Identification, Incidence, and Pathogenicity of Fungal Species Associated with Grapevine Dieback in Texas

Abstract

Grapevine cankers and consequent dieback have been commonly observed in Texas vineyards. However, identity of the grapevine canker-causing agents in Texas has not been reported. Between 2007 and 2009, diseased grapevine samples showing perennial cankers from 45 vineyards in Texas were collected and inspected for fungal identification. Eleven fungal species—<i>Lasiodiplodia theobromae</i>, <i>Botryosphaeria dothidea</i>, <i>Neofusicoccum parvum</i>, <i>Diplodia seriata</i>, <i>Diplodia corticola</i>, <i>Phomopsis viticola</i>, <i>Eutypella vitis</i>, <i>Diatrypella</i> sp., <i>Truncatella</i> sp., <i>Pestalotiopsis uvicola</i>, and <i>Pestalotiopsis</i> sp.—were isolated from grapevine cankers and identified based on morphological characteristics and analyses of nucleotide sequences of the internal transcribed spacer region (ITS1-5.8S-ITS2). Botryosphaeriaceae spp. were the most common fungi isolated from grapevine dieback in Texas followed by <i>Pestalotiopsis</i> spp., <i>P. viticola</i>, and Diatrypaceae spp. Pathogenicity of all species was verified by inoculation of excised mature lignified dormant canes of Redglobe and Cabernet Sauvignon grapevines under controlled laboratory conditions. Isolates of <i>L. theobromae</i> and <i>N. parvum</i> were the most virulent based on the length of vascular necrosis in the wood and percentage of fungal re-isolation. <i>Phomopsis viticola</i> isolates followed in virulence to <i>L. theobromae</i> and <i>N. parvum</i> and were shown to be capable of colonizing mature wood and cause vascular necrosis and cankers. The diatrypaceous fungi <i>E. vitis</i> and <i>Diatrypella</i> sp. were the least virulent to grapevines among all fungi tested. All these fungal species represent newly recorded fungal pathogens of grapevines in Texas. Moreover, the association of <i>D. corticola</i> with grapevines is reported.