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United States Department of Agriculture

Agricultural Research Service

Title: First Report of Phoma Exigua on Acroptilon Repens in Turkey

Authors
item Tunale, Berna - PL PROTN CNTRL RES TURKEY
item Eskandari, Farivar
item Berner, Dana
item Farr, David
item Castlebury, Lisa

Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: December 10, 2003
Publication Date: May 1, 2004
Citation: Tunale, B., Eskandari, F., Berner, D.K., Farr, D.F., Castlebury, L.A. 2004. First report of phoma exigua on acroptilon repens in turkey. Plant Disease. 87:1540.

Interpretive Summary: Russian knapweed is becoming a noxious weed in wheat fields in Turkey. It is also an invasive weed in the northwestern United States and a target of biological control efforts. In 2002, dying Russian knapweed plants were found near Cankiri, Turkey. Dying plants had irregular, charcoal-colored dead areas at the leaf tips and margins, and frequently, whole plants were dead. Diseased leaves were air-dried and sent to the Foreign Disease-Weed Science Research Unit (FDWSRU) of USDA/ARS at Fort Detrick, MD where the fungus Phoma exigua was isolated. Cultures of this fungus were sent to the Systematic Botany and Mycology Laboratory, USDA/ARS, at Beltsville, MD where molecular and morphological tests confirmed the identity of the fungus. At FDWSRU, tests were conducted to determine in this fungus was, indeed, responsible for the disease. This was done by spraying plants with spores of the fungus and observing the plants for disease development. All plants that were sprayed developed disease, and the fungus was recovered from all of these plants. Several plants died after being sprayed with fungus spores, and all sprayed plants were severely diseased. This fungus is destructive on Russian knapweed, and spraying foliage with suspensions of spores in water can produce severe disease. These characteristics make this fungus a potential candidate for biological control of this weed in both Turkey and the U.S. This is the first report of this fungus on Russian knapweed in Turkey.

Technical Abstract: Russian knapweed is becoming a noxious weed in wheat fields in Turkey. It is also an invasive weed in the northwestern United States and a target of biological control efforts. In 2002, dying Russian knapweed plants were found near Cankiri, Turkey. Dying plants had irregular, charcoal-colored necrotic lesions at the leaf tips and margins, and frequently, whole plants were necrotic. Diseased leaves were air-dried and sent to the Foreign Disease-Weed Science Research Unit of USDA/ARS at Fort Detrick, MD. There, diseased leaves were surface disinfested and placed on moist filter paper in petri dishes. Pycnidia producing one-celled hyaline conidia were observed after 4-5 days. Internal transcribed spacer (ITS) regions 1 and 2, including the 5.8S ribosomal DNA were sequenced for isolate 02-059. This sequence was identical to sequences in GenBank from six well-characterized strains of Phoma exigua Desmaz. Morphology was also consistent with P. exigua. Twenty plants were inoculated with an aqueous suspension of conidia. After six days symptoms were observed on all plants. Phoma exigua was re-isolated from all inoculated plants. In another test 12 plants were inoculated. After ten days, three plants were dead, and all other inoculated plants had large necrotic lesions. No symptoms occurred on control plants. This isolate of Phoma exigua is a destructive pathogen on Russian knapweed, and severe disease can be produced by inoculation of foliage with aqueous suspensions of conidia. These characteristics make this isolate of P. exigua a potential candidate for biological control of this weed in both Turkey and the U.S. This is the first report of P. exigua on Russian knapweed in Turkey.

Last Modified: 4/15/2014
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