Seed treatment with benzothiadiazole induces resistance against powdery mildew disease caused by Sphaerotheca fuliginea and increases the activities of pathogenesis-related enzymes in cucumber plants

Ramasamy, A. D.; Bokshi, A. I.; Phan-Thien, K.; McConchie, R. M.

Journal of Horticultural Science and Biotechnology 90(1): 63-70

2015


ISSN/ISBN: 1462-0316
DOI: 10.1080/14620316.2015.11513154
Accession: 066296495

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Abstract
Applications of acibenzolar S-methyl (ASM), commercially known as Bion (R) WG 50 [benzothiadiazole (benzo 1, 2, 3) thiadiazole-7-carbothioic acid S-methyl ester], or Milsana (R) by seed imbibition were evaluated for their efficacy in protecting cucumber plants against powdery mildew caused by the biotrophic fungus, Sphaerotheca fuliginea. Among the different concentrations of ASM (0, 25, 50, 75, or 100 mu g a.i.ml(-1)) or Milsana (R) (10 or 20 ml l(-1)) tested, soaking seed in 75 mu g a.i.ml(-1) ASM for 12 h was the optimum concentration and duration to induce systemic acquired resistance (SAR) without adverse effects on seed germination or seedling vigour. Higher concentrations of ASM delayed the germination of cucumber seed, and longer durations of seed treatment negatively affected the seedling vigour index. Seed treatment with ASM increased the activities of pathogenesis-related (PR) proteins, but not treatment with Milsana (R). The activity of chitinase in cotyledons from ASM-treated seed increased six-fold compared to its activity in untreated (control) plant tissue. Longer durations of soaking with ASM significantly increased chitinase activity in shoot tissues, reaching a peak at 12 h before declining. The enhanced levels of chitinase and peroxidase activity elicited by seed treatment with ASM were similar to those triggered by foliar application of ASM alone, or by seed treatment followed by foliar application of ASM. The application of ASM by seed imbibition significantly reduced the severity of powdery mildew in cucumber cotyledon-disc assays. Increased resistance to powdery mildew in ASM seed-treated cucumber plants was positively correlated with the enhanced activities of PR proteins that are known to be associated with pathogen resistance in cucumber leaves. This research indicates that ASM may be applied as a seed treatment to protect cucumber seedlings against powdery mildew.