Increased Occurrence of Target Spot of Soybean Caused by Corynespora cassiicola in the Southeastern United States

Abstract

Target spot of soybean (Glycine max (L.) Merr.) caused by Corynespora cassiicola (Berk. & Curt.), although found in most soybean-growing countries, is considered to be a disease of limited importance (1) and has never been reported to cause soybean yield loss in the southeastern United States (2,3). Soybean plants submitted to the North Carolina Plant Disease and Insect Clinic (NCPDIC) in August 2004 from Beaufort, Robeson, Wilson, and Johnston counties, NC had symptoms consistent with target spot. Symptoms consisted of roughly circular, necrotic leaf lesions from minute to 11 mm in diameter, though typically approximately 4 to 5 mm in diameter, and with a yellow margin. Large lesions occasionally exhibited a zonate pattern often associated with this disease. Microscopic examination of the lesions revealed the presence of spores (conidia) typical of C. cassiicola (1). Conidia were mostly three to five septate with a central hilum at the base and ranged in size from 7 to 22 wide × 39 to 520 μm long. Three commercial soybean fields near Blackville, SC (Barnwell County) were severely affected by this disease and it caused premature defoliation. Nineteen of twenty-seven maturity group VII and VIII genotypes in the 2004 Clemson University soybean variety trial near Blackville, SC had visible symptoms of target spot. Heavy rainfall associated with hurricanes during September 2004 probably enhanced the incidence of this disease, and yield suppression due to target spot was estimated at 20 to 40% in some fields. In 2005, 20 of 161 soybean samples submitted to the NCPDIC or collected in surveys from 16 counties were positive for target spot on the basis of microscopic examination. Target spot also was diagnosed in six counties (Baldwin, DeKalb, Elmore, Fayette, Macon, and Pickens) in Alabama and in four additional counties (Bamberg, Hampton, Orange-burg, and Calhoun) in South Carolina in 2005. Records from the NCPDIC indicate that target spot had not been diagnosed on soybean in North Carolina since 1981. The large increase in incidence of target spot in the southeast may be related to changes in weather patterns, changes in pathogen virulence, and/or the introduction of more susceptible host genotypes. References: (1) J. B. Sinclair. Target spot. Page 27 in: Compendium of Soybean Diseases. G. L. Hartman et al. eds. The American Phytopathological Society, St. Paul, MN, 1999. (2) J. A. Wrather et al. Plant Dis. 79:1076. 1995. (3) J. A. Wrather et al. On-line publication. doi:10.1094/PHP-2003-0325-01-RV. Plant Health Progress, 2003.

First characterization of endophytic Corynespora cassiicola isolates with variant cassiicolin genes recovered from rubber trees in Brazil

“…It has been found on leaves, stems, fruits and roots of more than 300 plant species primarily in tropical and subtropical areas (http://nt.ars-grin.gov/ fungaldatabases/; Farr and Rossman 2011). Principally described as a pathogen, it causes severe damage to economically important plants, including rubber tree, tomato, cucumber, cotton and soybean (Chee 1990;Koenning et al 2006;Oliveira et al 2006Oliveira et al , 2007Schlub et al 2009). However, C. cassiicola isolates were also obtained from dead organic material (Kingsland 1985;Lee et al 2004;Cai et al 2006) and Electronic supplementary material The online version of this article (doi:10.1007/s13225-012-0169-6) contains supplementary material, which is available to authorized users.…”

In vitro sensitivity of Corynespora cassiicola isolated from soybean to fungicides and field chemical control of target spot

“…Typical target spot symptoms are roughly circular necrotic leaf lesions ranging from little brown to 11mm-diameter spots, but they are typically large, circular, dark brown spots of approximately 4 to 5 mm in diameter, with a yellow margin. Large lesions occasionally exhibit a zonate pattern often associated with this disease, and the spots have a dark point in the center surrounded by darker concentric rings (19,16).…”

“…In Brazil, target spot outbreaks have occurred in the main soybean growing areas and yield reduction of up to 21% has been reported (15). In the USA, incidence of target spot has increased in the southeast region, probably due to changes in weather patterns, pathogen virulence, and/or introduction of more susceptible host genotypes (19).…”

Evaluation of inoculum potential of pathogens in seeds: relation to physiological quality and DNA quantification by qPCR

“…& M.A. Curtis), has increased in recent crop seasons and may cause estimated damage of up to 40% in the field (Godoy et al, 2012(Godoy et al, , 2013Koenning and Creswell, 2006). Another disease, anthracnose, caused by the fungus Colletotrichum gossypii var.…”