RESISTANCE TO PHYTOPHTHORA-INFESTANS IN POTATO GENOTYPES ORIGINATING FROM WILD-SPECIES

The reaction to P. infestans in the foliage and tubers of potato was evaluated in resistant genotypes and in their progeny. The genotypes originated from wild species known to carry genes for specific resistance. Evidence was obtained that three types of resistance to P. infestans were presented in the genotypes: (1) Resistance due to major, dominant genes was predominant. The presence of these genes was expressed in both foliage and tubers and did not influence maturity. Some of the genes were R genes, providing specific resistance, but for others this could not be determined as they were effective against the fungus inoculum with the highest virulence available: 1.2.3.4.5.7.10.11. (2) Resistance was present, associated with late maturity. (3) Tuber resistance was present, expressed after inoculation of whole tubers but not after inoculation of tuber slices. Testing of the progeny was essential for the determination of the type of resistance present in the genotypes evaluated.