Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/11/2008
Publication Date: 7/26/2008
Citation: Lygin, A., Li, S., Widholm, J., Lozovaya, V. 2008. Metabolic Events that are Important for Soybean Rust Resistance. Phytopathology 98:S95 Interpretive Summary:
Technical Abstract: Asian soybean rust, caused by Phakospora pachyrizi is an important new soybean disease that causes much concern at present in the US agricultural community. There are no commercial soybean varieties with resistance to soybean rust at this time and US cultivars are thought to be highly susceptible to this fungus. Efforts are underway to identify partial resistance or slow rusting traits. In order to understand the metabolic responses of soybean to P. pachyrhizi attack and to assist in development of cultivars with resistance to soybean rust, leaves of 14 days old soybean plants were inoculated with spore suspension of Phakospora pachyrzi. Leaf samples were taken 1 day, 1 week and 3 weeks after inoculation and soluble phenolic compounds were extracted by 80% methanol. Residues after extraction of soluble phenolics were used to prepare cell wall samples. Both soluble and cell wall-bound phenolics were analyzed by HPLC and spectrometry. We found that isoflavonoid and flavonoid synthesis in soybean leaves was strongly stimulated in response to rust infection. Several fold increases of flavonoids (quercetin and kempferol) and phenolic acid levels occurred in leaves of rust infected plants compared to the non-inoculated control. While the phytoalexin glyceollin and the precursor of glyceollin, daidzein were not detected in leaves of uninfected plants, both compounds accumulated at marked concentrations in rust infected leaves indicating that glyceollin is involved in the plant defense response to the soybean rust pathogen. Importantly, these compounds accumulated at much higher levels in plants that had better rust tolerance. The results obtained indicate that the soybean antibiotic glyceollin and cell wall-bound phenolics could be a good target for breeding and genetic engineering for resistance in soybeans to soybean rust disease.