Issue link: http://read.dmtmag.com/i/82830
type poa annua is extremely sensitive to heat, cold and drought, low shoot density and coarse texture, not ideal for consistent putting surfaces. For most grasses, propagation occurs through either self or sexual propagation. Where self pollination produces identical offspring, meiosis or sexual propagation produces offspring which share a combination of paired homologous alleles. The ploidy level, refers to the number of chromosomes within cells. When two paired species, (referred to as homologous pairs) combine, complete set of chromosomes combine to create the diploid cells or genome. However, where too diverse of pairs combine, the resulting offspring is sterile. This is evident in the hybrid Bermuda grasses, which cannot produce seed, and must be propagated vegetatively. However, occasionally in nature where diverse parents like poa supina and poa infirma combine, this non-homologous pairing or in-equivalent chromosomal combination, can still produce fertile offspring. In the case of poa annua, a whole genome duplication occurred WITHOUT cell division, and subsequently produced multiple sets of chromosomes, double the chromosomal attributes within each cell, from both parents. Subsequently, that whole genome duplication event, created those previously unpaired partners of poa supina and poa infirma a homologous pairing, and restored fertility through meiosis, the recombination of both diploid cells from parental chromosome. This created that fertile hybrid; Poa annua. While relatively rare in nature, 80% of all plant species have shown polyploidy somewhere in their evolutionary history, and is what makes poa annua so successful. Poa annua now carries both sets of genes from poa supina and poa infirma, and subsequently has the ability to express either attributes from its parents when faced by a selection force. Each time the poa hybrid reproduces, it results in modified gene expression or genetic diversity to avoid that selection force. With many possible expressions among the many poa biotypes, older poa putting greens can exceed 50+ biotypes on a single surface. Examples of many different poa biotypes are commonly seen as patchy greens, the darker, lighter, or denser poa patches on greens. Each biotype on your greens, are responding to the same selection forces, but in a different stage of evolution. The gradual development of biotypes continues to improve their fitness , instigated by the selection forces, in efforts to avoid them. We can define selection forces as all the cultural programs we employ to maintain upright, fast and firm surfaces, and which may threaten the plant; adversely impacting its growth or growing environment. Perhaps the most obvious selection force, is close mowing; and the evolution of the poa biotype to re-direct resources from top growth to lateral growth, thereby avoid the repeated wounding associated with daily mowing. In consideration of effective management strategies, the perennial biotype remains active all year long and is favored by less disruption. This greens-type variety produces little to no seed, producing several daughter tillers before flowering (and dying). This WESTERN CANADA TURFGRASS ASSOCIATION 39 behaviour is subsequently much slower to flower, and more tolerant of stress than annual types. These perennial bio-types are so well adapted to the cultural intensity of today s management practices, if they seed they do so only in spring, while maintaining a high shoot density adapted throughout the growing season. It has also been realized, that the range of perenniality in poa annua plants also show a range among managed surfaces. Where poa in the rough may show perennial attributes, the number of daughter tillers range from 1-3, where a progressive increase in fairways 4-8, and up to >9 daughter tillers can be found in greens. Clearly, as mowing height drops and cultural programs increase, the tillering capacity of poa annua increases, relative to its management intensity. The plant may inhibit gibberellin production, much like the effects of plant growth regulation, ultimately reducing the repeated wounding that superintendents inflict on a daily basis. In the most basic of maintenance programs such as mowing, is enhancing poa annua's ability to compete, and encouraging its adaptation. For years now, common practice was to minimize phosphorus applications as this was thought to encourage poas establishment. While we can certainly see the benefits of establishment by phosphorus, in some cases, this may cause a thinning and subsequent establishment of rough-type poas. Poa has adapted to this low phosphorus selection force, by becoming Continued On Page 44