Exploiting Unreduced Gametes for Improving Ornamental Plants.

The formation of gametes with somatic chromosome number or unreduced gametes (2 gametes) is an important process involved in the origin of polyploid plants in nature. Unreduced gametes are the result of meiotic mutations occurring during micro- and mega-sporogenesis. 2 gametes have been identified or artificially induced in a large number of plant species. Breeding of plants through 2 gametes can be advantageous because it combines genetic effects of polyploidy with meiotic recombination and sexual hybridization to produce tremendous genetic variation and heterosis. 2 gametes also occur in ornamental plants, but the potential of using 2 gametes in ornamental plant breeding has not been extensively exploited. Ornamental plants are primarily produced for their esthetic appearance and novelty, not for food and yield, and they can be readily propagated through vegetative means. Triploids, tetraploids, and plants with even higher ploidy levels produced through 2 gametes can be propagated through tissue culture to fix their phenotypes, thus leading to the development of new cultivars. In this review article, we intend to discuss the mechanisms underlying the formation of 2 gametes, techniques for 2 gamete identification, methods for enhancing 2 gamete formation, and the current status in the use of 2 gametes for development of novel ornamental plants. We believe that polyploidy breeding through 2 gametes represents a viable way of developing new cultivars, new species, and even new genera of ornamental plants.