Efficacy of UV-C radiation in inducing systemic acquired resistance against storage carrot rot caused by Sclerotinia sclerotiorum

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.