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College of Food, Agricultural, and Environmental Sciences


Researcher Seeks to Solve Tomato Shape Riddle, Develop New Varieties

September 11, 2003

WOOSTER, Ohio -- That round cherry tomatoes go in salads and long roma tomatoes go in cans is no mystery. What remains a puzzle for researchers is why tomatoes come in so many different shapes and how and when such variations occur. But not for much longer. Ohio State University geneticist Esther van der Knaap is leading a unique research project aimed at unraveling the tomato morphology code. Her goal is to understand vital development processes that determine whether tomatoes are round, elongated or shaped like a pear. "We are trying to identify a major gene that controls fruit elongation," said van der Knaap, a researcher with the Ohio Agricultural Research and Development Center (OARDC) in Wooster. "By identifying the gene that controls whether a fruit is round like a cherry tomato or shaped like a roma-type tomato, we can get a handle on the molecular process that is perturbed during fruit development and results in a differently shaped fruit." Funded by the National Science Foundation, van der Knaap's research is a crop with multiple benefits. First, it will help scientists understand how tomatoes grow -- from a few cells into an ovary, and from that ovary into the fruit we buy at the grocery store. What makes her laboratory unique is that van der Knaap looks at variations in fruit morphology as tools to study processes that regulate fruit development. "We have done studies to try to find out when a change in shape occurs," van der Knaap said. "Does it happen very early during flower development? Or does it happen later on, after fertilization? We have looked at different tomato varieties with different shapes, and it seems that each (shape-shifting) process is controlled independently. If we identify the genes that control each of those processes, then we’ll have the pieces of the puzzle and can start putting them together into one big story of how fruit develops." Flower development is another key aspect of fruit growth that van der Knaap is analyzing. Mapping this developmental process will allow her to pinpoint when and where a change in fruit shape first takes place, even before the flower is fertilized. For example, once van der Knaap identifies a gene that controls oval shape in tomatoes, she can look back at the whole development process and see when the oval shape is first evident. Thus far, nobody has described the entire flower development process of tomato. Van der Knaap is also studying how domestication has transformed the once small, round wild tomato into the varieties available today. "We don't know very well how domestication occurred," van der Knaap said. "We don't know what kind of genes caused the enormous increase in fruit size and variation in fruit shape. The wild-type tomato started out as a tiny fruit, made to propagate the species and not to feed us. Once we know all the genes that were mutated during domestication, we will be able to piece together how domestication shaped the tomato fruit." Beyond basic science, van der Knaap's research could lead to the development of new tomato varieties, helping growers to serve specialty tomato markets and processors to reduce costs. "Tomato processing companies are interested in developing varieties which carry very blocky, almost square-shaped fruit, in order to pack them more efficiently," van der Knaap pointed out. "Others might be interested in developing extremely elongated tomatoes shaped like cucumbers. These fruits would be very advantageous when preparing sliced tomatoes for hamburgers as less ends would have to be thrown away." Another potential application of this technology is the development of seedless tomatoes with the same taste and nutritional value of their seedy counterparts. Van der Knaap said there's much interest in separating fertilization and seed development in tomatoes, and her research could shed light into this process. "We know that what's important for fruit to develop is to have a good seed set,” she added. "But if you can uncouple fertilization and seed development, then you can actually get very good fruits that are nutritious and taste just like regular tomatoes but without any seeds. This might be of interest to seed companies and great news for consumers who don't tolerate tomato seeds or simply don't want to deal with them when preparing their dishes." Down the road, Van der Knaap is planning to create a tomato morphology database containing all the information derived from her research, which will be available to the public. She said this data could be used in the future as a model for the study of fruit development —- and possibly shape manipulation —- in other crops of the Solanaceae family, such as peppers and eggplants. Tomatoes are the second most important vegetable crop processed in the United States. Ohio ranks third in the nation in the production of processing and fresh market tomatoes, with a total farm value of $101.3 million in 2002. For more information, log on to, or contact van der Knaap at (330) 263-3822 or OARDC is the research arm of Ohio State's College of Food, Agricultural, and Environmental Sciences. -30- Editor: Photographs for this article are available. Please contact Ken Chamberlain at (330) 263-3779 or

Mauricio Espinoza
Esther van der Knaap