diploid vs tetraploid
The terms 'diploid' and 'tetraploid' ryegrass refers to the number of chromosomes per cell in the grass plant. Diploids have two sets of chromosomes per cell while tetraploids have four.
Diploids have tended to dominate mixtures in Ireland in recent years but tetraploid varieties are a key component of grass seed mixtures.
Because of the extra chromosomes, tetraploids have a bigger cell size and have a higher ratio of cell contents (soluble carbohydrates) to cell wall (fibre), indicating that they have a higher water content per cell.
Diploid plants have more tillers per plant and, due to the lower water content per cell, have a higher dry matter per kilogramme of feed and more energy than tetraploid plants. Both varieties have similar protein levels.
Compared to diploids, tetraploids are more palatable to livestock, leading to higher intake, and are more tolerant to drought. However, their higher water content goes hand in hand with a lower dry matter compared to diploids.
On heavy soils subject to poaching, the persistence of tetraploids may suffer, while seeding rates for tetraploid grasses will need to be higher because of the larger seed size.