Study On The Effect Of PGPR On Alfalfa Root Rot Disease

Plant growth promoting rhizobacteria(PGPR)is widely distributed in the tissues and organs of various plants.PGPR can promote plant growth by inducing plant tissue structure changes,inducing related defenseenzyme activity,inducingpathogenesis-related protein activity,inducing disease resistance-related gene expression,and improving plant resistance.With the rapid development of agriculture and animal husbandry,alfalfa(Medicago sativa.L)and other crops were paid attention to the healthy growth.Alfalfa root rot,which seriously affects the yield and nutritive value of alfalfa alfalfa,is one of the important diseases that endanger the growth of alfalfa.In this paper,PGPR strains isolated and preserved in the laboratory were used as experimental materialsto evaluate the biological control ability of alfalfa to root rot.The results are as follows: 1.PGPR inhibits phytopathogenic fungiThe antagonistic ability of 19 PGPR strains to nine pathogenic fungi was evaluated by dual culture assay.The results showed that Pseudomonas aeruginosa SLC-2 and Bacillus subtilis YJ20 were able to antagonize nine pathogenic fungi.The inhibitory rates of the two strains on the pathogen fungi Fusarium oxysporumof alfalfa root rot were 66.67% and 76.67% respectively.The fermentation broth of SLC-2 and YJ20 could inhibit the normal growth ofmycelia and sporesgermination ofpathogenic fungi.The number of spores decreased,make the myceliabreak,produce deformities and protoplasmic leakage,and thus could not grow normally.2.Biocontrol ofalfalfa root rotby PGPRThe results of pot experiments showed that SLC-2 and YJ20 could alleviate the sympotom root rot in different degree.The relative control effect of strain SLC-2 was 60.27%,and the relative control effect of strain YJ20 was 58.12%.Strains SLC-2 and YJ20 were used to treatthe alfalfa after infection with Fusarium oxysporum.The lignin,SOD,CAT,POD,PAL,LOX,chitinase and ?-1,3glycanase were increased various degrees.It is thus clear that related structural substances(such as:lignin),related defense enzymes(such:as: SOD,CAT,POD,PAL,LOX)and pathogenesis-related proteins(such as: chitinase,?-1,3 glucanase)were induced by Pseudomonas aeruginosaSLC-2 and Bacillus subtilis YJ20.And then to speed up the synthesis of related disease-resistant substances,induced alfalfa resistance to disease.3.Quantitative determination of disease resistance-related gene expression in alfalfainduced by PGPRThe expression of disease resistance-related genes induced by strainsof SLC-2 and YJ20 were detected by qRT-PCR technique with alfalfa ?-Actingene as a reference gene.The results showed that the expression of PR1,PDF1.2,VSP2 and LOX2 genes in alfalfa could be induced by SLC-2 after inoculation with Fusarium oxysporum,and the expression level was significantly higher than that of the sterile water control group and theFusarium oxysporum treatment group.The expression of PR1,PDF1.2,VSP2 and LOX2 in alfalfa could also be induced by inoculation of PGPR strain YJ20.The expression of PR1 and PDF1.2 genes were induced by YJ20 strain at all time points were significantly higher than those in the sterile water control group and the Fusarium oxysporum treatment group.The expression of VSP2 gene induced by YJ20 strain was significantly lower than that of the Fusarium oxysporum treatment group,but it was significantly higher than that of the sterile water control group.The expression of LOX2 gene induced by strain YJ20 was significantly higher than that of inoculated Fusarium oxysporum at 120 h.