|SCIUMBATO, GABE - Mississippi State University|
Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2013
Publication Date: 8/14/2013
Citation: Li, S., Sciumbato, G. 2013. Evaluation of soybean commercial varieties for resistance to Phomopsis seed decay in the Mississippi Delta, 2012. Plant Disease Management Reports. 7:FC137.
Interpretive Summary: Soybean Phomopsis seed decay is a major cause of poor seed quality in the United States, especially in the mid-southern region. To identify new sources of soybean lines resistant to Phomopsis seed decay, 16 commercial soybean varieties were evaluated for resistance. Those 16 varieties were selected based on the germination and seed visual quality data from seed assays of 50 commercial varieties in previous year. Results showed that Morsoy R2 491, Progeny 5650 and PI 42324B had the lowest percentage of Phomopsis seed infection among the varieties tested. These soybean lines may be used in breeding programs to further reduce loss to Phomopsis seed decay.
Technical Abstract: Soybean Phomopsis seed decay (PSD), primarily caused by Phomopsis longicolla, is a major cause of poor seed quality in the United States, especially in the mid-southern region. To identify new sources of soybean lines resistant to PSD, 16 commercial soybean varieties (MG IV and MGV) were planted on April 25, 2012 to evaluate them for resistance to PSD. Those 16 varieties were selected based on the germination and seed visual quality data from seed assays of 50 commercial varieties in 2011. Experiments were set up in a split-plot design in which inoculated and non-inoculated and treatments were the main plots, and the maturity groups were the subplots. In the inoculated trials, plants were inoculated at the R5 growth stage with a spore suspension (10,000/ml) that was prepared using a Mississippi isolate of P. longicolla. Seed were manually harvested either at normal maturity (R8 growth stage) or 14 days after maturity (delayed harvest). Randomly selected seed from each plot were tested for percent seed infected by P. longicolla. Based on the seed assay data, Morsoy R2 491 had the lowest percentage of Phomopsis seed infection in both normal and delayed harvest trials among the MG IV varieties evaluated. Although Morsoy R2S 480 also had the lowest Phomopsis seed infection (the same as Morsoy R2 491) in the normal harvest trial, it had the highest Phomopsis seed infection in the delayed harvest trial. This result indicates that a variety that is resistant to PSD at normal harvest time may be susceptible to PSD at delayed harvest time if the environmental condition is favorable to PSD development. Therefore, testing of varieties at delayed harvest time or under the conditions which favor PSD disease development is important for the identification of PSD-resistant varieties. In the testing of MGV varieties, Progeny 5650 and PI 42324B had the lowest percentage of Phomopsis seed infection in both normal and delayed harvest trials with either inoculated or non-inoculated treatments. All soybean varieties tested in 2012 will be reevaluated for resistance to PSD in 2013 field trials.