Selection for disease resistance in Brassica cultures

Haploid cell and embryogenic cultures of rape (Brassica napus L.) were used as starting material for experiments carried out with the aim to induce and select for resistance against the pathogenic fungi Phoma lingam and Plasmodiophora brassicae, causal agents of blackleg and clubroot diseases, respectively. After a mutagen treatment, the cultures were plated on a selective medium. In the case of Phoma this medium contained the phytotoxin produced by the parasite. Plants regenerated from toxin‐resistant, selected colonies and from control cultures were tested for resistance after inoculation with a defined number of pathogen spores. Whereas 22% of regenerants from selected cultures gave a resistance or tolerance response to the infection, only 4% of plants regenerated from control cultures showed an increased tolerance. Resistance tests carried out on the progenies of the regenerants showed that the acquired resistances were partially heritable. The observed segregation in some progenies‐often correlated with morphological variability‐is probably due to chromosomal variability. The in vitro selection system for possible resistance to clubroot was based on the fact that a massive infection of embryogenic rape cultures with resting spores of the fungus causes a strong growth inhibition and a loss of capacity to undergo embryogenesis. The cultivated tissues ultimately die. Green embryos occasionally regenerating from infected, necrotic cultures were selected. None of the about 300 plants regenerated from selected cultures showed increased resistance with respect to regenerants from non‐selected cultures after infection with the parasite. The nonspecificity (hence ineffectiveness) of the appplied selection system was demonstrated by means of infection experiments in vitro using resistant material.