Induction and Maintenance of Systemic Acquired Resistance by Acibenzolar-S-Methyl in Three Cultivated Tobacco Types

Induction and maintenance of systemic acquired resistance (SAR) in 'N' gene containing burley, flue-cured, and oriental tobacco cultivars were assessed by monitoring decreases in the number of local lesions caused by Tobacco mosaic virus (TMV) following treatment with acibenzolar-S-methyl (ASM). Leaf samples were collected from lower, middle, and top positions on seedlings at 3-day intervals over 21 days following ASM treatment and subsequent inoculation with TMV under laboratory conditions. Local lesion number for each leaf was recorded 7 days postinoculation. Reductions in TMV local lesion numbers on ASM-treated versus nontreated tobacco varied over time, and differed for each tobacco type. Based on reduced local lesion numbers, SAR was induced in burley and flue-cured tobacco by 3 and 6 days postinoculation, respectively, while oriental tobacco responded by 9 days. SAR was maintained in burley tobacco from 3 to 9 days after ASM application, and from 9 to 15 days after application in oriental tobacco. ASM treatment reduced local lesion numbers in flue-cured tobacco significantly at 6, 12, and 21 days postapplication, but not at 15 and 18 days after treatment. The SAR response was similar among lower, middle, and top leaves with no effect of ASM on response by leaf position, although TMV local lesion numbers were greater on lower leaves than on middle and top leaves 6 days after treatment, but significantly less on lower leaves 18 days after treatment compared to middle and top leaves.