Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 6, 2009
Publication Date: August 1, 2009
Citation: Li, S., Boykin, D.L., Sciumbato, G., Wrather, A., Shannon, G., Sleper, D. 2009. Reaction of Soybean Cultivars to Phomopsis Seed Decay in the Mississippi Delta, 2007. Plant Disease Management Reports. DOI:10.1094/PDMR03:FC096. Interpretive Summary: Phomopsis seed decay (PSD) can severely affect soybean seed quality and is a problem for many soybean farmers in the south USA. The disease is primarily caused by a fungus (mold). There are few management strategies for this disease, and these strategies have not completely protected soybean against PSD. Resistant varieties can provide some protection at no additional cost to the grower above the price of the planting seed. Fifty soybean cultivars were evaluated at Stoneville, Mississippi for resistance to PSD. Several soybean cultivars with less disease than PSD resistant SS93-6181 and SS93-6013 were identified and will be evaluated for resistance to PSD in 2009 field trials. These cultivars may be used to reduce loss to this disease.
Technical Abstract: Phomopsis seed decay (PSD) can severely affect soybean seed quality in the southern USA. There are few management strategies for this disease, and these strategies have not completely protected soybean against PSD. Resistant varieties can provide some protection at no additional cost to the grower above the price of the planting seed. Soybean lines may vary for resistance or tolerance to PSD. On May 4, 2007, 50 soybean cultivars were planted at Stoneville, Mississippi to determine their reaction to PSD. Two lines, SS93-6012 and SS93-6181, that were previously reported to be PSD resistant in Missouri were included, and cultivars, Hill and Williams 82, also were used as susceptible checks. Seed, 9 seed/ft of row, were planted in 9 ft long rows with 24-in row spacing. The experimental design was a randomized complete block design with four replications. Prior to planting, 30 seeds of each line were assayed for incidence of P. longicolla and germination rate. Plants were inoculated at the R5 stage with a spore suspension (10-4/ml) prepared from a combination of 10 isolates of P. longicolla collected from Mississippi. Seeds arbitrarily selected from each replication of each line were collected when the plants were mature. A total of 100 seeds of each line were assayed for the percentage of P. longicolla infection and germination rate. Seed protein and oil concentrations from each line were analyzed. The seeds of soybean lines selected for planting were generally healthy. Of 50 lines tested, six lines had 100% germination, 30 lines had germination rates that ranged from 80% to 97%, and 12 lines ranged from 63% to 77%. Two lines had germination rates of 50% and 53%, respectively. In the seed plating assay, 37 lines had no P. longicolla infected seed, 10 and three lines had P. longicolla incidence of 3% and 7%, respectively. Incidence of P. longicolla in seeds from inoculated field plots differed significantly (P = 0.05) ranging from 6% to 50% among soybean lines. Several lines with low disease incidence were identified and will be evaluated for reaction to PSD in 2009 field trials.