The dual role of oxalic acid on the resistance of tomato against Botrytis cinerea.

In order to define the role of oxalic acid (OA) in the invasion of Botrytis cinerea in tomato plants, the OA induction of resistance related to oxalate oxidase (O×O) and germin was examined. In greenhouse experiments, OA at 3 mmol/L significantly induced resistance in tomato plants against B. cinerea strains B05.10 and T4, reducing lesion size of 37.55% and 24.91% by compared with distilled water control, respectively, while 20 mmol/L OA increasing by 36.14% and 41.48%. OA contents were 98 and 46 µg/mL when tomato plants were infected by B. cinerea strains B05.10 and T4, respectively. To define the molecular-genetic mechanisms, we compared the gene expression under four different conditions: 3 mmol/L OA-treated plants, 20 mmol/L OA-treated plants, B. cinerea strain B05.10-infected plants (B05.10 Inf plants) and B. cinerea strain T4-infected plants (T4 Inf plants). In 3 mmol/L OA-treated plants, the expressions of O×O and Germin peaked at 48 h after spraying, with approximate threefold and 18-fold increase compared with the control expression, respectively. In T4 Inf plants, the expression (mRNA accumulation) of O×O and Germin reached the highest levels at 24 h after inoculation, with 3- and 13-times that immediately after inoculation, respectively. In total, these findings suggest that elevated levels of OA correlated with increased fungal invasion and lower OA induced resistance in tomato plants by increasing expressions of O×O and Germin.