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First Report of Charcoal Rot of Sunflower in Minnesota, USA
T. Gulya, USDA-ARS Sunflower Research Unit, Fargo, ND 58102; A. Mengistu, USDA-ARS Crop Genetics Research Unit, Jackson, TN 38301; and K. Kinzer, N. Balbyshev, and S. Markell, Department of Plant Pathology, North Dakota State University, Fargo, ND 58102
Corresponding author: S. Markell. email@example.com
Gulya, T., Mengistu, A., Kinzer, K., Balbyshev, N., and Markell, S. 2010. First report of charcoal rot of sunflower in Minnesota, USA. Online. Plant Health Progress doi:10.1094/PHP-2010-0707-02-BR.
A field of oilseed sunflower (Helianthus annuus L. hybrid ‘Pioneer 63M82’) was observed with uneven maturation in west central Minnesota near Aldrich (Todd Co.) in late September 2009. The field’s soil type was sandy loam and cropping history was oats in 2008 preceded by four years of alfalfa. Most plants were green, but 37% of the plants had a brown stem and wilted with senescent leaves. One-third of these prematurely dead plants (~12%) had 2 to 14 cm long (avg. 8.5) silvery grey girdling lesions at the soil line (Fig. 1). When cut open, every plant with such lesions had small black microsclerotia (Fig. 2A), but lacked horizontal pith compression typically associated with charcoal rot (Fig. 3). Additionally, some stalks exhibited pink pith discoloration, later determined to be due to multiple Fusarium species (3). After plating pith on acidified PDA and incubation at 35°C, colonies and microsclerotia (but no pycnidia) typical of Macrophomina phaseolina (Tassi) Goid. formed within 7 days. Microsclerotia recovered from plants and those in culture (Fig. 2B) both generally measured between 75 and 175 microns. To access prevalence of charcoal rot in the region, 500 sunflower plants in five strips, each strip approximately 25 m in length, were visually inspected in 20 fields in a 20 km radius from the primary affected field. Additionally, soil from 13 of those fields and from the primary affected field were collected by sampling 10 locations spaced at 25-m intervals in a W-pattern. Soil samples were bulked by field and assayed for Macrophomina on potato dextrose agar amended with rifampicin (100 mg/liter) and tergitol (0.1 ml) at the USDA-ARS Plant Pathology Lab in Jackson, TN (4). No charcoal rot symptoms were observed on sunflower plants in any visually inspected fields. However, nine of 13 soil samples (69%) were positive for Macrophomina, with microsclerotial numbers ranging from 1 to 4 per 1 g soil, which is low in comparison with counts from fields with other hosts in warmer areas of the Midwest (4). Grower estimated yield in the affected field was 2200 kg/ha, above the Minnesota state average of 1700 kg/ha, but it is unclear if charcoal rot impacted yield. This area of Minnesota received in July, August, and September 2009, 106, 75 and 15 mm of rain, with average monthly temperatures of 18, 18, and 17°C, respectively. These conditions were unlikely to stress sunflower or provide conditions optimal for charcoal rot development. Charcoal rot on sunflower is typically seen in hot, arid climates such as Texas (6). It was first observed on sunflower in North and South Dakota in 1998 (2), and was widespread on soybeans recently in Iowa (5), suggesting that Macrophomina may becoming more common in cooler growing areas of Midwestern United States. However, in surveys conducted by the National Sunflower Association (1), charcoal rot has been recorded only 35 times in 1854 fields surveyed between 2001 and 2009 in eight states and was not detected during 2007 to 2009. This infrequency of observation could be due in part to the persistent cool and wet climate in recent years, which is unfavorable for charcoal rot disease development. However, with the multitude of Macrophomina hosts in the northern Great Plains and the high incidence of microsclerotia we detected in soil, high disease potential may exist, suggesting that in drier, hotter years the sunflower crop may be affected by this disease.
2. Gulya, T., Krupinsky, J., Draper, M., and Charlet, L. 2002. First report of charcoal rot (Macrophomina phaseolina) on sunflower in North and South Dakota. Plant Dis. 86:923-923.
3. Mathew, F., Kirkeide B., Gulya, T., and Markell, S. First report of pathogenicity of Fusarium sporotrichioides and Fusarium acuminatum on sunflowers in the United States. Online. Plant Health Progress. In press.
4. Mengistu, A., Reddy, K. N., Zablotowicz, R. M., and Wrather, A. J. 2009. Propagule densities of Macrophomina phaseolina in soybean tissue and soil as affected by tillage, cover crop, and herbicide. Online. Plant Health Progress doi:10.1094/PHP-2009-0130-01-RS.
5. Yang, X., and Navi, S. 2005. First report of charcoal rot epidemics caused by Macrophomina phaseolina in soybean in Iowa. Plant Dis. 89:526-526.
6. Yang, S., and Owen, D. 1982. Symptomatology and detection of Macrophomina phaseolina in sunflower in Texas. Phytopathology 72:819-821.