Disease Preventing And Growth Promoting Effects Of Arbuscular Mycorrhizal Fungi And Rhizobium On Alfalfa Root Rot And Leaf Spot

Alfalfa(Medicago sativa)is a widely grown crop in northern China,providing hay and silage for livestock throughout the year.With the ever increasing demand for alfalfa,disease is becoming a limiting factor for alfalfa production.Alfalfa Microdochium root rot disease,caused by Microdochium tabacinum is a novel disease in China posing a risk for national alfalfa production.Alfalfa Phoma leaf spot disease,caused by Phoma medicaginis is a worldwide disease,also known as the sprig black stem and leaf spot disease,its destruction is very strong.Arbuscular mycorrhizal fungi(AMF)and rhizobim are two types of important microorganisms in the agro-ecosystem.AMF are known to associate with the majority of plant families,with estimates of up to 80% of all species potentially acting as hosts.It is well known that the rhizospheres of legumes contain large populations of rhizobia,which are specific to the legume species.The effects of inoculations of AMF and rhizobium on growth and nutrition uptake of the host plant.We designed this experiment to test for the effects of combined AMF and rhizobium(Sinorhizobium medicae)on the alfalfa Microdochium root rot disease or alfalfa Phoma leaf spot disease occurrence.The main findings are as follows:1.Both M.tabacinum and P.medicaginis are able to inhibit alfalfa seed germination.2.Effects of co-inoculation with AMF and rhizobium on alfalfa Microdochium root rot disease: A significant increase in alfalfa growth,induced by AMF,independent of inoculation with rhizobium.Inoculation with S.medicae had no effect on alfalfa biomass accumulation due to sufficient N in soil for growth.However,the plant inoculated with S.medicae had higher N concentration compared with un-inoculated plants.In the presence of both AMF and S.medicae,the N,P concentration of plant were significantly greater than in their absence,while M.tabacinum significantly reduced plant total dry weight as well as N,P concentration.Inoculation of M.tabacinum reduced root dry weight and tap root length of alfalfa.Infection of M.tabacinum significantly reduced AM root colonization.Inoculation of AMF increased nodule numbers,independent of the presence of other factors.The infection of M.tabacinum significantly reduced nodule numbers.Plant disease related enzyme,peroxidase(POD),and catalase(CAT)showed a positive response to both AMF and rhizobium,while the malondialdehyde(MDA)content responded negative.3.Effects of co-inoculation with AMF and Rhizobium on alfalfa Phoma leaf spot disease: Regardless of the AMF and Rhizobium alone,or a double inoculation AMF and Rhizobium,there are a significantly promote to alfalfa growth(leaves number,stem length),chlorophyll content,absorption of nitrogen and phosphorus,Chitinase activity,PAL activity,?-1,3-glucanase activity,JA content,plant lignin content and HRGP content.Combined AMF and Rhizobium than single inoculation Rhizobium or AMF,increased nodule number 3.33 times,enhanced mycorrhizal infection 24 %.There are the lowest incidence and disease index in co-inoculation with AMF and Rhizaobium treatment.Infection disease pathogens on the 17 th day,Compared with the control,AMF + Rhizobium reducing disease index by 72.3%.In summary,co-inoculation with AMF and Rhizaobium is able to enhance resistance of alfalfa on alfalfa Microdochium root rot and Phoma leaf spot disease,there are a certain value of biocontrol.