Effect Of Microorganisms From Microsclerotiniasphere On Microsclerotia Of Verticillium Dahliae

Dynamics of microsclerotia of V.dahliae was investigated periodically at the same sites of cotton naturally infested fields. Results showed that population of microsclerotia appeared two peaks at the middle of June and the late of September. At the same time, it also was found that the population of microsclerotia from heavily infested field was significantly higher than that of microsclerotia from lightly infested field. The total population of microorganisms isolated from microsclerotiniasphere of V.dahliae were 7024 strains, among them 1840 strains were antagonists, the rate of antagonists was 26%; 5069 strains were bacteria, among them 1593 strains were antagonists, the rate of antagonists was 31%; 1955 strains were fungi, among them 247 strains were antagonists, the rate of antagonists was 13%. Among all the antagonists, 87% strains were bacteria, and only 13% strains were fungi. Population dynamics of MS were negatively correlated with dynamics of antagonistic bacterial rate and positively correlated with dynamics of antagonistic fungal rate from microsclerotiniasphere. It showed that the population dynamics of microsclerotia in cotton soil was mainly affected by antagonistic bacteria. The rate of antagonists from microsclerotiniasphere had certain effect on the population of microsclerotia, when the rate of antagonists was high, the population of microsclerotia was correspondingly low, when the rate of antagonists declined, the quantity of microsclerotia went up. The effect of antagonists on microsclerotia was mainly found during June to September.The results of dual culture test showed that many strains of antagonists isolated from microsclerotiniasphere inhibited the mycelia growth of V. dahliae to different degrees. The result of two-circle-method test showed that microsclerotia of inner circle was inhibitited completely by some antagonists, while germination and growth of other microsclerotia were delayed and inhibited. The results convinced that antagonists isolated from microsclerotiniasphere had stronger ability for inhabiting germination and growth of microsclerotia. The colony diameters of microsclerotia ofout circle were larger than that of inner circle. It indicated that antagonistic microorganisms inhibited germination and growth of microsclerotia through secreting antibiotics.Observed through with scan electronic microscope, the colonization on microsclerotia by 2 strains of antagonistic bacteria (424-31-6, 454-11-13) isolated from microsclerotiniasphere and 1 strain of antagonistic bacteria (NCD-2) isolated from rhizosphere had been investigated. The results showed that the colonization abilities of three strains of antagonistic bacteria on the surface of microsclerotia were different, the colonization ability of strain 424-31-6 isolated from microsclerotiniasphere was the best, and many bacteria could be found attached on the surface of microsclerotia, while colonization ability of strain NCD-2 isolated from rhizosphere was the poorest.An effective selective medium on detecting microsclerotia of V. dahliae from cotton soil was modified. The new modified selective medium-MSM had 4 advantages on detecting microsclerotia compared to the other two common selective media: (1) Modified MSM was obviously more effective than the other two media on detecting V. dahliae and gave nearly nine times higher counts than that of Medium A and three times higher counts than that of Medium B.(2) Modified MSM was also more effective on inhibiting growth of other fungi and bacteria , the microsclerotia colony size was bigger and clearer, and it was easy to be observed and to be detected.(3) The retrieving rate of microsclerotia by artificially inoculated in soil was very high, it reached up to 68.4%~93.9%.(4)the components of modified MSM was easy to get.