Genetic divergence among carrot accessions belonging to different varietal groups using morphologic characters

The utilization of carrot hybrids has increased in the last decade in Brazil. The estimative of genetic divergence among genotypes is a tool to identify superior parents for heterotic hybrid production in breeding programs. However, little is known about the combining ability of tropical-adapted carrot germplasm. The objectives of the present work were: (1) to estimate genetic parameters, (2) to estimate the relative importance of set of four morphological traits in the discrimination of carrot accessions belonging to distinct varietal groups and, (3) to use this morphological dataset combined with clustering techniques to group distinct carrot accessions in order to identify the most promising hybrid combinations. Two experiments were carried out in the field, in the springs of 2000 and 2001, in random block design with two replications. Fifteen competitive plants per accession were evaluated at 90 days after planting for the following traits: leaf length (cm), root length (cm), root diameter (mm), and fresh root weight (g). Analysis of variance as well as dissimilarity analysis and relative importance of each morphological characteristic for accession discrimination were calculated for the traits under study. All four traits displayed either medium or high heritability values as well as ratio of genetic and environmental variation coefficients. The traits root length and root diameter presented the highest contribution to discriminate accessions. The 'Imperator' group was the most divergent one. Therefore, crosses involving this variety group with the remaining accessions would result in progenies with the highest heterotic effects. Tropical-adapted accessions belonging to the 'Brasilia' group could be crossed with the majority of the accessions (except for the ones corresponding to the 'Chantenay' and 'Danvers' groups) with a high probability of generating superior populations and/or heterotic gains.