Screening And Action Mechanism Of Antagonists From Microsclerotiniasphere Of Verticillium Dahliae

Germination of microsclerotia stored on the soil surface and 10 cm deep in the soil was monitored periodically in this paper. At the same time. microorganisms of microsclerotiniasphere were isolated. The result indicated that germination of microsclerotia declined after 120 days storage. Germination of microsclerotia on the soil surface declined steadily from 95.19% to 65.74%. While germination of microsclerotia stored 10cm deep in the soil was declined unsteadily. More kinds of microorganisms from microsclerotiniasphere in the soil were isolated. 453 strains of microorganisms were isolated from microsclerotiniasphere by direct isolation method. Among them 75.71% strains isolated were bacteria. The number of microorganisms isolated was different at different isolating time. The population of microorganisms was the lowest in July and increased up to the highest in Sept. It decreased again after Sept.The result of dual culture showed that 42 strains of microorganisms inhibited the growth of Verticillium dahliae in the different degrees, inhabiting rates were from 4.55% to 77.27%. The result of two-circle-method showed that some microsclerotia of inner circle was killed or inhibitited completely, while germination of other microsclerotia were delayed or their growth were inhibited, the inhibiting rates were from 22.5% to 100%. This result convinced that microorganisms isolated from microsclerotiniasphere had stronger ability for inhabiting germination and growth of microsclerotia. The colony diameters of microsclerotia of out circle were larger than that of inner circle. It indicated that antagonistic microorganisms inhibited germination and growth of microsclerotia by secreting antibiotics.Action mechanism of antagonistic bacteria were studied in this experiment. The result showed that the optium culture time of NCD-2 was108 hours, and culture condition was weak alkalescence. The optium culture time for secreting antibiotics was 108 hours to 120 hours. Protein and nucleic acid were detected by solvent extraction and DU600 testing. Using general method of protein extraction, some protein admixtures were extracted from the liquid culture of NCD-2. Dual culture testing showed that growth of Verticillium dahlias was inhibited by the admixture. Another testing showed that the protein mixture extracted was heat tolerant. The production abilities of p-l,3-Glucanase and chitinase of 10 strains of antagonistic bacteria were tested. The result showed that only strains CS-25 and NCD-25 can produce [3-1,3- Glucanase. The digestion diameter were 37.25mm and 30.00mm, respectively, after 7 days. No tested strains can produce chitinase.Colonization and transmission of antagonist C-28 on surface of cotton seed and inside cotton plants were studied by using the mutant strain of C-28 resistant to rifampicin on water agar media, plastic pots and rootrainers under greenhouse condition. On water agar media and in the plastic pot. C-28 not only colonized on the surface of cotton seed, but also colonized on the different sections of cotton radicles with the growth of cotton radicles. Population density of C-28 on the radicle decreased from the radix to the tip of cotton root. In greenhouse experiment, results showed that the bacterial strain C-28 could transmit up and down along the stem and root inside cotton plant. Within 28 days after inoculation of C-28 by injection on the stem, population density of C-28 in the cotton plant increased along in the root, stem and leaf. On the 28th day after inoculation, the isolation percentage of C-28 inside the root, stem and leaf were 45%. 72.5% and 90%. respectively.The result of bioassay in greenhouse showed that the biocontrol effect of bacterial strains ICB-18. NCD-2, CS-25 and CS-27 were 81.4%. 77.0%. 75.7 % and 72.3%, respectively. Disease index of cotton Verticillium wilt were significantly reduced by fungalstrains VL-1 and VL-2 in the greenhouse. The result of bioassay in the field showed that control effect of bacterial strain NCD-2 was 92.6% and control ef...