Modulation of defense genes and phenolic compounds in wild blueberry in response to Botrytis cinerea under field conditions

Abstract

Botrytis blight is an important disease of wild blueberry [<i>(Vaccinium angustifolium (Va)</i> and <i>V. myrtilloides (Vm)</i>)] with variable symptoms in the field due to differences in susceptibility among blueberry phenotypes. Representative blueberry plants of varying phenotypes were inoculated with spores of <i> B. cinerea </i>. The relative expression of pathogenesis-related genes (<i>PR3, PR4</i>), flavonoid biosynthesis genes, and estimation of the concentration of ten phenolic compounds between uninoculated and inoculated samples at different time points were analyzed. Representative plants of six phenotypes (brown stem <i>Va </i>, green stem <i>Va </i>, <i>Va </i> f. nigrum, tall, medium, and short stems of <i>Vm </i>) were collected and studied using qRT-PCR. The expression of targeted genes indicated a response of inoculated plants to <i> B. cinerea </i> at either 12, 24, 48 or 96 h post inoculation (hpi). The maximum expression of <i> PR3 </i> occurred at 24 hpi in all the phenotypes except <i>Va </i> f. nigrum and tall stem <i>Va </i>. Maximum expression of both <i>PR</i> genes occurred at 12 hpi in <i>Va </i> f. nigrum. Chalcone synthase, flavonol synthase and anthocyanin synthase were suppressed at 12 hpi followed by an upregulation at 24 hpi. The expression of flavonoid pathway genes was phenotype-specific with their regulation patterns showing temporal differences among the phenotypes. Phenolic compound accumulation was temporally regulated at different post-inoculation time points. M-coumaric acid and kaempferol-3-glucoside are the compounds that were increased with B. cinerea inoculation. Results from this study suggest that the expression of <i>PR </i> and flavonoid genes, and the accumulation of phenolic compounds associated with <i>B. cinerea </i> infection could be phenotype specific. This study may provide a starting point for understanding and determining the mechanisms governing the wild blueberry- <i> B. cinerea </i> pathosystem.