Inheritance of a pectate lyase mediated soft rot resistance in crosses between transgenic potato lines of cv. Désirée and S. tuberosum cultivars

Expression of the pectate lyase (PL) isoenzyme 3 in transgenic potato lines of cv. D6sir6e mediates an enhanced resistance of tuber tissue to Erwinia earotovora (Ec) soft rot due to a pre-activation of plant defence mechanisms. Therefore, the Solanum tuberosum cvs Agave and Adretta with a moderate level of soft rot resistance were crossed with such PLexpressing potato lines. The resulting progenies were assessed with respect to plant/tuber characteristics over a period of four years and then tested for PL3-expression as well as for soft rot resistance. 71% of the selected progeny lines exhibited a stable production of the PL3 enzyme. Statistical analysis revealed differences between the transgenic and the nontransgenlc progeny concerning the soft rot resistance of tuber tissue. Compared with the PLinactive progeny, extension of Ec-rotting on the wound surface of PL-transgenic potatoes was diminished on average by 51.8%. Similarly, the degree of cell lysis caused by bacterial maceration was significantly (P<0.05) reduced in tuber tissue of PL-expressing progeny lines. The latter also revealed an enhanced PPO and PAL activity in their tuber tissue indicating an active plant defence. It is concluded therefore that the PL-mediated soft rot resistance introduced into potatoes by means of molecular techniques is heritable.