Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2007
Publication Date: 7/21/2008
Citation: Xue, H., Upchurch, R.G., Kwanyuen, P. 2008. Relationships between seed oleic and linoleic acid content and seed colonization by Cercospora kikuchii and Diaporthe phaseolorum. Plant Disease 92:1038-1042. Interpretive Summary: Mid-oleic soybeans have sometimes shown increased seed infection by fungi during later stages of development in the field compared to standard varieties. In order determine how oleic and other fatty acids might contribute to infection of seed by fungi, we produced seeds with the same genetic background that had differing oleic and linoleic acid contents. To produced seeds with different oleic and linoleic content we grew soybean plants at three different temperatures. The seeds were harvested, individually analyzed for fatty acid composition, and then inoculated in the laboratory with a preparation of Cercospora kikuchii, the causal agent of purple seed stain or Diaporthe phaseolorum, the causal agent of Phomopsis seed decay. We used the sensitive ergosterol assay to measure the amount of fungal infestation in the infected seeds. Results show that seed infestation by C. kikuchii increased with increasing oleic and decreasing linoleic acid content, but no clear association was found between the extent of seed infestation by D. phaseolorum and the seed oleic and linoleic acid content. Our data suggests that the oleic and linoleic acid content can be an important factor for soybean seed infestation by C. kikuchii but may not be a factor for seed infestation by D. phaseolorum.
Technical Abstract: Seeds of soybean lines with the mid-oleic phenotype have sometimes shown increased colonization by fungi during later stages of development in the field. To approach this phenomenon experimentally, we manipulated the oleic and linoleic acid content in seeds of two near-isogenic soybean lines by allowing seed development of the lines to occur in three different air temperature environments. Seeds produced in these environments were harvested, individually analyzed for fatty acid composition, and then inoculated with mycelium preparations of the fungal seed pathogens Cercospora kikuchii (Matsumoto & Tomoy.). or Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. sojae. Fungal biomass of infected seeds and seed controls was quantified by measuring the in vitro ergosterol content. Results show that across the two soybean lines, seed colonization by C. kikuchii was positively correlated with the oleic: linoleic acid ratio (r = 0.55, P < 0.03) and oleic acid content (r = 0.61, P < 0.02), and negatively correlated with linoleic (r = -0.60, P < 0.02) and linolenic (r = -0.58, P < 0.03) acid content. In contrast, no clear association was found between the extent of seed colonization by D. phaseolorum and the seed oleic: linoleic acid ratio. Our data suggests that the oleic: linoleic acid ratio can be an important factor for soybean seed colonization by C. kikuchii but may not be a factor for colonization by D. phaseolorum.