Tetraploid Ryegrass

A perennial ryegrass species which has four sets of chromosomes, in contrast to the usual two sets (which is called diploid). Tetraploid cultivars can typically germinate quicker and also at lower temperatures than diploids, although this may be due to cultivar difference rather than ploidy difference. Tetraploids are often also less wear tolerant and persistent (being less effective at recovering from wear), with lower shoot density and a slightly broader leaf (although in most cases this latter feature is probably irrelevant) than diploid cultivars in winter pitch situations mown at 25mm height of cut (Source: ‘Turfgrass Seed 2025’, BSPB). Winter and summer colour are typically darker than diploids, whilst resistance to red thread disease is also better.

So, with a blend of benefits and limitations the use of tetraploids will depend on the specific requirements of the pitch. They can potentially improve surface coverage of some areas due to overseeding outside of the typical seeding periods, especially during colder conditions, although this might need to be on a routine overseeding basis, so will not typically be suitable from a cost-effect perspective for clubs with low and limited budgets.

Tetraploid ryegrasses were originally developed for the agricultural market and the concept has been transferred to turfgrass cultivars. Whilst they are quick to germinate at low temperatures, the other agricultural benefits are they are lusher which means they are potentially susceptible to wear and disease in a turfgrass situation (although for red thread this doesn’t appear to be the case), whilst longevity is also questionable when compared with diploid cultivars. Oversowing with tetraploid ryegrass cultivars can offer complementary benefits with diploid cultivars, although it is important to understand the purpose and expected outcomes. Continued grass breeding will no doubt improve certain traits further with the aim to make tetraploids more comparable with diploids.