Cold-Hardy Citrus Research Initiatives

Josh McGill Cold Hardy, Research

The Fruit Crop Physiology Lab at the North Florida Research and Education Center (NFREC) in Quincy is focused on developing a sustainable and profitable cold-hardy citrus industry in the southern United States. To do that, it is conducting research-driven Extension projects. The NFREC is part of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS).

UF 950 mandarin is being evaluated on eight different rootstocks.

The lab collaborates with experts at UF/IFAS stations and several multi-county Extension agents around Florida, Alabama and Georgia to address establishment and production issues. NFREC horticulturist Muhammad Shahid discusses new research initiatives in that effort.

UF 950 is a seedless and easy-to-peel mandarin cultivar. This cultivar has been evaluated for more than six years. It has shown great cold tolerance in North Florida. In a new project, researchers are evaluating UF 950 on eight different HLB- and cold-tolerant rootstocks from citrus breeding programs at UF/IFAS and the U.S. Department of Agriculture. The main objective is to identify the best rootstock for 950 which can produce good quality and high yield while limiting the chances of alternate bearing.

This hybrid produces large fruit with Brix of about 10 or more, with less acidity than grapefruit. Fruit gets ready for harvesting in October. It produces uniform red-fleshed and large fruit. The unique attribute in 914 is it is low in furanocoumarin compounds (FCs), which are high in grapefruit and cause the so-called “grapefruit juice effect.” Due to the high FCs, consumers on various medications are advised not to consume grapefruit or its juice products. However, since 914 has very low FCs, clinical studies demonstrated that 914 juice behaves differently than grapefruit juice in cell culture studies, and clinical trials are underway to confirm this in human subjects.

Cold tolerance potential and yield of 914 is being evaluated on two rootstocks and will begin another trial with 10 to 12 additional rootstocks.

There is a lack of proper nitrogen management guidelines for cold-hardy citrus for the fresh fruit market. Current citrus nutrient guidelines are based on research conducted in Central and South Florida, where soils and climatic conditions differ compared to North Florida. Also, most current recommendations are for the juice market, while citrus in North Florida is grown primarily for the fresh market. The objective of this project is to identify best nitrogen application rates and timing for getting optimum yield and good quality while having minimal environmental impacts.

Current citrus nutrient guidelines are based on studies of healthy citrus trees conducted in the pre-huanglongbing (HLB) era and may no longer be valid for the present situation. Research is being conducted on different nitrogen and phosphorus sources and their application rates for young and mature citrus cultivars in North Florida. Using fertigation and controlled-release fertilizer sources, researchers should be able to develop and provide site-specific guidelines for young and mature Satsuma mandarins.

Super high-density and ultra-high-density plantations of fruit crops are advanced production systems to improve the efficiency of inputs while getting maximum yield.

Increasing the number of trees per acre could be a good strategy to increase production per acre, while increasing grower profitability, for the cold-hardy citrus industry. However, identifying more effective tree spacing, which can efficiently convert biomass into the maximum number of good quality fruits, is very critical. A high-density research project on Owari was initiated at two locations. In this project, researchers will be regulating plants’ reproductive and vegetative growth through root pruning. They will evaluate the effect of root pruning on nutrient use efficiency, plant physiology, production and fruit-quality characteristics under a high-density production system.

The Fruit Crop Physiology Lab has developed a Cold-Hardy Citrus website. The objective of this website is to assemble all useful resources related to cold-hardy citrus in one place. Grower suggestions regarding the improvement of the website will be highly appreciated.

Source: UF/IFAS