This is according to John Hampton from Lincoln University’s Seed Research Centre, who spoke to farmers about brassica seed vigour at the Foundation for Arable Research’s annual Crops Expo.
“It’s all to do with seed physiology and the aging process.”He explained that seed vigour is a component of quality but it is possible to have seeds with high rates of germination but low vigour.
Damage to the cell mitochondria and cell membrane will reduce the seed’s ability to function and form the new enzymes and proteins needed for growth and seedling production.
This can be due to exposure to high temperatures during seed development or through poor harvesting techniques, especially harvesting at high moisture levels which can cause bruising.
The problem becomes apparent if the seed, when sown into the seed bed, is placed under some sort of stress such as water or low temperature stress. Under such conditions seedling emergence can be poor.
If sown into a benign seedbed the seed is usually able to cope.
Hampton says brassicas struggle more in a direct-drill situation and farmers might have issues with emergence in what is a slightly harsher environment.
“Conventional tillage is kinder to the seed.”
Problems with seed vigour can go back to the temperature during the seed development phase.
Hampton says 25 degrees is the critical temperature and the longer the seed is subjected to temperatures higher than that while developing the worse the problem becomes.
There is little that can be done about this exposure to high temperatures other than altering the sowing date to try to avoid temperature stress at the critical seed development time. Another option being explored is taking the top off forage rape seed plants.
Hampton says the seeds at the top of the plant tend to be of poorer quality and work is being done to explore the option of removing the top of the plant to improve the quality of the seeds.
Initial work suggests there is no yield loss with this practice as removing the top allows secondary seed-heads to develop.
“This may not be an option for all crops but where you have crops with uneven development it may be an option – but it needs more work.”
Another aspect of research in this area is looking at how seed can repair damage done by oxygen scavengers and increase the efficacy of the seed’s defence mechanism to the aging process. This requires the identification of genetic markers that will allow plant breeders to improve seed quality.
This work is being done as part of an advanced seed production programme of which Lincoln University, AgResearch, Plant & Food, Canterbury University, the Foundation for Arable Research, Agriseeds and Seed Force are all a part of.