Evaluation of grapevine rootstocks against soilborne pathogens associated with trunk diseases

The susceptibility of the grapevine rootstocks most commonly used in Spain to black-foot (Ilyonectria liriodendri and Dactylonectria macrodidyma-complex) and petri disease (Cadophora luteo-olivacea, Phaeomoniella chlamydospora and five species of Phaeoacremonium) pathogens was evaluated. Rooted cuttings of rootstocks 110R, 1103P, 140Ru, 161-49C, 196-17C, Fercal and SO4 were inoculated with blackfoot pathogens by dipping their roots in conidial suspensions (5x10(5) conidia mL(-1)), planted in pots containing sterilized peat moss and placed in a greenhouse. After four months of incubation, root disease severity index and dry weights of shoots and roots were recorded for each plant. Regarding petri disease pathogens, one-year-old grapevine cuttings of five rootstocks (41B, 140Ru, 161-49C, 1103P and 110R) were vacuum-inoculated with spore suspensions (10(6) conidia mL(-1)) of the fungal species and planted in two fields. After four months, the proportion of vines that sprouted in spring was visually determined. At the end of the growing season, dormant plants were uprooted, washed, and assessed for undried shoot weight. Then, the stem of each grapevine cutting was transversally split at 10 cm from the base of the plant to estimate the percentage of vascular tissue discoloured on a scale of 0 to 4. All rootstocks inoculated with Ilyonectria and Dactylonectria species were affected by the disease in some degree, the rootstock 110R being the most susceptible to black-foot. Petri disease pathogens caused a significant reduction of sprouting and shoot weight, as well as a significant increase of disease severity percentage in all grapevine rootstocks with the exception of 161-49C. Both 110R and 140Ru were the most susceptible. Grapevine rootstocks showed different levels of disease resistance, being the rootstock 110R the most susceptible to both diseases and the 161-49C rootstock the most tolerant to petri disease infection.