Emerging Collar Rot of Young Table Grapevines Associated with Pleiocarpon sp. in Coastal Peru.

Severe decline and death of young table grapevines (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 (ITS) region 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 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 was estimated at 28.7-29.3 °C, with maximum colony growth recorded at 30 °C, consistent with the warm conditions that prevail during vineyard establishment in coastal Peru. Designated here as collar rot, the syndrome represents an atypically severe form of black foot disease, characterized by extensive belowground collar necrosis and rapid vine collapse soon after planting. Its recurrence across regions and seasons, together with the near-exclusive deployment of a single rootstock (Salt Creek), indicates that Pleiocarpon-associated collar rot is an emerging threat to young table grape plantings in Peru, underscoring the need for early diagnosis, pathogen-free nursery material, and preventive management during vineyard establishment.