On Production Conditions,Physi-Chemical Characteristics,Mechanism And Disease Prevention Of Bacillus B₁ And B₂ Antifungal Substances

Screen of the antagonistic bacteria and identification of the potential biocontrol strains. 110 bacteria strains with antagonistic activity against Fusarium . oxysporwn f.sp. psi. in vitro were obtained through massive isolation from 174 samples collected from Lanzhou . Yuzhong Dingxi .lsolation from vegetable soil indicated that root surface and rizosphere soil were the best positions to isolate strongly antagonistic bacteria.Strongly .antagonistic bacteria was 10.9% from wide distribution antagonistic bacteria. B1 and B2 isolated from the root surface of tomato plant and rizosphere of hot pepper plant, respectively~ were finally selected as the biocontrol agents,and both were identified as Bacillus spp.. Optimum conditions for B1 and B2 to produce antibiotic substances. Cultures ofB1 grown in 4OmL D-liquid tnedium(pH=8.0,lSOmL conical flasks) at 27? C in continuous lightness for 72 hours produced high antagonistic cell-free filtrates by the means of centrifugation. Such a filtrates were also obtained after centrifugation from cultures of B2 grown in the same manner( pH6.0) as B I for 48hours,but shaked (1 OOr/min). The Antagonistic spectrum and efficiency of cell-free filtrates of B1 and B2 . Dose responses of two cell-free filtrates against the pathogen both were 1000 and their EC~ were 3.30/o(B1)and 2.0% (B2) cell-free filtrates. Of the total 13 plant pathogenic fungi species tested,5 ones were seriously inhibited in liner growth, inhabiting rates ranged from 93% to 99%,was 38.5 percent of the total pathogenic fungi tested.6 ones were moderately inhibited with a inhibiting rate over 70%,was 46.2 percent of the total. Inhibiting rate against F. solani f.sp. pisi. was the worst,only 32%.It showed that B1 and B2 had a broad spectrum and high antagonistic activity against pathogenic fungi tested. 41 Physi-chemical characteristics and stability of antifungal substances produced by B1 and B, The results showed that continuous culturing ,even up to 12 times, of the two strains had no negative influences on inhibitory activity of their antifungal substances against the pathogen at w 0.05 in the pairing culturing .Their cell-free filtrates after heating at 70條oOt for 60 min,almost had no change in their inhibitory activities ,but decreased significantly after autoclaving at 121 t for 30min,however,the cell-free filtrates of B2 was more tolerant to autoclaving than that of ~ .The antagonistic substances were more tolerant to acid situation and autoclaving in acid situation than alkaline one. The microscopic characteristics of antagonism of B~ and B2 against F. oxysporum f.sp. pisi. The results of the simultaneous and dis-simultaneous pairing culturing implied indirectly that there were competition action of colonizing site existed between antagonistic bacteria and pathogenic fungus. After treatment with the cell-free filtrates of ~ or B2,the colony appearently became white from grey,the gas hypha increased and entangled into the groups.Microscopic observation discovered that the characteristic micro-phenomena of the antagonism were as follows: malformed and concentration of cytoplasm in hyphal and spores, abnormal germination or failure to germination in spores,inhibited apical growth in hyphal because of lots of bursicles in top of them,and lyses of spores and hyphal. Purification and molecular weight of antifungal protein...