The efficacy of acibenzolar-S-methyl, an inducer of systemic acquired resistance, against bacterial and fungal diseases of tobacco

Acibenzolar-S-methyl, a benzothiadiazole (BTH), is a novel plant protection product that mimics the pathogen-host interaction and results in systemic acquired resistance in plants. It protected tobacco plants against several diseases. Few necrotic lesions of wildfire (Pseudomonas syringae pv tabaci tox +), and angular leaf spot (Ps. syringae pv tabaci tox-) were apparent on 10-week-old seedlings sprayed with acibenzolar-S-methyl (Bion 50% wg) alone or plus copper oxychloride (60% sc), and point-inoculated with the pathogens 7 days later. In outdoor seedbeds, seedlings were sprayed two or three times with acibenzolar-S-methyl (0.05 g-0.1 g a.i. m(-2)), copper oxychloride (0.52-1.56 g a.i. m-2) or, in the 1996-97 season only, a mixture of both, starting 7 weeks after sowing. All plots, including the unsprayed, were inoculated with Ps. syringae pv tabaci tox + (10(7) cfu ml(-1)) 7 days after the first spray. Although copper oxychloride reduced the incidence of wildfire, plants that had been sprayed with acibenzolar-S-methyl were disease-free but there was mild phytotoxicity. Wildfire symptoms were not evident on these seedlings at field transplanting, but in 1996-1997, 9 weeks later 72% of the unsprayed and 2.7 and 4.7%, respectively, of plants treated with acibenzolar-S-methyl and acibenzolar-S-methyl + copper oxychloride in the seedbed plus one field spray (30 g a.i. acibenzolar-S-methyl ha(-1)) had symptoms. In both seasons, a natural infection of rhizoctonia leaf spot (Thanatephorus cucumeris) was less prevalent on plants sprayed with acibenzolar-S-methyl. In the 1997-1998 season, both seedbed-sprayed only and seedbed plus two field sprays of acibenzolar-S-methyl reduced the incidence of frogeye leaf spot on field plants and the amount of barn spot ( both caused by Cercospora nicotianae) in the colouring phase of leaf curing. Yield and quality were not adversely affected by acibenzolar-S-methyl. (C) 1999 Elsevier Science Ltd. All rights reserved.