Heterokaryon formation in planta by genetically marked strains of Tilletia caries

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Abstract
Genetically marked and wild-type haploid cultures of Tilletia caries were mixed and used as inocula to analyze their potential for heterokaryon formation in the susceptible spring wheat variety ''Red Bobs'' (Triticum aestivum L.). Of the fungus-treated plants inoculated by hypodermic needle injection into the boot at the flag leaf stage, 30 to 64% proceeded to maturity; the remainder failed to head. Tilletia caries was recovered from each of 38 representative plants which failed to head and from 3 plants which headed but showed no visible signs of infection. None of the inoculations resulted in teliospore formation within mature heads or other plant tissues. Genetic analysis of hyphal fragments obtained from mycelium in infected plants indicated that a heterokaryon had formed in each of two pairings of different auxotrophic strains of the fungus. The number of nuclei present in hyphal cells was variable. However, secondary sporidia derived from the heterokaryon were mononucleate with one exception and exhibited the nutritional requirement of one or the other parental strain. Results are discussed in relation to the development of a system for mitotic and meiotic analysis of single gene traits in the bunt fungi.