Submitted to: Journal of Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2008
Publication Date: 8/21/2008
Citation: Bellaloui, N., Mengistu, A., Paris, R.L. 2008. Soybean Seed Composition in Cultivars Differing in Resistance to Charcoal Rot (Macrophomina phaseolina). Journal of Agricultural Science. vol. 146(6):667-675 Interpretive Summary: Charcoal rot disease is caused by a soilborne fungus (mold). The disease is a major problem in the southern soybean regions of the USA and throughout the world causing reduction in yield of 10-50% and loss of seed quality. Soybean seed is used for human consumption and animal feed. Seed composition (protein, oil, fatty acids) determines seed quality and it is important for soybean seed industry. Investigation of charcoal rot infestation of soil on soybean composition has not been well investigated, especially under the non-traditional early soybean production system that is used in the midsouth of U.S.A. Scientists from USDA-ARS at Stoneville MS conducted a field experiment to assess the above components under soil charcoal rot infestation under irrigated and non-irrigated conditions. No significant differences in protein levels in the moderately resistant germplasm line DT 97-4290 were observed under charcoal rot infestation. However, in the susceptible varieties Pharoah and Egypt a significant decrease in protein and linolenic fatty acid, and an increase in oleic fatty acid were recorded under diseased conditions. Oleic and linolenic fatty acids are important for oil stability. Soybean varieties with moderate resistance to charcoal rot may maintain normal levels of seed oil and protein when plants are grown in fields infested with the fungus.
Technical Abstract: Soybean [Glycine max (L) Merr.] cultivars of maturity group (MG) IV were selected based on their susceptibility to charcoal rot disease caused by a soilborne fungus (Macrophomina phaseolina). Seed composition and nitrogen fixation in soybean has not been well investigated under charcoal rot infestation under irrigated and nonirrigated conditions. Therefore, the objective of the experiment was to evaluate protein, oil, fatty acids, and nitrogen fixation as influenced by susceptibility of soybean cultivars to charcoal rot when grown under charcoal rot infestation with irrigated and nonirrigated conditions. No significant differences in protein levels in the moderately resistant germplasm line DT 97-4290 were observed between irrigated-noninfested (IC) and irrigated-infested/diseased (ID) or between nonirrigated-noninfested (NC) and nonirrigated-infested (ND). However, in the susceptible cultivar Egyptian protein was significantly higher under IC than under ID. The opposite was observed when Egyptian was grown without irrigation, where protein was higher under ND than NC consistently in both years, suggesting that the effect of charcoal rot infestation on protein may depend not only on cultivar but also on the use of irrigation. Pharaoh showed a consistent increase in protein percentage under IC and NC for both years compared with ID and ND. Oleic acid percentage in the susceptible cultivars was significantly higher under infested conditions (ID and ND) than under noninfested conditions (IC and NC) compared with the moderately resistant breeding line DT 97-4290. Linolenic acid percentage did not change significantly in DT97-4290, but for the susceptible cultivars the percentage of linolenic acid was significantly higher under IC and NC than under ID and ND conditions. The enrichment of Delta 15N in susceptible varieties Pharoah and Egyptian, especially under ND plots indicated that nitrogen fixation was substantially inhibited. These results indicate that charcoal rot infestation significantly affected seed composition and nitrogen fixation in soybean.