Characterisation and management of trunk disease-causing pathogens on table grapevines

[摘要] ENGLISH ABSTRACT: Phaeomoniella chlamydospora, Eutypa lata, Phomopsis, Phaeoacremonium, andBotryosphaeria spp. are important trunk disease pathogens that cause premature decline anddieback of grapevine. Previous research has focused primarily on wine grapes and the incidenceand symptomatology of these pathogens on table grapes were largely unknown. A survey wastherefore conducted to determine the status and distribution of these pathogens and associatedsymptoms in climatically diverse table grape growing regions. Fifteen farms were identified inthe winter rainfall (De Doorns, Paarl and Trawal) and summer rainfall (Upington andGroblersdal) areas. Samples were taken in July and August 2004 from Dan-ben-Hannahvineyards that were 8 years and older. Distal ends of arms were removed from 20 randomlyselected plants in each vineyard. These sections were dissected and isolations were made fromeach of the various symptom types observed: brown or black vascular streaking, brown internalnecrosis, wedge-shaped necrosis, watery necrosis, esca-like brown and yellow soft wood rot, aswell as asymptomatic wood. Fungal isolates were identified using molecular and morphologicaltechniques. Pa. chlamydospora was most frequently isolated (46.0%), followed byPhaeoacremonium aleophilum (10.0%), Phomopsis viticola (3.0%), Botryosphaeria obtusa(3.0%), B. rhodina (2.2%), B. parva (2.0%), Fusicoccum vitifusiforme (0.6%), B. australis, B.dothidea and an undescribed Diplodia sp. (0.2% each), while E. lata was not found. Most ofthese pathogens were isolated from a variety of symptom types, indicating that disease diagnosiscan not be based on symptomatology alone. Pa. chlamydospora was isolated from all areassampled, although most frequently from the winter rainfall region. Pm. aleophilum was foundpredominantly in Paarl, while P. viticola only occurred in this area. Although B. obtusa was notisolated from samples taken in De Doorns and Groblersdal, it was the most commonly isolatedBotryosphaeria sp., being isolated from Upington, Paarl and Trawal. B. rhodina occurred onlyin Groblersdal and B. parva in Paarl, Trawal and Groblersdal, while B. australis was isolatedfrom Paarl only. The rest of the isolates (33%) consisted of sterile cultures, Exochalara,Cephalosporium, Wangiella, Scytalidium, Penicillium spp. and two unidentified basidiomycetes,which were isolated from five samples with yellow esca-like symptoms from the Paarl area. These findings clearly illustrate that grapevine trunk diseases are caused by a complex of fungalpathogens, which has serious implications for disease diagnosis and management.Protection of wounds against infection by any of these trunk disease pathogens is themost efficient and cost-effective means to prevent grapevine trunk diseases. However, previousresearch on the effectiveness of chemical pruning wound protectants has mostly focused on thecontrol of Eutypa dieback only. Fungicide sensitivity studies have been conducted for Pa.chlamydospora, P. viticola and Eutypa lata, but no such studies have been conducted for thepathogenic Botryosphaeria species from grapevine in South Africa. Ten fungicides weretherefore tested in vitro for their efficacy on mycelial inhibition of the four most common and/orpathogenic Botryosphaeria species in South Africa, B. australis, B. obtusa, B. parva and B.rhodina. Iprodione, pyrimethanil, copper ammonium acetate, kresoxim-methyl and boscalidwere ineffective in inhibiting the mycelial growth at the highest concentration tested (5 μg/ml;20 μg/ml for copper ammonium acetate). Benomyl, tebuconazole, prochloraz manganesechloride and flusilazole were the most effective fungicides with EC50 values for the differentspecies ranging from 0.36-0.55, 0.07-0.17, 0.07-1.15 and 0.04-0.36 μg/ml, respectively. Thesefungicides, except prochloraz manganese chloride, are registered on grapes in South Africa andwere also reported to be effective against Pa. chlamydospora, P. viticola and E. lata. Resultsfrom bioassays on 1-year-old Chenin Blanc grapevine shoots indicated that benomyl,tebuconazole and prochloraz manganese chloride were most effective in limiting lesion length inpruning wounds that were inoculated with the Botryosphaeria spp after fungicide treatment. Thebioassay findings were, however, inconclusive due to low and varied re-isolation data of theinoculated lesions. Benomyl, tebuconazole, prochloraz manganese chloride and flusilazole cannonetheless be identified as fungicides to be evaluated as pruning wound protectants inadditional bioassays and vineyard trials against Botryosphaeria spp. as well as the othergrapevine trunk disease pathogens.

[发布机构] Stellenbosch University