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The presence of dhurrin and cyanogenic activity in roots of sorghum was tested utilizing gas liquid chromatography and color reagents. Of 15 Sorghum bicolor (L.) Moench accessions tested, all gave a positive response for cyanogenic activity in the seminal root system based on a qualitative assay. Dhurrin concentrations of 18 to 25 g/kg were detected in freeze-dried, primary roots of NK262 and ATx399 x RTx430. The lateral roots of ATx399 x RTx430 contained less dhurrin (3 to 5 g/kg dry weight) than did the primary root (25 g/kg dry weight) of the seminal root system. Pathogenesis of the primary root by the lesion nematode Pratylenchus zeae Graham or the root-rot fungus Pythium arrhenomanes Dresch. decreased the hydrogen cyanide potential of lesion tissue by ca. 50% 48 h after inoculation relative to healthy roots. Dhurrin concentrations in lateral roots of the seminal root system were too low to measure the effect of pathogenesis on hydrogen cyanide potential. The possible significance of the effect of pathogenesis on hydrogen cyanide potential of root tissues is discussed.
Key Words: Lesion nematode Pratylenchus zeae Root-rot Pythium arrhenomanes Plant disease Sorghum bicolor
2 Associate professor, Dep. of Plant Sciences, Texas A&M Univ.; associate professor, Dep. of Forest Science, Texas A&M Univ.; and professor, Dep. of Soil and Crop Sciences, Texas A&M Univ.; College Station.
Received for publication August 8, 1983.
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