Mimicking nature brings hope to peach growers

If you want to visit the perfect testing ground for Georgia peaches, visit Tom Beckman’s plot of land in Byron, Ga. There you’ll find tens of thousands of trees spaced closely together on heavily infected plots with intense disease and fungal pressure. You read that right. Beckman is a research horticulturist at the USDA ag research station in Byron. Since his primary focus is breeding peach rootstocks with disease and pest resistance, he has to make his seedlings and young trees run the gauntlet to see if they can withstand the pressure.

Honeybees pollinating some out-of-season bloom on peaches.

“When I get them out to grower’s sites, we use a normal spacing,” he explains. The commercial test sites are 3 to 5 acres. The time between when Beckman initiates a cross and when he refines a hybrid to the point he can bring it to a test site is over a decade.

Some pests and diseases are no more than a nuisance. Others, like plum curculio and brown rot, can be held at bay with chemical treatments. Plum curculio isn’t known west of the Rockies, but it and brown rot are so prevalent along the East Coast that they essentially eliminate the possibility of successful large-scale organic peach growing in these states, according to Beckman. Worse are the deadly fungi and diseases that attack the trees and can destroy an entire orchard in a few seasons. So, when Beckman breeds a rootstock that resists all the disease, pest and fungal pressure present in his test plots, he knows he’s struck gold.

Peach alchemy

There’s gold, and there’s fool’s gold. To make sure he’s working with the former, Beckman does extensive testing on every hybrid he develops. He has devised some unusual methods to reach his goals, but for 23 years has managed to do all the breeding nature’s way.

Peaches are self-fertile, meaning the flowers will pollinate themselves without any help. In an orchard, bees may assist the process by disturbing the peach flowers and sending pollen into the air, or by carrying pollen from among flowers on the same tree or from others within the field.

Beckman mimics nature as much as possible when developing new fruiting varieties and rootstocks. He collects the pollen from the male parent from one variety and applies it by hand to the female parent from another variety. Then, to ensure the peaches do not pollinate themselves and undo his careful work, Beckman removes their potential pollen source, their anthers and their petals. “In the case of peaches, the flowers are quite large, so it’s easy to do, but plum flowers are so small and they’re all tightly bound together in spur clusters, so it’s very difficult to manipulate without damaging the flowers to the point where they won’t actually set,” reports the researcher.

At this point, you may be thinking “Plums? I thought he was working with peaches.” He is, but due to limitations in the range of disease resistance available in peach rootstocks, Beckman had to seek outside sources of disease resistance. He found it in plums. (More about that in next month’s column.)

Unlike peaches, plums are self-infertile, so they must outcross to reproduce. To efficiently cross peaches with plums, Beckman often uses bees. He cages the bees with a female parent tree and places either bouquets of plum or peach flowers or small potted trees inside the cage. The bees typically visit the tree to collect pollen, inadvertently settle on the bouquet just long enough to gather pollen there, and then return to the tree, transferring the pollen from the bouquet to the tree. The cross results in a fruit that has a hybrid seed inside.

Beckman grows the seeds of each hybrid to see what the fruit will look like on those trees, and whether it has potential to be a marketable variety. “These seeds are very valuable; there’s a lot of personal effort in producing these, and we don’t get real high percentage takes,” he says. “We put a lot of hand labor in the field, it’s somewhat slow and tedious and you want to get as many finished seeds as you can from any given effort.”

Beckman brings all the fruit into the laboratory, cracks the seeds out of the pit, ensures they’re fully imbibed, and then artificially stratifies the seeds in cups of perlite in the refrigerator for eight to 10 weeks. This process maximizes seed germination.

Dry seed will keep almost indefinitely in the refrigerator, with gradual loss in viability as the seed ages. This is due to the natural germination inhibitors found in peach and other temperate species. These compounds keep seeds that fall on the ground underneath the tree from germinating immediately and then getting killed in winter. In nature, when a pit is left on the ground during the course of the winter, moisture will penetrate through the pit to the seed, which then absorbs it. This combination of cold and moisture is required to dissipate the seed germination inhibitors and overcome dormancy. Beckman and his small team artificially recreate the natural process.

Once the seeds germinate, they’re moved to the greenhouse where they’ll grow into seedlings. In the spring, the seedlings are planted in the field, where they’ll later be evaluated.

Beckman also needs to evaluate the rootstock crosses; this process is more complicated.

A rootstock may be utilized as seed rootstock or cloned as cuttings.

The next step for seed-propagated rootstocks is to grow the tree and test the seed from the mother tree of every viable hybrid he develops. He’s examining each new rootstock to see how uniform it is and how consistently it will express the characteristics he hoped to impart to it in the course of the breeding process. For hybrids incapable of producing seed, Beckman grows each one into a tree and clones the tree by taking cuttings, which are all genetically identical, for testing.

It usually takes three years to grow a tree to sufficient size to produce a viable crop worth managing – worth thinning, spraying and picking. Then it takes a few more years to get into peak production, when the tree is about five to seven years of age. After another five to seven years, the peach tree starts to decline. During the short life of a peach tree at the USDA’s Byron research station, Beckman is able to determine a lot about a variety: whether it’s strong enough to withstand the disease and fungal pressures of the region, whether the fruit is physically attractive, how the fruit will react to processing, how well the fruit handles shipping and storage, and, most importantly, how the fruit tastes.

In 23 years, Beckman has developed or co-developed a number of fruiting varieties and rootstocks that have made a difference for southeastern peach growers. Some have only recently been released for commercial trials. Others are nearing that stage. In addition, as he nears retirement, Beckman expects to hand on some parents to his successor. Whatever methods his successor chooses, he or she will find golden nuggets awaiting the alchemist’s touch.

The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.