Soaking seeds in methyl jasmonate or benzothiadiazole induces resistance to an insect pest and stem decay in Brassica campestris L. ssp. chinensis

Abstract

SummaryFlowering Chinese cabbage (Brassica campestris L. ssp. chinensis), a leafy vegetable with a flowering stem, is susceptible to larvae of the striped flea beetle (Phyllotreta striolata) during growth, and to stem decay during storage. The aim of this study was to investigate the effects of methyl jasmonate (MeJA) or benzothiadiazole (BTH) applied by seed-soaking on insect damage and on the severity of stem decay in relation to the levels of expression of three defence-related genes. Soaking seeds in 1.0 µM MeJA, or in 24 µM or 240 µM BTH, significantly alleviated pest damage, and soaking seeds in 1.0 µM MeJA or in 240 µM BTH controlled post-harvest decay. These results suggest that seed treatment was effective in enhancing the quality of flowering Chinese cabbage. Applying MeJA or BTH by seed-soaking treatment elevated the levels of expression of the PDF1.2, PR1, and WRKY33 genes at 2, 10, and 20 d after germination, respectively. However, MeJA or BTH applied by seed-soaking only elevated expression of PDF1.2 during storage of flowering Chinese cabbage at low temperature (2ºC) or at room temperature (20ºC). These results suggest that seed treatment with MeJA or BTH can induce plant defence against insect pests and bacterial diseases in flowering Chinese cabbage. The enhanced resistance to insects may involve elevated expression of the PDF1.2, PR1, and WRKY33 genes, while increased resistance to post-harvest decay may be related to up-regulation of PDF1.2.