Author
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Gulya Jr, Thomas |
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Charlet, Laurence |
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Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/31/2002 Publication Date: N/A Citation: N/A Interpretive Summary: Sunflower is a host for five different rusts, although only one rust is commonly seen. The fungus "Puccinia xanthii" causes a rust disease on cocklebur, and as such, it is referred to as "cocklebur rust." Cocklebur rust had been observed on sunflower in Australia in the late 1970's, but has not been seen on sunflower in any other country since then, despite the fact the fungus attacks cockelbur plants all over the world. In 1999, spots were seen on cultivated sunflower in western North Dakota which looked like cockelbur rust. This was confirmed by microscopic inspection. The disease was found only in one field, and would not be considered an economic problem. The appearance of the disease, however, should be noted, so that others may realize a "new" disease has been found on sunflower, and it may be identified correctly. Technical Abstract: Puccinia xanthii Schw., commonly known as cocklebur rust in the U.S., is widespread on Xanthium and Ambrosia spp. in North America, southern Europe and Australia. The microcyclic rust has been observed on sunflower (Helianthus annuus L.) only once, in Australia (1). In September, 1999, plants of a oilseed sunflower hybrid (Dekalb 3790) near Hettinger, North Dakota were observed to have large (4-10 mm) raised chlorotic pustules on a few of the upper leaves, with teliospores on the abaxial surface of the pustules. No cocklebur plants were found within the field, but some rusted cocklebur (Xanthium strumarium L.) plants were collected several km. away. About 10% of the sunflower plants within the field were affected, but generally only one or two upper leaves had pustules, and each affected leaf had only one or two pustules. In contrast, affected cocklebur plants commonly had a dozen or more pustules per leaf. Teliospores from sunflower pustules were brown, two-celled, and averaged 49 x 17u, with a distinctly thicker wall at the spore apex, and a persistent pedicel averaging 40u long. Teliospores from cocklebur pustules averaged 46 x 16 u. Both teliospore measurements are within the reported range for P. xanthii of 36-60 x13-19u (2). P. xanthii can easily be distinguished from the ubiquitous P. helianthi, since the later has telia 1-2 mm in diameter, and teliospores of similar length, but 21-30u wide. Puccinia xanthii was not found in 20 other sunflower fields in southwestern North Dakota surveyed during the same trip, nor in any fields inspected in eastern ND during September, 1999. This is the first report of P. xanthii on sunflower in any country other than Australia. |
