The Groundsman

May 2015

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TECHNICAL UPDATE 28 the Groundsman May 2015 Visit for more information and digital editions oa annua resulted from a natural cross between Poa infirma and Poa supina. These were likely sterile but as a chance event, the chromosomes spontaneously doubled in number which resulted in a fertile plant and, of course, Poa annua will make seed. Why do we see so many different kinds of Poa and why is it so well adapted to wet, cold, dry and hot environments? Poa annua can cross with other Poa annua plants to create new variant plants, though in most cases it prefers to pollinate itself (pollen fertilises the seeds of the same plant). When this occurs, individual genes in the plant quickly become fixed in a 'double base condition'. After four or five generations of self-pollination, the plants are highly uniform genetically and those that have the right combination of genes (for that environment) have an advantage over neighbouring plants, whether they are other Poa plants or other turf grass plants. P Poa annua - a true survivor Poa annua (annual bluegrass) is the most prevalent grassy weed in turf grass settings and over the past 50 years a number of studies have been conducted into how to control it. This Q&A looks into why Poa has an incredibly resilient - and versatile - survival strategy By: Professor David Kopec For example, in another turf grass field 200 miles away, a collection of Poa plants will have different gene combinations initially, and they become genetically uniform in that environment for the same reason (inbreeding and gene fixation). The result is a lot of Poa plants in a relatively short period of time, which quickly become highly adapted in the environments they are found in. When only a few Poa plants are alive in a very stressful environment, Poa then starts to 'outcross' with neighbouring Poa plants. This outcrossing mixes up a new 'batch' of unique gene combinations, which can then go through the self-pollinating process again, which produces a new set of uniform plants which have a double dose of the 'new' desirable genes. So, Poa uses both systems to its advantage. Why do some plants produce abundant flower heads while some barely produce any? Again, Poa has a trick up its sleeve. The answer is in the height of cut of the turf. When Poa is mowed tall (3/4inch or above) it produces seed heads abundantly. At a low height of 1/4inch or less, it produces fewer seed heads and, at 1/8inch or less, it often produces no seed heads. The partial reason for this is because at a high mowing height, Poa has lots of leaf Seed heads appear when Poa annua is allowed to grow high

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