The development of a new apple variety, such as Cosmic Crisp®, is often the work of an entire career. Retired Washington State University breeder Bruce Barritt spent many years looking for just the right apple—and Cosmic Crisp® still took another handful of years before his successor, Kate Evans, released the apple to growers.
Tymon James (’18 Integrated Plant Sci.) thinks he might be able to take a few steps that will speed that process up. But he’ll have to take a walk on the wild side to do so.
As an undergraduate intern mentored by horticultural scientist Cameron Peace, James started working with domesticated apples’ wild relatives in the student-run Palouse Wild Cider apple breeding program.
Students noticed that the 20 or so species of wild apples being grown in Pullman as part of the program had many desirable attributes sought by domesticated apple breeders, including a very short juvenility phase.
In an apple tree, juvenility ends when the tree reaches reproductive age and first begins to flower. That’s when crossbreeding work can begin. Anything that might reduce the typically five to 12 years it takes for a domesticated apple to reach maturity would be welcomed by apple breeders everywhere.
Now a doctoral student in Peace’s lab, James investigates short juvenility in wild apples. Several crab apple species have already shown promising results, including zumi, a species that had previously been noted by WSU researchers to have short juvenility. “We saw flowers for the first time at the end of last summer when small potted trees grown from seed came out of their second cold cycle,” he says.
Apples and pears need a prolonged period of cold, called vernalization, to induce flowering. In the wild, winter chilling does the trick, but trees grown from seeds in pots can be moved into a cold room for a couple months to vernalize. To simulate spring and summer, the trees are then moved to a warm greenhouse for a growing period of about five months.
James is analyzing the tree’s genetics to see if he can nail down sources of short juvenility. “Once you know the chromosomal location, and the gene variants, called alleles, you can create a DNA test” that detects genetic factors indicative of short juvenility. From there, it may be possible to crossbreed a trait into domesticated apples.
But, James cautions, it’s also possible that the alleles that produce short juvenility may be “tightly linked to alleles associated with undesirable phenotypes such as small fruit size or flesh astringency.”
Identifying desirable attributes in wild relatives of domesticated apples is likely to turn up other gems in addition to short juvenility.
Wild apples, as Peace says, are rich with “jewels in the genome.” As James and his colleagues write in a recent paper, “Apple’s wild relatives also harbor many other alleles for valuable attributes such as disease resistance, abiotic stress tolerance, and desirable productivity and fruit quality.”
Just understanding the genetics of such traits would be rewarding, but they may also provide insight on ways that wild apples adapt to changing environments.
(This article originally appeared in the Fall 2020 issue of Washington State Magazine.)