ARS | Publication request: Characterization of species of Diaporthe from wood cankers of grape in eastern North American vineyards

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 2013
Publication Date: N/A

Interpretive Summary: In eastern North American vineyards, Phomopsis cane and leaf spot (causal fungus Phomopsis viticola) is a destructive disease on the foliage of grape, but another type of symptom is sometimes also found in the wood (wood canker). To determine the association between foliar and wood-canker symptoms, we recovered the fungus Phomopsis from wood cankers in 23 vineyards with foliar symptoms, in eight northeastern US states and Quebec, Canada. Identification of the fungus was based on the size of its spores and on molecular analyses of different regions of the fungal genome. We identified nine isolates as P. viticola, which was the most aggressive on woody stems of Vitis labruscana ‘Concord’ and V. vinifera ‘Chardonnay’ in spore inoculations of potted grape plants (average canker size of 13.5 mm). The 20 remaining isolates were identified as P. fukushii, Diaporthe eres, and P. cuppatea, the latter of which did not sporulate and was, thus, not included in inoculation assays. Diaporthe eres and P. fukushii were pathogenic (canker sizes of 7.4 and 7.1 mm, respectively), but less so than P. viticola. Our findings suggest that foliar and wood-canker symptoms co-occur frequently. If these fungi directly infect woody tissues, then controls for preventing the foliar symptoms of the disease may not prevent wood cankers.

Technical Abstract: In eastern North American vineyards, Phomopsis cane and leaf spot (causal fungus Phomopsis viticola) is a destructive foliar disease, but is also associated with wood cankers, along with other fungi. To determine the association between foliar and wood-canker symptoms, we recovered Phomopsis isolates from wood cankers in 23 vineyards with a history of foliar symptoms, in eight northeastern US states and Quebec, Canada. Identification of was based on morphology and molecular analyses of internal transcribed spacer region (ITS), elongation factor subunit 1-alpha, and actin. We identified nine isolates as P. viticola, which was the most aggressive on woody stems of Vitis labruscana ‘Concord’ and V. vinifera ‘Chardonnay’ in spore inoculations of potted plants (mean lesion length of 13.5 mm). The 20 remaining isolates were identified based primarily on high ITS identity to known isolates as P. fukushii, Diaporthe eres, and P. cuppatea, the latter of which did not sporulate. Diaporthe eres and P. fukushii were pathogenic (mean lesion lengths of 7.4 and 7.1 mm, respectively), but less so than P. viticola. Our findings suggest that foliar and wood-canker symptoms co-occur frequently. If these species directly infect woody tissues, then controls for preventing foliar symptoms may not prevent wood cankers.