Collar Rot of Grapevine Caused by a Novel Pleiocarpon Lineage in Peru

Severe decline and death of young table grape vines (1 to 2 years old) have been observed recurrently in commercial vineyards in Peru since 2022. Affected plants developed rapid shoot wilting associated with extensive necrotic lesions at the rootstock collar below the graft union, leading to plant death within days of symptom onset. A Cylindrocarpon-like fungus was consistently isolated from symptomatic collar tissues. Morphological characterization, cardinal temperature assays, and phylogenetic analyses based on the internal transcribed spacer region (ITS) and histone H3 (his3) gene identified the pathogen as a member of the genus Pleiocarpon. Bayesian inference of concatenated sequences resolved the Peruvian isolates as a distinct lineage sister to P. strelitziae (posterior probability = 1.00). Greenhouse pathogenicity tests with two representative isolates on cv. Red Globe grafted onto Salt Creek rootstock reproduced collar lesions and shoot wilting, fulfilling Koch's postulates. Optimal mycelial growth occurred between 25.7 to 26.1°C, and maximum experimental growth was observed between 28.8 to 31.5°C, consistent with warm conditions during vineyard establishment in coastal Peru. The disease, designated here as collar rot of grapevine, is pathologically distinct from classical black-foot disease due to its extensive belowground collar necrosis and rapid vine collapse. Recurrent outbreaks and the near-exclusive use of the susceptible Salt Creek rootstock indicate that Pleiocarpon-associated collar rot is an emerging threat to table grape production in Peru.