Effect of Salicylic and Acetyl Salicylic Acids on Inducing the Systemic Resistance of Broadbean Plants Against the Fungus Alternaria alternata Causing Leaf Spot Disease

Abstract

Different concentrations of Acetyl salicylic acid (ASA) and Salicylic acid (SA) were tested on the mycelial growth of the fungus Alernaria alternata, the causal agent of leaf spot disease of broad bean. All tested conc. (1,3,5,10,20,30,60) mM gave significant inhibition in accordance with the increase of conc., and the growth of the fungus was inhibited completely at (10) mM of (ASA) and (20) mM of (SA). Results indicated that the addition of different conc. of (ASA) and (SA) to the liquid media Potato Sucrose Broth (PSB) caused complete inhibition to the fungal growth at (10) mM of (ASA), the same effect was noticed when (20) at (3 (5-mM of (SA) applied in greenhouse experiments, seeds were soaked mM of (SA) and (ASA) for 24 hrs. as a protective treatment, then planted in soil contaminated with the pathogen caused significant reduction in percent infection and disease severity of leaf spots. Dual treatment by soaking the seeds with the same conc. along with spraying the shoot system was the most efficient in reducing percent infection by (100)% and disease severity of the disease and improving growth characters of the treated plants. Studying the biochemical changes occurred as indicators for induced resistance in the treated plants, caused high increase in peroxidase activity as compared to untreated plants. The best treatment was soaking the seeds in (5) mM of (ASA) as well as spraying the shoot system.