The evolution of differing strains of Phytophthora infestans, a major cause of late-blight disease on potato and tomato plants, was studied and recently featured in “Scientific Reports.” Plant pathologists studied the genomes of about 140 pathogen samples – historic and modern – from 37 countries on six continents. The historic lineage called FAM-1 was found in 73 percent of the samples on all six continents.
“FAM-1 was much more widespread than previously assumed, spreading from Europe to Asia and Africa along British colony trade routes,” said Jean Ristaino, a professor of plant pathology at North Carolina State University and corresponding author of the study. “The lineage also was found in a span of more than 140 years.”
FAM-1 caused outbreaks of potato late blight in the United States in 1843 and then two years later in Great Britain and Ireland. It also was found in historic samples from Colombia, suggesting a South American origin.
FAM-1 caused massive and debilitating late-blight disease outbreaks in Europe, leaving starvation and migration in its wake. Ristaino theorized that the pathogen arrived in Europe via infected potatoes on South American ships or directly from infected potatoes from the United States. FAM-1 survived for about 100 years in the United States but then a different strain of the pathogen called US-1 displaced it.
“US-1 is not a direct descendant of FAM-1, but rather a sister lineage,” Ristaino said. “We found US-1 in 27 percent of samples in the study and they were found much later.”
Even more aggressive strains of the pathogen that originated in Mexico have since outpaced US-1. Winter tomato crops grown in Mexico and imported into the United States harbor the pathogen, Ristaino said.
The study also indicates that the pathogen spread first in potatoes and later moved into tomatoes. Spread of the pathogen in ripe tomatoes in ships’ holds would have been unlikely, Ristaino said.
The pathogen’s effects aren’t limited to the decimation of Ireland’s potato crop about 175 years ago. Billions are spent worldwide each year in attempts to control the pathogen, Ristaino said. Potatoes in the developing world are vulnerable because fungicides are less available and often unaffordable. Visit nature.com and search for "Global historic pandemics caused by the FAM-1 genotype" for more information.
June 29, 2021 at 01:00PM
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