Thermotherapy via aerated steam is an effective alternative for non-chemical management of cryptic infection of strawberry by Colletotrichum acutatum.

Abstract

Annual strawberry production in Florida is threatened by anthracnose, caused by Colletotrichum acutatum. This disease is often transmitted through quiescently infected transplants from strawberry nurseries. Managing anthracnose has become even more difficult in both nursery and fruit production fields since the rise of strains resistant to QoI fungicides. In this study, thermotherapy was evaluated as a potential alternative to manage the disease by reducing inoculum in plant stock. Initial laboratory assessments demonstrated that the germination of C. acutatum spores was entirely suppressed upon exposure to 44°C for 120 min, 48°C for 10 min, or 52°C for 5 min. Conversely, a minor proportion of C. acutatum spores (less than 10%) sustained viability, even after being subjected to 40°C for 240 min. Heat treatment of strawberry transplants at 44°C for 240 min, with or without a preheating step (37°C for 1 h), via aerated steam, significantly reduced the colonization of petioles by C. acutatum. Early season harvest data from field trials showed that heat-treated plants, with or without a pre-heating phase, had considerably lower fruit disease incidence and higher yield than the nontreated controls. These findings suggest that heat treatment via aerated steam might be a viable means to decrease C. acutatum inoculum in strawberry transplants, thereby reducing anthracnose in fruit-producing areas.