Parasexual Recombination in Penicillium chrysogenum

SUMMARY: Roper's (1952) technique for the isolation in filamentous fungi of strains carrying in their hyphae diploid nuclei heterozygous for known markers has been applied with minor modifications to a third species: Penicillium chrysogenum. One of these modifications is the use of 'dwarf' (stunted growth) mutants for growing balanced heterokaryons. Heterozygous diploid strains of P. chrysogenum behave like those of the other two species in yielding, vegetatively, new strains with recombined properties. This behaviour can be marshalled for the deliberate breeding of improved industrial strains.