Induction effect of Salicylic acid and Chitosan on Frogeye Leaf Spot in Soybean

Plant induced resistance is a new measure of plant protection,Frog-eye leaf spot,caused by Cercospora sojina Hara,is one of important diseases of soybean.Resistant soybean varieties were mainly used to resistance to frog-eye leaf spot at present soybean production,while the study on induced resistance of soybean to frog-eye leaf spot is rarely reported.Two common chemistry induced factors,salicylic acid and chitosan,were used to discuss the effects of induced resistance to frog-eye leaf spot.Two soybean varieties,Heinong 35(susceptible)and Dongnong 42(middle resistance),were used as experiment material.For salicylic acid(SA),the seeds were sowed in the pots.When the 4th compound leaf of soybean spreaded completely,SA sprayed with 3 concentration at the same day and 5 days and 10 days later.But for chitosan,seed soaking,seed coating,spraying and mixture of above were used.3 concentrations for each treatment were used.The spraying time of chitosan was the same as that of SA.The pathogen of frog-eye leaf spot were inoculated at 5 days and 12 days after the last treatment.The progressions of disease spots were investigated at 15 days after inoculation.Results showed that all the treatments of SA and chitosan reached significant level.The induced resistance of SA reached 72.2% and 66.7% for Heinong 35 and Dongnong 42,respectively.The best concentration by leaf spraying three times of SA was 1 000 mg·L-1.In addition,the induced resistance effects among all treatments of chitosan reached 88.9% and 72.2% for Heinong 35 and Dongnong 42,respectively,when seed soaking by 10 000 mg·L-1 Chitosan solution mixed with leaf spraying by 1 000 mg·L-1 Chitosan solution.Then,the induced resistance effects of Chitosan reached 72.2% and 55.6% for Heinong 35 and Dongnong 42,respectively,when Chitosan concentration was 1 000 mg·L-1 by spraying three times.Whereas the induced resistacne effects was the lowest by seed soaking.The conclusion of the research is that two inducers could both induce higher resistance to frog-eye leaf spot in Heinong 35 and Dongnong 42,but there were some difference between the two genotypes.The effects of induced resistance of Heinong 35 were obviously higher than that of Dongnong 42,when the concentration of SA was appropriate.However,this difference such as the former was not obvious among all the treatments induced by chitosan.These factors including inducer concentrations,spraying times and application methods all affected the effect of induced resistance.The the best treatment is seed soaking mixing with leaf spraying three times by 1 000 mg·L-1 Chitosan solution.