WSU apple breeding program’s fruit evaluation system
Members of the breeding program’s Industry Advisory Council visit a Phase 3 evaluation site at Quincy in 2010. They are: (from left) Dave Gleason, Kershaw Companies; Harold Schell, Washington Tree Fruit Research Commission member and field services manager at Chelan Fruit Cooperative; Jeff LaPorte, Chelan Fruit; and Tim Welsh, Columbia Fruit Packers Inc.
The Washington State University apple breed- ing program was established in 1994 to provide Washington growers with a portfolio of new varieties with high consumer acceptance that are well suited for Washington growing conditions.
How does the WSU apple breeding program achieve this vision?
Going back just a few years, apple breeders had few tools and little new science to assist the program. Today, Dr. Kate Evans, the program leader, collaborates with an international team of scientists working in tree fruit genetics, genomics, and breeding (GGB). Team members, working with WSU in Pullman and the U.S. Department of Agriculture in Wenatchee, Washington, are international leaders in their fields. They bring the latest technology to the program and help develop methods to implement the technology for the benefit of the breeding program.
One of the first benefits of the genetics research is to be able to fully characterize the parent varieties using molecular markers that are linked to important traits and therefore be able to make more informed decisions about which two parents to combine in the crossing program. These markers can also be used to screen the seedlings to determine which have inherited the trait without having to grow a tree and wait for fruit.
Seeds from the crosses are harvested and planted in the greenhouse. Some are tested for resistance to fireblight, and any susceptible seedlings or those with severe mildew are discarded. As the effectiveness of the genetic markers identified has improved over the last couple of years, they are being used to screen the seedling population prior to planting outside in a nursery row. After planting out, the seedlings are grown until the wood and buds are large enough to be used in budding onto precocious rootstocks (Malling 9 T337).
Genotypes that have spines, indicating low yield potential, and severely mildewed trees are discarded. The trees are transplanted to the seedling orchard at a WSU research farm in year five after the cross is made. This is Phase 1 of the five phases in the breeding program.
Selections are made from Phase 1 trees based on appearance and fruit quality. A series of instrumental and sensory tests are completed on fruit at harvest, and after two and four months of regular cold storage. The most promising genotypes are identified over the course of three to four fruiting cycles and are advanced to Phase 2.
Phase 2 plantings are in three different climatic zones in Washington and are replicated for statistical evaluation. Industry standards such as Gala, Fuji, and Honeycrisp are included in the plantings. The best of the Phase 2 selections are placed into the commercial variety portfolio to evaluate their place in the commercial line-up. The decision to advance a genotype is made annually by Evans. If no genotype meets the requirements of the industry, none will be advanced. At least 23 commercial apple varieties, not including color or spur sports, are currently produced and sold from the state of Washington. In order to improve the product line of our industry, the new products from the breeding program must be outstanding and fit within the existing variety portfolio.
An Industry Advisory Council participates in the apple genetics, genomics, and breeding program in several ways. Ranking the importance of traits of apple is one activity. The GGB team prepares a list of traits that is frequently updated, and the advisory team and GGB team members vote on the importance of the traits listed (see current list in Table 1). Of the 21 traits rated, flavor out of storage and crispness were the top two. Six of the top ten traits are related to appearance, packout, or yield, which would be considered commercial traits rather than consumer traits. The intended use of this ranking is to prioritize genetic targets for the GGB team.
In Phase 3 trials, further phenotyping—the observation of properties of a genotype (variety) that are produced by the interaction of the genotype and the environment—is undertaken under the leadership of Tom Auvil and Dr. Ines Hanrahan (both with the Washington Tree Fruit Research Commission’s internal program). There are four Phase 3 sites, with environmental differences driven mostly by elevation. The aims of Phase 3 trials are fourfold:
- Provide adequate volumes of fruit from different environments to determine storage and postharvest handling behavior
- Observe the interaction of a genotype and the various environments in which it is grown.
- Allow growers to visit trial sites to see the trees and fruit in production prior to engaging in evaluation agreements
- Provide fruit for nursery trade show booths and gift box volumes for marketing organizations
The Industry Advisory Council meets annually in November to review results from the growing season.
The most commonly shared trait of the ten selections currently in the Phase 3 plantings is crisp texture. Most genotypes do not have sunburn damage. A couple of genotypes have some bitter pit, but far less than Honeycrisp. Mildew has not been an issue with any of the genotypes, though it can be found if sought out. The greatest challenge has been stem end splitting, which has been seen in several genotypes at or just prior to commercial harvest maturity. Two selections have compact growth habit, two are vigorous, the rest are intermediate. Two have high crop densities (will overcrop), and two are not precocious, leaving six intermediate. Fruit size ranges from moderate to very large, which means bigger than Gala for moderate and equal to Honeycrisp for very large. All of the Phase 3 genotypes have responded well to 1-MCP. A few do not have the storage life needed for a commercial variety, and their evaluation will likely be discontinued. Of the ten selections, two (WA 2 and WA 5) have been released into Phase 4 grower evaluation, with WA 2 already moved into Phase 5 commercialization. At least one and possibly more releases are expected from this batch of Phase 3 genotypes. New material has been propagated for Phase 3 plantings in 2012.