Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2009
Publication Date: November 15, 2009
Repository URL: http://hdl.handle.net/10113/38779
Citation: Lygin, A., Li, S., Vittal, R., Hartman, G.L., Widholm, J., Lozovaya, V. 2009. The Importance of Phenolic Metabolism to Limit the Growth of Phakopsora pachyrhizi. Phytopathology. 99:1412-1420. Interpretive Summary: Asian soybean rust is a new soybean disease in the continental United States and poses a potential serous threat to the U. S. soybean industry. Understanding the metabolic responses of the plant will assist in development of cultivars resistant to this disease. In this study, differences in phenolic metabolism were analyzed between inoculated and non-inoculated plants using two susceptible and three resistant soybeans. Concentrations of anti-microbial compound glyceollin and cell wall fortifying compound lignin were much higher in resistant soybean than that in susceptible soybean in response to the pathogen infection. Selecting for increased synthesis of these plant chemical compounds can help soybean breeders to improve resistance to soybean rust.
Technical Abstract: Understanding the metabolic responses of the plant to a devastating foliar disease, soybean rust, caused by Phakopsora pachyrhizi, will assist in development of cultivars resistant to soybean rust. In this study, differences in phenolic metabolism were analyzed between inoculated and non-inoculated plants using two susceptible and three resistant soybean genotypes with known resistance genes. Accumulation of isoflavonoids and flavonoids in soybean leaves was greatly increased in response to rust infection in all genotypes tested. While the soybean phytoalexin glyceollin was not detected in leaves of uninfected plants, accumulation of this compound at marked levels occurred in rust infected leaves being substantially higher in genotypes with a red-brown resistant reaction. In addition, there was inhibition of P. pachyrhizi spore germination by glyceollin, formononetin, quercetin and kaempferol. Lignin synthesis also increased in all inoculated soybean genotypes while there was no significant difference in all non-inoculated soybean genotypes. Cell wall lignification was markedly higher in inoculated resistant lines compared to inoculated susceptible lines indicating a possible protective role of lignin in rust infection development. An increase of synthesis of the soybean plant chemicals, such as the anti-microbial compound glyceollin and cell wall fortifying compound lignin, could help soybean breeders to improve resistance to soybean rust.