By Peter Chaires
Photo by Muhammad Shahid
The citrus research program at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) North Florida Research and Education Center (NFREC) includes several projects aimed at assisting growers in the cold-hardy citrus region. Let’s take a look at what researchers are working on.
EVALUATING SCIONS AND ROOTSTOCKS
Presently, the citrus industry in North Florida faces greater threats from winter cold and freeze events than from HLB. Despite exposure to temperatures as low as 15 to 20 F, growers have successfully cultivated numerous citrus varieties. The University of Florida citrus breeding programs in Lake Alfred and Gainesville, along with the U.S. Department of Agriculture Agricultural Research Service (USDA-ARS) in Fort Pierce, are actively developing new citrus cultivars with varying levels of disease tolerance.
There are also several previously released varieties that are being tested in the northern production area. Examples of the latter group include Marathon, UF-950, UF-914 and Sugar Belle from Lake Alfred, and UFDawn, UFGlow, and UFSunrise from Gainesville. Additionally, new rootstocks are being introduced by citrus breeding programs at UF/IFAS and USDA-ARS.
There is a pressing need to evaluate these new scion and rootstock cultivars to pinpoint combinations that are cold-tolerant, disease-resistant and early-maturing, thus diversifying the fresh market cold-hardy citrus industry. A primary aim is to initiate a replicated scion/rootstock trial at the NFREC to identify combinations that are both early maturing and exhibit resilience to cold and disease, fostering sustainability and profitability within the region’s citrus industry. To this end, researchers will assess the performance of three selected scions across 20 rootstocks, as well as 20 different scions across three selected rootstocks.
DEVELOPING NITROGEN RECOMMENDATIONS
The cultivation of cold-hardy citrus, particularly satsuma mandarins for the fresh market, is a rapidly expanding industry in North Florida. Currently, approximately 8,000 acres are dedicated to citrus production in the cold-hardy region (North Florida, South Georgia and Alabama), with acreage steadily increasing each year. However, there exists a notable gap in nitrogen (N) management guidelines tailored specifically for early-maturing, fresh market cold-hardy citrus. Existing citrus nutrient guidelines are primarily derived from research conducted in Central and South Florida, where soil and climatic conditions differ from those in North Florida.
North Florida’s soils, characterized by higher clay content and greater fertility and moisture retention, may necessitate lower annual fertilizer requirements compared to peninsular Florida. Moreover, existing recommendations predominantly target citrus varieties for processing, whereas citrus cultivation in North Florida is primarily geared toward the fresh market. Thus, this project aims to determine the optimal N levels and application timings for non-bearing, young and mature cold-hardy citrus production.
UNDERSTANDING THE MECHANISM OF COLD HARDINESS
Assistant Professor Muhammad Shahid reports that his team at the NFREC is engaged in a comprehensive multi-omic analysis encompassing physiolomics, proteomics, phenomics and metabolomics. This endeavor aims to decipher the underlying mechanisms of cold hardiness in satsumas. This long-term project is poised to not only enhance understanding of cold hardiness in satsumas but also pave the way for improving cold hardiness in other targeted citrus cultivars. Ultimately, these insights will contribute to the sustainable production of citrus in North Florida.
RESEARCHING ADDITIONAL AREAS
The NFREC team is also investigating various freeze-protection techniques to shield plants from unpredictable freeze events during winter and spring. These techniques include the use of plant growth regulators, different freeze protection structures and modifications in irrigation systems.
Furthermore, researchers are exploring high-density production systems to enhance per-acre yield. While growers typically plant 116 to 145 trees per acre, a denser planting scheme of 363 trees per acre is being evaluated for satsuma production. Research is also looking at different cultural practices such as pruning training, fruit thinning, canopy management and growth hormones to improve fruit color, taste, quality and yield.
As research supporting the main citrus production areas pursues all avenues possible to resolve/combat HLB and maintain capacities in all sectors, citrus research at the NFREC is working hard to support a burgeoning interest in fresh citrus. Shahid has assembled a strong team to address these unique challenges, and we can look forward to increased engagement with this center.
Acknowledgment: Article contributions supplied by Muhammad ShahidPeter Chaires is the executive director of the New Varieties Development and Management Corp.
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