For Citrus Variety Development, The Drawing Board Is Full

Citrus variety development white board illustrationDue to the rapidly changing landscape of plant patents and licensure, much has been written about commercialization models and the processes through which citrus nurseries and growers can access, trial, and/or produce new citrus varieties. However, the support of variety development projects lies at the core of New Varieties Development & Management Corp.’s (NVDMC) mission.

Though some sponsored projects are annually adjusted long-term programs, others are new and innovative efforts to improve the development and commercialization process. Florida is making substantial investments in the development side of the equation, and this month’s article will highlight the 2016-2017 projects approved by the NVDMC Board of Directors and supported through the Florida Department of Citrus and the Florida Citrus Commission.

Citrus Scion Variety Development At UF-CREC

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The UF/IFAS Citrus Research and Education Center (CREC) citrus breeding team has been working for more than 30 years on the development of new sweet oranges for processing, fresh market consumer-friendly mandarin/tangerines, improved grapefruit and unique acid fruits, and other novel innovations. Dr. Fred Gmitter has frequently reminded us that “citrus variety development is a continual process, one that builds successively on the work already undertaken,” it is truly an incremental process, but one that grows more focused and efficient year to year.

Though it is incremental and gradual, constant adjustments and redirection — necessitated by changing growing and market conditions fueled by industry input — enhance the value and utility of new releases. Below is a top-line overview of this project:

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  • The CREC team has developed by far the largest library of diploid and tetraploid citrus breeding parents in the world. They continue to use somatic hybridization and other methods to expand the collection and improve the breeding value of the parents; in particular, those which demonstrate a propensity to pass along disease resistance are increasingly utilized. This approach will lead to development of new, high-quality processed and fresh varieties with elevated levels of resistance to disease.
  • There are thousands of unique hybrids planted in the field, many of which are fruiting for the first time. The most promising individuals are identified through bi-weekly observations for advanced trials and potential release.
  • New hybrid families are made annually using the best parent lines developed over the past three decades.
  • Recent and future crosses are focused on maximizing the necessary disease-resistance genes.
  • There is a focus on improved fruit quality and resistance in very early and late-maturing easy peel mandarins as well as grapefruit and oranges for juice and fresh markets.
  • Tissue culture methods have been used to incorporate genetic seedlessness from Satsuma mandarin into Florida varieties through cybridization and to recover triploid seedless hybrids through embryo rescue. Seedless fresh mandarin types also have been developed by moving the genes for female sterility from Seedless Kishu into new hybrid families.
  • Improved grapefruit hybrids that may incorporate tolerance to citrus canker and HLB are being produced. Some of this work is being done through cybridization where the nuclear genomes of grapefruit are combined with the cytoplasm of other disease-resistant types of citrus or relatives.
  • Somaclonal variation (difference found in citrus that has undergone some form of tissue culture regeneration) is being exploited to develop sweet oranges with superior traits. This process already resulted in the release of earlier maturing Valencias and an improved Hamlin and the OLLs (Orie Lee Late) with exceptional fresh fruit and processing quality.
  • Botanical descriptions of promising selections are prepared to support commercialization. Research is continuously conducted to better characterize varieties already released. The FAST TRACK release program moves the most promising material into the industry as quickly as possible.

USDA-ARS Citrus Breeding Trust

The USDA citrus breeding program has been actively developing improved citrus varieties for more than 120 years. It is one of the oldest sustained citrus breeding programs in the world. The breeding team has access to a tremendous genetic base of plant material and operates two 100+ acre research farms. A major focus of the USDA program is to identify resistance and tolerance to HLB, characterize it, and incorporate it into genotypes with outstanding fruit quality in a range of market phenotypes. Below is a top line summary of the USDA-sponsored project:

  • Photo courtesy of USDA-ARS

    Photo courtesy of USDA-ARS

    Sweet orange cultivars range widely in traits (flavor, appearance, maturity, juice quality, etc.) and arose through mutations identified over generations. Unfortunately, they are almost identical in their genetics, leaving them susceptible to disease. USDA has been making hybridizations for more than 100 years to expand the genetic diversity of the sweet orange, and through the support of this project, is finally achieving success. Six hybrids have been identified that look and taste like a sweet orange, appear to mature about the same time as Hamlin, and appear to have improved tolerance to HLB. Five of these have juice color similar to Valencia. Aroma volatiles are practically identical to sweet orange.

