Resistance to late blight (Phytophthora infestans (Mont.) de Bary) of potato plants regenerated fromin vitro selected calli

Summary Cells of seven potato cultivars were selectedin vitro with culture filtrate (CF) ofPhytophthora infestans (Mont.) de Bary. Regenerated plants were tested for late blight resistance. The aim of the study was to check the efficacy of CF in the selection of potatoes for resistance to late blight and to evaluate the effects of additive factors on general resistance. One selection cycle, applied to a cell culture system, selected cells resistant to toxic metabolites of CF.In vivo screening of clones regenerated from selected cells was done in two steps: on whole plants, assessing foliage late blight, and on detached leaves, assessing single factors of horizontal resistance. In general, the frequency of resistant variants selected with CF did not differ from that of resistant somaclonal variants. Nevertheless, high concentrations of CF in the growth medium seemed to induce an improvement of some partial resistance factors as compared with the source plants.