How the Next Generation of Citrus Variety Development Is Growing Forward

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grapefruit variety trial in Florida

While breeding to create the next generation of citrus varieties will not cease, there is an increasing demand for rootstock and scion field trials.
Photo by Rhuanito “Johnny” Ferrarezi

Spencer Johnson might say that “someone moved our cheese.” But Florida citrus folks operating in an HLB-endemic environment know that the cheese has its own passport. This is to say that circumstances are shifting, and funding is quickly being redirected to address the most current pain.

While breeding to create the next generation of citrus varieties will not cease, there is an increasing demand for rootstock and scion field trials. Citrus Research and Development Foundation (CRDF), Citrus Research and Field Trials (CRAFT), Florida Citrus Mutual, Indian River Citrus League, and other organizations are pressing forward to address this need.

Data is the Driver

Early access to new varieties that enable grower observations and early adoption remain valuable, but the complexity of producing citrus in the presence of HLB is driving demand for more data to substantiate decisions related to rootstock/scion combinations, production models, and nutrition schemes. The current emphasis is shifting a bit toward the arrows that are already in the industry’s collective quiver. Legislative funding emerging from the recent session certainly reflects this reality. Consider the following:

Round one of CRAFT approved 43 grower trial sites, and round two is moving forward with 100-plus grower trial sites. Each are testing a myriad of rootstock/scion combinations, fertility and nutrition, pest management, biostimulants, and management of resets. Data will be collected, compiled, and reported. As the trees begin to produce fruit and their health is assessed, the industry can quickly employ the best production practices.

The Millennium Block at the Indian River Research and Education Center (IRREC) in Ft. Pierce is a comprehensive field study of new grapefruit scions and other fresh citrus varieties on a broad range of rootstocks to find the best option for Florida’s renowned fresh citrus crop. At present, the project is testing 18 grapefruit varieties on three commercial rootstocks and three independent rootstock trials with ‘Ray Ruby’ grapefruit, ‘Glenn’ navel orange, and ‘UF 950’ mandarin scions. ‘UF 5-1-99-2’ Pummelette developed the largest canopy volume in the grapefruit scion trial with US-942 rootstock inducing the larger canopy volume and trunk diameter than Sour Orange and X-639.

CRDF’s Select Committee on Plant Improvement initially trained its focus on rootstock trials and has now advanced to include scion trials. Data collected at stage 1 generally includes tree survival, fruit yield per tree, fruit quality, tree size, tree health rating, and HLB status. Stage 1 trials might typically use numerous scions and one to two standard rootstocks. The most promising material from stage 1 will move to stage 2 where there are fewer selections being tested, but experiments are at a larger scale. The cream that rises to the top in stage 2 trials will advance to stage 3. This is a complex and time-consuming process, but resources and expertise are being employed to ensure consistency of process and standardization of evaluation. The results should be of great value.

The USDA HLB MAC grapefruit variety trial is a partnership between the Indian River Citrus League, Florida Department of Agriculture & Consumer Services/Division of Plant Industry, and the UF/IFAS IRREC to plant approximately 46,000 grapefruit trees in 300 acres in the Indian River Citrus District and a few other counties across Florida. The project aims to determine the best grapefruit and rootstock combination for the Indian River and is divided into an experimental portion and grower’s choice, with an average of 10 acres per grower. The experimental portion has 42 scion and rootstock combinations replicated in 41 independent plots in several locations, with 294 trees per plot. The remaining 34,000 trees are the grower’s choice, planted with scion and rootstocks selected by growers from the previous combinations. Tree size data has been collected from the experimental portion only, and fruit yield and quality results are expected in three years.

New Varieties Development & Management Corp. (NVDMC) has worked with FCRF to establish a demonstration planting at the A.H. Whitmore Foundation Farm near Leesburg. This site has been designed for growers who want to visit, walk the rows, and make general observations about released, processed, and fresh varieties.

USDA-ARS currently is designing a planting of elite scion-breeding lines that are potential candidates for release. This block will be located at the A.H. Whitmore Foundation Farm, and each selection will be on a couple different rootstocks. This will give the industry an advanced snapshot of what’s in the ARS’ varietal bullpen.

Nothing Stands Still

While this work moves forward, other changes are in the works:

  • The CRDF’s Select Committee on Plant Improvement is exploring models that will increase the level of engagement between the industry and citrus varietal development.
  • USDA and UF/IFAS’ citrus-breeding teams
    will continue to identify promising new selections, but the industry will be more engaged in the evaluation and advancement process.

It’s no secret that Florida is a processing state. Fresh fruit takes a back seat in many ways. As such, much of the development work moving forward will be focused on processing.

When growers generated the research dollars, each segment could decide how the funds were expended. When much or all the funding originates from public sources, it is pre-supposed that the focus will be on the dominant segment. This will be orange, with a bit of grapefruit, and little else. Development, selection, and evaluation of fruit for the fresh market and high value citrus crops for smaller-scale growers requires an entirely different approach.

The fresh segment will need to make some decisions about how or whether to continue fresh breeding, evaluation, and testing. Funding will be a challenge. The issues facing Florida’s processed segment are monumental and will absorb resources. The certainty of a substantive commitment to fresh and funding for small-grower breeding and evaluation is ambiguous. Thankfully, both fresh and processed have benefit of a rich pipeline from which to make selections over the next few years.

NVDMC is adjusting its sponsored project mix to reflect a smaller budget. We’ll highlight the focus of these projects in my column next month.

Author’s note: Special appreciation to the following people for reviewing descriptions for their respective projects: Kristen Carlson (CRAFT), Dr. Johnny Ferrarezi (Millennium Block and MAC trials), Rick Dantzler (CRDF), Dr. Brian Scully (USDA).