The effects of moisture on the production of T-2 and HT-2 toxins and their ratio in wheat contaminated with Fusarium langsethiae

Mycotoxins are secondary metabolites produced by filamentous fungi that often play an important role in plant pathogenesis and spreading of fungal infection.

T-2 and HT-2 toxins are type-A trichothecenes produced by different Fusarium species.

⇰ T-2 toxin is rapidly metabolized to HT-2 toxin which is also the main metabolite in vivo (Eriksen y Alexander, 1998; Visconti, 2001).

Fusarium langsethiae, F. poae and F. sporotrichioides are the predominant species that invade cereal crops and produce T-2 and HT-2 toxins under cool and moist conditions in the field (Krska, 2014).

T-2 and HT-2 toxins are produced under conditions that are not optimal for the growth of these moulds (Hodgson, 2000).

Various studies propose different temperatures to be optimal for trichothecene production.

• Mateo (2002) reported that 20 °C was the most suitable for trichothecene production in general.
• Medina (2010) found 20–30 °C as optimal range for F. langsethiae.
• Nazari (2013) reported 15 °C for F. langsethiae as the optimal temperatures for T-2 and HT-2 production.

In this small-scale experiment, the effect of different moisture levels on T-2 and HT-2 toxin production — and on the changing ratio between both toxins — by the Fusarium langsethiae strain Fe2391 was evaluated.

The mould was cultivated on 100 g of whole wheat grains in 450 ml aluminium trays (130 × 105 × 40 mm).

The wheat was inoculated with one-sixth of a mould culture grown on potato dextrose agar in a 90 mm Petri dish.

The samples were incubated for 14 days at 20 °C.

Three moisture levels were tested by adding 30 ml, 40 ml, and 50 ml of tap water and leaving the samples to soak overnight.

The samples were covered with aluminium foil, and in half of them the foil was perforated to test the effect of allowing water to evaporate from the sample.

At the end of the incubation period, the cultures were dried in a drying oven, milled, and the T-2 and HT-2 toxin yields were quantified using LC-MS/MS.

All experiments were carried out with one sample per treatment.

The results revealed a trend in T-2 and HT-2 toxin production and in their changing ratio (FigurE 1).

• Samples with 30 ml of added water showed the highest T-2/HT-2 toxin ratios (1.88 and 1.77).
• In samples with 40 ml of added water, the ratio decreased (1.09 and 0.98).
• Adding 50 ml of water inverted the T-2/HT-2 ratio (0.86 and 0.80).

The highest total toxin level was recorded at 40 ml of added water in both the perforated and non-perforated foil samples, with equal levels of T-2 and HT-2 produced.

Perforating the aluminium foil only affected T-2 and HT-2 production significantly when 30 ml of water was added, resulting in a 47.9 % decrease in total toxin production.

In samples with 40 ml and 50 ml of added water, perforating the foil decreased total toxin production by 3.3 % and 17.4 %, respectively (Figure 2).