Tetraploids

  • Some ryegrass, red clover, lotus and brassica cultivars are tetraploids.
  • Tetraploids have four sets of chromosomes per cell, twice as many as normal diploid plants.
  • Tetraploids usually have bigger darker leaves than diploids.
  • In perennial ryegrass, tetraploids need different management for best performance.

 

What is a tetraploid?

Ryegrass, red clover, lotus and brassicas occur in nature as diploids, meaning each cell in the plant has 2 sets of chromosomes. Tetraploids have been developed by plant breeders using controlled mutation from a standard cultivar (diploid) to double the number of chromosomes in each plant cell.

This practice was first developed in Holland in the 1960s and has now become common in plant breeding. Tetraploiding does not involve gene modification.

 

Tetraploid characteristics

Tetraploiding creates larger cells, leading to larger plants and larger seeds. Due to the increased cell size, tetraploid plants have a higher ratio of soluble carbohydrates (cell contents) to fibre (cell wall), potentially improving animal preference and performance over diploid cultivars.

Tetraploids can be identified by their large, dark leaves, and may visually appear superior to diploids. However they tend to have 10-20% less dry matter content. Tetraploid seeds are larger than diploid seeds and because of this a higher sowing rate is required to obtain a similar number of seeds per hectare.

 

Feed value

Tetraploid perennial ryegrasses have higher palatability than diploids, as well as greater digestibility and voluntary feed intake by stock. However they are less robust, and don't fit all farm systems.

 

Tetraploid annual and Italian ryegrasses

Tetraploiding annual or Italian ryegrass appears to have little affect on their palatablity. This is probably because they are already very palatable.