| Banana fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foe) is a destructive soil-born fungal disease. Till now, the banana fusarium wilt was distributed in the major banana production areas of Guangdong, Hainan, Fujian, Guangxi, Yunnan, Taiwang provinces of China. It brought a great threat to banana production in China for high infection, dissemination speed and difficult controlled. Based on the potting soil and field soil samples, the correlation among the toxin from Foe, the infection degrades of banana plants and soil microorganisms amount were analysed. Based on former studies on biocontrol bacterial strains and inactivation of toxin of the tropical fruit tree diseases research group of Environment and Plant Protection Institute, Chinese Academy of Tropical Agriculture Sciences, combining with the aqueous extracts from different parts of plants against Foe, tests were conducted to explore the ecological control measures of banana fusarium wilt targeting on pathogenic toxin. The results of the study are summarized as follows:(1) Pot experiments were carried out to study the effects of spore suspension from Foe on its toxin, soil microorganisms amount and the banana plants disease development. The results indicated that spore suspension concentration and its toxin have a strong influence on the numbers of cultured microorganism and the severity of disease. The amount of spore showed positive correlation with toxin and soil fungus, but negative with soil bacteria and actinomyces. Test data showed that there was clear difference between Foe and the numbers of culturable bacteria, actinomyces and fungi. With more inoculation amount, the quantity of Foe and soil fungus increased but soil bacteria and actinomyces decreased. There was clear difference of large dose of spore suspension concentration (1×104cfu/g soil and1×105cfu/g soil) in45d, but was a few differences after45d. There are no differences between disease index and toxin after52d. High concentrations of toxin from Foe decreased significantly the soil bacteria and actinomyces quantity and made banana fusarium wilt become serious.(2) To investigate the relationship between Foe toxin and the quantity of microbe, soil samples were collected from the infection degrades of banana plants. The results indicated that there was clear difference among Foe toxin, the number of Foe and culturable microbe. With increasing of susceptible level of banana plants, disease toxin (FA) and Foe increased and bacteria and actinomyces declined. Foe toxin (FA) extracted from field soil increased positively with Foc and fungus,,but negatively with bacteria and actinomyces.Foc toxin destroied the balance of ecological environment and the banana wilt disease became serious. (3) The inhibitory effects of aqueous extracts from different parts of20plants were studied against Foc based on the methods of mycelial growth and spore germination. The results showed that all plants tested had suppressing effects on the pathogen in some degree, especially, sunflower and lettuces exhibited the better antifungal properties. Among them, crude extracts from the entire sunflowers, above ground parts of sunflowers and the sunflower roots exhibited the better antifungal properties at87.0%,51.0%and88.5%at a concentration of200ml/L, and crude extracts from the entire lettuces, above ground parts of lettuces and the lettuces roots exhibited the best antifungal properties at83.9%,36.4%and75.5%at a concentration of200ml/L, respectively. The results had no significant difference compared with Chinese leek. When the extracts is mixed with equal volume spore suspension, tests on spore germination indicated that sunflower, lettuces, wormwood,mustard and Chinese leek extracts had best inhabitation of81.19%,74.78%,70.66%,64.09%,98.49%against Foc, respectively.(4) The suppressive and control effect of lettuces extracts, sunflower extracts, TY strain, DF strain and compounds of toxin inactivation (Fe2SO4ˇ7H2O+EDTAˇNa2) on banana fusarium wilt was studies in greenhouse. The results showed toxin of Foc was inhibited by five experimental treatments, among them the inhibitory rates of sunflower and lettuces were the best, toxin reduced37.22?g/g soil and35.09?g/g soil by average. All the treatments had a strong influence on the number of cultured microorganism, which decreased the numbers of Foc, added the numbers of culturable bacteria, actinomyces and fungi, especially the added quantity of bacteria was obviously. Five treatments increased the quantity of bacteria52.10-fold,47.53-fold,46.67-fold,44.96-fold,24.12-fold after8weeks, respectively. Disease index of five treatments obviously lower than that of the control group. Lettuces extracts significantly reduced disease index of banana wilt, followed by sunflower extracts, TY strain, DF strain and compounds of toxin inactivation (Fe2SO4ˇ7H2O+EDTAˇNa2). |
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