The Secret Ingredient of Developing New Citrus Rootstocks

Tacy Callies Citrus, Rootstocks

Figure 1

By Bill Castle

Creation, evaluation, release and commercial acceptance are dynamic, interactive activities that together constitute new rootstock development. Underpinning each of them is a commonly overlooked and rarely mentioned activity, professional judgment. Yet, it is something everyone has and recognizes as getting better with time and experience. It is a skill developed and refined over time from knowledge of a relevant subject plus the sum total of one’s professional and personal experiences.

Farmers, consultants, teachers, administrators, law enforcement officers, health professionals, coaches and scientists are just a few of the many who routinely exercise professional judgment.

In the rootstock development process, professional judgment expresses itself at each level. Plant breeders gain insights as to which selections make good parents. Those who conduct fieldwork gain a sense about trial design and rootstock candidates that are most appropriate for particular trial conditions. New rootstocks are formally released by institutions through a standard procedure that requires decisions about which rootstocks are submitted for release. Then, as new releases are presented to growers, professional judgment certainly helps in deciding which ones to pursue further.

For a researcher, professional judgment is a constant part of life. Take for example rootstock field trials in which data are generated annually. Those data are analyzed and interpreted. Both activities are time-honored elements of the scientific method. Interpretation requires a good measure of professional judgment primarily because of the forces of nature, i.e., variability.

To illustrate that point, I had an opportunity early in my career to simultaneously plant two identical trials in Florida. The Valencia orange trees were raised in the Citrus Budwood Registration Office field nursery in Dundee. The trees were divided into two identical sets with one planted in Indiantown on beds and the other in Avon Park. The same statistical design was used at both locations, but there were differences in tree spacing, plot size and number of replications.

Data were collected for nearly 15 years. Interpretation of data related to such questions as what was evident among the rootstocks at the beginning, middle and end of the trials. Did the relationship among rootstocks change? Were there any obvious interactions among the trees and specific locations within each trial? Citrus blight was a possible confounding factor. Was its movement through the trials independent of rootstock? In addition, a financial analysis was applied to the data and changed the way trial results were interpreted.

The rootstock outcomes of the two trials were similar, but not identical. The role of professional judgment in this instance was to apply critical thinking to explain differences and draw conclusions leading to recommendations.

Professional judgment, in this case, takes “experience” (knowledge of variability) and integrates it into a skill that is foundational for interpretation.

How does anyone acquire professional judgment? During my career conducting field trials, I was frequently asked for advice and recommendations about rootstocks. That experience eventually led to a protocol combining what I learned from talking with growers and our field trial cooperators. That protocol mainly involved asking questions about the circumstances into which the trees were going to be planted.

Often, data were involved in a recommendation because they were asked for or I volunteered to support my advice with relevant data. Eventually, as the learning curve continued, I realized that professional judgment, a concept like a stool with three supporting legs (Figure 1), had emerged as a player in the business of rootstock development and providing advice.

There is also a social component to acquiring professional judgement. The Turnpike Holiday Inn at Fort Pierce, the restaurant in downtown Babson Park and Flo and Ella’s in LaBelle were among the many places where Florida industry professionals gathered to talk citrus. Those were places where judgments were tossed out for debate and refinement.

Today, professional judgment may have a heightened significance in rootstock and scion development given the unknowns of HLB. Interpretation of yield and fruit and juice quality data might be extra challenging because of uneven distribution of HLB effects among trees and the fruit on each tree independent of scion or rootstock. Moreover, differences among rootstocks in their tolerance of HLB could be confounding.

Note that professional judgment and personal opinion are not the same thing. Those who exercise good professional judgment are on a self-reflective, rigorously unbiased, ethical journey. They are constantly learning, amending, correcting and revising.

Professional judgment should not be overlooked or undervalued but be actively sought and engaged as a key element in the process of rootstock development and in growers’ decision-making processes.

Acknowledgments: Many thanks to friend and colleague, Adair Wheaton, who was the first one to broach the subject of professional judgment many years ago and to unnamed friends, growers and colleagues whose review comments enriched this article.

Bill Castle is a professor emeritus at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.

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