Application of acetyl salicylic acid and chemically different chitosans against storage carrot rot

•Chitosans and acetyl salicylic acid are able to induce systemic resistance against carrot rot.•The fungicidal effect of chitosans increased when the degree of N-deacetylation decreased.•Chitosans and acetyl salicylic acid increased SAR enzyme activities in inoculated carrots.

This study was conducted to evaluate antifungal activity of three chemically different chitosans named as A, B and C at different concentrations against three isolates of Sclerotinia sclerotiorum, the causal agent of storage carrot rot, by in vitro and in vivo tests. In addition, potential of SAR (systemic acquired resistance) induced by the chitosans and acetyl salicylic acid (ASA) was assessed against the disease. The degree of N-deacetylation (DN) and the molecular weight of chitosans A, B and C were 85%–1129 kDa, 95%–521 kDa and 75%–607 kDa, respectively. The concentrations 2 g/L and 5 g/L of all chitosans were significantly able to decrease mycelial growth, sclerotia formation and carpogenic germination of the pathogen. Four hours and three days before inoculation with the pathogen, application of chitosans and ASA reduced severity of carrot rot in all isolates. However, mycelial growth and sclerotia formation of isolate 2 was more reduced than other isolates. In accordance with in vitro tests, chitosan B showed the highest inhibitory efficacy against the disease. The fungicidal effect of chitosan increased when the DN decreased and there was a negative correlation between the mycelial growth inhibition and the molecular weight of chitosans. The enzyme analysis showed that the activity of phenylalanine ammonia layse, polyphenoloxidase and peroxidase increase in the inoculated carrots after application of different chitosans and ASA.