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Purple seed stain (PSS) of soybean (Glycine max (L.) Merr.) is a prevalent seed disease. It results in poor seed quality and reduced seed lot market grade, and thus undermines value of soybean worldwide. The objectives of this research were to evaluate the reaction of selected soybean genotypes collected from 15 countries representing maturity groups (MGs) III, IV, and V to PSS, and to identify new sources of resistance to PSS based on three years of evaluation of natural field infection by Cercospora spp. in the Mississippi Delta of the U. S. In this study, 42 soybean genotypes were evaluated in 2010, 2011, and 2012. Seventeen lines including six MG III (PI 88490, PI 504488, PI 417361, PI 548298, PI 437482, and PI 578486), seven MG IV (PI 404173, PI 346308, PI 355070, PI 416779, PI 80479, PI 346307, and PI 264555), and four MG V (PI 417567, PI 417420, PI 381659, and PI 407749) genotypes had significantly lower percent seed infection by Cercospora spp. than the susceptible checks and other genotypes evaluated (P ≤ 0.05). These genotypes of soybean can be used in developing soybean cultivars or germplasm lines with resistance to PSS and for genetic mapping of PSS resistance genes. In addition, among these 17 lines with different levels of resistance to PSS, nine soybean genotypes (PI 417361, PI 504488, PI 88490, PI 346308, PI 416779, PI 417567, PI 381659, PI 417567, and PI 407749) were previously reported as resistant to Phomopsis seed decay. Therefore, they could be useful in breeding programs to develop soybean cultivars with improved resistance to both seed diseases., Competing Interests: The authors have declared that no competing interests exist.

Phomopsis seed decay (PSD), caused by Phomopsis longicolla (syn. Diaporthe longicolla), is an economically important soybean disease causing poor seed quality. Planting resistant cultivars is one of the most effective means to control PSD. In this study, 16 commercially available maturity groups IV and V soybean cultivars, including two previously identified PSD-resistant and two PSD-susceptible checks, were evaluated for seed infection by P. longicolla in inoculated and noninoculated plots, and harvested promptly or with a 2-week delay in harvest. The test was conducted at Stoneville, Mississippi, in 2012 and 2013. Seed infection by P. longicolla ranged from 0.5 to 76%, and seed germination ranged from 18 to 97%. One MG IV cultivar (Morsoy R2 491) and five MG V cultivars (Progeny 5650, Progeny 5706, Asgrow 5606, Asgrow 5831, and Dyna-Gro33C59) had significantly (P ≤ 0.05) lower percent seed infected by P. longicolla than their respective susceptible checks and other cultivars in the same tests. Information obtained from this study will be useful for soybean growers and breeders for selection of cultivars for planting or breeding and future genetic studies in the development of cultivars with improved resistance to PSD.

False smut, caused by Ustilaginoidea virens, occurs on rice, corn, and other Gramineae, but is of little economic importance. False or green smut of corn resembles most closely false smut of rice (1). During surveys in 2000 at Mississippi State University, Delta Experiment Station, Stoneville, 32 (2.5%) of 1,280 commercial and inbred corn hybrids had false smut on the tassel. The percentage of plants infected with false smut ranged from 5 to 15% based on a sample of 20 corn plants from a single 4.9-m row plot. Galls (sclerotia), which are similar to ergot, replaced flowers on tassels of infected plants. Disease severity ranged from 2 to 50% infected flowers per inbred. Mature sclerotia were spherical, 6 to 17 mm in diameter, olive green to black, and velvety with white interiors. The fungus could not be isolated on potato dextrose agar. Only the tassels were infected, which resulted in little damage to the plant, except for a decrease in pollen production. Although the disease has been reported to infect other parts of the corn plant, the injury will likely be less on corn than rice. In 2001 and 2002, the disease was not observed. Disease incidence was more prevalent in 2000 because of hot, wet weather immediately after the crop was planted. The observation of the disease in one growing season suggests the pathogen may be common in the Mississippi Delta and the disease may occur under favorable environmental conditions and susceptible corn hybrids. Reference: (1) J. K. Pataky. False smut. Page 35 in: Compendium of Corn Diseases, 3rd ed. D. G. White, ed. American Phytopathological Society, St. Paul, MN, 1999.