Defense responses of harvested tomato fruit to burdock fructooligosaccharide, a novel potential elicitor

Burdock fructooligosaccharide (BFO) can induce resistance against a number of plant diseases. However, its controlling effects on postharvest diseases still remain unclear. The effects of BFO on the control of postharvest diseases in tomato fruit and the underlying mechanisms were investigated with chitosan oligosaccharide (CO) as a positive control. Both BFO and CO could effectively inhibit natural postharvest diseases and reduce incidence of disease from inoculation with Botrytis cinerea in tomato fruit. BFO increased the mRNA level of genes encoding pathogenesis-related proteins (PRs), such as PR-1a, PR-2a (extracellular β-1,3-glucanase), PR-2b (intracellular β-1,3-glucanase), PR-3a (extracellular chitinase) and PR-3b (intracellular chitinase), and induced the mRNA accumulation of the phenylalanine ammonia lyase (PAL) gene in tomato fruit. Furthermore, it evoked the activity of peroxidases (POD) and enhanced the biosynthesis of phenolic compounds, but did not affect the activity of polyphenol oxidase (PPO). These results suggest that controlling effects of BFO on both natural diseases and gray mould in tomato fruit might be attributed to systemic acquired resistance (SAR).