Pistachio leptosilliosis

Leptosilliosis is a significant fungal disease caused by the pathogen Leptosillia pistaciae. This microorganism is a specialized parasite that primarily affects the woody parts and leaves of pistachio trees. The disease belongs to the group of ascomycetes that thrive under the specific climatic conditions found in regions where this crop is cultivated.

The main host for this pathogen is the true pistachio (Pistacia vera). The pathogen attacks both young shoots and mature branches, causing necrotic tissue changes. In some cases, the infection can spread to the leaves, leading to premature defoliation and significantly weakening the tree before the dormant winter season.

The symptoms of the disease appear as distinct spots on the affected organs. At the point of infection, dark necrosis develops, which may eventually girdle the shoots.

• Spotting on leaves and branches.
• Dieback of shoot tips.
• Formation of small fungal fruiting bodies (pycnidia) on dead bark.
• Bark cracking and damage to the cambium layer.

The development of Leptosillia pistaciae is favored by high humidity, frequent rainfall during the growing season, and the presence of wounds on the tree bark. Fungal spores are dispersed by wind, water splashes, and insect pests. The optimal temperature for mycelial growth falls within moderate ranges, making orchards particularly vulnerable during the spring and autumn months.

The economic impact of the disease stems from the loss of photosynthetic area and the disruption of nutrient transport within the tree. Chronic infestation leads to progressive branch dieback, which reduces pistachio yields and can eventually kill the tree if neglected. To protect orchards, growers should practice sanitary pruning of infected parts followed by disinfection, along with preventative applications of copper-based fungicides during dormancy and active growth periods.