Phys.org reports that the international team decoded the genomes of 11 historical samples of Phytophthora infestans from potato leaves collected and preserved over more than 50 years. A modern strain called US-1 was long thought to have been the cause of the fatal outbreak but a strain new to science -- one possibly now extinct -- was responsible.
The HERB-1 strain of Phytophthora infestans likely emerged in the early 1800s and continued its global spread throughout the 19th century. In the twentieth century new potato varieties were introduced, and HERB-1 was replaced by another Phytophthora infestans strain, US-1.
Researchers examined the historical spread of the fungus-like oomycete pathogen and found connections to historical events and human activity. First contact between Europeans and Americans in Mexico coincides with a dramatic increase in the genetic diversity of Phytophthora.
The dried potato leaves tested for the study are between 170 and 120 years old, and were preserved in the herbaria of the Botanical State Collection Munich and the Kew Gardens in London. This study marks the first time scientists have decoded the genome of a plant pathogen and its plant host from dried herbarium samples, open up new research possibilities.
"The degree of DNA preservation in the herbarium samples really surprised us," said co-author Johannes Krause. Kentaro Yoshida notes that this study shows the effect of plant breeding on the evolution of a pathogen. "This type of work paves the way for the discovery of many more treasures of knowledge hidden in herbaria," he said.