Induced resistance against Sclerotinia sclerotiorum in carrots treated with enzymatically hydrolysed chitosan

We have measured the susceptibility of carrots to the storage pathogen Sclerotinia sclerotiorum after roots were treated postharvest with a 0.2% (w/v) chitosan hydrolysate (number average degree of polymerisation = 7) prepared using Streptomyces N-174 chitosanase. Whereas the hydrolysate did not affect radial growth of S. sclerotiorum colonies on potato dextrose agar plates, it reduced the frequency and size of rot compared to untreated controls when applied to carrots 3 days before inoculation with S. sclerotiorum. When carrots were treated at time zero with either chitosan hydrolysate or high molecular weight chitosan then inoculated at intervals over the next 5 days, there was a decline in Sclerotinia infection, with the hydrolysate showing a greater effect than the high molecular weight chitosan. Our results suggest that the chitosan treatments induced host resistance to the pathogens. (C) 2004 Elsevier B.V. All rights reserved.