Pruning debris of grapevine as a potential inoculum source of Diplodia seriata, causal agent of Botryosphaeria dieback

Inoculum longevity of Diplodia seriata occurring in grapevine pruning debris was studied to determine its role as a potential source for new infections on grapevines. Pruned canes naturally colonised by D. seriata were collected 2 years after pruning and kept outdoors in an experimental vineyard under natural conditions. Conidia production was monitored at the collection time and 6, 12 and 18 months later. In each monitoring period, the percentage of pycnidia containing conidia, the estimated average amount of conidia per pycnidium and the conidial germination percentage were assessed. A significant decrease in the percentage of pycnidia containing conidia was observed throughout the experiment. The average amount of conidia per pycnidium was reduced significantly, from 270 conidia per pycnidium 24 months after pruning, down to 25 conidia per pycnidium at the end of the assessment period. Germination percentage of conidia also decreased significantly, from 63 to 44 % within the same period. Overall, these results confirmed the reduction in the D. seriata inoculum available from the pruning debris through all the studied variables. However, 42 months after pruning viable conidia of D. seriata were still detected, thus revealing that pruning debris may become an important long-lasting inoculum source.