The effect of pea root exudate on the germination of Pythium aphanidermatum zoospore cysts

Abstract

Zoospore cysts of Pythium aphanidermatum germinated well without external nutrient supply, but pea root exudate increased percentage germination and germ tube growth. Zoospore cyst germination and growth varied with different concentrations of the substrate supplied. Alone, the neutral fraction (sugars) increased percentage germination but had little effect on germ tube growth; the cationic fraction (amino acids) suppressed germination and growth somewhat, except at very low concentrations; the anionic fraction (organic acids) mildly stimulated both processes. Neutral and anionic fractions combined approached the stimulatory effect of root exudate. Amongst the components of root exudate tested as pure chemicals, fructose, histidine, homoserine, proline, and tartaric acid promoted germination and growth at low concentrations. Alpha-alanine, glutamine, serine, and valine became stimulatory at high concentrations. A combination of glucose with one of the organic acids was more effective than either alone.