Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2003
Publication Date: 11/1/2003
Citation: Lozovaya, V.V., Lygin, A.V., Zernova, L.V., Li, S., Hartman, G.L., Widholm, J.M. 2003. The role of isoflavonoids in the soybean root resistance to the soil-borne pathogen fusarium solani f.sp. glycines. Planta; 2003. Interpretive Summary: The important soybean disease, sudden death syndrome (SDS), is caused by the soilborne fungus Fusarium solani f. sp. glycines (FSG). There is a lack of knowledge about the role of roots in providing partial resistance to FSG and the biochemical events involved in soybean-FSG interactions. This paper records the changes in certain phenylpropanoid pathway compounds that occur in root tissues and culture medium following FSG infection or FSG culture filtrate elicitation of soybean hairy roots of partially resistant and susceptible genotypes. These compounds include the different isoflavone compounds including one called glyceollin that is known to be a compound that provides resistance to other soybean pathogens. These results indicate that the ability of soybean roots to rapidly produce sufficient amounts of glyceollin in response to FSG infection might be important in providing partial resistance to this fungus. The soybean hairy roots provide an ideal model system for the study of plant-soilborne pathogen interactions. This information is useful for other researcher studying host-pathogen interactions as well as those studying the biochemical basis of plant resistance to pathogens.
Technical Abstract: Soybean hairy root cultures were initiated to study the role of phenylpropanoid metabolism in cvs. sensitive (Spencer) and partially resistant (PI56774) to the disease sudden death syndrome caused by the soil-borne fungal pathogen Fusarium solani f. sp. glycines (FSG). FSG mycelia grew more slowly on inoculated PI56774 hairy roots than on Spencer hairy roots. The phytoalexin glyceollin content was higher in FSG-inoculated PI56774 hairy roots than in Spencer hairy roots even though the glyceollin precursor, the isoflavone daidzein, was higher in Spencer. The de novo synthesis of isoflavones and glyceollin was confirmed by [14C]Phe incorporation and the incorporation into glyceollin was higher both in the FSG-inoculated roots and surrounding medium of the cv. PI56774 than Spencer. The use of hairy roots demonstrated active glyceollin secretion, since the total amount of glyceollin in the medium was greater than that in the roots. Thus to accurately measure phytoalexin levels, glyceollin should be measured both in root tissues and that secreted into the medium. Glyceollin was the most inhibitory to FSG growth of the eight isoflavones tested including coumestrol. The levels of coumestrol, a putative phytoalexin, did not change upon FSG inoculation. The defense response was also elicited by FSG culture filtrates in liquid cultured hairy roots. These results indicate that the ability of soybean roots to rapidly produce sufficient amounts of glyceollin in response to FSG infection might be important in providing partial resistance to this fungus. The soybean hairy roots provide an ideal model system for the study of plant-soilborne pathogen interactions.