Thoughts on the Scion and Rootstock Selection Process

Tacy CalliesRootstocks, Scions

scion

By Bill Castle

If timing is everything, then let me suggest that the timing is right to consider the following proposals about making scion and rootstock choices in the Florida citrus industry:

  • What to plant? That is a huge question that could be initially addressed by a one-day program carefully planned as to objectives, format and participants. I was reminded of this concern at a recent lunch with the owner of a large nursery. He remarked early in our conversation that his scion and rootstock mother trees and nursery now consisted of a large number of selections, unlike the old days of basically Hamlin, Valencia, Swingle, Carrizo and sour orange. What to recommend?
  • One of the most meaningful sources of direct, grower-friendly information is commercial groves and their performance. In the aftermath of assessing sources of such information [e.g., University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) and U.S. Department of Agriculture cooperative field trials and more recently, the Citrus Rootstock and Field Trials project], it is obvious that commercial groves are a valuable and instructive resource. Information from them can be quickly gathered. For example, consider that there are lots of groves of various scions in the industry on US-897 rootstock. There are other groves on even newer rootstocks being planted every day with the latest scions. However, they are on private property and may not be accessible because of owner concerns. Fortunately, we have a long, excellent history of cooperative work in our industry that continues today. It is foundational and built on trust. There are ways to systematically gather valid data and information while respecting owner privacy.
  • Visit https://citrusresearch.ifas.ufl.edu/rootstock-field-data/ for a wealth of additional information.
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The reasons motivating these suggestions are threefold:

  1. The portfolio of planting options has increased considerably to include many new scion and rootstock choices along with renewed interest in planting density.
  2. There is continued concern about evaluating and defining HLB tolerance.
  3. There is a need to measure the impact of HLB on field trees. For example, in a field experiment markedly affected by HLB, is tree size mostly an expression of genetic potential or is it modified by the disease? Likewise, when fruit samples are collected, is the fruit from a given tree wholesome, HLB-affected or some mixture of both?

We are at the beginning of a new era characterized by unprecedented choices and circumstances that invite the increased exercise of professional judgement because of the current absence of the usual data foundation and the confounding impacts of HLB.

Let’s shape the future rather than the future shaping us. It’s time to … dialog!

Author Acknowledgement: Thanks to Pete Spyke for his thoughtful contributions.

Bill Castle is professor emeritus at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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