Armillaria root and crown rot disease in pistachio orchards

Pistachio is one of the most important horticultural products in Iran which its production is always affected by biotic and abiotic limiting factors. Armillaria crown and root rot caused by Armillaria mellea, is an important disease in pistachio orchards, which causes the death of fertile trees. Control of the disease is difficult, costly and rarely successful. Symptoms of the disease in shoots of affected trees includes yellowing, early defoliation, sudden wilting, dieback of branches and reduction shoot growth. These symptoms, together with the decay and browning of woody tissues and the formation of white to creamy mycelial sheets in the roots and crown, as well as the observation of rhizomorphs of the fungus, are sufficient evidence for definitive diagnosis of Armillaria crown and root rot in pistachio trees. The infection process begins with the growth of hyphae or rhizomorphs and their firm attachment to the surface of the roots. The pathogen uses a combination of methods such as mechanical pressure, toxin production, and cell wall-degrading enzymes to penetrate the root tissues. Successful control of the disease is possible only by combining chemical, cultural, biological control methods and use of resistant rootstocks and cultivars due to delay in diagnosis of the disease before the spread of the pathogen in plant and soil and the appearance of symptoms, the presence of an extensive network of rhizomorphs at a distance from the tree and deep in the soil and formation of the mycelium beneath the plant bark or inside dead wood.