Refining the biological factors affecting virulence of Botryosphaeriaceae on grapevines

Botryosphaeriaceae isolates of six species were assessed for their potential to infect grapevine tissues other than their tissues of isolation, primarily to determine sources of inocula that could contribute to bunch rot. Pathogenicity tests were conducted in vitro on berries and wood and in vivo on dormant buds of cultivars Chardonnay and Shiraz in glasshouse and field experiments. Tissue specificity and variation in virulence for different isolates was assessed. All isolates were able to infect and cause symptoms on detached 1-year-old canes and mature berries. Virulence was not affected by origin tissue and varied between isolates and within species. Inoculation of dormant buds did not affect bud burst or further development of shoots and fruit, however, a small number of Botryosphaeriaceae were reisolated from bunches at later growth stages. We conclude that Botryosphaeriaceae species are important pathogens of both the vegetative tissues and wood of grapevines. Grapevine wood infected with Botryosphaeriaceae could act as a source of inoculum for reproductive and vegetative tissue. Equally, the vegetative and reproductive tissues can also act as inoculum sources for wood infection. Therefore, all sources of inocula should be taken into consideration when developing management strategies for Botryosphaeria bunch rot and Botryosphaeria canker diseases.