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First Report of Neoscytalidium dimidiatum Causing Canker, Shoot Blight, and Root Rot of Pistachio in Turkey

Derviş, S., Türkölmez, Ş., Çiftçi, O., Ulubaş Serçe, Ç., Dikilitas, M.
Plant disease 2019 v.103 no.6 pp. 1411
DNA primers, Neoscytalidium dimidiatum, Pistacia vera, bark, blight, cambium, cankers (plants), cultivars, decline, fungal anatomy, fungal diseases of plants, genes, host-pathogen relationships, new geographic records, pathogenicity, pistachios, plant pathogenic fungi, ribosomal DNA, root rot, trees, Turkey (country)
Turkey is the fourth largest pistachio (Pistacia vera L.) producing country worldwide, providing over 7% of the world’s supply with more than 78 kt annual production, mainly centered in the Southeast Anatolia Region. In June 2018, decline symptoms and an unusual canker disease on the surface of stems and/or branches of pistachio were observed on about 6 to 15% of 5- to 35-year-old pistachio trees of cultivars Uzun and Kırmızı in the orchards of Şanlıurfa (Haliliye, Bozova, and Siverek districts). The most striking symptom on young plants was the deep bark cracks or cankers on trunks and main branches including shoot blight, whole tree decline, defoliation, and death. A black sooty layer of conidia under the peeled bark of trunks and main branches was clearly visible. This sooty layer was visible on the surface of the bark in severe cases. Older trees (20 to 35 years old) showed lack of vigor, foliar chlorosis, branch cankers, reduced foliage, and dead branches. When slightly cracked bark of trunks was peeled off, tan to dark brown necrosis was observed on the underlying wood. Declining trees in all orchards exhibited dry root rot symptoms extending from the taproot to the crown, which led to loss of fine root systems. The sections of samples taken from canker margins, blighted shoots, and root lesions of five trees per location were surface sterilized in 2% NaOCl solution for 3 min, rinsed in sterile distilled water twice, blotted dry with sterilized filter paper, placed on potato dextrose agar (PDA), and incubated at 28°C. A fungal species with identical cultural characteristics was consistently isolated from the symptomatic tissues. On PDA, the mycelium growth was white and then transitioned into black with age. Mycelia were disarticulated into 0- to 1-septate, cylindrical-truncate or rod-shaped, thick-walled, hyaline to brown arthroconidia occurring singly or in arthric chains and averaged 8.7 ± 3.5 × 4.5 ± 2.3 μm with a length/width ratio of 1.73. These morphological characteristics were consistent with the description of Neoscytalidium dimidiatum (Penz.) Crous & Slippers (Crous et al. 2006). The rDNA internal transcribed spacer (ITS) and large subunit (LSU) genes of six single conidial isolates (ND161 and ND162 isolated from underbark tissues, ND169 and ND170 from blighted shoot tissues, and ND181and ND182 from root tissues) were amplified with ITS6/ITS4 and NL1/NL4 primer pairs, respectively, and the amplicons were sequenced (GenBank accession nos. MK343742 to MK343746 for ITS and MK343747 to MK343752 for LSU). BLAST searches of ITS and LSU sequences had 99 to 100% identity with many N. dimidiatum isolates in the NCBI database, which confirmed the morphological identification. Pathogenicity tests were performed on 10 replicates of 1-year-old P. vera ‘Uzun’ seedlings in pot conditions by removing a 0.5-cm-diameter bark plug from the stem with a cork borer and placing an equal size of 7-day-old culture disc of ND161 onto the vascular cambium. The wound was then covered with wet, autoclaved cotton wool and sealed with Parafilm. The control plants were wounded and inoculated with sterile PDA discs. The treated plants were then maintained in a growth chamber with a 16/8-h light/dark photoperiod at 28°C with 55% relative humidity and watered on demand. Within 3 weeks, average lesion lengths on all inoculated stems were over 4 cm, and the lesions were covered with a black sooty layer. Discoloration, death, and defoliation of leaves were observed similar to those observed in naturally infected trees. Control plants remained healthy via producing new calli around the wound point (average length 0.7 cm) throughout the course of the experiment. N. dimidiatum was reisolated from the lesions of inoculated stems, thus fulfilling Koch’s postulates. In Turkey, N. dimidiatum had previously been reported only as a new blight of tomato, which had devastating effects on vegetative and generative parts of tomato plants (Türkölmez et al. 2019). To the best of our knowledge, this is the first report of N. dimidiatum infection on pistachios worldwide. The commercial loss owing to the pathogen could be quite significant because it causes the death of young trees and decreases the economic life of old trees. Apparently, this pathogen may have a wider host range to devastate than previously thought.