Identification And Antagonism To Fusarium Oxysporum F. Sp. Vasinfectum And Control On Cotton Fusarium Wilt Of Actinomycetes K5

Although disease-resistant varieties of cotton were planted in many areas, Fusarium wilt of cotton occurred widely and severely. This paper studied a Streptomyces which has antagonism against Fusarium oxysporum f. sp. vasinfectum in order to provide an effective way for integrated management of Fusarium wilt of cotton.207 strains of actinomycetes were isolated from some soil samples collected from various areas with different ecology conditions. From them 32 strains of actinomycetes with antagonism against many pathogens such as F. oxysporum f. sp. vasinfectum were obtained by the inhibition zone method, which accounted for 15.46% of total strains. K5 strain exhibited the strongest antagonism against F. oxysporum f. sp. vasinfectum among all strains and the size of inhibition zone to pathogen was 8mm. Meanwhile, it also showed antagonistic effect on some other pathogenic fungi, such as Pyricularia grisea et al.The better culture conditons for K5 to exert its antagonism were listed as follows: The strains was cultured for 7 days at 28-31℃in the oybean and glucose medium, in which pH value was 6.5-7.0, 10% inoculation amount, and shaking at 120r/min.The culture filtrate of K5 revealed obvious damage and inhibitory effects on the mycelial morphology and growth of F. oxysporum f. sp. vasinfectum. When the pathogen was cultured in amended medium with K5'culture filtrate, it was observed by microscope that the hypha became abnormal, cell wall was destroied, which could lead to leakage protoplasm from the wound and even lysis of hypha . The mycelium cultured for 9h in above amended medium present non-normal, and for 17 hours the cells of mycelium were destroyed. There was some difference in mycelium treated by culture filtrate with different concentration. The hyphal cell lysis occurred soon at the high concentration of the culture filtrate. When the culture filtrate was diluted 100 times, the culture filtrate could also destroy the hypha. The culture filtrate could inhibit the growth of hypha and sporulation, the rates of inhibition were 88.41% and 77.45%, respectively; the inhibitory rates to conidial germination and growth of germ-tube were 98.62% and 49.72%, respectively. As the dilution of the filtrate was increased, the inhibitory effect on pathogen of the filtrate could decline. Although the culture filtrate was diluted 100 times, it still showed inhibition to the growth of hypha, sporulation and conidial germination.The results of pot tests showed that the control effect of the ferment filtration of K5 on seedling Fusarium wilt of cotton was 46.50%, which resembled those of chemical fungicide carbendazim. Not only K5 had no any damage on cotton seedlings, but also it could promote the cottons'growth, the seedling height and weight were significantly higher than that of control plants.K5 could produce substrate mycelia and aerial mycelia. The aerial mycelia formed catenarian spore-filaments, the shape of spore was oval or round and the surface of spore was smooth. K5 grew well in Gause's No.1 medium, the color of aerial mycelia was grey-red and the color of substrate mycelia was filemot, and there was no soluble pigment. K5 could well make good use of maltose, galactose, the ability of using glucose and rhamnose was moderate while it could not use sucrose, arabinose and fructose. Some physiology phenomena of the strain such as gelatin liquefaction, milk peptonization, starch hydrolysis, and melanin-like substance production could be observed. Its characteristics of morphology, physiology and biochemics were similar to those of Streptomyces roseochromogenus. K5's 16S rDNA sequences analysis were achieved, the overall similarity value between K5 and S. Roseochromogenus was 99.63% and the hereditary distance was 12.4. According to above experiment, the strain K5 was identified to be S. roseochromogenus.