Conversations with Dr. Charles Rick:

A 57 Year (and Counting!) Affair with Tomatoes

It is always a pleasure to chat with someone about a topic that is a mutual passion. I recently had the great fortune of spending about 2 hours on the phone with Dr. Charles Rick, and felt that it would be interesting to share what I learned with the readers of Off The Vine. Dr. Rick is perhaps the leading expert in tomato genetics, and his work has made a great impact on commercial tomato growing in the United States. I asked many questions, and was humbled by his knowledge, of which a mere fraction appears below, and his warmth and wit, which were infectious. It is always humbling to find out how much more there is to learn about something that you are quite familiar with, and that was certainly the case in our conversations. What was reassuring was the interest that Dr. Rick showed as I described some of the wonderful and unusual tomatoes in the SSE collection. It reinforced the notion that there will always be something new to grow, and something new to learn!

Dr. Charles Rick has been working with tomatoes since 1937, when he began carrying out research in graduate school. Though no thesis resulted from this early work, he returned to tomatoes for good in 1942, after spending two years studying asparagus at the University of California at Davis. His growing interest in tomatoes led to an odyssey that continues to this day, spanning over 50 years. One of the advantages to doing research at Davis is that 90% of the tomatoes that are processed in the U. S. A. come from California, mostly in the Central Valley. These vast plantings provide an immediate and captive audience for field research. Over the next 20-25 years he worked on analyzing the tomato genome. This work is not complete, and will not be completed until all of the genes located on the chromosomes of the tomato have been identified. The information located in these genes is responsible for all of the characteristics of a particular tomato variety, such as color, flavor, and leaf shape. Actually, we know an awful lot about tomato genetics due to the research of Dr. Rick and others. It is from this work that we can now begin to predict what will result when different varieties of tomatoes are crossed. For example, red (yellow skin over red interior) is dominant over pink (clear skin). So, if a cross is made between a pink and red tomato, seed saved from that cross, which is the first generation or F₁ hybrid, will produce red tomatoes. One extremely useful outcome of this work is the ability to breed various disease resistances into tomato varieties, the best source of which are the wild species from the Andes region of South America. There are nine species of Lycopersicon, including L. esculentum (which includes most of the varieties that we grow in our gardens), L. pimpinellifolium (currant tomato), and other wild species, such as L. peruvianum and L. cheesmanii. The amount of genetic variation in the wild species is vast; in fact, according to Miller and Tanksley, more genetic variation exists in a single wild population of L. peruvianum than among all accessions of L. esculentum. Dr. Rick has made 13 major collecting trips to the Andean region. In the wild species, all sorts of variation is noted, such as many different growth habits, leaf shapes, colors, and hairiness of the stems, leaves, or fruit. All the wild type fruits are cherry sized or smaller, and most are green or colorless in the ripe state. Although not toxic, their foul taste renders them inedible. So, the collecting trips were obviously not culinary adventures! As a consequence, the natives consider the plants to be useless weeds. Dr. Rick, on the other hand, considers them to be useful treasures. Some of the obstacles that are now being studied by Dr. Rick and others are using the genetic material from these wild tomato varieties to produce edible varieties that will have insect resistance, drought tolerance, ability to set fruit and flourish under different temperature extremes, and ability to tolerate salt water conditions.

Dr. Rick, when asked to comment on the SSE, has a favorable attitude, and commented on some of the interesting accessions in the collection. I felt that he is not aware of the remarkable and amazing variety in the SSE collection, as he seemed to feel that most, if not all, of the heirlooms are in the immense USDA collection. On the contrary, Carolyn and I feel that there is very little overlap between the SSE and USDA collections. In his opinion, native outcrossed crops like maize might be best for the SSE to concentrate upon. Because they are highly variable, heirloom collections from different areas should be sought for their potential value. Dr. Rick stated that the Davis collection contains 3,000 accessions, which overlap to a limited extent with the much larger (10,000) collection of the USDA. The Davis collection consists mostly of wild types and genetic mutants, which are accessible for interested investigators. What seems obvious is the remarkable resource that is now available when considering all three collections coexisting together! In other words, a tomato researcher has at their choosing somewhere around 16,000 varieties to choose from! He also noted the problems with the possibility of different names for the same varieties in the various collections; even with the help of analysis of the genetic material, it would be difficult to determine which varieties are distinct. One would think that after spending over 50 years studying one particular crop, there would reach a point when you had seen it all. Amazingly, a few years ago, David Cavagnaro sent Dr. Rick seeds of one of the SSE collection bicolor tomatoes, such as Georgia Streak. Well, it was the first time that Charles had ever seen a bicolor tomato! I was discussing some of the other observations that I have noted over the years, such as tomatoes with wispy, carrot-like foliage, or purplish-pink coloration. Again, these were new to him, and he was quite interested in receiving seed from those who had something truly different and unusual. He loves tomatoes, and plants in his own garden Caligrande and Celebrity, which are F₁ hybrids that carry the needed resistance to TMV and other diseases. Such resistances are generally unexplored in the older types introduced before 1940.

When asked about the frequency of spontaneous mutations or sports, he said that they do indeed occur, but at low frequency. If they interfere with fruiting, their unfruitfulness leads to easy detection. Such “bull” plants, not being held to the ground by fruit load, become large, vigorous, erect plants that are conspicuous, even at a distance. He mentioned Honor Bright (now known as Lutescent) as most likely being a spontaneous mutation. This variety, listed by Livingston in the late 1890’s, is currently in the SSE collection. The foliage is a light green color that gradually fades to bright yellow as the season wears on. The fruits also go through an interesting color change on their way to ripening (green to white to orange to red). Regarding crossing, he feels that it is up to the regional bee population. He observes that it is rare for bumblebees to visit L. esculentum in the fields at Davis, but they love the wild species. Plantings are done in short rows close together, and about 1% crossing is typically observed. The crossing, of course, is spotted by growing out the next generation.

Finally, I asked Dr. Rick about germination enhancement of dormant or stubborn tomato seed. This is a topic that has interested Carolyn and I for a few years, as we have each had old samples of seed from this one and that one that have resisted all attempts at germination. Dr. Rick has had good luck with using half strength chlorox for 30 minutes for stubborn seeds. Generally, the wild types have more problems with dormancy, and some types need to go through the digestive tract to grow. This is not to suggest that readers of Off The Vine should try this rather exotic method. Actually, we have been experimenting with, and have had limited success with, combinations of soaking seed in dilute potassium nitrate, and/or gibberellic acid, and/or brief exposure in the microwave oven! We will talk about this topic in more detail in a future newsletter.

Dr. Rick has been retired officially for 12 years, but continues as Director of the Davis tomato collection and conducts a limited amount of research. He is currently studying the behavior and linkage of traits derived from crosses with wild Lycopersicon and other Solanum species.