Effects Of Nitric Oxide And Methyl Jasmonate On Fusarium Root Rot Of Alfalfa

Alfalfa（Medicago sativa L.）is a leguminous forage that is widely cultivated in many countries and regions because of its excellent forage and ecological effect.Alfalfa root rot caused by Fusarium is a common disease in all major production areas of the world,and has become the main factor to restrict the development of alfalfa industry.The resistance and pathogenicity of Fusarium is extremely strong,and the chemical control and agricultural management measures are difficult to achieve the purpose of disease prevention and control.Plant induced resistance is a kind of acquired resistance produced though induced by exogenous factors,which is an ec-friendly and cost-effective way to prevent and cure root rot and enhance the resistance of alfalfa.In this study,three groups of experiments were carried out,（1）the resistance of the 9 alfalfa varieties（Gannong No.3,Gannong No.9,Longmu 803,Daye No.1,Daye No.2,Gold empress,Gongnong No.1,Zhongmu No.1 and Zhonglan No.2）to three root rot pathogens（Fusarium tricinctum,Fusarium oxysporum and Fusarium equiseti）was evaluated;（2）the effects of exogenous NO and MeJA on the mycelial growth of Fusarium oxysporum was estimated by measuring colony diameter,and an orthogonal matrix experimental design with four factors（SNP concentration,MeJA concentration,spore suspension concentration and treatment time）was performed to quantitatively investigate the effects and pairwise interactions on the spore pathogenicity of Fusarium oxysporum;（3）three orthogonal matrix experimental designs with three factors（alfalfa varieties,SNP or MeJA concentration and treatment time）were performed to explore the effects and pairwise interactions of NO and MeJA on resistance of alfalfa（Gannong No.3,Longmu 803 and Zhongmu No.1）to root rot caused by Fusarium oxysporum,and the optimal treatment conditions to enhance the resistance of alfalfa to root rot was optimized by factor analysis.The corresponding results were showed as follows:（1）The resistance of the 9 alfalfa varieties to the three Fusarium pathogens was different.In general,the average resistance of 9 varieties to Fusarium equiseti was stronger,while the average resistance to Fusarium oxysporum was weaker.Gannong No.1 and Daye No.2showed disease tolerance to three pathogens infection,Zhongmu No.1 and Gold empress showed susceptibility after infection.The pathogenicity of the three pathogens from strong to weak was:Fusarium oxysporum>Fusarium tricinctum>Fusarium Fusarium equiseti.（2）0.1 mmol·L^-11 SNP and 0.1¹.0 mg·mL^-1 MeJA had significant inhibitory effects on mycelial growth,but had no significant effect on spore pathogenicity（P<0.05）.Treatment time was the most important factor to affect the spore pathogenicity.The optimal treatment conditions to weaken the pathogenicity of Fusarium oxysporum spores was OD₆₀₀ value of0.069,1.0 mmol·L^-11 SNP,0.1 mg·mL^-11 MeJA and the 60 min treatment.（3）The incidence and diseae index were significantly decreased when treatment by SNP or MeJA,while the two indicators were only partially decreased by SNP and MeJA mixture.The activities of superoxide dismutase（SOD）,peroxidase（POD）and phenylalnine ammonialyase（PAL）and the phenolic and chlorophyll were increased,and the content of malondialdehyde（MDA）was significantly decreased after exogenous SNP or MeJA treatment.Besides,after exogenous treatment,the fresh weight and dry weight of shoots were significantly increased,but the soluble protein content was significantly reduced.The SNP or MeJA concentration was the most important factor to affect different indicators when MeJA and SNP were treated respectively,there was no main factor to affect all indicators when SNP and MeJA mixture.The results of factor analysis showed that the optimal treatment conditions to enhance the resistance to Fusarium oxysporum was Gannong No.3,0.1 mg·mL^-11 SNP,inoculation and treatment simultaneously.