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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED RESISTANCE TO SOYBEAN PATHOGENS AND PESTS

Location: Soybean/maize Germplasm, Pathology, and Genetics Research

Title: Characterization and quantification of fungal colonization of Phakopsora pachyrhizi in soybean genotypes

Authors
item Vittal, Ramya -
item Paul, Chandra -
item Hill, Curtis -
item Hartman, Glen

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 25, 2013
Publication Date: January 2, 2014
Citation: Vittal, R., Paul, C., Hill, C.B., Hartman, G.L. 2014. Characterization and quantification of fungal colonization of Phakopsora pachyrhizi in soybean genotypes. Phytopathology. 104:86-94.

Interpretive Summary: Soybean rust is an economically important disease of soybean with potential to cause severe epidemics resulting in significant yield losses. Host resistance is one of the management tools to control this disease. Our study detailed the infection process of the fungus in soybean visually using stains and microscopic observations and quantitatively by measuring the amount of fungal DNA using quantitative polymerase chain reaction. Early events of the infection process including spore germination and fungal penetration were monitored. Differences in infection among soybean genotypes were evident once the fungal hyphae penetrated into the intercellular spaces of the leaf. Soybean genotypes UG5 (immune or complete resistance), plant introduction (PI) 567102B and PI 567104B (incomplete resistance) had significantly lower quantities of fungal sporulation and fungal DNA than four other genotypes with lower levels of resistance. These results demonstrated that resistance in soybean is because of the restricted fungal development due to a hypersensitive response. This information is useful for scientists interested in host-pathogen interactions and the mechanisms of host plant resistance.

Technical Abstract: Soybean rust, caused by the fungus Phakopsora pachyrhizi Syd., is an economically important disease of soybean with potential to cause severe epidemics resulting in significant yield losses. Host resistance is one of the management tools to control this disease. Our study detailed the infection process of P. pachyrhizi in soybean visually using stains and microscopic observations and quantitatively by measuring the amount of fungal DNA (FDNA) using quantitative polymerase chain reaction (QPCR). Soybean genotypes varying in their reaction to inoculation, from complete resistance to susceptible, were compared. Early events of spore germination, appressorium formation, and fungal penetration occurred within 24 hours post inoculation, and were similar among the selected soybean genotypes. Differences in infection among the genotypes were evident once the hyphae penetrated into the intercellular spaces between the mesophyll cells. Soybean genotypes UG5 (immune or complete resistance), plant introduction (PI) 567102B and PI 567104B (incomplete resistance) had significantly lower (P < 0.05) quantities of uredinia and FDNA than four other genotypes with lower levels of resistance. There was a significant positive correlation (r = 0.30, P < 0.001) between quantities of hyphal interaction sites in mesophyll cells with FDNA. These results demonstrated that incompatible soybean-P. pachyrhizi interaction results in restricted hyphal development in mesophyll cell tissue, likely due to hypersensitive apoptosis.

Last Modified: 10/1/2014
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