Researches on resistance to downy mildew induced by copolymer of chlorine and potassium ions in cucumber

The resistance to downy mildew ［Pseudoperonospor cubensis(Berk.et Curt.)Rostov.］ of cucumber can be induced when the cucumber seedlings are treated by the copolymer of chlorine and potassium ions with 2g/kg,5g/kg,10g/kg,15g/kg and 20g/kg concentration at the stages of cotyledon and first true leaf.In the experiment of a natural disease infection,the disease in treated plants is observed 3 to 6 days later.The mean rates of disease plants which are induced by copolymer of chlorine and potassium ions with 2g/kg,5g/kg,10g/kg,15g/kg and 20g/kg concentration are 25.26%,26.63%,31.46%,39.12% and 33.38%lower than those of the control,respectively;the mean rates of disease leaf are 22.89%,28.08%,34.02%,38.36%,and 36.59%lower.The mean disease indexes are 18.32%,28.97%,34.80% 35.89% and 36.77% lower with significant differences between the treatments and the control.The mean relative immunization efficiencies are 31.99%,43.75%,51.23%,53.43%and 53.70%,respectively.In experiment of an artificially inoculated disease infection,the mean disease indexes are 38.51%,44.86%,40.81%,43.00%and 43.33%lower than those of the control,respectively;and the most significant differences between the treatments and the control are attained.The lag period of the induced resistance to downy mildew of cucumber is 2～4 days,the latent period is 7～9 days,the protection period of induced resistance is 27days.In addition,the study shows that the optimum concentration of the copolymer of chlorine and potassium ions are 10g/kg and 15g/kg.