Effects of plant defence activators on anthracnose disease of cashew

Abstract

The plant defence activators acibenzolar-S-methyl (Benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester, ASM), 2,6-dichloro-isonicotinic acid (DCINA), salicylic acid (SA), and dibasic potassium phosphate (K2HPO4) were tested for their ability to protect cashew (Anacardium occidentale) seeds and leaves from anthracnose disease caused by Colletotrichum gloeosporioides. No inhibition of the early stages of pathogen development was caused by concentrations equal to or lower than 1.1 mM a.i. ASM, 1.2 mM a.i. DCINA, 5 mM SA and 50 mM K2HPO4. Maximum reduction of the disease in detached leaves, without phytotoxic effects, was obtained with 0.07 mM a.i. ASM and DCINA, 5 mM SA, and 50 mM K2HPO4, with a time interval of at least 72 h between application of the activator and inoculation with the pathogen. On attached leaves, foliar sprays were slightly more efficient than soil drench treatments, with 5 mM SA being the most effective treatment, while 50 mM SA as well as 0.3 mM a.i. ASM and DCINA caused phytotoxic effects. In field-grown plants, protection was conferred by a soil drench of concentrations as low as 12.6 µM a.i. ASM and DCINA and 2.6 mM SA. These concentrations were not phytotoxic suggesting that plant defence activators have potential for control of anthracnose disease in the field.