Efficacy of disinfectants against Tropical Race 4 causing Fusarium wilt in Cavendish bananas

Fusarium wilt is one of the most damaging diseases of banana that currently puts the global production and food security at risk. The causal agents belong to the genus Fusarium and the soilborne species that is currently threatening Cavendish varieties and many locally important cultivars is F. odoratissimum, colloquially called Tropical Race 4 (TR4), which spreads easily and rapidly within and between farms. Even though limited information exists on the efficacy of disinfectants, they are promoted as a front-line defense against the spread of TR4 in the banana production areas by equipment and human activity. In this study, 13 disinfectants, the majority marketed in the Philippines, were tested for efficacy on TR4 mycelium, conidia, chlamydospores suspensions and chlamydospore-infested soil. They encompass five chemical groups, quaternary ammonium, halogens, alcohols, diamidines and aldehydes, and were tested at a range of concentrations and exposure times. Conidiospores were sensitive to all tested disinfectants at the manufacturer’s suggested rates. Ten disinfectants controlled mycelial growth with the exception of the quaternary ammonium-based disinfectant GUAA. Eleven disinfectants showed adequate efficacy at all tested concentrations towards chlamydospores in suspension, whereas a calcium hypochlorite-based disinfectant lacked efficacy at all concentrations tested. Despite in vitro efficacy, all disinfectants, except the diamidine-based disinfectant Formo, were largely ineffective in treating chlamydospores present in soil (in situ). However, Formo is corrosive to metals, making it less suitable for various applications. The in vitro results illustrate that overall efficacy of disinfectants depends on the fungal propagule, exposure time, and the environment in which they are exposed. We also determined the exposure times of footwear and vehicles in sanitation baths under field conditions and conclude that those significantly deviate from the minimal required contact time under in vitro conditions. Suboptimal quarantine measures, therefore, are likely to contribute to continued local, regional, and international TR4 dissemination.