REDUCING SOYBEAN YIELD LOSSES THROUGH GENETIC IMPROVEMENT
Location: Crop Genetics Research Unit
Title: Evaluation of Soybean Cultivars for Resistance to Soybean Phomopsis Seed Decay in the Mississippi Delta
Submitted to: Southern Soybean Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: February 27, 2009
Publication Date: March 11, 2009
Citation: Li, S., Boykin, D.L., Sciumbato, G., Wrather, A., Shannon, G., Sleper, D. 2009. Evaluation of Soybean Cultivars for Resistance to Soybean Phomopsis Seed Decay in the Mississippi Delta. In Abstracts of the 36th Annual Meeting of the Southern Disease Workers, (Pensacola Beach, FL, March 11-12, 2009). p.5
Phomopsis seed decay of soybean is the major cause of poor soybean seed quality in the United States, especially in the mid-southern USA. The disease is caused primarily by the fungal pathogen Phomopsis longicolla. To identify soybean lines resistant to this pathogen, 50 soybean cultivars were selected based on the recommendation by Mississippi State University (MSU) Variety Test Program in 2007. Two lines that were previously reported to be resistant in Missouri also were included. Susceptible cultivars, Hill and Williams 82 were used as susceptible checks. Thirty seeds of each line were assayed for incidence of P. longicolla and germination rate before planting. A field experiment was established using a randomized complete block design with four replications at Stoneville, Mississippi in May 2007. 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 incidence of P. longicolla and germination rate. Seed protein and oil concentrations from each line were analyzed.
The seeds of soybean lines obtained from MSU were generally healthy. Of 50 lines tested, six lines had 100% germination, 30 lines had germination rates with range from 80% to 97%, and 12 lines ranged from 63 to 77%. Only 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 was significantly different (P = 0.05) among soybean lines. Several lines were identified that had low disease incidence and good seed quality. These lines will be confirmed for resistance in the 2009 field trials. Inoculation with P. longicolla of soybean lines grown in the field may be a useful method for screening lines for resistance to this pathogen. Collaborative research between USDA and university scientists on germplasm screening is underway to identify resistance sources to Phomopsis seed decay of soybean.