First Report of Phaeoacremonium mortoniae Associated with Grapevine Decline in Iran.

Abstract

In July 2009, a survey was conducted in individually owned rooted vineyards in Iran to determine fungal pathogens associated with grapevine decline. Symptoms of grapevine decline such as slow dieback, stunted growth, small chlorotic leaves, and reduced foliage were observed on 7-year-old grapevines (cv. Askari) in Bavanat (Fars Province, southwestern Iran). Internal wood symptoms such as black spots and dark brown-to-black vascular streaking were observed in cross and longitudinal sections of stems and trunks. Wood samples were collected from symptomatic trunks and cordons. The bark of each fragment was removed and 10 thin cross sections (2 to 3 mm thick) were cut from symptomatic vascular tissue of the samples. These disks were immersed in 1.5% sodium hypochlorite solution for 4 min, washed thrice with sterile distilled water, and plated onto malt extract agar (MEA) supplemented with 100 mg liter-1 of streptomycin sulfate. Plates were incubated at 25°C in darkness. All colonies were transferred to potato dextrose agar (PDA) and incubated at 25°C. Five isolates of a Phaeoacremonium sp. were obtained. Single-spore isolates were transferred to PDA, MEA, and oatmeal agar (OA) media and incubated at 25°C for 8 to 16 days in the dark (2). Colonies reached a radius of 9.5 to 12 mm after 8 days of incubation. Colonies were flat and yellowish white on PDA and OA and white-to-pale gray after 16 days of incubation on MEA. Conidiophores were short and unbranched, 14 to 38.5 (23.5) μm long, and often ending in a single terminal phialide. Phialides were terminal or lateral and mostly monophialidic. Conidia were hyaline, oblong to ellipsoidal or reniform, 2 to 6.5 (4.9) μm long, and 1.1 to 1.7 (1.4) μm wide. On the basis of these characteristics, the isolates were identified as Phaeoacremonium mortoniae (1,2). Additionally, identity of the PMH1 isolate was confirmed by sequencing a fragment of the -tubulin gene with primers T1 and Bt2b (GenBank Accession No. JF831449). The sequence of this isolate was identical to the sequence of P. mortoniae (GenBank Accession No. HM116767). Pathogenicity tests were conducted on 2-month-old grapevine seedlings of cv. Askari by watering the roots with 25 ml of a conidial suspension (107 conidia ml-1) harvested from 21-day-old cultures grown on MEA. Controls were inoculated with 25 ml of sterile distilled water. Fifteen replicates were used for each isolate with an equal number of noninoculated plants. All plants were grown under greenhouse conditions (25 to 30°C). Two months after inoculation, inoculated seedlings showed reduced growth, chlorotic leaves, epinasty, severe defoliation, and finally wilting, while control seedlings remained healthy. The fungus was reisolated from internal tissues of the stems of inoculated seedlings. To my knowledge, this is the first report of P. mortoniae causing grapevine decline in Iran.