Yeast spot

Nematospora coryli is a pathogenic yeast-like fungus belonging to the kingdom Fungi, known as the primary cause of a condition commonly referred to as "yeast spot." Unlike filamentous fungi, this organism acts as a yeast pathogen that colonizes the internal tissues of seeds and fruits, causing significant physiological and structural damage.

This pathogen affects a diverse range of crops, including hazelnuts, pistachios, soybeans, tomatoes, and cotton. The disease is characterized by the internal decay of the seed or fruit. Because the infection often occurs inside the fruit, the external appearance might remain relatively normal, while the inside of the kernel or seed is discolored, necrotic, and tastes bitter or spoiled.

The life cycle of Nematospora coryli is uniquely dependent on insect vectors, particularly hemipteran bugs such as stink bugs. The insect feeds on the plant tissue, and through its piercing-sucking mouthparts, it inoculates the fruit with yeast cells. The fungus then utilizes the nutrients within the seed to multiply, causing tissue maceration and enzymatic breakdown of storage proteins and lipids.

Environmental conditions that favor the disease include warm and humid weather, which is also conducive to the activity of the insect vectors. The severity of the outbreak is often tied to the population dynamics of the insects present during the fruit development stage. High humidity can also promote the survival of the fungus on plant debris, serving as an inoculum source for the next season.

Economic damage caused by this pathogen can be severe, as it renders the harvest unmarketable due to the bitter taste and poor quality. Integrated pest management strategies are essential for effective control:

• aggressive management of insect vector populations;
• removal and destruction of symptomatic or damaged fruits;
• maintaining orchard hygiene to reduce potential inoculum;
• timely application of pesticides during the fruit set period.