وقوع خشکیدگی برگ نخل خرما ناشی از Pestalotiopsis palmarum در خوزستان

Date palm (Phoenix dactylifera L.) with a surface area of about 31300 hectares with 144.200 tons production is one of the most important and strategic gardening products in Khuzestan province, which plays an important role. In early spring of 2015, signs of drying and burning were observed in the lower leaves of various cultivars of Berighi, Sayer, Deyri and Zahedi on the palm groves of Abadan, Ahvaz, Shadegan and Khorramshahr areas south of Khuzestan province. Signs and symptoms were found mainly on the leaves, the main rachis and the petiole's leaves. The first symptoms spread on elderly leaves and then to the higher leaves of the palm crown. The development of the disease was limited only to the leaf blade, on the petiole and the leaf rachis. Spots began to appear in very yellow, brown or black spots. Under favorable environmental conditions, the spots spread and their numbers increased, combined and formed a large dark spot on the leaf rachis. Two to three months later, in early of summer, welds appeared on the surface of the epidermal leaves, full of fungal brown spores and in the form of spiky spots. The wounds were then removed, and the brown to brownish mass was observed under the skin and exposed to the wind. Internal and lower tissues were observed in dark brown color and the petioles were brittle and fragile. Cankers were developed on the axis of contaminated leaves without gum secretion. Internal brown to black discoloration was observed in the petiole cross-sections. Also, fungal spores were formed in the area below of the epidermis. Older leaves were dying prematurely as a result of this rachis and petiole blight. To diagnose the disease, samples were taken from infected leaves of affected palm trees. After transferring the infected samples to the laboratory, the petioles were thoroughly washed with water. Then contaminated tissues were cultured on potato, dextrose agar (PDA) medium. After surface sterilization with 90% ethyl alcohol and Pestalotiopsis palmarum (Cooke) Steyaert was isolated and identified. The Conidiomata acervulus, were globose or ellipsoidal, subepidermal in origin and Conidiophores were indistinct. Conidiogenous cells discrete, simple, short, filiform. Conidia were 17–25 × 4.5–7.5 µm, fusiform to ellipsoid, mainly straight, 4-septate; apical and basal cells hyaline; with three appendages, 5–25 µm long. Pathogenicity on the petiole cultivar was performed according to Koch's principles. This is the first report on the occurrence of rachis blight disease caused by P. palmarum in date palm in Khozestan province.

Keywords: Blight, Phoenix dactylifera, Pestalotiopsis palmarum, Khozestan province