Photo by Kim Bowman
By Kim D. Bowman, Matt Mattia, Ranjeet Shinde and Flavia Zambon
Profitability of the historic kings of citrus in Florida, sweet orange juice and fresh market grapefruit, has been severely reduced by the impact of huanglongbing (HLB) disease. Previous studies have demonstrated that lemon cultivars are generally more tolerant to HLB than sweet orange and grapefruit. Lemon trees continue cropping well even after trees are affected by HLB.
Cultivation of lemons for the fresh market or for juice may be a reasonable alternative approach to produce profitable citrus in the presence of HLB. However, little information is available to evaluate field performance of specific commercial lemon scions in combination with some of the newest and best rootstocks. With some lemon types, especially Eureka lemons, graft compatibility issues are known with some specific rootstocks. Therefore, researchers conducted a field evaluation of graft compatibility and fruit production for Eureka lemon on a series of common and commercially available rootstocks in order to provide useful guidance for growing lemons in Florida.
FIELD TRIAL
A multiyear field trial was conducted on Florida’s east coast in St. Lucie County to explore the relative influence of rootstock on Eureka lemon tree performance, including tree survival, fruit yield and fruit quality. The trial was established in 2020 at a planting density of 311 trees per acre and included Eureka lemon scion on about seven replications of 14 different rootstocks. The trees were not planted with individual protective covers (IPCs), so all trees were affected by HLB at a young age, and there was no injection of trees with antimicrobials.
Overall performance of trees in the trial was strongly affected by the rootstock. Trees on some rootstocks grew vigorously and fruited well. Trees on other rootstocks declined and produced very little fruit.
Tree health and growth were evaluated each year of the trial. Beginning in the third year of the trial (2023), fruit production was assessed on the trees in the typical lemon harvest season of October–November. A focused fruit quality evaluation was conducted in the 2024 and 2025 seasons. For 2025, fruit harvest data was collected the first week of November.
GRAFT COMPATIBILITY
Clear differences in graft compatibility with Eureka lemon scion were apparent among the rootstocks in the trial.
The rootstocks Macrophylla, US-812, US-1284, C-57 and standard sour orange appeared graft-compatible with Eureka lemon. They formed healthy productive trees through the first five years in the field.
The rootstocks Swingle, US-942, US-897, US-802 and US-1516 appeared graft-incompatible with Eureka lemon. Trees on these rootstocks clearly began declining during the first two to three years. Most of the trees had died by 5 years of age.
Other rootstocks were somewhat intermediate in response. Trees were not completely declining but they were not growing or yielding well.
Similar rootstock trials indicated that Bearss lemon (unlike Eureka lemon) is graft-compatible with all the tested commercial rootstocks. Bearss lemon performance in rootstock trials will be the subject of a future report.
YIELDS
In general, Eureka trees on the graft-compatible rootstocks yielded about 5 to 10 pounds of fruit per tree in the third year, 30 to 40 pounds in the fourth year and 60 to 80 pounds in the fifth year. At the tree density used for this trial, that would equate to about 24,000 pounds of Eureka lemon fruit per acre in year five.
The best-yielding rootstocks with Eureka lemon scion in the trial were Macrophylla, US-812 and US-1284.
FRUIT QUALITY
Although rootstock had a large effect on tree survival and fruit yield in the trial, most traits associated with fruit quality did not show any significant differences among the group of rootstocks identified as graft compatible with Eureka. This includes average weight per fruit (0.22 to 0.25 pounds), percent juice (53% to 56%), juice Brix (7.7% to 8.1%), juice acidity (4.9% to 5.3%) and juice color (CN 29.1 to 29.5).
The influence of rootstock on Eureka lemon fruit quality did not appear to be an important consideration in the choice of rootstock when Eureka lemon is being grown for juice, as long as that rootstock is graft-compatible. Evaluation of rootstock influence on Eureka lemon traits that are important for the fresh market is the subject of continuing study.
POSITIVE RETURNS
Payment for lemons for the 2025–26 season from the juice plant showed an average industry return of $3.60 per gallon of lemon juice. A yield of 24,000 pounds of fruit per acre with 55% juice translates to 13,200 pounds of juice, or about 1,506 gallons of juice. This equates to a juice value of $5,422 per acre for 5-year-old Eureka lemons grown in the Indian River region. This return excludes fruit pick and haul costs.
While considerably more evaluation is needed to determine optimum management practices and continuing multiyear fruit production of Eureka lemons, returns per acre for Eureka lemon to be used in juice appear competitive in the HLB environment. Another factor not considered in these evaluations is the potential additional value of peel oil, which may be important in processed lemons.
TAKE-HOME MESSAGE
Eureka lemon grows well and is highly productive on the Florida east coast in the HLB-endemic environment. Although many rootstocks are graft-incompatible with Eureka, planting of Eureka trees on graft-compatible rootstocks, especially US-812, US-1284, and Macrophylla, proved highly productive during the first five years with common citrus management practices, and without IPCs or oxytetracycline injection. Additional years of evaluation, other lemon cultivars and rootstocks, and consideration of lemon production for the fresh market are the subjects of continuing study.
Acknowledgment: This project was supported with funds from the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS), Citrus Research and Development Foundation, and the USDA National Institute of Food and Agriculture Award #2023-70029-41305.
Kim Bowman (kim.bowman@usda.gov) and Matt Mattia are research geneticists at the USDA-ARS U.S. Horticultural Research Lab in Fort Pierce, Florida. Ranjeet Shinde is a postdoctoral scholar with the University of California, located at the USDA San Joaquin Valley Agricultural Sciences Center in Parlier, California. Flavia Zambon (f.zambon@ufl.edu) is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences Indian River Research and Education Center in Fort Pierce.