Cameron Peace, geneticist with WSU, checks seedlings
As Washington State University’s apple breeder Dr. Bruce Barritt surveys the 30,000 selections in his evaluation plots, he remarks wistfully that perhaps the future of the Washington apple industry is there. Somewhere.
Each year, Barritt makes crosses of promising parent apples, hoping that the offspring will inherit the best qualities of both. In the fall, he picks the fruit, removes thousands of seeds, and grows them into seedlings in the greenhouse the following spring.
Which out of all those thousands of seedlings have the sought-after qualities, if any? Until recently, the only way to have a clue would be to grow them into trees and plant them out in an orchard until they fruited.
It costs about $10 each to grow a seedling, have it budded on a dwarfing rootstock, and plant it in an evaluation orchard, and Barritt has been planting between 5,000 and 8,000 annually. The more crosses you make, and the more seedlings you evaluate, the greater the chance of finding what could become the next successful commercial variety.
Those that don’t impress are yanked out after four years to make room for more seedlings coming through the pipeline. "Ninety-nine percent of them are dogs," is Barritt’s assessment.
But with new technology, Barritt can have a better idea at the seedling stage which he should throw out, or which are worth making into trees and evaluating further.
Scientists around the world are working to understand the genetic makeup of the apple to help breeders to quickly develop new varieties that have traits that consumers desire, and as few undesirable traits as possible.
They are developing molecular markers, which link genetic information in the plant with physical traits in the tree or fruit. By taking leaf samples from a young seedling and analyzing the DNA, they can predict if the fruit will have a particular trait.
For example, scientists in Japan and Italy identified genes in apple that regulate ethylene production. Now, WSU, in collaboration with molecular biologist Dr. Yanmin Zhu with the U.S. Department of Agriculture in Wenatchee, Washington, can screen Barritt’s seedlings to identify those that will produce apples with high ethylene levels. Fruit with high ethylene tends to soften quickly and not store well. This genetic screening eliminates the need to propagate and plant out many thousands of seedlings each year.
Scientists are also working to develop markers for a range of quality aspects, such as skin or flesh color, acid level, or disease resistance. It might also be possible to figure out which gene is critical in the production of flavonoids, which are thought to have health benefits.
As well as improving the efficiency of the selection process, use of genetic markers could also allow breeders to evaluate more material. The objective is not to plant fewer trees in the evaluation orchard, Barritt stressed. He’ll plant the same number, but because they’ll already have gone through genetic screening, the odds of hitting the jackpot should be greater.
Last year, WSU hired two new scientists, Dr. Amit Dhingra and Dr. Cameron Peace, to work on tree fruit genomics. Genomics is the study of genes and their functions. Peace was previously with the University of California, Davis, where he studied the genes associated with firmness and mealiness of stone fruits. In his new position, Peace is devoting a year to assessing the current technical infrastructure of WSU’s apple breeding program and identifying genomics resources and tools that could be used. Ideally, it needs a high-throughput system for extracting DNA and screening the many thousands of seedlings that the program produces.
Peace is also looking at what is being done with genetic markers and statistics around the world and is fostering collaboration among apple genomics scientists.
An apple has about 50,000 different genes, and the task of identifying which of them are associated with the specific traits that interest breeders is a complex process that’s too huge for any single scientist or even lab to tackle alone, Peace said.
He and other scientists from New Zealand, the Netherlands, and the United States met in Wenatchee this spring to discuss how they might exchange genetic information in order to speed up the development of genetic markers for tree fruits.
Dr. Eric van de Weg, senior scientist for plant breeding and genetics at the University of Wageningen in the Netherlands, said marker research is a powerful tool for breeding, but it’s not something that’s developed in a short time. Each group around the world has its strengths in terms of knowledge and technology. "It’s great if we can find ways to collaborate at an international level," he said.
In addition, Peace has been looking for sources of apple germplasm around the world that might be used to help the breeding program achieve its goal of producing apples with better flavor, firmness, crispness, and more interesting appearance than those already available. One source he’s identified is the UK National Fruit Collection, which has close to 2,000 varieties of apples, some dating back almost 200 years. Some heritage varieties have good traits but were dropped for other reasons. Perhaps they didn’t store well, even though they looked attractive or tasted wonderful, Peace said. "Through breeding, we want to bring in those good traits, and combine them with good traits from other parents."
Van de Weg commended WSU scientists on their efforts to promote an international effort in marker research. "It’s great to feel the drive that’s present at WSU to make it happen," he said. "I think the industry can have confidence in what you are doing."