Inheritance of cold temperature tolerance in progeny isolates of Phytophthora infestans from mating

Late blight of potato, caused by Phytophthora infestans, remains a threat to the production of high quality potatoes. Optimal temperature for mycelial growth is around 10°C with maxima and minima of 30 and 3°C, respectively. Recent studies have indicated that some isolates of different genotypes of P. infestans can survive about 5 days continuous exposure to -3°C. To observe more variation in the tolerance to cold temperature, isolates were tested for tolerance at -5°C for 5 days. This phenotypic trait has serious implications for potato production and disease protection. In this project mating type is used as a biological tool for enhancing the mutation in the pathogen. Crosses were carried out between isolates that were highly variable for temperature tolerance and identified as tolerant, sensitive or intermediate in tolerance of exposure to -5°C. To determine if temperature tolerance is a genetically inherited trait or occurs as a result of physiological adaptation of different P. infestans genotypes the progeny isolates from these crosses were assessed by using the phenotypic and genotypic characteristics of progeny such as mating type, isozyme analysis, Simple Sequence Repeats, metalaxyl sensitivity, virulence and pathogenicity tests. Progeny isolates from crosses performed have indicated that cold tolerance is a continuous variable showing both inheritance and hybridity. These data illustrate the potential variation in different characteristics of the pathogen after recombination or mutation occurs. Survival potential of inoculum may be increased under recent reported climatic changes in north-central US production areas.