3.7.61
YOUNG GRAPEVINE DECLINE CAUSED BY PHAEOACREMONIUM SPP. AND CYLINDROCARPONSPP. IN CALIFORNIA

WD GUBLER, HJ SCHECK and SJ VASQUEZ

Department of Plant Pathology, University of California, Davis 95616, USA

Background and objectives
Vineyard replanting because of outbreaks of Phylloxera infestations is occurring in many of the premium wine production areas of California. New rootstocks are being used to combat this insect pest but their use is also resulting in more diseases caused by soilborne fungal pathogens. For the past four years, young vines in some production areas exhibited symptoms of decline including leaf stunting, chlorosis, interveinal chlorosis followed by necrosis. and leaf fall. Vine death occurred in few instances, however, affected vines showed little promise of recovering to the point of normal productivity. Internally, vascular tissue was discoiored and pith was discolored and compacted. In cross section, black gumming occurred in or near occluded vessels. Data was compiled from various production areas to determine relative occurrence of pathogens on new rootstocks. Research was conducted to establish the aetiology of young vine decline.

Materials and methods
Samples of declining young vines were submitted between 1994 and 1998. lsolations made from symptomatic tissue revealed three species of Phaeoacremonium: P. inflatipes, P. chlamydosporum, P. aleophilum, fungi previously recorded as pathogens of old vines, andlor Cylindrocarpon obtusisporum. Cuttings of 'Thompson Seedless' vines were rooted and roots were soaked for 30 minutes in a spore suspension (108) of P. inflatipes. Rooted cuttings were held for 6 months in a greenhouse at 24C. P. inflatipes, P, chlamydosporum, P. aleophilum, and C. obtusisporum were used in separate pathogenicity studies with cv. 'Carignane' seedlings. Seedlings were inoculated by the same method, and held in a controlled environment facility at 24C. Roots of control cuttings and seedlings were soaked in distilled water. Plants were destructively sampled, symptoms recorded, and isolations made to verify Koch's postulates.

Results and conclusions
We have consistently isolated four species of plant pathogenic fungi from symptomatic young vines from a variety of important new rootstocks including 5BB, 5C, 11OR, 101-14, 3309, Freedom, Harmony and St. George. P, aleophilum has only been isolated from high temperature growing areas in southern CA, while P, chiamydosporum, P. inflatipes and C, obtusisporum are distributed throughout the northern and central production areas. Cuttings inoculated with P. inflatipes developed root lesions, vascular discoloration, and leaf chlorosis and necrosis within 6 months. Seedlings inoculated with P. inflatipes, P. chlamydosporum, P. aleophilum or C. obtusisporum developed root lesions, stem lesions, and vascular discoloration, and wilted within 12 weeks. Individual pathogens were reisolated at high frequency. All three Phaeoacremonium spp. are associated with wilt and decline diseases in older vines in Africa and Europe [1]. We propose that the common name Phaeoacremonium grapevine disease be used with all three species. Both C. obtusisporum and C. destructans are reported as pathogens on young vines in Europe [2]. We propose the common name Cylindrocarpon black-foot disease be used with both species. No obvious relationship exists between rootstock variety and the severity of either Phaeoacremonium grapevine decline or Cylindrocarpon black-foot disease.

References
1. Crous PW, Gains W, Wingfield J, vanWyk PS, 1996. Mycologia 88, 786-796.
2. Grasso S, Magnano-di-San-Lio G, 1975. Vitis 14, 36-39.