سبب شناسی بدشکلی درختان نارگیل در استان هرمزگان

In June 2017, symptoms of vegetative malformation on coconut palm (Cocos nucifera) trees were observed in a garden located in Qeshm island, Hormozgan province. Symptoms of malformation included hypertrophied, tightly grown and wrinkled leaflets, producing misshapen, thickened and dwarfed leaves. Dark brown to black small lesions were also observed on leaflets and rachises. Symptomatic tissue fragments were surface-disinfested with 2% sodium hypochlorite solution for 3 min, rinsed three times in sterile distilled water, dried on sterilised paper, and plated onto potato dextrose agar (PDA) supplemented with 150 μg ml−1 of streptomycin sulfate and petri dishes were incubated at 28 °C for 6 days. After three days, isolates of Fusarium were permanently obtained from malformed tissues. In culture, the aerial mycelium of the colonies was initially white, becoming purple-violet with age. Macroconidia were slender, thin-walled and relatively straight with 3-5 septa. Microconidia were club shaped with a flattened base and 0-septate that found in chains of varying length, false heads, or aggregates of a few microconidia. Conidiogenous cells were monophialides and polyphialides. The morphology of the isolates was identical to that described for Fusarium proliferatum. Isolates were identified at the molecular level by amplification and sequencing of the internal transcribed spacer region (ITS1-5.8S-ITS2) and translation elongation factor 1‐α (tef‐1α) gene. BLASTn search of the sequence (Accession No. MH425306) showed 100% identity with sequences of F. proliferatum (KY785020.1, FJ538242.1 and KU872092.1) obtained from National Center for Biotechnology Information (NCBI). To establish pathogenicity, discs (3 cm in diameter) were detached from healthy and disease-free leaves of coconut palm trees and placed on sterile petri dishes lined with sterile moist filter paper. Agar plugs containing F. proliferatum culture were placed directly on the adaxial side of the leaf discs and the plates were incubated in the dark, at 28 °C. Control leaf discs were inoculated with agar plugs free of the fungus. Six days after inoculation, leaf discs began showing chlorosis along with partial necrotic lesions around the inoculation site that resulted in complete necrosis of leaf tissue by 11 days of inoculation. No symptoms were observed on control leaf discs. F. proliferatum was reisolated only from inoculated leaf discs. This is the first report of coconut palm malformation disease caused by F. proliferatum in the world.