Phytopythium helicoides Associated with Root Rot of Sweet Cherry in Chile: Identification, Pathogenicity, and Incidence of Decline Symptoms.

Species within the genus Phytopythium have recently been recognized as significant soilborne pathogens impacting various crops globally. However, their occurrence and pathogenicity in sweet cherry (Prunus avium) have not been studied in Chile before. This study aimed to identify Phytopythium isolates associated with root rot decline in cherry plants and to assess their pathogenicity under controlled conditions and in the field. Symptoms were recorded, and cherry plants grafted onto Maxma14 samples were collected from a commercial orchard in the Valparaíso region. We obtained isolates using selective media and characterized them based on morphological characteristics and molecular analysis of the internal transcribed spacer (ITS), cytochrome c oxidase subunit I (COX I), and β-tubulin regions. Phylogenetic analysis based on the three concatenated regions supported the placement of the three isolates within the Phytopythium. helicoides clade. Incidence across three sectors of a commercial orchard ranged from 24.3% to 42.8%. Pathogenicity tests involved inoculating one-year-old Prunus avium 'Lapins' plants grafted onto MaxMa14 rootstock by drenching the substrate with 300 mL of a zoospore suspension (1 × 104 zoospores/mL) and evaluating them 90 days post-inoculation. Inoculated plants exhibited reduced growth, foliar symptoms, and root necrosis, compared with non-inoculated controls. These findings confirm that Phytopythium helicoides can be pathogenic in cherry trees and underscore its emerging role as a soilborne pathogen in Chilean cherry production systems.