18×103 cfu/g FW and 0.31×103 cfu/g FW respectively.Endophytic bacteria had a good control effect on Lychnee downy mildew disease. After inoculating for 3d, the control effects were 77.77 - 86.20 % on Lychnee fruit (cultivar No.1 Luidong),and for 4d,the control effects were 31.58-67.15% (cultivar Yuanhong).The test results of control mechanisms by the two bacterial strains showed as follows. (1)The bacteria could actively invaded the skin of fruit and colonized there. The colonization quantity had a positive correlation with control effect. (2)The bacteria could increase the activity of protective enzymes and retard the membrane lipid peroxidation of fruit skin. When the fruit was treated with strains BS-2 and TB2,when treated for 4d the catalase enzyme (CAT)in the fruit pericarp was 61.56%and 46.35% higher than control respectively, and after treating 6d the activity of superoxide dismutase (SOD) was 297.43% and 312.02% higher than control separately, but the malondialdehyde (MDA) and the production rate of superoxide radical (O2-) were lower. After treating 6d, the production rate of superoxide radical (O2-) was 21.52% and 20.14% lower than control respectively.(3)The bacteria could induce the pathogenesis-related proteins in Lychnee tissues and raise the activities ofβ-1,3-glucanase and chitinase. So that they could increase resistence of the host to pathogens. When the Lychnee ftuit was tereated by strians BS-2 and TB2 for 5d and 6d, the activity of chitinase in the fruit pericarp was 46.52%,172.73% and 30.76%,224.24% higher than control respectively, moreover the activity ofβ-1,3-glucanase also was 60.97%,158.34% and 70.73%,175.00% higher than control separately.