Strategies of selection for carrot seed germination at high temperatures

Among the carrot cultivars developed for summer cultivation, stand out those from the "Brasilia" group. These cultivars present higher performance in relation to the others commercialized in the country due to their productivity, resistance to leaf-blight diseases and higher adaptation to the Brazilian summer conditions. However, it is necessary to increase, by selection, the potential for carrot seed germination at high temperatures (above 35 degrees C), resulting in seed economy and more uniform plant establishment, especially during warm weather conditions. Thus, the objective of this study was to select carrot populations with seeds able to germinate under conditions of high temperature. The experiment was carried out in Brasilia, DF, in the year of 2007. Four replications of fifth seeds from forty-seven carrot half-sib families were incubated at 20 degrees C and 37 degrees C in a randomized block design. The data were submitted to the analysis of variance, application of selection indexes and estimation of gains with the selection. The selection for germination of carrot seeds at high temperatures (37 degrees C) were not effective. The values of vigor and germination at 37 degrees C were low, suggesting that this temperature is approaching the biological limit of the populations of the carrot group Brasilia. At 20 degrees C it is possible to differentiate the genotypes regarding to physiological quality of seeds.