Genetics of Gibberella fujikuroi. III. Significance of heterokaryosis in naturally occurring corn isolates

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Abstract
Among the stalk rot fungal organisms, Gibberella fujikuroi (Saw.) Wn. (conidial anamorph Fusarium moniliforme Sheld.) was abundant in naturally infected com plants. Numerous phenotypically different isolates of F. moniliforme were recovered from the host. Some of these isolates formed heterokaryons more frequently in a given stage of plant growth. Frequently occurring heterokaryons were termed major and became the subject of this report. The component homokaryons exhibited differences in colony color, texture, growth rate, and sporulation. Based on these differences, ratios of two homokaryons recovered from a single representative of each of the four major heterokaryons were found to be balanced. Representative natural and laboratory-induced heterokaryons were compared for stability and balance of nuclear ratios on MM and SRM (stalk residue medium). Different heterokaryons predominated at different growth stages of the corn plant indicating preferential adaptation. Possible role of these heterokaryons in generating and maintaining natural variability was evaluated.