First Report of Perithecia of Phaeoacremonium viticola on Grapevine (Vitis vinifera) and Ash Tree (Fraxinus latifolia) in California

Abstract

Esca and Petri diseases on grapevine are caused by Phaeomoniella chlamydospora and species of Phaeoacremonium including P. aleophilum, P. viticola, P. angustius, P. parasiticum, P. inflatipes, P. rubrigenum, and P. mortoniae. The teleomorphs of P. aleophilum and P. mortoniae have been recently confirmed as Togninia minima(Tul. & C. Tul.) Berl. (2,3), and T. fraxinopennsylvanica (Hinds) Hausner, Eyjólfsdóttir & J. Reid, respectively (1,2,3). Teleomorphs of other Phaeoacremonium spp. have not been identified, although molecular data suggests that Phaeaoacremonium spp. are linked to the genus Togninia. Naturally infected vineyards with symptoms of esca disease were surveyed during the summer and fall of 2004. Samples were collected from declining ash trees surrounding the vineyards, as well as from symptomatic grapevine trunks, cordons, and spurs. Samples were processed as previously described (1). Sterile isolations were also made from symptomatic vascular tissue of the samples and cultured on potato dextrose agar (PDA)-tet medium. Perithecia were found on the surfaces of old pruning wounds and in the cracks of cordons and trunks on Vitis vinifera cvs. Thompson Seedless, Riesling, and Cabernet Sauvignon. Perithecia were observed on grapevines in vineyards in six of nine counties, viz. Yolo, Mendocino, El Dorado, Tulare, Madera, and Sonoma. Perithecia were also observed in dead vascular tissue of declining ash tree branches (Fraxinus latifolia) located in the vicinity of vineyards in Sonoma and Yolo counties. Perithecia were black, globose to subglobose, ranging from 160 to 215 μm in diameter, and were both embedded in and superficial on the wood tissue. Neck lengths ranged from 55 to 340 μm. The asci were hyaline, clavate, and ranged in size from 12.5 to 19.5 × 3.2 to 4.5 μm. Ascospores were hyaline, ellipsoid to allantoid, and ranged in size from 3.1 to 4.1 × 1.8 to 2.1 μm. Morphologically these perithecia resemble those of Togninia spp. When plated onto PDA-tet medium, ascospores formed colonies of P. viticola after 10 days of incubation at room temperature. Additionally, P. viticola was isolated from vascular tissue of the collected plant specimens. To our knowledge, this is the first time that P. viticola has been linked to a sexual state. References: (1) A. Eskalen et al. Plant Dis. 89:528, 2005. (2) L. Mostert et al. Mycologia 95:646, 2003. (3) S. Rooney-Latham. Plant Dis. 89:177, 2005.