Effect of Various Carbon Sources on Growth and Sexual Reproduction of Aphanomyces Euteiches

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Abstract
SUMMARY Growth and sexual reproduction of 6 isolates of Aphanomyces euteiches were studied in synthetic media containing DL-glutamic acid, mineral salts, phosphate buffer, methionine or sodium thiosulfate, and various carbon sources at 5 g carbon/liter. Forty-three carbon sources representing monosaccharides, oligosaccharides, polysaccharides, pectic substances and derivatives, carbohydrate derivatives, and Krebs cycle intermediates were tested. d-Glucose and maltose were the best carbon sources, whereas D-galactose, D-fructose, D-ribose, cellobiose, glycerol, and sodium pyruvate supported considerable but less growth than glucose and maltose. Pectic substances were slightly utilized for growth. All other sources tested were not utilized by the fungus. Glucose was always detected by paper chromatographic analyses in the filtrates from maltose and cellobiose media. No monosaccharides were detected in the lactose, melibiose, sucrose, and raffinose media. The fungus was unable to utilize D-mannose in the first 25 days of incubation, but it utilized this sugar after 30 days of incubation, or when mannose was supplied with glucose and galactose. The highest mycelial yields of A. euteiches were obtained in media containing autoclaved glucose (autoclaved with the medium or separately) and the smallest yields in Seitz-filtered media. Seitz filter pads soaked in distilled water for 24 hr were responsible for reducing growth of this fungus in media prepared with that distilled water. Seitz filter pads washed with distilled water reduced growth to a smaller extent than unwashed pads. D-Glucose and D-fructose were the best carbon sources for sexual reproduction. Oospore production by A. euteiches was dependent on the inherent ability of the isolates for sexual reproduction. Oospores were formed in abundance by some isolates even on carbon sources supporting sparse growth.