Scleromitrula shiraiana

Scleromitrula shiraiana is a pathogenic fungus that specifically targets mulberry trees (Morus spp.), causing a devastating disease known as mulberry sclerotinia or flower-fruit mummification. This pathogen belongs to the Ascomycota phylum and is known for its ability to transform healthy developing fruit into hardened, black, non-viable structures called sclerotia.

The fungus primarily attacks the reproductive organs of the tree. Infection typically occurs during the flowering stage, where airborne spores land on the stigmas of the flowers. Once inside, the fungus colonizes the tissues, leading to the distortion and complete decay of the young fruit buds before they can mature into edible berries.

Environmental conditions play a crucial role in the disease cycle. High relative humidity and frequent rainfall during the spring, which aligns with the blooming period, create the perfect conditions for the germination of overwintering sclerotia. These sclerotia produce fruiting bodies that release spores, which then spread the infection rapidly throughout the orchard.

The economic impact of Scleromitrula shiraiana is significant, as it can lead to total crop failure. In heavily infested orchards, the yield reduction can exceed 80%, severely affecting the fruit production. Furthermore, the persistence of sclerotia in the soil ensures that the disease cycle will continue in subsequent years unless aggressive management is implemented.

To effectively manage and prevent the spread of this pathogen, producers should follow these practices:

• Sanitation: Regularly collect and destroy all mummified fruits and debris under the canopy.
• Cultivation: Deep plow the soil in late winter to bury sclerotia, preventing them from producing spores.
• Chemical control: Apply appropriate fungicides at the onset of the flowering stage to protect healthy blooms.
• Orchard hygiene: Ensure proper spacing and pruning of trees to increase airflow and reduce moisture levels.