Enhanced Onion Resistance against Stemphylium Leaf Blight Disease, Caused by Stemphylium vesicarium, by Di-potassium Phosphate and Benzothiadiazole Treatments

In this study, we investigated the induced defense response and protective effects against Stemphylium vesicarium by application of benzothiadiazole (Bion (R)) and di-potassium phosphate salt (K2HPO4) to onion. Onion leaves were sprayed with Bion (R) and K2HPO4, then inoculated 2 days later with a virulent strain of S. vesicarium under greenhouse conditions. Disease severity and activities of peroxidase (PO), polyphenoloxidase, phenylalanine ammonia-lyase (PAL) and phenol contents were evaluated in the treated leaf tissues. Reduction in the disease severity was observed in plants treated with Bion (R) and K2HPO4. Onion plants treated with Bion (R) and K2HPO4, and inoculated with the pathogen showed significantly higher PAL activity, PO activity, and phenol contents than inoculated water-treated plants 2 days after the treatment. In conclusion, the results of this study provide evidence that application of simple non-toxic chemical solutions as di-potassium phosphate and Bion (R) can control Stemphylium leaf blight of onion.