First report of Colletotrichum godetiae causing grape (Vitis vinifera) berry rot in Italy

In October 2016, rotting grape berries were detected on grapevine (Vitis vinifera) in Livorno (Nugola, Tuscany, Italy). Symptoms on grape berry skins varied from circular brown spots to rotting fruits. Both berries and petioles were covered with creamy salmon-colored masses of conidia. Rotten grape berries lost turgor and turned into ‘mummies’ over time. Symptoms suggested that a member of the genus Colletotrichum could be involved. Single spore cultures were obtained from conidial masses and grown in the laboratory at 25°C with a 12-h light period on potato dextrose agar (PDA). Monoconidial isolates had light gray cottony aerial mycelium with colony color ranging from whitish to dark gray, while the reverse ranged from whitish to salmon-pink. Conidia were hyaline and unicellular, cylindrical or clavate, and often with a light median constriction. However, Colletotrichum spp. are often difficult to distinguish morphologically. Total genomic DNA was extracted from monoconidial isolate SS354. The ITS region of rDNA and partial GAPDH, CHS-1, HIS3, ACT, and TUB2 genes were amplified and sequenced according to Damm et al. (2012). Sequences were deposited in GenBank (accession no. KY293406 for ITS, KY293407 for TUB, KY293403 for CHS, KY293405 for HIS3, KY293402 for ACT, and KY293404 for GAPDH). The multilocus phylogenetic analysis carried out with the obtained and reference sequences (Damm et al. 2012) revealed that the SS354 isolate clustered within C. godetiae. Pathogenicity tests were performed in laboratory by inoculating detached grape berries with or without petioles at the petiole insertion point with 20 µl of a conidial suspension (105 conidia/ml) of the isolate SS354. Grape berries without petiole developed symptoms similar to those observed in the field. Fungal colonies reisolated from the lesions on berries were morphologically identical to isolate SS354. Control grape berries inoculated with sterile water remained healthy as well as grape berries with petioles inoculated with the pathogen. This suggests that C. godetiae is able to infect wounded grape berries. However, information regarding other infection routes were not searched, as this was not the aim of this work. This is the first report of C. godetiae causing grape berry rot in Italy. The phylogenetic analysis reveals that C. godetiae SS354 is closely related to C. godetiae RB118, the causal agent of anthracnose on grapevine in the U.K. (Baroncelli et al. 2014). Since C. godetiae is polyphagous, cross-infections between grape and other crops are possible. Remarkably, Cacciola et al. (2012) reported C. clavatum (syn. C. godetiae) as the prevalent Colletotrichum species associated with epidemic outbreaks of olive anthracnose in Italy. However, at present, no information regarding cross-infection of C. godetiae between grapevine and olive are available. Due to the high economic and social value of wine production in Italy (in 2013 only in Tuscany the production of grapes accounted for 8 million tons), a monitoring plan based on simple molecular identification tools should be advisable.