Fungi associated with healthy grapevine cuttings in nurseries, with special reference to pathogens involved in the decline of young vines
Little information is presently available on the disease aetiology and epidemiology of the fungi involved in the decline of young vines. To address this question, four rootstock-scion combinations, originating from three commercial nurseries in the Wellington area of the Western Cape Province of South Africa were investigated during the 1999/2000 season. The first isolations were made in September from callused cuttings prior to planting in nurseries. After planting, asymptomatic rooted cuttings were selected from nurseries after 3, 6 and 9 months. Isolations were made from the roots, rootstock, grafting union and scion. Isolations from callused cuttings prior to planting clearly demonstrated that primary pathogens associated with Petri disease, such as Phaeomoniella chlamydospora and Phaeoacremonium spp. were already present in the apparently healthy rootstock propagation material as endophytes. However, Cylindrocarpon spp., which cause black foot disease, rarely occurred in propagation material at this time. Species of this genus were isolated at higher percentages later during the season. Less than 1% of the plants were infected with Cylindrocarpon spp. before planting in the nursery (October), whereas 50% or more of the plants were infected at the end of the season (June). These findings suggest that the low percentage survival of vine plants observed in recent years is partly due to infected propagation material, and to new infections established in nurseries.