Puccinia acroptili on Russian Knapweed in Colorado, Montana, and Wyoming

Abstract

Acroptilon repens (L.) DC. (Russian knapweed) is a long-lived perennial weed from central Asia that is widely distributed in the western United States (U.S.). Recently, accessions of a rust disease were collected from Colorado (CO), Montana (MT), and Wyoming (WY) for comparison with Eurasian isolates. U.S. accessions had two-celled teliospores with slight constrictions in the middle and urediniospores with three germ pores ± equatorial in location. Urediniospores were (state, width × length, [n = 100]): CO, 16.4 to 25.7 × 19.2 to 27.0 μm; MT, 18.4 to 23.1 × 17.4 to 24.6 μm; and WY, 18.0 to 26.2 × 20.2 to 26.7 μm. These were similar to those of 16.6 to 25.7 × 21.2 to 28.0 μm from two New Mexican (NM) herbarium specimens (BPI Nos. 1107952 and 1110177) (1). Teliospores measured 19.9 to 27.7 × 29.8 to 47.4 μm, 17.4 to 26.0 × 32.4 to 44.2 μm, 16.5 to 27.5 × 29.4 to 45.7 μm, and 18.7 to 27.6 × 31.0 to 46.4 μm for CO, MT, WY, and NM accessions, respectively. These rust isolates have been identified as Puccinia acroptili Syd. on the basis of host plant record and spore morphology (2). To our knowledge, this is the first record of P. acroptili in CO, MT, and WY. Besides NM, P. acroptili has been reported in North America from California, British Columbia, and Saskatchewan. References: (1) M. E. Palm and S. G. Vesper. Plant Dis. 75:1075, 1991. (2) D. B. O. Savile. Can. J. Bot. 48:1567, 1970.

Comparison of Puccinia acroptili from Eurasia and the USA

“…Although differences in spore dimensions between Eurasian and USA isolates were clear and consistent, they were also within expected limits reported for the species (Bruckart et al 2006;Cummins 1978;Dugan and Carris 1992;Mortensen and Molloy 1989;Palm and Vesper 1991;Savile 1970b;Sydow and Sydow 1904;Wei and Wang 1986). Considering that there was a negative correlation between teliospore width and length, it is conceivable that teliospores from the various isolates could actually be the same volume, a metric not possible to measure in this study.…”

“…), Asteraceae, tribe Cardueae. Russian knapweed, which is native to Mongolia, western Turkestan, Iran, Turkish Armenia, and Asia Minor (Moore and Frankton 1974), is diseased by P. acroptili most likely wherever the host occurs, including western North America (Bruckart et al 2006;Cummins 1978;Dugan and Carris 1992;Mortensen and Molloy 1989;Palm and Vesper 1991;and Savile 1970b). Although diseased plants are common in North America, the effect of P. acroptili on density of Russian knapweed has not been tested.…”

The Importance of Reporting New Host-Fungus Records for Ornamental and Regional Crops

“…Records of natural enemies (potential biological control agents) for plant pests, pathogens, or weeds are also a legitimate purview of first reports, e.g., for fungi on Dipsacus fullonum (common teasel) in the Pacific Northwest (14,19), or Puccinia acroptili on Russian knapweed in the western USA. (8). First reports also document alternative weedy hosts for fungi pathogenic on regional or ornamental crops, e.g., powdery mildews on weedy hosts (15), or Sclerotinia minor on the weed Sida spinosa (prickly sida) in peanut production (41).…”

“…For these reasons, many plant health professionals submit first reports only in instances of the disease having obvious actual or potential major impact on plants of direct interest to them. Because the submission and review processes involve considerable effort, records are sometimes bundled into a single manuscript, especially if pathogens are similar, e.g., various powdery mildews (15,18,55), or if the same host-fungus record is documented in multiple locations (8).…”