Scions Might Be Joining Rootstocks In Citrus Tissue Culture Club

It is believed by many that tissue culture (TC) represents the best opportunity to produce the quantity of trees necessary to replace idle Florida citrus acreage and restore supply. Until recently, nurseries and labs were limiting the application of TC techniques to rootstocks. Not anymore.

UF/IFAS’ third suite of FAST TRACK selections includes the 7-6-27 mandarin. This selection is unique in the sense that it appears to have the characteristics sought by today’s fresh citrus consumer (easy peel, seedless, dark-orange color, and great flavor), early maturity and productivity for the grower, and the hope of improved performance in the face of HLB. The original 8-year-old tree of 7-6-27 has been qPCR tested on numerous occasions and remains negative for CLas. Though this is certainly encouraging, it is by no means conclusive. While work is ongoing to explore the reasons for the 7-6-27’s health and vigor in the presence of HLB, it has been patented and promoted by registered growers to the FAST TRACK Tier-II level for commercial production. Growers in need of a viable marketable option are interested in taking a risk on this variety.

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The 7-6-27 rose to prominence so fast there was little time to supply the conventional means of citrus tree production. The early registration period for the 7-6-27 ran 30 days and resulted in orders for approximately 100,000 trees. Dilley Citrus Nursery and CitriSun Citrus Nursery were licensed by New Varieties Development & Management Corp. (NVDMC) to propagate the first 7-6-27 trees for trial and commercial production. These nurseries received all available certified (clean) budwood and invested substantially in budwood increase to meet the demand.

7-6-27 mandarin hybrid orange

Photo by Tyler Jones

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The standard registration period for the third FAST TRACK suite ran until Nov. 24, 2015 and resulted in additional grower and nursery registrations. It is expected the first trees will be budded this month.

The vast majority of budwood available for the 7-6-27 is in the two original propagating nurseries. It is estimated they will have more wood available for new orders within two months. However, supplies within UF/IFAS and DPI are quite limited. Though citrus nurseries interested in licensing for Tier II production of the 7-6-27 will be limited to supplying only licensed growers, numerous nurseries have requested Tier II nursery licenses. This indicates demand continues to exceed supply. This has highlighted a challenging scenario likely to repeat itself in the years ahead. Promising selections will be identified and rapid escalation of demand will instantly exceed the supply of budwood for conventional propagations. While nurseries can establish budwood increase blocks of their own, this takes time and many growers want trees yesterday.

Accounting For Scions

Several of the state’s TC labs have requested a license to move forward with production of the 7-6-27. While scion varieties of other crops and plants have been successfully produced via TC for many years, this is new ground for citrus. As recently as 2014, Florida and California labs estimated that citrus tissue culture production would be limited to rootstocks. Circumstances have caused some companies to revisit the use of TC as a means of rapidly producing large quantities of trees.

Recognizing existing regulations cover only TC production of citrus rootstocks and that scion production is unique, the FDACS Bureau of Citrus Budwood Registration called a meeting with scientists, regulators, nurseries, and stakeholders in September. The meeting resulted in:

  • Confirmation that existing regulations will need to be expanded to cover production of citrus scion material via TC. A subcommittee was formed to initiate this process;
  • Confirmation that nurseries and labs are interested in moving forward with TC production of scion varieties;
  • An expression from some that scion production via TC could result in increased risk of mutation compared to conventional production. The group was reminded that somaclonal variation is used as a breeding technique to induce and identify unique and marketable traits. The risk of mutation varies by variety, fruit type, and lab process. However, there is always a chance of variation arising in citrus trees even from standard budwood propagation;
  • An understanding that what must be balanced against the risk of variation arising in budwood source trees from TC is the risk of delaying commercialization of promising new varieties and the opportunity to capture market share;
  • Confirmation that it takes time to develop appropriate media and protocol and that labs need to get started right away — with the understanding they will be subject to whatever new regulations are adopted, including a possible prohibition of the practice. One lab commented it takes 12 to 24 months before some varieties reach maturity in culture.
  • Realization that lab practices should minimize risk of mutation/variation and that regulations must protect the interest of the Florida citrus grower;
  • An understanding some lab techniques used to minimize the risk of variation may be proprietary and cannot be discussed in a public forum. Growers will either function under a “buyer beware” scenario and/or new regulations may need to include a requirement for additional statements on tree tags and paperwork.
  • Revelation that some labs will produce budwood source material from TC for use by nurseries and others will seek to produce a finished tree micro-grafted to a TC rootstock plantlet.

Nurseries may have interest in purchasing some of this material and growers should be aware of their options. Next month, we will explore how labs and nurseries are planning to address this opportunity.

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