Identification and pathogenicity of Botryosphaeriaceae species associated with blackcurrant dieback in New Zealand

Abstract

Worldwide, fungal species belonging to the Botryosphaeriaceae are major pathogens causing dieback of many horticultural crops including blackcurrants (Ribes nigrum) resulting in significant economic losses. The species of Botryosphaeriaceae associated with the dieback of blackcurrant in New Zealand is unknown. Isolations were carried out from symptomatic plant tissues collected from different blackcurrant orchards in the main growing areas of Canterbury and Tasman, New Zealand. For one site, grapevines growing in an adjacent vineyard were also sampled. The pathogenicity of three representative isolates from the species recovered were determined on detached blackcurrant shoots by inoculating wounds with mycelial plugs. Botryosphaeriaceae species were recovered from plant samples from all four orchards sampled. Of the 79 Botryosphaeriaceae isolates recovered D. seriata (45 isolates) and D. mutila (22 isolates) were the most prevalent species, with N. australe (7 isolates), N. cryptoaustrale (4 isolates) and one isolate of Diplodia sapinea also recovered. Isolates identified as D. seriata, D. mutila, N. australe and N. cryptoaustrale were recovered from symptomatic grapevine tissues sampled from the adjacent vineyard and all but N. cryptoaustrale were found in the blackcurrant crop adjacent to this vineyard. All isolates from all species were pathogenic, with D. sapinea (52.7 mm), N. australe (40.8-55.0 mm) and N. cryptoaustrale (38.7-47.3 mm) the most pathogenic producing the longest lesions compared with D. seriata (15.6-28.0 mm) and D. mutila (28.9-34.9 mm). This is the first study on the identification and pathogenicity of species of Botryosphaeriaceae from blackcurrant orchards in New Zealand.