An efficient in vitro test to determine carrot genotypes resistance to cavity spot

As part of a carrot breeding programme, our objective was to develop a test for determining genotypes resistance against two Pythium species responsible for cavity spot. Ten different media were tested for carrot callus culture, Pythium culture and dual cultures. Carrot callus growth was greater on Murashige and Skoog medium plus 1.25 microM 2.4D plus 2.5 microM BA plus 2.5 microM NAA. Pythium violae was more sensitive to medium composition than Pythium sulcatum. When carrot callus were inoculated by Pythium violae or sulcatum on Murashige and Skoog mineral medium, callus growth of Bolero, an resistant cultivar in the field, was highly inhibited whereas Nanco, a susceptible cultivar was not. Such a medium should be used for screening genotypes resistance to Pythium. A Murashige and Skoog medium supplemented with 1.25 microM 2.4D, 2.5 microM BA and 2.5 microM NAA, where callus growth was highly reduced whatever the genotype used, should be useful for selection of cell lines tolerant to Pythium.