Heat tolerance of <i>Colletotrichum fioriniae</i> and cranberry cutting viability following hot water treatment

Cranberries are vegetatively propagated, yet the industry lacks standardized treatments or regulations to prevent pathogen transmission through field-sourced propagative material. This study evaluated heat treatments as a potential strategy for mitigating fruit rot fungi survival. A three-part experiment was conducted. First, <i>Colletotrichum fioriniae</i> conidia were tested in vitro for heat tolerance, against 25, 37, 42, 44, 47, and 49°C, showing reduced survival at 44°C and complete mortality at 47°C and 49°C. Second, greenhouse trials assessed cranberry cutting survival following hot water treatments. Field-sourced cuttings of two cultivars ('Stevens' and 'Mullica Queen') were exposed to 37, 42, 44, 47, and 49°C, alongside a non-treated control (25°C). Cuttings remained viable up to 49°C, with no significant differences in survival compared to controls (P = 0.991 and P = 0.365 for 'Stevens' and 'Mullica Queen', respectively). Finally, two trials tested the efficacy of heat treatments on cuttings inoculated with <i>C. fioriniae</i> conidia. Treatments at 47°C and 49°C significantly improved survival for 'Stevens' (P = 0.0081 and P = 0.0045) and 'Mullica Queen' (P = 0.0427 and P = 0.00000021). These results indicate that short-duration hot water treatments can reduce survival of <i>C. fioriniae</i> conidia under controlled conditions while maintaining cranberry cutting viability, supporting further evaluation of heat treatment as a potential sanitation step for cranberry propagation material.