Phenotypic and Genotypic Characterization of Phytophthora infestans Isolates Associated with Tomato and Potato Crops in Colombia

Reconstructing the Global Migration History of Phytophthora infestans Toward Colombia

The evolution of new variants of plant pathogens is one of the biggest challenges to controlling and managing plant diseases. Of the forces driving these evolutionary processes, global migration events are particularly important for widely distributed diseases such as potato late blight, caused by the oomycete Phytophthora infestans. However, little is known about its migration routes outside North America and Europe. This work used genotypic data from population studies to elucidate the migration history originating the Colombian P. infestans population. For this purpose, a dataset of 1,706 P. infestans genotypes was recollected, representing North and South America, Europe, and Asia. Descriptive analysis and historical records from North America and Europe were used to propose three global migration hypotheses, differing on the origin of the disease (Mexico or Peru) and the hypothesis that it returned to South America from Europe. These scenarios were tested using approximate Bayesian computation. According to this analysis, the most probable scenario (posterior probability = 0.631) was the one proposing a Peruvian origin for P. infestans, an initial migration toward Colombia and Mexico, and a later event from Mexico to the United States and then to Europe and Asia, with no return to northern South America. In Colombia, the scenario considering a single migration from Peru and posterior migrations within Colombia was the most probable, with a posterior probability of 0.640. The obtained results support the hypothesis of a Peruvian origin for P. infestans followed by rare colonization events worldwide.

Genetic structure and population diversity of Phytophthora infestans strains in Pacific western Canada

Late blight caused by Phytophthora infestans is an economically important disease of potato and tomato worldwide. In Canada, an increase in late blight incidence and severity coincided with changes in genetic composition of P. infestans. We monitored late blight incidence on tomato and potato in Pacific western and eastern Canada between 2019 and 2022, identified genotypes of P. infestans, and examined their population genetic diversity. We identified four major existing genotypes US11, US17, US8, and US23 as well as 25 new genotypes. The US11 genotype was dominant in Pacific western Canada, accounting for 59% of the total population. We discovered the US17 genotype for the first time in Canada. We revealed a higher incidence of late blight and quite diverse genotypes of P. infestans in Pacific western Canada than in eastern Canada. We found high genetic diversity of P. infestans population from Pacific western Canada, as evidenced by the high number of multilocus genotypes, high values of genetic diversity indices, and emergence of 25 new genotypes. Considering the number of disease incidence, the detection of diverse known genotypes, the emergence of novel genotypes, and the high number of isolates resistant to metalaxyl-m (95%) from Pacific western Canada, the region could play a role in establishing sexual recombination and diverse populations, which could ultimately pose challenges for late blight management. Therefore, continuous monitoring of P. infestans populations in Pacific western region and across Canada is warranted. KEY POINTS: • Genotypes of P. infestans in Pacific western were quite diverse than in eastern Canada. • We discovered US17 genotype for the first time in Canada and identified 26 novel genotypes. • Approximately 95% of P. infestans isolates were resistant to metalaxyl-m.