Submitted to: Soybean Research World Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/5/1999
Publication Date: N/A
Technical Abstract: Phenylpropanoid compounds, including phytoalexins, are induced by various abiotic and biotic stresses. Wall-bound phenolic esters, ethers and lignins may act as defense compounds (barriers for pathogen attack). The alteration in phenolic metabolism was studied after inoculating a susceptible soybean cultivar (Spencer) and a partially resistant plant introduction (PI567.374) with Fusarium solani f. sp. glyinces (causal organism of sudden death syndrome - SDS). After 3 weeks, the foliar severity of Spencer was 3.4 while that of PI567.374 was 2.2 on a 1 to 5 scale where 1 is most resistance and 5 is most susceptible. Root lesion lengths were 2.5 mm for each entry. There were differences between inoculated and noninoculated within each entry for all the growth parameters measured. Soluble phenolics were analyzed in 80% methanol extracts by HPLC. Inoculated plants from the resistant and susceptible entries had increased levels of isoflavones in leaf and stem tissues compared to noninoculated plants. Roots of the infected plants had decreased isoflavone levels both in susceptible and resistant entries, but levels were higher in plants of the inoculated resistant entry. The lignin was characterized by HPLC after oxidation of cell walls in alkaline nitrobenzene. Lignin content was higher in noninoculated plants from PI567.374 than Spencer. In infected plants of both entries, the level of lignin in root cell walls was considerably lower than in healthy plants, although root cell walls from plants of PI567.374 contained more lignin 3 weeks after inoculation than from plants of Spencer.