  • USDA is characterizing material from other programs as well, specifically looking at disease tolerance that may be useful for local production. Currently, more than 50 cultivars and selections are in a field trial.
  • It also is creating new hybrids that capitalize on advanced U.S. Horticulture Research Lab selections with specific focus on combining tolerance and fruit quality. The target is aimed at mandarin, sweet orange-like, and grapefruit-like selections.
  • Buds of the most promising grapefruit-like seedy selections showing HLB tolerance in an effort to develop market acceptable low-seeded or seedless variants are being irradiated.
  • Efforts are being made to establish and maintain priority seedlings on a juvenility trellis. Trees also are planted outdoors to screen for tolerance to HLB, canker, scab, alternaria, etc.
  • Planting is being done in a screenhouse to assess pollination needs.

CREC: Postharvest Evaluations Of Promising New Fresh Citrus Selections

The popularity and suitability of fresh citrus selections can be scored at the variety display days. However, the performance of the fruit postharvest must be studied as early as possible before substantial investments are made by the industry. This project seeks to:

  • Determine the ability of fruit from promising new fresh citrus selections, developed by the CREC team to maintain excellent quality through simulated commercial harvest and postharvest, degreening (when necessary), packinghouse, transportation, and marketing process.
  • Evaluate about 30 selections annually.
  • Expand the breadth of testing as larger quantities of fruit become available.
  • Evaluate very early season mandarins, early mandarins, mid- to late-season mandarins, grapefruit and grapefruit-like selections, and triploid sweet orange-like hybrids.

Sensory And Consumer Insight System

This project is built on the premise that the successful development and marketing of new citrus varieties should be consumer driven. However, consumer behavior is affected by individual factors (genetics, age, gender, etc.), product-specific factors (sensory), and environmental factors. This project will systematically seek to:

  • Study the relationship between consumer acceptance and sensory attributes of fruit.
  • Study the relationship between consumer acceptance and individual factors.
  • Bridge sensory and consumer insight and establish an informational database to inform decisions by variety segments (growers, packers, shippers, and marketers).

UF-Gainesville: Citrus Breeding

This smaller program has been funded for a number of years with an exclusive focus on easy peeling, seedless mandarins. Because all material had been planted outdoors in Gainesville, there also was a focus on cold tolerance. More recently, with the addition of field plantings in Ft Pierce at the Indian River Research and Education Center (IRREC), there has been an expansion of breeding and screening for disease tolerance. Tolerant sweet orange-like selections for processing also are now included. The project’s focus includes:

  • Photo courtesy of UF/IFAS Communications

    Photo courtesy of UF/IFAS Communications

    Evaluation of seedling populations segregating for the seedless trait.

  • Generation of new seedless mutants.
  • Planting of additional populations at the IRREC using parental populations known for enhanced tolerance and fruit quality. This includes those that are genetically seedless and the irradiation of high-quality seedy selections.
  • Using rare HLB-resistant citrus relatives taken through generations of crosses to impart resistance and maintain fruit quality. Expand genetics.
  • Development and evaluation of orange-like selections with potential for processing.

Collection And Organization Of Variety Display Data And Rapid Generation Of Reports

Variety display days present an opportunity to gather valuable insight and data from nurserymen, growers, processors, packers, marketers, retailers, etc. This data has always been collected and processed manually, with the use of clipboards, forms and pencils. Compilation of this data is time consuming and report generation needs to be faster and more meaningful. A project is being sponsored to develop a means through which the collection and organization of data can be improved, and reports can be provided to the breeding teams in a more expeditious manner.

In Summary

It is incredible to consider see how far the Florida breeding effort has come in a relatively short period of time. These programs are developing varietal solutions of value to nurseries, growers, processors and packers. Great focus is paid to fruit quality and the ability of the tree to survive and produce high quality fruit. Due to budget limitations, the NVDMC Board of Directors targets its support to valuable work that would otherwise go unfunded or underfunded. The Board invests considerable time evaluating projects, considering industry needs, avoiding overlap and matching needs with resources.

The name of the game is results, and these projects are certainly paying huge dividends. Stay tuned.

Author’s note: Special appreciation to Dr. Fred Gmitter, Dr. Jude Grosser, Dr. Mark Ritenour, Dr. Ed Stover, Dr. Yu Wang, Dr. José Chaparro, and Dr. Steve Rogers. Project documentation was accessed for some article content.

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