Elucidating VOC dynamics and molecular mechanisms in nonanal-treated postharvest tomatoes infected with Botrytis cinerea

In this study, an 0.054 mol·L^-1 nonanal treatment decreased the incidence rate of gray mold on tomato and enhanced the defense capacity by altering the activities of the main defense-related enzymes, including NADPH-cytochrome <i>c</i> reductase, aminopyrine-<i>n</i>-demethylase, aniline-4-hydroxylase, and erythromycin <i>N</i>-demethylase. Defense mechanisms are associated with cell degradation. PUFAs are closely related to the maintenance of cell integrity. The enzymes related to PUFAs showed weak activities until 36 h after the 0.054 mol·L^-1 nonanal treatment, afterwards, their activities increased. The 0.054 mol·L^-1 nonanal treatment decreased the energy wasted by decreasing NAD⁺, NADH, and ATP levels. These changes may respond to nonanal application, further regulating the defense capacity of tomato. The nonanal treatment also decreased the contents of key substances required for the synthesis of PUFAs [volatile aldehydes and alcohols (VAAs)]. The most important substances for disease resistance (hexanal, 2-hexanal, and citral) also significantly decreased after the 0.054 mol·L^-1 nonanal treatment. The transcriptome data revealed <i>FAD2</i>, <i>OPRs</i>, <i>Alpha-DOX1</i>, and <i>KCS</i> related to PUFAs, Of these, 14 were down-regulated and 5 were up-regulated after the 0.054 mol·L^-1 nonanal treatment compared with the control. and the genes in the plant-pathogen interaction pathway were up-regulated in the control group. This indicated that the nonanal treatment increased the postharvest tomato plant's resistance capability and helped maintain cell integrity, which meant that less genes and substances were required to fight the <i>Botrytis cinerea</i> infection.