Studies of the interactions of SCN with brown stem rot of soybean

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Investigators: Gregory L. Tylka, Girma Tabor, Charlotte Bronson, David Soh
Funding: North Central Soybean Research Program, Iowa Soybean Association

Iowa fields are commonly infested with both SCN and brown stem rot (BSR). In the early 1990s, researchers observed that BSR-resistant soybean varieties had much greater than expected levels of BSR disease in fields infested with SCN than in those without SCN.

Research was initiated in the mid 1990s to study how SCN affects the fungus that causes BSR (Phialophora gregata, now sometimes called Cadophora gregata) and how the nematode affects BSR disease symptom development, infection and colonization by the BSR fungus, and soybean yield.

Key findings from the work are:

  • In BSR-resistant soybean varieties, SCN infection resulted in significant increases in severity of the internal stem discoloration symptoms caused by the BSR fungus.
  • SCN infection resulted in earlier infection and more widespread colonization by the BSR fungus in BSR-resistant soybean varieties.
  • SCN increased BSR disease symptom development, and infection and colonization by the BSR fungus even in varieties with both BSR resistance and SCN resistance.
  • The higher the SCN population, the greater the effect of SCN on BSR disease symptom development, and on infection and colonization by the BSR fungus.

Most of the research described above was done with the common genetic type of the BSR fungus, called “genotype A”. In 2000, another genetic type of the BSR fungus, genotype B, was reported. Genotype B causes no foliar disease symptoms and much less internal stem discoloration than genotype A. Research now is focusing on determining how SCN interacts with genotype B of the BSR fungus to affect BSR disease and yield loss. This research will continue through 2009.

Leaf symptomsHealthy stem compared to the internal stem browning of a plant with brown stem rot.

Field microplots used to study the interaction of SCN with brown stem rotField microplots used to study the interaction of SCN with brown stem rot

Soybean stem pieces plated on a medium to allow the BSR fungus to emerge. This test is used todetermine how much of the stem was colonized by the fungus 	Click on image to view a one-page information sheet information sheet (mini poster) in pdf format

Colonization of BSR-resistant soybeans by the BSR fungus increases when plants are infected with SCN

Scientific articles published about this research with links to abstracts

Genotypes A and B of Cadophora gregata differ in ability to colonize susceptible soybean. Tabor, G.M., G.L. Tylka, and C.R. Bronson. 2007. Plant Disease 91: 574-580.

Soybean stem colonization by genotypes A and B of Cadophora gregata increases with increasing population densities of Heterodera glycines. Tabor, G.M., G.L. Tylka, and C.R. Bronson. 2006. Plant Disease 90: 1297-1301.

A new greenhouse method to assay soybean resistance to brown stem rot. Tabor, G.M., S.R. Cianzio, G.L. Tylka, R. Roorda, and C.R. Bronson. 2006. Plant Disease: 90: 1186-1194.

Resistance to Phialophora gregata is expressed in the stems of resistant soybeans.Tabor, G.M., G.L. Tylka, S.C. Cianzio, and C.R. Bronson. 2003. Plant Disease 87: 970-976.

Heterodera glycines infection increases incidence and severity of brown stem rot of soybeans. Tabor, G.M., G.L. Tylka, J.E. Behm, and C.R. Bronson. 2003. Plant Disease 87: 655-661.