Effect of temperature, relative humidity and incubation time on the mycotoxin production by Fusarium spp. responsible for dry rot in potato tubers

Potato is the fourth most consumed crop around the world. More than half of the potato crop is stored for three to nine months at cold temperatures (3- 10°C) for the fresh and seed market. One of the main causes of fresh potato waste in the retail supply chain is the appearance of fungal and bacterial rots during storage, around 3-5% of the potato crop is lost every year. Dry rot is a fungal disease that mainly affects the potato crop during storage and is responsible for a large volume of waste and associated economic losses. It is produced by Fusarium spp., such as Fusarium sambucinum and F. oxysporum. Understanding the ecophysiology of these fungi is a key point to mitigate their occurrence under commercial storage conditions. Therefore, this work aimed to elucidate the effect of three different temperatures (5, 10 and 15°C) and two different water activities (aw; 0.97, 0.99) on the ecophysiology and mycotoxin accumulation of F. sambucinum and F. oxysporum in a potato-based semi-synthetic medium. The mycotoxin accumulation was then studied in vivo, in potato tubers stored for 40 days at 8.5°C. Results showed that higher temperatures and aw enhanced fungal growth, lag time and mycotoxin accumulation in vitro. Six different mycotoxins (r-2, HT-2, diacetoxyscirpenol, 15-acetoxyscirpenol, neosolaniol and beau-vericin) were detected in vitro and in vivo. Due to the long period of time that potato tubers spend in storage, the fluctuations of environmental factors, such as temperature and relative humidity, could promote the development of fungal rots, as well as mycotoxin accumulation. This could result in important food and economical losses for the potato market, as well as a threat to the food safety of potato tubers