Expression of male sterility in Pelargonium crispum L'Her. ex Ait.

Summary

Hybridization was carried out between two cultivars of Pelargonium crispum, ‘Prince Rupert’ and ‘Lemon crispum’. The parental cultivars both had 2n=22 chromosomes, and their hybrids had the same chromosome number. In most of the hybrids eleven bivalents were usually formed at metaphase 1, but in one plant asynapsis occurred in one to three pairs of homologous chromosomes. ‘Prince Rupert’ is male-sterile, but ‘Lemon crispum’ is male-fertile. The hybrids were more or less partially male-sterile in that their flowers had fertile and sterile anthers in varying degrees. The number of fertile anthers per flower differed between individual hybrids and also varied from flower to flower and from season to season even in the same hybrid. The fertile anthers contained both viable and abortive pollen grains, but the sterile ones abortive grains only. When anatomically examined, young microspores developed normally in all anthers. In the sterile anthers the microspores suddenly stopped their growth, and their cytoplasm became unrecognizable. In the fertile anthers, however, the microspores continued to grow and became mature pollen grains filled with cytoplasm. Such a type of male sterility as observed here is common in various Pelargonium species. It seems probable that the cause of the male sterility is not chromosomal but genic, and its expression is greatly influenced by environmental conditions.