Hybrids in the making
A new generation of hybrids is on the way. Lucy Stephenson assesses their merits.
THE push for even greater yield is on. Conventional varieties have closed the hybrid yield gap, but the race is on to regain that lead with a new generation of three-way hybrids.
To understand the new generation, first you need to know that a hybrid is a cross between two varieties. Sounds simple, but it has not been easy for scientists to achieve because oilseed rape is naturally self-pollinating. So you cannot simply create a hybrid by planting two varieties side by side – the resulting seed would be a mix; some hybrid seed, but most of it self-set seed of the two individual parents.
The breeders have overcome this difficulty by making one of the parents male-sterile and therefore unable to produce pollen. These are the three hybrid types:
1. Varietal Association (VA)
Synergy, the first commercial UK hybrid is a varietal association. It is a mix of seed: male sterile hybrid seed and a conventional variety to provide the pollen. The conventional variety Falcon is used as Synergys pollinator. Concept however has two different pollinators: early flowering Pactol and late flowering Briol.
Yields are apparently enhanced with such hybrids because the sterile plants in the seed association do not have to channel plant energy into pollen production, so seed yield is potentially higher.
But it is vulnerable to adverse conditions at pollination such as poor weather and insect damage; the pollen beetle spraying threshold is one insect to every five plants compared with three insects for the other hybrid types.
Gemini takes the VA concept one stage further; instead of a conventional variety as a pollinator it uses a fertile hybrid which boosts yield potential.
2. Fully restored hybrid
This is a fully fertile hybrid, so pollination is obviously better but seed production more tricky. Artus, Pronto and Elite are examples of this type of hybrid.
Reliable seed production and no risk of poor pollination would make the ideal hybrid and that is what breeders are aiming for.
3. Three-way hybrid
A three-way hybrid essentially has three parents – two to create a hybrid, which is crossed once more. There are two types of three-way hybrids; the difference being whether the hybrid parent is fertile or sterile.
Cargills Comodor has been bred by crossing a fertile hybrid with a male sterile line, which produces a 50/50 mix of male fertile and male sterile plants in the commercial crop. Cargills Chris Black claims that the three parents give Comodor the ability to perform under a wider range of conditions.
Advanta have created a fully restored three-way hybrid – Triangle. Its pollinator is an in-bred variety with a restorer gene and the male sterile is the hybrid. The seed set on the female plant will produce fully restored plants in the commercial crop. The companys Paul Hickman says the variety is up for recommendation this autumn.
4. Top cross hybrids
Top cross hybrids are produced in the same way as three-way hybrids. However, the first hybrid is produced from lines that are genetically identical except for the genes to make one male sterile and one pollen-producing.
When this is crossed with the second male sterile line, the hybrid is more uniform than three-way hybrids and more vigorous, claims Novartis Nigel Padbury. Spirit is one such and will be available in autumn 2000.