Genetic diversity in heirloom tomato genotypes

The objective of this research was to study the genetic diversity of a group of heirloom tomatoes genotypes from Universidade Federal Rural do Rio de Janeiro, Brazil, using descriptors recommended by the Bioversity International Institute (formerly International Plant Genetic Resources Institute). Similarity between genotypes was quantified by principal component analysis followed by clustering methods. Ten genotypes of large-fruit tomatoes and twelve of cherry-type tomatoes were grown from May to September 2004. In each fruit size group, both heirlooms and commercial genotypes were present. Quantitative data were submitted to principal component analyses followed by cluster analyses by the Ward's minimum variance method. Qualitative data were transformed into a binary matrix, from which similarity indexes (Jaccard) were generated and submitted to a cluster analysis by the UPGMA method in order to generate dendrograms. Results showed the formation of clusters where local and commercial genotypes were separated from imported heirlooms, indicating diversity. Clusters formed by either qualitative or quantitative variables discriminated these two groups, although the clusters formed were not identical. Hence, these two techniques combined are adequate to exploratory analyses of large numbers of genotypes, since they are fast and easy to perform.