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This research was carried out to assess inhibitory effect of UV-C (0.88 kJ m−2) against four isolates of Sclerotinia sclerotiorum, causal agent of carrot rot, in vitro and in vivo. A bank of seven germicidal tubes was used to produce UV-C radiation with peak emission at 254 nm. The carrot roots were subjected to UV-C irradiation for five min. The tubes were located 40 cm above the roots. In order to be exposed to UV radiation on all sides, the carrot roots were rotated five times at the interval of one min. Based on the results, UV radiation was able to significantly increase levels of pathogenesis-related proteins (chitinases, peroxidases, β-1,3-glucanases) as well as polyphenoloxidase, phenylalanine ammonia-lyase and 6-methoxymellein (6-m) in carrot roots. The levels of enzymes and 6-m were found to be higher in the whole treated carrots than half treated carrots in most of treatments. Despite increase of systemic acquired resistance (SAR) related enzymes in half treated carrots, the results of in vivo tests showed that UV-C irradiation can not reduce severity of carrot rot after 15 d. In addition, UV-C radiation for 5 min markedly decreased myceliogenic and carpogenic germination of sclerotia in four isolates. This study showed that UV-C cannot be considered as abiotic inducer of SAR.

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.