Abstract
Sporangia of Pythium ultimum were placed in polycarbonate membrane sandwiches and buried in raw Nunn sandy loam amended with increasing concentrations of bean leaves, oatmeal, glucose + l-asparagine (4:1 w/w) or glucose alone. After 24 h, there was a significant negative correlation between the concentration of substrates added to the soil and the formation of secondary sporangia. Glucose + l-asparagine also inhibited the formation of secondary sporangia in an axenic system. The formation of secondary sporangia in soil amended with P. nunn (300 cfu g −) + 0.3% (w/w), bean-leaf or oatmeal was significantly greater than in the amended treatments without P. nunn at 7, 14 and 21 days after amendments were added to the soil. Results suggest that competitive saprophytric activity of P. nunn rapidly depletes substrates usually utilized by P. uttimum. This results in sporangial germination then immediate formation of survival structures (in some instance of lower inoculum potential) by the latter fungus.
Published Version
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