WILD TUBER-BEARING SPECIES OF SOLANUM AND INCIDENCE OF PHYTOPHTHORA-INFESTANS (MONT) DEBARY ON THE WESTERN SLOPES OF THE VOLCANO NEVADO-DE-TOLUCA .5. TYPE OF RESISTANCE TO P-INFESTANS

Plants of wild Solanum species (S. demissum (dms), S. verrucosum (ver), S. iopetalum (iop), S. brachycarpum (bra), and an unidentified species (unsp), from the natural habitat were inoculated in the laboratory with Phytophthora infestans race 0, to see if major genes for resistance were present, and with the most complex and aggressive race available in an attempt to reveal the level of general resistance. No plant with a susceptible reaction to race 0 was found in 120 plants of dms, and 34 plants of unsp. Plants with a hypersensitive reaction to race 0 and susceptible plants were found in ver. When infected with a complex aggressive isolate of the fungus 73.5 % of the WSS plants were susceptible. It was concluded that WSS in the area possess both complex race specific resistance and a high level of general resistance, whose effects cannot yet be separated.