First report of Diplodia corticola on grapevine in Italy

Vines with dieback of young shoots, chlorosis/necrosis of interveinal leaf tissues and early defoliation were observed during surveys in several grape-growing areas of Apulia (southern Italy). Sub-cortical brown streaks of variable length were present on the canes, and wedge-shaped necrotic areas within trunks and branches. Isolations made on potato dextrose agar (PDA) from discoloured wood, yielded eight different anamorphic species of Botryosphaeria, involved in the aetiology of black dead arm (BDA) of grapevines (Lehoczky, 1974). Occasionally, a fungus morphologically similar to Diplodia corticola, the causal agent of oak canker (Alves et al., 2004), was also isolated. This fungus grew well in the dark at 22±3°C (13 mm/day) and produced pycnidia and conidia on half-strength PDA supplemented with pine needles (Lazzizera et al., 2008). Conidia were unicellular, hyaline, with a thick smooth wall, 23.9-30.32 x 12.14-12.94 mm in size. Some turned dark and 1- septate with age. The fungus in question had nucleotide sequence of the internal transcribed spacer region (ITS1-5.8SITS2) of ribosomal DNA (accession No. FJ225332), 96% identical to that of a comparable sequence of Botryosphaeria corticola (accession No. AY259100), and was therefore identified as D. corticola (Alves et al., 2004). Artificial inoculations were carried out in June 2006 and 2007 by introducing a small (0.5 cm2) colonized agar plug into a U-shaped incision on second basal internode of green shoots of 5-year-old pot-grown vines of cvs Italia and Lambrusco. Within 30 to 50 days, brown streaks (3.5 to 11.8 cm in length) developed in all inoculated plants, followed by death of the shoots. The pathogen was re-isolated from discoloured tissues, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of D. corticola as the cause of a severe disease of the grapevine, which represents a new host for this fungus. Alves A., Correia A., Luque J., Phillips A.J.L., 2004. Botryosphaeria corticola sp. nov. on Quercus species, with notes and description of Botryosphaeria stewensii and its anamorph Diplodia mutila. Mycologia 96: 598-613. Lazzizera C., Frisullo S., Alves A., Lopes J., Phillips A.J.L., 2008. Phylogeny and morphology of Diplodia species on olives in southern Italy and description of Diplodia olivarum sp. nov. Fungal Diversity 31: 63-71. Lehoczky J., 1974. Black dead-arm disease of grapevine caused by Botryosphaeria stevensii infection. Acta Phytopathologica Academiae Scientiarum Hungarica 9: 319-327.