EFFECTS OF TEMPERATURE AND LIGHT ON NON-RACE-SPECIFIC RESISTANCE OF POTATO LEAFLETS TO LATE BLIGHT

Effects of temperature and illumination on colonization by Phytophthor a infestans of detached leaflets of five potato cultivars differing in field resistance to blight were investigated using an ELISA system to quantify the pathogen. Leaflets of cvs Teena and Shelagh, and in one experiment cv. Brodick, were more resistant to colonization when infec ted leaflets were incubated at 10 degrees C than at 20 degrees C, but temperature conditions before inoculation had little effect. Both phot operiod and light intensity during illumination of intact plants befor e inoculation interacted with genotype to determine subsequent coloniz ation of infected leaflets incubated in darkness. Leaflets from plants of cv. Teena were more resistant to colonization after exposure to lo w, rather than to high, light intensities but photoperiod had no appar ent effect. Leaflets of cv. Shelagh grown in a 20 h day were more resi stant than those grown in a 10 h day but light intensity had no effect . Leaflets of cv. Brodick were more resistant after a 20 h day than a 10 h day and after exposure to low, rather than to high, light intensi ties. Leaflets of cv. Bintje were extensively colonized and those of c v. Torridon remained relatively resistant to colonization, irrespectiv e of temperature and lighting conditions. There was a high level of un explained variation in all the experiments.