THE EFFECTS OF A TOXIN PREPARATION FROM PHYTOPHTHORA-INFESTANS ON POTATO PROTOPLASTS AND MICROSPORES

The effect of a semi-purified toxin preparation from Phytophthora infestans was tested on the development of calli from protoplasts and microspores of different dihaploid and commercial cultivars of potato. In the protoplast assay the effect of the toxin was strongly dependent on protoplast density and plant line. Plant line specific differences to the toxin preparation were observed in relation to browning of the protoplast or of microcalli and the number of protoplasts developing to form calli. While in one dihaploid clone all the protoplasts were killed by the lowest toxin concentration tested, all other genotypes reacted to give a greater or lesser callus regeneration rate than the controls. Similar reactions were observed in the microspore cultures. Two lines reacted with a two-to threefold increase in the number of embryoids regenerating at the lowest toxin concentration tested, while others showed a reduction in the number of embryoids regenerated. No correlation was found between toxin resistance of the protoplasts and microspores and resistance of the plants. Thus the toxin preparation of Phytophthora infestans we have used is unlikely to be useful as an in vitro selection agent for the development of resistant cultivars. © 1992.