Allelic differences at two loci govern different mechanisms of intraflower self-pollination in self-pollinating strains of periwinkle.

Periwinkle [Catharanthus roseus (L.) G. Don], an ornamental and medicinal plant, is a self-compatible, insect-pollinated plant species in which intraflower self-pollination does not occur because of spatial separation of the stigma and anthers. Recently three self-pollinating strains-MJ, VI, and OR-were identified. Self-pollination in these strains was found to be brought about by continuous increase in gynoecium length from anthesis to self-pollination, in contrast to non-self-pollinating strains, in which the stigma remained below the base of the anthers from anthesis to flower drop. Self-pollination in these strains was found to be controlled by duplicate, recessive genes. Self-pollination in strains MJ and VI was brought about by an increase in gynoecium length resulting from an increase in the length of the ovary, while in the strain OR, the increase in gynoecium length was because of an increase in the length of the style from anthesis to self-pollination. The three strains were intercrossed to determine the relationship between genes governing self-pollination in these strains. The F(1) plants and all plants of the F(2) generation of the cross MJ x VI exhibited self-pollination that was brought about by an increase in the length of the ovary, indicating that the same genes were involved in these two strains. The F(1) plants of crosses OR x MJ and OR x VI, exhibited self-pollination that was brought about by an increase in the length of the ovary, indicating that self-pollination brought about by an increase in the length of the ovary was dominant over self-pollination brought about by an increase in the length of the style. In the F(2) and backcross [(OR x MJ) x OR and (OR x VI) x OR] generations, both self-pollinating and non-self-pollinating plants were observed. The ratio of plants with self-pollination brought about by an increase in the length of the ovary, non-self-pollinating plants, and plants with self-pollination brought about by an increase in the length of the style in the F(2) and backcross generations fit 9:6:1 and 1:2:1 ratios, respectively. All plants of the backcrosses [(OR x MJ) x MJ and (OR x VI) x VI] exhibited self-pollination brought about by an increase in the length of the ovary. The results thus supported the earlier finding that self-pollination in the studied strains was controlled by duplicate, recessive genes and suggested that three alleles at two loci determine the occurrence or nonoccurrence of intraflower self-pollination in periwinkle.