Effect of Nitrogen Nutrition on the free Amino Acid Pool of Choanephora Cucurbitarum and Parasitism by two Haustorial Mycoparasites

SUMMARY

The susceptibility of Choanephora cucurbitarum to parasitism by the biotrophic haustorial mycoparasites, Tieghemiomyces parasiticus and Piptoccphalis virginiana, was markedly affected by both the nitrogen (N) source and carbon/nitrogen (C/N) ratio in host culture media. Parasitism could not be correlated with host growth or pH of culture filtrates. Analyses of the free amino acid pool in host mycelium by gas-liquid chromatography revealed high concentrations of glutamic acid and to a lesser extent other amino acids when N sources or C/N ratios favorable for parasitism were present in media. Poor N sources for parasitism resulted in low levels of all pool amino acids except those used as the N source. When the C/N ratio was increased in media initially favorable for parasitism, concurrent reductions occurred in levels of free amino acids in host mycelium and in growth of the parasite. Reductions in parasitism could not be correlated to the absence of specific amino acids in the host pool. Axenic growth of T. parasiticus on a glycerol medium amended with the amino acid pool from host mycelium was markedly affected by the N source used in host culture media. Excellent axenic growth occurred after amendment with clarified amino acid extracts from host mycelium cultured in media having a favorable N source for parasitism, whereas poor axenic growth resulted after amendment with extracts from mycelia grown in media having an unfavorable N source. In the fungal host-haustorial mycoparasite relationship, it appearss that the quantitative aspects of the free amino acid pool of the host are a primary determinant of the degree of susceptibility of host mycelium to parasitism.