First report of cauliflower collar rot caused by globisporangium ultimum in Italy

During October 2015, severe symptoms of collar rot were observed in a commercial field of two month-old cauliflower (Brassica oleracea L. var. botrytis) in BAT province (Apulia, southern Italy). Among several cultivars grown in the same field (6 ha), only cultivar Tipoff F1 (Bejo) showed disease symptoms with ca. 5% of plants affected. First symptoms appeared on collar tissues and consisted of wide water-soaked lesions which progressively darkened, rotted and extended to the midrib of basal leaves. Pythium-like colonies were consistently isolated from decayed plants on potato dextrose agar (PDA), and one representative isolate, designated DiSSPA P8, showed morphological characters consistent with those described by van der Plaats-Niterink (1981) for the type specimen CBS 398.51 of Pythium ultimum Trow var. ultimum, recently renamed Globisporangium ultimum (Trow) Uzuhashi, Tojo & Kakish. (Uzuhashi et al., 2010). The coxII gene as well as ITS and D1/D2 regions of rDNA were sequenced and deposited in GenBank under accession Nos. KY753869, KY392755 and KY753868, respectively. Once these sequences were included in the phylogenetic trees constructed by Uzuhashi et al. (2010), DiSSPA P8 clustered with G. ultimum strain UZ056 with a 99% sequence identity to the corresponding sequences from this isolate. Furthermore, the representative isolate induced collar rot symptoms, similar to those observed in the field, on six week-old cauliflower plants cv. Tipoff F1 after two days at 26°C from inoculation with colonized PDA discs on superficially wounded stem. To the best of our knowledge, this is the first report of collar rot caused by G. ultimum on cauliflower in Italy.