Studies on the occurrence of polyploidy and its contribution to flower plants breeding. III. On the characteristics and biological significance of a hypotriploid plant obtained from intervarietal crossing in freesias.

Abstract

In the course of intervarietal crossing in freesias since 1956, a hypotriploid plant (2n=33-1) was obtained unexpectedly from crossing between tetraploid Golden Buttercup (2n=44) and diploid Super Giant Yellow (2n=22). It grows slowly and has a few slender, short, somewhat twisted and palegreen leaves. Each flowerlet born on a curved flower stalk is very small and light-brownish colored, consisting of 5 perigons (3 inner and 2 outer). The maturation division in pollen mother cells is so irregular that almost all pollen grains are degenerate, and thus the plant is completely sterile. Regarding the occurrence of such an abnormal hypotriploid plant, some inferences are described as follows. It is well known, hitherto, that many normally growing aneuploid plants or cultivars have been found in some popular bulbous flowering plants euch as crocus, hyacinth, daffodils etc. These peculiar plants grow vigorously in most cases at present, probably due to their genomic heterognity, namely, partial allopolyploid constitution, transmitted from different kinds of ancestors, and also due to successive natural and artificial selections against long term inferior or lethal characteristics. On the contrary, in some bulbous plants such as canna or freesia, which were derived from ancestors af closely-related or of almost similar genomic constitutions and also were introduced into the horticultural circles in recent centuries, vigorous-growing aneuploid plants would not occur yet, although the normal polyploid levels are present and many tri- or tetraploid strains are used as cultivars already. Furthermore, it is considered that any aneuploid plants will ntver appear in species such as babiana or tritonia which only has single Stable diploid genomes and was newly introduced into Europe in this century from Southern Africa.