Tracy Kahn: A Love Affair with Citrus

Tracy Kahn, photo by Elena Zhukova

As the curator of UC Riverside’s Citrus Variety Collection, Tracy Kahn has handled fruits as big as a person’s head, and as small as a pea.

Some are hued in vivid orange, while others are the palest purple. A number are smooth and round, and some could be confused for modern art sculptures, with long, dappled, finger-like segments.

The collection is one of the world’s most diverse batches of citrus cultivars — plants produced through selective breeding. Established in the early 1900s, most of the collection is on 22 acres near the UCR campus, and it includes more than 4,000 plants from around the world.

Kahn, who earned her Ph.D. in botany and plant sciences from UCR in 1987, oversees the collection as principal museum scientist in the Department of Botany and Plant Sciences. She facilitates research for citrus researchers, growers, nursery owners, produce providers, chefs, students, and the public. Kahn’s lab also conducts research funded by growers in collaboration with the lab run by Mikeal Roose, the department chair and a professor of genetics. Together, they develop and evaluate new citrus cultivars for the California citrus industry.

Kahn has been a UCR employee for 30 years and was appointed the Givaudan Citrus Variety Collection Endowed Chair in 2015. Givaudan is a Switzerland-based company that is the global leader in the creation of fragrances and flavors. Kahn’s appointment to the $1 million endowed chair runs through June 30, 2020, but the endowment is funded and allows the collection to be supported and maintained in perpetuity.

Photo by Elena Zhukova

My love affair with citrus began after I took a class with W.P. Bitters, or Bill Bitters, in 1982 as part of my graduate education. It was called “Citrus and Its Relatives.” In addition to learning about the diversity of citrus, you got to taste fruit from the (Citrus Variety Collection) twice a week. I got excited about citrus then and ended up doing my dissertation on citrus because of that class.

It dates back to the beginnings of our campus history when the Citrus Experiment Station opened in 1907. The collection has many more cultivars and species now. It has a website (citrusvariety., a microsprinkler irrigation system, and two endowed funds. We’re still actively using it for research and teaching and as a resource to extend knowledge on citrus diversity to the industry and the world.

In 1996, I started the Citrus Variety Collection Endowed Fund because, as the curator, I needed to find permanent funding for the collection. It started with $100. I learned about raising money and people offered to give donations. Now the fund has a little more than $500,000.

The first endowment was to support the collection — to provide funds to maintain the collection. Givaudan’s (endowment) had a component in it to enhance the collection and expand the collection with new genotypes of citrus.

I feel like I really grew up here. I got my Ph.D. here, and I met my husband (Norman Ellstrand, distinguished professor of genetics) when I arrived as a graduate student. He was a young assistant professor. I had my child here in Riverside. It’s an amazing campus because there’s a lot of freedom to do a lot of amazing things. People work well together; they support each other.

Photo by Elena Zhukova

I want to make sure the collection is financially and physically secure so that it can continue to be a resource for research and teaching about citrus diversity in the future at UCR. I always thought I was going to be a “pointy-headed” basic botanist teaching at a small liberal arts college. But learning about myself along the way, I realized I’m very attracted to teaching and research that has applications. Things that change the world.

Don’t ask that! People always ask me, “What’s your favorite?” But I have lots of favorites. As with food, you like certain foods for a while. I’m like that with citrus.

I’ve been teaching that course for more than 16 years. After I did my Ph.D., I did a postdoc at Berkeley. When I came back to UCR, I got hired by the Department of Botany and Plant Sciences to work as a postdoc on cherimoyas. I also had an 8-month-old baby, so I was looking for part-time jobs. Riverside Community College had an opening to teach human reproduction and health behavior at Moreno Valley, so my dad said, “You should do that one. All you have to do is be one lecture ahead.” I was pretty angry with him about the ninth week because RCC was on semesters, so I had 15 weeks of staying one lecture ahead! But once I had done that and was hired at UCR and given the opportunity to teach the course, I thought, I may as well do it again.

(It’s) a multidisciplinary subject with a focus on biology. When I started, and with the help of the UCR LGBT Resource Center, there was an LGBT panel in the lecture. Numerous students would walk out! We’ve come so far since then. Discussions on sexual orientation are much more interactive and students are more accepting.

The citrus industry helped create a great deal of wealth in Southern California, Tracy Kahn explained. Riverside was at one point the richest city west of the Mississippi River because of citrus, according to historians.

“This collection is unique because it traces back to our roots as a campus; because it’s one of the world’s most diverse collections; and because it’s about a crop that built significant wealth in California,” she said.

Photo by Elena Zhukova

The recent discovery of a Huanglongbing-infected tree in Riverside less than 3 miles from the Citrus Variety Collection groves crystallized the need to further protect this amazing diversity of citrus from possible spread of this disease.

While Kahn and her team have created smaller, backup trees in screened greenhouses since 2008 with help from the USDA National Clonal Germplasm Repository for Citrus and Dates, the possibility of losing field trees has created a need for two additional 1-acre structures that could house new mature trees of each of the cultivars and species in the collection.

These larger, mature trees would be able to flower and fruit, permitting UCR to continue preserving citrus diversity while also creating cross-species cultivars, evaluating fruit quality, and providing essential security for the collection.

If you would like to help UCR secure funding for the collection, please visit