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.