First report of Trichothecium roseum causing postharvest fruit rot of tomato in Argentina

The presence of microorganisms is one of the most important factors in the depreciation in quality of fresh fruits. Commercial value of fruit decreases due to different pathogens, especially fungi, which manifest their destructive action during storage (Puia et al. 2003). Furthermore, contamination of foodstuffs with moulds such as Trichothecium spp. causes a real risk to the health of consumers because these fungi are producers of mycotoxins (Lugauskas et al. 2005). In particular, tomatoes are susceptible to numerous fruit decays, from the field through postharvest handling.

During the summer of 2008, postharvest fruit rot was found on fresh-market tomatoes (Lycopersicon esculentum Mill.) at storage facilities in La Plata city (34°55′S; 57°57′W). Symptoms started as circular, water-soaked lesions, which enlarged and coalesced into a soft rot covered with white to pinkish powdery mycelium (Fig. 1). The fruit became watery and emitted a sour smell. The pathogen was readily isolated by transferring conidia from diseased tissue onto potato dextrose agar (PDA) amended with 250 mg/L of chloramphenicol. Isolates were incubated with a 12/12 h light/dark cycle using cool white fluorescent and near ultraviolet light, at a temperature of 20 ± 2°C for 7 days. After 4–5 days, the fungus produced abundant septate mycelia, white at first, then pale rosy pink as the conidia developed; conidiophores long, slender, simple and septate with conidia which were borne apically and singly, attached in groups or chains; conidia hyaline or brightly coloured, 2-celled, ovoid, 12–22 × 5–10 µm (Fig. 2), appearing in basipetal succession from the tip of the conidiophore. Based on the morphological structures after single-conidium cultures were established on PDA, the causal agent was identified as Trichothecium roseum (Pers.) Link (Howard et al. 1994).

Pathogenicity was tested by inoculating surface-sterilised healthy, ripe tomato fruits with a 20 µL drop of aqueous conidial suspension (10⁵ conidia/mL) which was injected to a depth of ~1 mm. Fruits inoculated in the same way using sterilised water were kept as a control. Inoculated fruit were placed in a sterilised plastic container at room temperature (21–25°C). Spots similar to those observed on naturally infected fruits developed on inoculated tomatoes within 5 days; whereas control fruits remained healthy (Fig. 1c). Trichothecium roseum was successfully reisolated from the lesions, fulfilling Koch’s Postulates.

The fungus has been cited causing fruit rot on many crops including tomato (Welch et al. 1975; Farr et al. 2007). To our knowledge, this is the first report of T. roseum causing pink mould rot on tomato in Argentina.