Potato Famine Pathogen More Infectious Now than Ever

The same plant pathogen responsible for the devastating Irish Potato Famine of the 1840s is even more virulent now, after going through more than a century of genetic mutations that provide the pathogen with a greater means to harm and kill plants, according to researchers studying early and modern strains of the pathogen.

Plant pathologists from North Carolina State University and the University of Copenhagen analyzed the genomes of five 19th century strains of Phytophthora infestans and compared the results to modern strains of the pathogen, which is still known to wreak havoc on potato and tomato crops.

Genomes from historical samples of P.infestans in preserved plants from the mid- to late-1800s were found to be markedly different from genetic material found in modern day samples of the pathogen. Such a difference, the researchers report, makes the pathogen more infectious to plants than the historical strains of the pathogen.

In one example, a gene variant called AVR3a that was not virulent in the historical samples was shown to be virulent in the modern-day samples.

"The genetic blueprints, or genotypes, of the historical strains were distinct from modern strains, and genes related to infection were also quite different," said plant pathologist Jean Ristaino of NCSU.

"In the areas of the genome that today control virulence, we found little similarity with historical strains, suggesting that the pathogen has evolved in response to human actions like breeding more disease-resistant potatoes."

Some of the genetic evidence suggests that differences in the pathogen from samples dated to different decades in the 1800s indicate that the pathogen was brought to Europe more than once - a suggestion that goes against the theory that the pathogen was introduced to Europe just once and then expanded its range. Ristaino contends the pathogen was introduced to Europe multiple times, probably from South American ships.

A better understanding of the history of the P.infestans pathogen and how it evolved into what it is today will further enable farmers and scientists to protect crops. Ristaino said an estimated $6.2 billion was spent each year on crop damage and attempts to control the pathogen.

"Late blight is still a major threat to global food security in the developing world," she added. "Knowing how the pathogen genome has changed over time will help modern-day farmers better manage the disease."

Ristaino and her colleagues' study is published in the journal Nature Communications.