Hybridization Studies on a Zinc-Induced Variant of Hypomyces Ipomoeae

SUMMARY

A striking variant has been produced by cultivation of monoploid hyphae of Hypomyces Ipomoeae on medium containing a sub-lethal concentration of zinc nitrate.

Analyses of 5 consecutive single-conidium culture-series, consisting of 25 cultures each, have proved the mutant strain, aborta, to be homocaryotic. Single-conidium and mass-transfer cultures of the aborta strain have shown a high degree of uniformity.

The most striking feature associated with the variant was that four, rather than eight, spores were formed in aborta × normal asci, due apparently to inability of nuclei carrying the aborta factors to delimit spores.

Evidence strongly indicated that in rare instances ascospores in aborta × normal asci may include more than one of the eight nuclei resulting from maturation of the zygote nucleus. Thus, in two instances, single ascospores isolated from hybrid perithecia yielded mixed cultures containing both normal and aborta hyphae. The two f_x aborta strains thus obtained bore opposite sexual-reaction factors. In two other instances, single ascospores from hybrid perithecia yielded cultures containing normal hyphae of both sexual reactions, as was evidenced by the appearance of fertile perithecia in both cultures.

The inability of aborta nuclei to delimit ascospores may be attributed to the inactivation or to the deletion of one or more genes determining ascospore delimitation. The ascospore-delimitation factors and the sexual-reaction factors are in different linkage groups.

The genie alteration or mutation, although having occurred on medium containing a sub-lethal concentration of zinc, cannot be considered a specific effect of zinc ion without further evidence.