Seed and Pollen Fertility in Colchicine Induced Polyploid Zoysiagrasses.

Zoysiagrasses (Zoysia Willd.) are perennial turfgrass species that require low fertility, have varying leaf textures, and slower growth rates that make them ideal for lawns, golf courses, and commercial landscapes. Zoysiagrasses are characterized as allotetraploids (2x = 4x = 40) with high outcrossing rates and the ability to hybridize with other Zoysia spp. Despite all the morphological and genetic variation available from interspecific crosses, the species still lacks genotypes with the ability to recuperate quickly from damage and wear. Additionally, chemical mutagenesis has long been used in plant breeding to produce crops that have novel traits such as larger flowers or compact growth habit, however it can also be used to produce sterile plants. Sterility is useful in vegetatively propagated turfgrasses to maintain uniformity and stability in farm fields, golf courses, and landscapes by reducing or eliminating the production of segregating seedlings. In a long-term breeding effort initiated in 2009 to increase vegetative growth rates, tetraploid (4x) zoysiagrasses were treated with colchicine to induce chromosome doubling. This effort resulted in the creation of octaploid (8x) genotypes, and with further self- and cross-pollination, pentaploid (5x), hexaploid (6x), and septaploid (7x) genotypes were produced. To assess the effects of induced polyploid on fertility, we evaluated in vitro pollen germination of these higher-level polyploid zoysiagrasses to estimate pollen viability as compared to that found in tetraploid (4x) lines. Pollen tube length was examined 24 and 48 hours after collection. We also looked at chromosome pairing during meiosis in pollen mother cells to identify any meiotic abnormalities that would affect fertility.