HLB Tools for Today and Tomorrow

By Frank Giles and Tacy Callies

The Citrus & Specialty Crop Expo hosted two citrus educational sessions during the Aug. 16–17 event held at the Florida State Fairgrounds in Tampa. The sessions included both long-term research aimed at delivering trees resistant to HLB as well as what growers can do today to help mitigate the effects of the disease in groves.

Rob Gilbert, dean for research for the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) and director of the Florida Agricultural Experiment Station, kicked off the first session. Gilbert also is interim senior vice president of UF’s College of Agriculture and Life Sciences and leader of UF/IFAS while Scott Angle is serving as interim UF provost.

PLANT TRANSFORMATION CENTER ANNOUNCED
During the session, Gilbert announced a new initiative aimed at speeding up the process of bringing HLB-resistant trees to growers. The new Plant Transformation Center will be established on the UF Gainesville campus to facilitate transgenic and gene editing research. The first crop focus will be citrus, and other Florida crops will be added in the future.

“Plant transformation is a powerful tool being used to speed up the process of variety development,” Gilbert said. “When you also combine that with artificial intelligence, it can make it happen even faster. In the case of citrus, the ultimate goal is to develop plants resistant to HLB.

“In addition to a (transgenic) GMO plant, we also are working with gene editing, which includes CRISPR technology. In Gainesville, we will provide additional capacity to what we already have in Lake Alfred to transform even more plants in order to hopefully find more winners, soon.”

Michael Rogers, director of the UF/IFAS Citrus Research and Education Center in Lake Alfred, provided an update on current plant transformation research projects already underway and stressed it is important growers have a realistic timeline of when to expect this research to bear fruit.

According to Rogers, CRISPR is a long-term effort. Just to get from gene editing to creating plants that are capable of being tested takes about two years. And the current success rate of creating a correctly edited plant is about 1%.

Rogers also discussed UF/IFAS scientist Nian Wang’s work with CRISPR in citrus.

“There is a lot of trial and error with this research,” Rogers said. “Dr. Wang has been working to perfect this in citrus. He is the only person in the world who has been able to use CRISPR to develop new citrus plants that are non-transgenic. He has spent about five years perfecting this process and is now able to do it a lot more reliably. There is a lot of (gene-edited) plant material coming out of his program.”

A key take-home message Rogers emphasized is that this work takes time, but UF/IFAS has been working on these projects now for several years. So, this research is moving down the road, and the new Plant Transformation Center will help facilitate and speed up the process.

WHAT TO DO NOW
With long-term goals laid out, the session turned to what growers can do now in their groves to mitigate HLB. Much of this focused on current research topics like fertilizer and irrigation management, utilizing individual protective covers (IPCs) on young trees and the use of plant growth regulators like gibberellic acid, 2,4-D and brassinosteroids to promote tree health and fruit retention.

While much attention has been placed on trunk injection of oxytetracycline, another take-home message of these presentations stressed that trunk injection alone will not save HLB-infected trees. It must be done in conjunction with a solid production program.

ADDING AUTOMATION
Day two of the citrus seminars began with UF/IFAS researcher Yiannis Ampatzidis discussing his work with artificial intelligence for precision grove management, including a new automated delivery system of oxytetracycline that takes less than a minute to inject a tree trunk. Ampatzidis is looking for partners to commercialize the system.

WORKING TOWARD HLB RESISTANCE
Wang gave an update on citrus genome editing with CRISPR. Canker-resistant varieties are being tested to see if they also offer HLB resistance. Wang is in the process of lab testing more than 30 lines for HLB resistance. It will be about another year before field testing begins.

SOIL HEALTH FINDINGS
Soil microbiologist Sarah Strauss discussed her UF/IFAS research on soil health. She reported that compost impacts on soil differ based on rootstock. Strauss also noted that soil health changes occur faster in young groves than in mature groves.

WEED WISDOM
UF/IFAS weed scientist Ramdas Kanissery shared tips on enhancing weed control. He said that the period from bloom to early fruit set is when weed management has the most impact on yield. He cautioned growers not to mix the following post-emergent herbicides:

• Fluazifop-butyl and 2,4-D
• Glyphosate and carfentrazone
• Glyphosate and glufosinate

IPCs ARE TOP TOOL
UF/IFAS entomologist Lauren Diepenbrock spoke on new tools to support establishment of young groves. Although reflective mulch has been shown to improve tree growth and reduce psyllids, it is expensive, requires a specialist for proper installation and is easily damaged. Kaolin, used to suppress psyllids, can be problematic because it does not adhere well to flush and can clog irrigation jets.

Based on nearly three years of study, IPCs outperform reflective mulch, red-dyed kaolin and monthly insecticide applications for psyllid and leafminer control as well as overall tree development. While IPCs offer advantages, UF/IFAS plant pathologist Megan Dewdney noted some downsides. More phytophthora root rot occurs, sooty mold is more common, and greasy spot tends to be more severe in IPCs.

VARIETIES FOR CUPS
Matt Mattia of the U.S. Department of Agriculture Agricultural Research Service shared information on what varieties appear promising for production in citrus under protective screen (CUPS). US Early Pride, an early-season mandarin, is completely seedless in CUPS, has high yields and colors well. New early-maturing hybrids Fallglo x Kishu are seedless, easy peeling and bear large fruit. Mattia warned that grapefruit-like hybrids are not the best option for CUPS.

SWEET ORANGE UPDATE
Citrus breeder John Chater gave an update on sweet oranges from the UF/IFAS citrus breeding team. He reported that B9-65 Valencia (a variety for processing) was the best of 30 selections in a trial evaluating yield and soluble solids. Tree health of the OLL-4, OLL-8 and OLL-20 seems to be superior to Hamlin and Valencia under HLB conditions, Chater said. He also noted that the UF 1859 hybrid has HLB tolerance, high Brix and attractive fruit for the fresh market.

GROWER PRODUCTION PRACTICES
The seminars concluded with a grower panel taking questions from the audience and sharing their production practices. Participants included Joby Sherrod of Alico, Matt Machata of Rolling Meadow Ranch, Aaron Himrod of Himrod Citrus Nursery and Cody Lastinger of Consolidated Citrus.

Sherrod said root health management has become a major focus of Alico’s production program and that automated irrigation is a wise investment.

Machata listed his priorities in order as 1) water, 2) fertilization, 3) reducing tree stress and 4) protecting flush.

Himrod had some advice for new citrus growers: Select a rootstock well adapted to your soil and compatible with your scion and use IPCs.

Lastinger said he has changed his focus from the quantity of acres to the quality of acres. One way he is helping trees mitigate stress is with the application of seaweed products.

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