Different response of winter oilseed rape calli and seedlings to Leptosphaeria maculans

The study investigated physiological and biochemical responses of winter oilseed rape (Brassica napus) callus and seedlings to secondary metabolites of Leptosphaeria maculans, an ascomycete causing stem canker. Three winter oilseed rape cultivars, 'Leo', 'Bolko', and 'Gorczariski' were investigated during this study. The evaluated parameters included total phenolics content, the activity of L-phenylalanine ammonia-lyase, catalase and total peroxidases, respiration intensity, heat emission and metabolic activity. Callus elicitation and seedling inoculation were performed at 2 degrees C, and at optimum growth temperature, i.e., 20 degrees C for the calli and 12 degrees C for the seedlings. Elicited 'Gorczanski' calli exhibited resistance to secondary metabolites of L. maculans, as only in this cultivar no drop in cell viability was observed, neither at 2 degrees C, nor at 20 degrees C. Similarly, a significant drop in average severity index (ASI) in hardened seedlings of the 'Gorczafiski' cultivar was linked to a stimulation of defense mechanisms triggered by low temperature. In the 'Gorczaiiski' cultivar, the response of the calli and seedlings to L. maculans was identical, with the same pattern of changes for all analyzed parameters at both temperatures. In the 'Leo' cultivar, the same response of the calli and seedlings was observed for heat emission, catalase activity and phenolics content, however in the 'Bolko' cultivar only for cellular respiration. A similar response of 'Gorczafiski' calli and seedlings to L. maculans toxins was probably due to stable peroxidase activity.