The germplasm collection: a library of apples
A collection of apple genetic resources, known as a germplasm collection, is maintained by Plant & Food Research at their Hawke’s Bay orchard to provide a source of new apple traits for the future.
Storing genetic information from apples
A germplasm is a library of genetic resources for an organism. Germplasm collections can be stored in several ways – as seeds in cool storage, as whole plants in a nursery or orchard or as cryopreserved dormant buds. At Plant & Food Research (PFR), the apple germplasm collection is maintained in the form of trees in the orchard. 2 trees of each genotype are planted.
It’s important to maintain an apple germplasm collection as trees because apples don’t breed true. This means that the genetic make-up of the seeds will be different to that of the tree that bears them. Growing the trees is the only way to know how the apples they produce will look and taste.
History of the apple germplasm collection
The germplasm collection in New Zealand began in the 1950s, when approximately 500 distinct cultivars (including heritage cultivars, crab apples and cider apples) were brought together at the then HortResearch site (now PFR) in Hawke’s Bay. Then, in the 1990s, a large number of seeds (approximately 30,000) were brought in from around the world, including Central Asia (particularly Kazakhstan) and added to the collection. For this 2nd set of material, PFR has developed a breeding programme that generates additional genetic diversity within the collection.
Wild apples in Central Asia are genetically diverse
Central Asia (particularly Kazakhstan) is the region where modern apples originated. The area has many wild apple forests, which contain apples of all shapes, sizes and colours (including red-fleshed apples). The apple trees have been open-pollinated (pollinated in the wild, without human control) for many generations, so they are highly genetically diverse.
The apple trees of this region have several desirable characteristics. For instance, some are resistant to the diseases apple scab and fire blight. Because of growing conditions in Central Asia, it’s also likely that the trees have genes that allow them to adapt to mountainous terrain and a near-desert, cold and dry climate.
HortResearch (now PFR) wanted to have access to the genetic diversity of the wild apple trees for breeding and conservation purposes. Access to such a wide germplasm gives breeders opportunities to introgress novel traits and breed a wide variety of new cultivars.
A source of new traits and genetic diversity
Many of the apple trees in the germplasm collection contain specific traits that might enhance existing apple varieties. These can be used as parents in breeding programmes, with the aim of producing new, better apples with that trait. For instance, some trees in the collection produce apples with red flesh. These aren’t good eating apples, but crossing them with existing white-fleshed cultivars has the potential to produce a high-quality eating apple with red flesh – the basis of the red-fleshed apple breeding programme.
More broadly, the germplasm collection is a source of genetic diversity. Historically, apple breeders have used a very narrow range of trusted cultivars as parents when breeding new varieties. The problem with this is that breeding parents are often closely related. In fact, all today’s major apple cultivars have been bred from only about 10 founder plants! Including apples from the germplasm collection in breeding programmes can help avoid the risks associated with inbreeding (including disease susceptibility) and improve apple quality.
In practice, breeding programmes make use of apples from the germplasm collection as well as higher quality apples. The pyramid diagram illustrates how the germplasm collection contributes to apple breeding.
A form of insurance
All trees of a given cultivar are clones. This means that they are all equally susceptible to disease. Having a germplasm collection means there’s genetic diversity to fall back on in the event of widespread disease or extreme climatic conditions or events. The germplasm collection also forms part of a long-term strategy to manage economic risk by aiding the development of new product types.
When PFR started their germplasm collection, cryopreservation wasn’t as advanced as it is today and the cost was higher than planting trees. In the future, cryopreservation may be used as a supplementary form of storage for added safeguarding of the collection. Ideally, planting the collection at 2 different sites would reduce the risk even further.
- 27 May 2011