Effect of Different Genotypes of Phytophthora infestans (Mont. de Bary) and Temperature on Tuber Disease Development

The interactions of different cultivars/Advance Breeding Lines (ABL) of potato with different genotypes of the potato late blight pathogen (Phytophthora infestans) at three storage temperatures on tuber late blight development were evaluated. The contribution of the medullar storage tissues was assessed rather than the periderm and outer cortical cell tissue. Tuber late blight severity measured as tuber darkening [mean Relative Average Reflectance Intensity [RARI (%)] generally increased with temperature. There was little difference in tuber late blight development between 7°C and 10°C treatments and in some combinations significantly more tissue darkening developed at 7 than at 10°C but little or no development occurred at 3°C. Resistance in tubers was observed only in Torridon and Stirling and to some extent Jacqueline Lee, but the cultivar Missaukee had weak tuber resistance. The US-8 genotype isolates were the most aggressive in tubers in most years causing rapid and significantly more tuber damage than any other genotype of P. infestans and similar to the US-6, US-10 and US-14 isolates used in 2006.