Seeking A Better Peach Rootstock

Seeking A Better Peach Rootstock

Armillaria Root Rot Symptoms

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Editor’s Note: Much of the information in this story comes from an under-review research report on peach rootstock development for the Southeastern U.S. by Tom Beckman (USDA-Agricultural Research Service, Byron, GA) and J.X. Chaparro (University of Florida, Gainesville).

Over the years, peach tree short life (also known as bacterial canker complex) and Armillaria root rot (ARR) have been the most common causes of premature mortality among peaches in the Southeastern U.S. The introduction of the Guardian rootstock by the USDA-Agricultural Research Service and Clemson University in 1993 helped many growers control peach tree short life. However, Guardian was still quite susceptible to ARR, leaving growers without a viable option for managing this devastating disease complex.

There are some cultural practices growers can take to alleviate the damage caused by ARR, such as planting trees on raised berms, leaving the root zone above the area where it would be most vulnerable. In the meantime, USDA’s rootstock development program in Byron, GA, has shifted its emphasis to the development of materials with improved ARR resistance. Much of this research focus has come in cooperation with Clemson and the University of Florida’s peach breeding program in Gainesville.

Improved Resistance

In the past five years, testing at Byron and Gainesville resulted in the naming and release of two new rootstocks that have demonstrated strong ARR resistance (as an added bonus, they’ve also shown resistance to peach tree short life and root-knot nematodes). The first, Sharpe, has shown resistance in all these areas, but it has one major drawback: It is unable to match the production efficiency and fruit size offered by Guardian. Because of this, Sharpe is being suggested mostly as a semi-dwarf rootstock for home gardeners.

The second rootstock is MP-29, a clonal plum-peach interspecific hybrid that was released in 2011. MP-29 improves on all the resistance traits of Sharpe, while peach productivity and fruit size are equal if not superior to Guardian.

According to USDA’s Tom Beckman, MP-29 produces a tree capacity 70% to 75% the size of trees on Guardian. As a result, planting density will have to be increased by 50% to compensate. Beckman notes that peach tree short life resistance is comparable to Guardian, ARR resistance is significantly better, and “it has not galled on sites infested with root-knot nematodes.”

When it comes to productivity, Beckman says MP-29 is as good and perhaps even better than Guardian, especially if tree spacing is reduced. It also produces fruit similar in size to that produced by Guardian and other peach seedling stocks.

Economic Benefits

Beckman says the utility of ARR resistance provided by MP-29 can best be assessed by considering what it might add to orchard life on a severe site. “The decision to pull a commercial block depends on many factors, but productivity per acre is a primary one,” says Beckman. “Several Georgia growers have indicated that they routinely remove blocks once tree occupancy falls below 50%.”
Testing at the Byron site showed that while Guardian had tree losses exceeding 50% of its starting population after only six growing seasons, MP-29 did not reach this threshold until its 12th season on the site (Sharpe reached 50% loss in its 10th season).

Even better news is that MP-29 will likely be just the first of other new rootstocks coming out of this program. “The ideal rootstock must possess exceptional disease resistance, as well as horticultural qualities such as ease of propagation, good graft compatibility and anchorage, few or no rootstock suckers, reasonable vigor, and good productivity and fruit size.” Beckman says there are more than 100 advanced selections at the final testing level in Byron, and “it is our intention to develop and release a series of rootstocks that will provide a wide range of vigor control in combination with broad disease resistance.”

A plant patent has been granted for MP-29, and license agreements are available through Florida Foundations Seed Producers. Virus-indexed budwood is available for licensees from the National Virus-Tested Fruit Tree Program in Prosser, WA.