Genetic diversity, agronomic potential and reaction to downy mildew in genotypes of biofortified mini lettuce

Lettuce is one of the most consumed leaf vegetables in the world, highlighting itself as a novelty in the market as mini type cultivars. During the winter the downy mildew can lead to severe damage. Thus, the objective of this work was to evaluate the genetic diversity, agronomic potential and downy mildew reaction in biofortified mini lettuce genotypes. The experiment was carried out in the University of Uberlandia, Monte Carmelo Campus. The statistical method used for the field experiment was the randomized complete block design, with 19 treatments (17 genotypes of the generation F3:4 and two cultivars of commercial lettuce) and two repetitions. The following parameters were evaluated: crowndiameter (cm); rod diameter (mm); number of leaves per plant and spad index. The data were submitted to multivariate analyses were performed. The genetic divergence was represented by dendrogram obtained by the hierarchical UPGMA method and by the Tocher optimization method. The laboratory experiment was carried out in a completely randomized design with 18 genotypes, two Bremia lactucae breeds (3 and 4) and three repetitions. In order to select resistant genotypes, inoculations were carried out, using distilled water mixture with the sporangia of the pathogen and Tween 20. The monitoring was performed daily and when the first sporulation appeared on cotyledonary leaves of the susceptible cultivar, the genotypes were evaluated, verifying the presence or not of sporulation and necrosis. The use of Mahalanobis distance Dii2 as a measure of dissimilarity allowed the formation of two groups by the Tocher method. The grouping of the accesses by the UPGMA hierarchical method formed four groups, with the cut-off point established at the 7% similarity distance. The all lettuce genotypes F3:4 showed low percentage of necrotic plants and sporulated plants.