Occurrence and diversity of black-foot pathogens on asymptomatic nursery-produced grapevines in Turkiye

Black-foot (BF) disease of grapevines in nurseries and young vineyards is caused by soil-borne Cylindrocarpon-like asexual morphs. They can be found both in symptomatic and asymptomatic vines, being spread to new grape growing areas during vineyard establishment. In this study, 42 grapevine nurseries located in different geographical regions in Turkiye were surveyed in 2021 to determine the presence of BF pathogens on asymptomatic marketable plants. Black-foot fungi were isolated from the roots or basal ends of asymptomatic dormant vines in 39 of the nurseries (92.9%). The percentage of isolation of BF pathogens ranged from 1.4 to 51.4% (average 18.4%). Seven species: Cylindrodendrum alicantinum, Cylindrocladiella peruviana, Dactylonectria macrodidyma, D. novozelandica, D. torresensis, Ilyonectria liriodendri, and I. robusta were identified based on DNA sequencing of histone H3 gene and phylogenetic analyses, D. torresensis being the most frequent. From these species Ca. peruviana, D. novozelandica and I. robusta were detected for the first time on grapevines in Turkiye. Pathogenicity tests on 1103P rootstock cuttings revealed that all species significantly decreased root biomass and increased root disease severity index, when compared with the non-inoculated control, D. novozelandica being the most virulent. Pathogenicity of Cm. alicantinum to grapevine was confirmed for the first time, thus this species should be included as causal agent of BF of grapevines. These findings point out that BF pathogens are highly prevalent in the nurseries and could represent a serious threat for Turkish viticulture.