White sooty blotch

White sooty blotch is a fungal disease caused by the pathogen Gloeodes pomigena (and related species), characterized by the development of light-colored, superficial spots on the surface of fruit. Unlike systemic infections, this disease affects only the cuticle and the outer layers of the fruit skin, making it primarily a cosmetic issue that impacts the market value of the crop.

The pathogen hosts a wide range of fruit species, including pome fruits like apples and pears, as well as various tropical crops such as the Indian mango. The fungus persists on twigs and branches, acting as a recurring source of inoculum that spreads to developing fruits during the growing season when environmental conditions permit.

Symptoms are manifested as white to greyish-white, roughly circular spots that often have a velvety or powdery appearance. These colonies are superficial and can sometimes be removed with friction, but they cause significant discoloration and marring of the fruit's surface, which is detrimental to the visual quality required for fresh market sales.

The development of White sooty blotch is heavily dependent on high humidity and rainfall. The disease thrives in orchards with poor air circulation, often found in dense or unpruned canopy structures where moisture persists for extended periods. Warm, humid summers provide the optimal environment for spore germination and colony establishment on fruit skins.

Economic damage is largely due to the downgrading of fruit quality. Produce with noticeable blotches is often rejected by retailers or fetch significantly lower prices. Additionally, the presence of these fungal colonies can slightly increase the transpiration rate of the fruit, leading to faster shriveling and reduced shelf life during cold storage.

Prevention and management strategies focus on modifying the orchard environment and minimizing pathogen spread:

• Implementing annual pruning to improve light penetration and air movement within the tree canopy.
• Maintaining proper spacing between trees to prevent the formation of humid microclimates.
• Sanitation practices, including the removal of dead or infected branches.
• Applying prophylactic fungicide sprays during periods of high humidity and rainfall.