Courtesy of UCR Today

UC Riverside scientists have created three varieties of avocado rootstocks that are able to overcome the fatal Phytophthora root rot disease (PRR). “The pathogen infects the feeder roots of the avocado tree so the trees cannot uptake water and nutrients and causes the trees to die. The disease is a significant problem in most avocado production areas globally,” stated Greg Douhan, assistant professor of plant pathology and microbiology, in an interview with the Highlander.

The sturdy rootstocks, known as Zentmyer, Steddom and Uzi, are able to help other types of avocado through a procedure known as grafting. “The quick definition [of grafting] is: if you take two types of different avocados…you basically just cut one open and match the plant material up and it will grow together,” stated research staff associate Brandon McKee. “Since we work with the root system, [we] cut it and put Hass avocado on top; that’s the market acceptable fruit.”

Each of the rootstocks is best suited for different environments based on the content of salt in the soil. “With the release of these high-performing rootstocks, avocado growers worldwide will have more options in choosing PRR-tolerant rootstocks to determine which ones perform better under their own growing condition,” stated Douhan in an interview with UCR Today.

The process of selecting the best rootstocks relies on a significant amount of manual labor by UCR Riverside scientists. “We have trees out here at Ag Ops (Agricultural Operations). We collect seed from there [and] screen the seeds here in the greenhouses. We roughly collect around 5,000 seeds a year and then inoculate them all with the Phythphthora cinnamomi and then visually assess each one for natural resistance,” stated McKee.

Along with the testing done on campus, the team also has farms in other parts of Riverside, San Diego, Ventura, San Luis Obispo and Santa Barbara counties. “We locate growers through the help of the farm advisers. Also, when they come to avocado meetings or when someone might have questions,” stated McKee in an interview with the Highlander.

“We look for people who are having trouble managing their property—their trees are dying and then we provide them with [our] trees and we test them under real world circumstances…We have approximately 20 test sites with 200 trees each, going at all times.”

The products of these tests, the Zentmyer, Steddom, and Uzi rootstocks, are what initially garnered the team some exposure after the patent office put out a press release in an effort to establish commercial use. The research will be featured in the upcoming issue of HortScience.

Douhan explained that UC Riverside has had long a history of efforts aimed at addressing PRR. Douhan himself joined the enterprise in 2005 when he collaborated with John Menge, plant pathologist and emeritus professor of plant pathology and microbiology. Meanwhile, McKee has over 14 years of involvement with similar research endeavors.