Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 23, 2010
Publication Date: May 1, 2011
Citation: Labate, J.A., Robertson, L.D., Balch, T., Sheffer, S.M. 2011. Diversity and population structure in a geographical sample of tomato (Solanum lycopersicum L.) accessions. Crop Science. 51:1068-1079. Interpretive Summary: Tomato (Solanum lycopersicum) is one of the most popular vegetables in the world. It is eaten as fresh and canned fruit and in products such as sauces, juices, soups and condiments. In 2008 nearly 130 million tons of tomatoes were grown in an area of more than 5 million hectares. Because it is so highly consumed, tomato is an important source of vitamins and minerals in the human diet. The nutrient lycopene, which gives the red fruit color, is believed to reduce risk of certain cancers and chronic diseases. The USDA-ARS Plant Genetic Resources Unit (PGRU) conserves seeds for thousands of diverse tomato lines. These seeds serve as a resource for breeders and researchers to find new genes to continue to improve the crop in traits such as nutritional value, taste, size and shape. The purpose of this study was to help predict where to find new genes in the PGRU tomato seed collection that influence these traits. We compared tomato lines that originated in different parts of the world (Europe, USA/Canada, Mexico/Central America, Asia or South America). South America showed slightly more gene diversity than the other regions. Traits such as lycopene, vitamin C, sugar, color, size and shape were highly diverse in our sample. South American germplasm seems promising as a source of new genes but, based on overall results, no geographical region should be viewed as a poor source of new genes to help improve the crop.
Technical Abstract: Cultivated tomato (Solanum lycopersicum L.) dispersed out of Latin America beginning in the 16th century but little is known about worldwide patterns of diversity. A sample of 30 accessions was assembled to represent five regions (Europe, USA/Canada, Mexico/Central America, Asia or South America) and three time ranges representing recent breeding history (1930s – late 1940s, late 1950s – 1960s or 1980s – 2000s). DNA sequences were generated for 49 gene fragments (22.9 kb) in two plants per accession. All accessions were grown in the field for evaluation of highly heritable horticultural traits and assayed for nutritional content. °Brix, vitamin C and lycopene ranged from 4.3 – 8.5, 33.80 ug/ml – 99.02 ug/ml and 5.81 ug/g – 13.76 ug/g, respectively. Overall estimated p = 0.00112 (95% CI = 0.0090, 0.00134). South America was the only region with a significantly higher mean p relative to the other four regions. When accessions were grouped according to date of collection or year of cultivar release, mean p values did not significantly differ from each other. Based on AMOVA, significant variation was partitioned into accessions within regions (35.87%, df = 10, P = 0.000), individuals within accessions (60.74%, df = 45, P = 0.000) and within individuals (3.30%, df = 60, P = 0.000) but not among regions. Population structure analysis defined two clusters that were not strictly associated with a priori groups. South American germplasm seems promising as a source of new alleles but no geographical region should be viewed as a poor source of tomato genetic variation.