By Flavia Zambon and Mac Hossain
The Millennium Block is located at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center (IRREC). It is designed to support long-term citrus trials under real-world growing conditions, including HLB pressure, but without oxytetracycline injections.
Currently, the block has 19 distinct grapefruit and pummelo scions in a trial from the University of Florida and U.S. Department of Agriculture breeding programs. Several of these scions are newly developed and have never been tested in the field, especially not in a long-term variety trial. They were bred for traits such as improved HLB tolerance, superior fruit quality and harvest windows.
Supporting extended research blocks allows researchers to uncover traits and adaptations that short-term projects may overlook. Since the trees began bearing fruit in 2022, the IRREC Horticulture Production Lab has collected pre-harvest juice quality data. Researchers sample four to six fruits from border trees, then perform juice extraction, titration and Brix analysis.
Border trees are selected for pre-harvest sampling to preserve the integrity of the main harvest, scheduled for November. Early sampling helps determine which selections are ready for the November harvest and which should be left for January.
The graphic shows an increase in pre-harvest sugar content in selections such as US 4-4-1, US 1-83-179, UF 5-1-99-2, Seedless Surprise and Triumph. This data reinforces that splitting the harvest into two phases, before and after December, is the most effective approach for this block.
These small-scale assessments are especially valuable for scion materials not yet commercially established. By tracking sugar-acid balance and peel coloration gradients, researchers aim to distinguish HLB-symptomatic from asymptomatic fruit. Peel-gradient determination will begin this year during routine fruit maturity check-ups.
For commercial groves, pre-harvest data serves as a strategic tool by informing the optimal harvest scheduling and helping identify promising new scions to fill market gaps. For growers facing disease challenges and changing consumer preferences, these insights are both timely and practical.
Flavia Zambon is an assistant professor, and Mac Hossain is a research assistant, both at the UF/IFAS IRREC in Fort Pierce.
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