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Title: First report of stem canker of Salsola tragus caused by Diaporthe eres in Russia

Author
item KOLOMIETS, TAMARA - ALL RUSSIAN INSTITUTE
item MUKHINA, ZHANNA - ALL RUSSIAN RICE INSTIT.
item MATVEEVA, TATIANA - ST. PETERSBURG ST. UNIV.
item BOGOMAZ, DENIS - ST. PETERSBURG ST. UNIV.
item Berner, Dana
item Cavin, Craig
item Castlebury, Lisa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2008
Publication Date: 1/1/2009
Citation: Kolomiets, T., Mukhina, Z., Matveeva, T., Bogomaz, D., Berner, D.K., Cavin, C.A., Castlebury, L.A. 2009. First report of stem canker of Salsola tragus caused by Diaporthe eres in Russia. Plant Disease. 93:110.

Interpretive Summary: Russian thistle or tumbleweed is a problematic invasive weed in the western United States and a target of biological control efforts. In September of 2007, dying tumbleweed plants were found along the Azov Sea at Chushka, Russia. All of the plants in the area were diseased and about half of these were dead or dying. Diseased stem pieces were taken to the All Russian Research Institute of Phytopathology, Moscow, Russia. There, a fungus with characters conforming to the description of a Phomopsis species was isolated from the diseased stems. Pure cultures from these isolations were sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit, USDA, ARS, Fort Detrick, MD for testing. Morphology was consistent with that of Phomopsis oblonga, the imperfect stage of Diaporthe eres. Analysis of DNA sequences confirmed this identification. Healthy stems and leaves of ten, 30-day-old plants of S. tragus were spray-inoculated with an aqueous suspension of conidia (1.0 x 106 alpha conidia/ml plus 0.1 percent v/v polysorbate 20) harvested from 14-day-old cultures grown on 20 percent V8 juice agar. Another ten control plants were sprayed with water and surfactant without conidia. Plants were placed in an environmental chamber at 100 percent humidity (rh) for 16 h with no lighting at 25 degrees C. After ca. 24 h, plants were transferred to a greenhouse at 20-25 degrees C, 30-50 percent rh, and natural light. Stem lesions developed on three inoculated plants after 14 days and another three plants after 21 days. After 70 days, all of the inoculated plants were diseased, four were dead, and three had more than 75 percent diseased tissue. No symptoms occurred on control plants. The Phomopsis state was recovered from all diseased plants. To our knowledge, this is the first report of stem canker on S. tragus caused by D. eres.

Technical Abstract: Salsola tragus L. (Russian thistle, tumbleweed), family Chenopodiaceae, is a problematic invasive weed in the western United States and a target of biological control efforts. In September of 2007, dying Salsola tragus plants were found along the Azov Sea at Chushka, Russia. About 30 plants in the area were diseased and about half of these were dying. Dying plants had irregular necrotic canker-like lesions near the base of the stems, and most stems showed girdling and cracking. Lesions on the stems were dark brown with brown pycnidia evident within the lesions and extending along lesion-free sections of the stems and basal portions of leaves. Diseased stems were cut into pieces and disinfested in 70 percent ethyl alcohol. After disinfestation, stem pieces were placed into Petri dishes on the surface of potato-glucose agar. Numerous dark immersed erumpent pycnidia with a single ostiole were observed in all of the lesions after 2-3 days. Axenic cultures were sent to the Foreign Disease-Weed Science Research Unit, USDA, ARS, Fort Detrick, MD for testing in quarantine. Conidiophores were simple. Alpha conidia were one-celled, hyaline, ovoid, 6.3-11.5 x 1.3-2.9 um (mean 8.8 x 2.0 um). Beta conidia were one-celled, filiform, hamate, hyaline 11.1-24.9 x 0.3-2.5 um (mean 17.7 x 1.2 um). The isolate was morphologically identified as a species of Phomopsis, the conidial state of Diaporthe. The teleomorph was not observed. Morphology is consistent with that of P. oblonga (Desm.) Traverso, the anamorph of D. eres, and DNA analyses confirmed this identification. Healthy stems and leaves of ten, 30-day-old plants of S. tragus were spray-inoculated with an aqueous suspension of conidia (1.0 x 106 alpha conidia/ml) harvested from 14-day-old cultures grown on 20 percent V8 juice agar. Another ten control plants were sprayed with water and surfactant without conidia. Plants were placed in an environmental chamber at 100 percent humidity (rh) for 16 h with no lighting at 25 degrees C. After ca. 24 h, plants were transferred to a greenhouse at 20-25 degrees C, 30-50 percent rh, and natural light. Stem lesions developed on three inoculated plants after 14 days and another three plants after 21 days. After 70 days, all of the inoculated plants were diseased, four were dead, and three had more than 75 percent diseased tissue. No symptoms occurred on control plants. The Phomopsis state was recovered from all diseased plants. To our knowledge, this is the first report of stem canker on S. tragus caused by D. eres.