Novel Seimatosporium Species from Grapevine in Northern California and Their Interactions with Fungal Pathogens Involved in the Trunk-Disease Complex.

Seimatosporium spp. and closely related "pestalotioid fungi" have been isolated from vineyards worldwide, but their ecological status in grapevine wood is unclear. To determine their involvement in the grapevine trunk-disease complex, we tested the pathogenicity of Californian isolates obtained from vines with general symptoms of Botryosphaeria, Eutypa, and Phomopsis diebacks. Multilocus phylogenetic analyses revealed three species: Seimatosporium vitis and two newly described and typified species, S. luteosporum sp. nov. and S. vitifusiforme sp. nov. Inoculations to woody stems of potted grapevines of both isolates of S. vitis and one isolate of S. vitifusiforme, but not S. luteosporum, were associated with significantly larger lesions than those of noninoculated controls. Coinoculations with trunk pathogens (Cryptovalsa ampelina, Diaporthe ambigua, Diatrypella verruciformis, Diplodia seriata, and Eutypa lata), coisolated from the same wood cankers in the field, brought about increased lesion lengths for S. vitifusiforme paired with D. seriata, and S. luteosporum paired with Diaporthe ambigua. In contrast, there were no differences in lesion lengths of S. vitis and Diatrypella verruciformis or S. vitis and E. lata, inoculated alone or together. Our findings suggest that Seimatosporium spp. are involved in the grapevine trunk-disease complex, and their virulence may depend on or affect that of trunk pathogens.