Biocontrol Effects Of Arbuscular Mycorrhizal Fungi Against Cotton Verticillium Wilt And Its Related Mechanisms

Arbuscular mycorrhizal fungi (AMF)are a potential microbial resource for its application in the biocontrol of soil-borne diseases and plant resistance or tolerance enhancement. In this paper, two strains of AMF Glomus mosseae and Glomus etunicatum has been studied on its disease control effect and furthermore the basic parameters of the application technology and the mechanism in order to develop the integrated approaches to cotton verticillium wilts.The results show that the formation of cotton-AMF symbiote after AMF inoculation could reduce the disease index of cotton verticullium and achieve a relative control effect of 14.27%～69.7%. AMF strain and cotton variety influence the AM colonization rate and the control effect. In the aspect of control effect, Gl. etunicatum is superior to Gl. mosseae, and both of the two AMF stains have the better effect on the susceptible cotton variety Junmian 1 than the tolerant variety Xinluzao 17.The effect of different AMF inoculation dosage and period on cotton verticillium wilts has been studied. The results indicated that the control effect enhanced by the increase of AMF inoculation dosage which shows a dosage effect, but when the dosage is above 5 mL per pot, the control effect was embodied in alleviation of disease degree instead of disease rate. The cotton mycorrhizal seedlings inoculated by seed dressing could develop obvious tolerance against verticillium wilts, whilst the cotton seedlings inoculated by pathogen Verticillium dahliae first and then AMF shown no distinct tolerance.For the cotton plants, the AMF inoculation improved the up-ground and underground biomass, dry matter content, leaf area and chlorophyll content, and uptake of nitrogen and phosphorus, therefore enhanced significantly plant nutritional status and growth.AMF inoculation introduced the improvement of the contents and activities of defensive enzymes in root including phenylalanine ammonialyase (PAL), chitinase, peroxidase (POD), and a new band of POD isoenzyme. AMF inoculation could also increase the contents of total phenol, soluble sugar and proline in root, and decrease the content of malondialdehyde (MDA) in root which indicates the degree of membrane lipids peroxidation that plant cells are suffering.AMF inoculation could also increase the quantity of bacteria and actinomycetes but decrease that of fungi including V. dahliae in root-sphere. The inverse relation between the quantity of saprophytic fungi in root-sphere and AMF spores number shows the competitive relationship between AMF and other fungi including V. dahliae. At the same time, a series of structural changes occurred after AMF colonization to the root cells which are favorable to structural tolerance enhancement of cell wall and pathogen tolerance improvement of root system, such as cell wall broadening, gummy material occurance in vessels, and material deposition on cell walls.The study proved that the tolerance enhancement of cotton against verticillium wilts introduced by AMF inoculation is the result of the comprehensive effect of many factors.