Rhodotorula gracilis

Rhodotorula gracilis is a species of basidiomycetous yeast recognized for its ability to produce carotenoid pigments, which give its colonies a distinct pink or red hue. While often found in soil and aquatic environments, it is increasingly documented as a factor in the spoilage of fruits and vegetables. In agricultural practice, it acts as an opportunistic pathogen that thrives on damaged plant tissues, leading to significant economic losses during storage and transit.

This pathogen primarily targets fleshy fruits and vegetables, including tomatoes, cucumbers, and various stone fruits. It does not typically attack healthy, intact plant surfaces but exploits micro-cracks, punctures, or areas damaged by insect activity. Once inside the tissue, the yeast proliferates rapidly, utilizing the sugars available in the fruit, which often leads to the development of secondary bacterial or fungal rots that destroy the integrity of the product.

The symptoms of Rhodotorula gracilis infection are highly characteristic. Growers and inspectors can identify it by the appearance of a glossy, slimy, reddish-orange film on the surface of the fruit. Unlike filamentous fungi, which produce fuzzy mycelium, this pathogen creates a smooth, wet appearance. Infected tissues often become soft, lose their structural integrity, and emit a faint, acidic, or fermented odor, signaling advanced microbial activity.

Environmental conditions are the primary drivers of spread for this microorganism. It favors environments with high humidity and temperatures ranging from 20°C to 25°C. In the field, the yeast can be disseminated by wind, rain splashes, and insect vectors. Once in the storage environment, if ventilation is poor and relative humidity is high, the pathogen spreads through contact and contaminated equipment, quickly turning minor localized infections into widespread spoilage of the stored crop.

Control measures must focus on both field-level prevention and post-harvest management. Effective strategies include maintaining proper orchard and field hygiene by removing decaying organic matter, minimizing mechanical injury to crops during harvest, and ensuring optimal storage conditions with controlled temperature and humidity. Chemical control typically involves broad-spectrum fungicides used during the late stages of crop maturation, while sanitation of storage facilities remains the most critical step to prevent cross-contamination.