Basal tomato defences to Botrytis cinerea include abscisic acid-dependent callose formation

In Arabidopsis, abscisic acid (ABA) application can induce resistance by priming for callose deposition; this resistance is impaired in ABA-deficient and -insensitive mutants. In tomato, ABA-deficiency causes resistance to Botrytis cinerea. Here, we show that callose deposition after B. cinerea inoculation is weaker in the ABA-deficient sitiens tomato mutant compared to the wild type (WT). Inhibition of callose synthesis did not affect resistance in sitiens, but caused additional susceptibility in WT. These findings indicate that callose deposition is not part of sitiens defence responses that are effective in blocking B. cinerea and suggest that callose deposition only contributes to WT basal resistance. Furthermore, also in tomato callose formation is at least in part ABA-dependent. However, it seems that in contrast to Arabidopsis, basal ABA levels in tomato are sufficiently high to prime for callose deposition.