Why Is 4N Tetraploid Perennial Ryegrass So Special?
By Nik Wall, Premier Pacific Seeds
Modern day turf grasses have drastically improved over the last 40+ years. Some turf managers may remember when varieties such as Linn perennial ryegrass was the newest and latest new variety.
Oregon State University's Tom Cook notes that "Linn...has poor mowing quality, forms a relatively thin turf, and basically has all of the bad qualities we associate with perennial ryegrass". Since that time there has been multiple generations of improvement to get to the point we are at today with 4N Tetraploid perennial ryegrasses. 4N Tetraploid perennial ryegrass is being used on the 2019 FIFA Women's World Cup in France, and has been used at huge sporting events like the 2018 FIFA World Cup in Russia and 2016 Summer Olympics in Brazil among others.
So how does a turf type tetraploid perennial ryegrass come to be? According to DLF International Seeds, "polyploidy- the term to describe plants with more than two sets of chomosomes is common in the plant world [however] in its natural state, perennial ryegrass is diploid: it has two sets of chromosomes. By using a natural substance, [DLF I.S.] R&D teams have developed tetraploid varieties (four sets of chromosomes)". This is no small task according to DLF I.S. as "the route to tetraploidy is long because first-generation plants produce a mixture of diploid and tetraploid shoots within the same plant.[DLF R&D] teams have to count the number of chromosomes on each shoot so [they] can pick out the tetraploid ones... [Then they] need several [plants] to make a population that avoids inbreeding depression". Lastly, based on information from DLF I.S., new varieties must be tested "to prove that ...selected tetraploid shoots perform better than their corresponding diploid shoots".
The benefits of 4N Tetraploid Perennial Ryegrass are many. According to DLF I.S., "The strength of [Tetraploid perennial ryegrass] plants is obvious right from the start. Seeds kick off faster, even at lower temperatures. They grow into stronger seedlings that cover the ground faster without suffocating the other seedlings in your mixture". It has been observed that this aggressive characteristic is great for the natural competition against weed establishment. Based on testing done by DLF I.S. shown below, "[tetraploid perennial ryegrass] has better germination at 4 C compared to a diploid [plant]".
Figure 1. Germination trial comparing tetraploid perennial ryegrass and diploid perennial ryegrass
Figure 2.Tetraploid perennial ryegrass is referred to as 4turf in the graphic above.
Based on evidence from trials completed by DLF International Seeds "during autumn and winter seasons [Tetraploid perennial ryegrass] shows improved tolerance to diseases".
OSU Horticulture Department's Tom Cook noted that "in climates west of the Cascade Mountains throughout the PNW ryegrass has been widely used since it was first introduced" although "in areas east of the mountains ...potential loss from cold winters is still a concern". However, 4N tetraploid perennial ryegrass has been been observed to overwinter well without winterkill east of the Cascade Mountains in Kamloops, and Kelowna. DLF I.S. is confident that "[Tetraploid perennial ryegrasses] are comparable to some of the best diploids" and it is exciting think about what the future holds for new, improved tetraploid perennial ryegrasses.
Figure 3. Tetraploid Perennial Ryegrass (left) and Diploid Perennial Ryegrass (right) root depth study by DLF International Seeds (DLF Seeds and Science)
Dept., T. C.-O. (n.d.). Perennial Ryegrass Lolium perenne L. Retrieved June 04, 2019, from Oregon State Agricultural Science: https://agsci.oregonstate.edu/sites/agscid7/files/horticulture/beaverturf/PerennialRyegrass.pdf\
DLF Seeds and Science. (n.d.). 4turf Stronger Plants. Retrieved 05 27, 2019, from DLF Seeds and Science: https://www.dlf.com/professional-turf/4turf-stronger-plants