Comparison of induced resistance activated by benzothiadiazole, (2R,3R)-butanediol and an isoparaffin mixture against anthracnose of Nicotiana benthamiana

Resistance in Nicotiana benthamiana against anthracnose caused by the hemibiotrophic fungus Colletotrichum orbiculare was activated by benzothiadiazole (BTH), (2R,3R)-butanediol or PC1, an isoparaffin-based mixture. In inoculation experiments, BTH, (2R, 3R)-butanediol and PC1 reduced the number of lesions per leaf area caused by C. orbiculare by 98%, 77% and 81%, respectively. Foliar application of BTH induced expression of genes for the acidic pathogenesis-related (PR) proteins, NbPR-1a, NbPR-3Q and acidic NbPR-5. In contrast, soil application of (2R, 3R)-butanediol or PC1 primed expression of genes for the basic PR proteins, NbPRb-1b, basic NbPR-2 and NbPR-5dB. These results are consistent with the activation of salicylic-acid-dependent systemic acquired resistance (SAR) by BTH and that of jasmonate/ethylene-dependent induced systemic resistance (ISR) by (2R, 3R)-butanediol or PC1, and show that (2R, 3R)-butanediol and PC1 can affect gene expression similarly to plant growth-promoting rhizobacteria. However, the effects of (2R, 3R)-butanediol and PC1 were not identical. In addition to priming, (2R, 3R)-butanediol induced expression of basic NbPR-2, whereas PC1 treatment induced expression of both NbPRb-1b and basic NbPR-2. Although a number of microbial products, such as (2R, 3R)butanediol, have been shown to produce ISR, this is the first demonstration that an isoparaffin-based mixture, not derived from a microorganism, can produce ISR.