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Diploid vs Tetraploid

Any ryegrass species may be available in either tetraploid or diploid varieties. The ‘ploidy’ characteristics arise because tetraploid plants have four sets of chromosomes, while diploid plants have two. As a result, tetraploid plants have larger cells, a higher ratio of soluble carbohydrates (sugars) to cell wall (fibre) and a higher water content. Below are some of the practical implications of choosing diploid or tetraploid varieties for your farm.

Valley Seeds diploid cell illustration
Representation of a diploid cell

Diploid plants have thinner leaves, are more densely tillered and have smaller seeds than tetraploids. This means they can be sown at a lower rate per hectare to achieve the same plant density as tetraploids.

Grazing management

They can be grazed harder than tetraploiods and recover more quickly from hard grazing. They can also be allowed to grow past 15cm high and will be less likely to lodge than tetraploids.

This makes them a good choice for farms where there is not a lot of focus on grazing management.

Choose diploids for hay

At heading, diploids maintain their forage quality better than a tetraploid.

This is because they need less fibre in the stem to hold up the lighter seed. This makes diploids a better choice than tetraploids for hay.

Valley Seeds tetraploid cell
Representation of a tetraploid cell

Tetraploid plants have larger leaves, are less densely tillered and have larger seeds than diploids.

Grazing management

The higher water soluble carbohydrates (sugars) in their leaves means that livestock will prefer tetraploids, particularly in winter and early spring.

Tetraploids should not be grazed lower than 5cm in height. Their larger leaves mean it takes them longer to recover. The heavier leaves also increase the tendency to lodge, so if grazed, they should not be allowed to grow higher than 15cm.

Once tetraploids go to head they lose their forage quality quicker than diploids due to the extra fibre needed in stems to hold up the heavier seed.

Choose tetraploids for silage

The sugar content makes tetraploids ideal for silage, which requires larger amounts of sugars for fermentation.

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