Genetics of Gracilaria tikvahiae (Rhodophyceae). VII. Further observations on mitotic recombination and the construction of polyploids

Abstract

Tetrasporophytes of the marine red alga Gracilaria tikvahiae produce spermatia as well as tetraspores. It has been demonstrated previously that these spermatia are diploid and are produced as a consequence of mitotic recombination in somatic cells of the fertile thallus. It has now been demonstrated that female tissue is also present, often adjacent to the male tissue as would be expected, but is more difficult to recognize because it rarely becomes fertile. However, it was found that female tissue could be excised from the tetrasporophyte and induced to regenerate into complete fronds. Crossing experiments indicated that this female tissue was functional and diploid like the corresponding male tissue. Diploid male and female fronds have been established in culture as free-living plants. Morphological mutants of Gracilaria were found useful in obtaining stocks of diploid gametophytes. Triploid and tetraploid sporophytes were readily synthesized by using the diploid gametophytes (or spermatia from normal diploid tetrasporophytes) in crosses to each other or to normal haploid gametophytes. In one case an apparent tetraploid was synthesized by crossing a haploid female with a triploid tetrasporophyte. In this work polyploid designations are made on the basis of the method of construction and the reproductive behaviour of the polyploids. Cytological confirmation (made for a triploid previously) is incomplete for tetraploids but supports the designations that have been made.