Factors Affecting Growth and Reproduction in Selected Species of Aphanomyces

SUMMARY

Factors affecting growth and reproduction in single-spore isolates of Aphanomyces cochlioides, A. stellatus and A. sp. were studied using a defined medium and natural substrates. All grew well in a medium containing D-glucose, DL-glutamic acid, L-cysteine and minerals. No special substances were necessary for normal growth. The unnamed species grew through a range of temperatures between 5 and 45 C. The other two did not grow at temperatures above 35 C. A pH of 7 was optimal for all three species. All utilized a relatively wide range of amino acids as sources of nitrogen. DL-glutamic acid, L-glutamine, DL-aspartic acid, L-arginine and L-asparagine were excellent nitrogen sources. Sulfur from sodium sulfate was not used by any of these fungi, but L-cysteine, L-cystine and L-methionine were excellent sources of sulfur.

Temperature and pH over wide ranges had no specific influence on the induction of reproductive processes. Light, however, inhibited the formation of oogonia. A. cochlioides formed oogonia on corn meal agar and formed both asexual and sexual reproductive structures in the liquid, defined medium when the medium lacked a source of sulfur or a source of nitrogen or when certain amino acids which supported only limited amounts of growth were substituted for DL-glutamic acid in the defined medium. A. stellatus formed sexual structures in corn meal agar and in the liquid medium which lacked a source of nitrogen.