A Demonstration of the Role of het Genes in Heterokaryon Formation in Neurospora under Simulated Field Conditions

An experimental system was developed for assessing the role of het genes in heterokaryon formation in Neurospora in nature. Burned sugar cane segments planted in soil were infected using a mixture of mutant ascospores of two genotypes. Neurospora ramified in the cane and erupted as distinct pustules of conidia. When ascospores carried identical het alleles, the (macro) conidial pustules which formed were heterokaryotic. On the other hand, when ascospores carried dissimilar het alleles, the pustules were homokaryotic. These results showed that stable heterokaryons between compatible strains can form in nature. When two strains are growing together on a natural substrate, heterozygosity at het loci serves to maintain their individuality.