Releasing Rootstocks: Balancing Responsibility With Urgency

Josh McGillRootstocks, Tip of the Week

By Bill Castle, Fred Gmitter and Jude Grosser

The rootstock development cycle, from creation to eight years in the field to release, is presently about 10 to 15 years. However, if multiple trials are involved, then the time required is increased. The criteria used to advance new selections through the system are commercially based. Rootstocks for juice fruit are assessed on pounds solids per acre. For fresh-market fruit, rootstocks are evaluated on the yield of flavorful, high-quality fruit of profitable sizes.


However, the environment in which those criteria are employed has changed largely because of HLB. New rootstocks are formally evaluated over a shorter period of time because of the urgency imposed by HLB. As a result, the distribution of performance risk has shifted with a greater portion now assumed by the grower with the release of a new selection.

New rootstocks are released with smaller data sets, meaning they may not have been evaluated over 15 years with all commercial scions under a range of site or management conditions. Today, candidates are identified for release essentially at any time or place in the assessment process as long as there is evidence of superior, consistent performance.

Such an approach requires responsibility to ensure that data and observations are sufficient to support growers’ long-term financial investment decisions regarding rootstock choices. Balancing responsibility with urgency is a constant challenge.

The last step in the rootstock development pipeline is what happens after release, when the industry begins to propagate, plant and gain real world experience. Of the thousands of new cultivars of citrus and other fruit that have ever been released, most were released by breeders based on the best data they could generate over time, with the expectation and hope that they would be commercially successful. Yet of these literally thousands of released cultivars, an extremely small number actually achieve commercial significance and success.

In one sense, all trials are public enterprises. It has been and remains our desire to share resulting information. Many growers who were acquainted with us and the work we were doing, would frequently call or visit with us, to discuss progress and results. We have come to recognize that even though that is the best way for us to communicate with growers, not everyone has the time or inclination to engage personally, and that a better mechanism accessible to all was needed for broad access to trial information.

Past, present and future citrus rootstock field trials have only one goal: Help our industry identify and exploit superior rootstocks. The goal is simple: productive trees that survive with sustained profitability. Built into that goal is the concept that further improvements always are possible and, indeed, actively pursued and tested.

Many thanks to the diligent nursery owners and progressive grower-cooperators who have been the mainstay of our field program.

Learn more about citrus rootstock trials here.

Bill Castle is an emeritus professor, and Fred Gmitter and Jude Grosser are professors — all at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.

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