Hybridization studies within the genus Kluyveromyces van der Walt emend. van der Walt.

Hybridization studies based on the prototrophic selection technique, involving the use of auxotrophic mutants of strains of all accepted species of the genus Kluyveromyces, are reported. Two main groups of mutally interfertile taxa were established withinthe genus. the first group comprises Kluyveromyces bulgaricus, K. cicerisporus, K. dobzhanskii, K. drosophilarus, K. fragilis, K. lactis; K. marxianus, K. phaseolosporus, K. vanudenii and K. wileenii. The second group consists of K. doazhanskii, K. drosophilarum, K. lactis, K. vanudenii and K. wickerhamii. Hybrids were also detected in crosses involving K. drosophilarum and K. waltii as well as K. marxianus and K. thermotolerans. In terms of the concept of the biological species and in compliance with requirements of the International Code of Botanical Nomenclature, taxa which hybridize with K. marxianus and form fertile recombinants at frequencies observed in intraspecific crosses, are accepted as varieties of K. marxianus.