Variation in ploidy level, fertility, and breeding Behavior in cultivated Schlumbergera (Cactaceae)

Chromosomes were counted in pollen mother cells and root tips of seven Schlumbergera clones. Two of the clones were diploid (2n = 2x = 22), two were triploid (2n = 3x = 33), and three were tetraploid (2n = 4x = 44). Female fertility was assessed by percent fruit set and numbers of viable seeds per fruit, and pollen viability was assayed by the fluorochromatic reaction (FCR). All seven clones produced viable pollen and eggs. The diploid clones and one triploid clone were self-incompatible (SI) whereas the other triploid and the three tetraploid clones were self-compatible and yielded S-1 progeny when selfed. There was a positive correlation between pollen diameter and ploidy level. Pollen was collected from a diploid, triploid, and tetraploid clone and 200 pollen grains were measured per clone using an ocular micrometer. Pollen diameter was more uniform in the diploid clone than in the triploid or tetraploid clones. Number of viable seeds per fruit was highest in 2x x 2x (female x male) matings, but viable seeds were also obtained in 4x x 4x, 4x x 2x, 3x x 4x, 3x x 3x, 3x x 2x, 2x x 4x, and 2x x 3x matings. The significance of these findings with regard to the breeding of cultivated cacti and chromosome evolution in the Cactaceae are discussed.