Tracking the Evolutionary History of the Potato Late Blight Pathogen with Historical Collections

Abstract

in the mid 19th century in Ireland led to what isknown as the Irish potato famine. Approximately 1.5 millionpeople died from starvation and another 1.5 million weredisplaced and forced to emigrate from Ireland to otherregions of the world. The disease was first observed onpotatoes in the United States in 1843 in areas around theports of Philadelphia and New York (Peterson, Campbell, G Peterson, Campbell, & Griffith, 1992). Thepainstaking work of J. Teschemacher in the United States,M.J. Berkeley in Great Britain, Montagne in France, andlater DeBary in Germany, clearly elucidated that a fungus-like organism was responsible for late blight (Berkeley, 1846,DeBary, 1876; Peterson, Campbell, & Griffith, 1992).Research by early mycologists who studied the late blightpathogen was some of the first to document that fungi werecapable of causing plant disease and laid the groundwork forthe disciplines of microbiology and plant pathology(Berkeley, 1846, DeBary, 1876).Late blight has become an increasingly important diseaseworldwide in recent years, more than 150 years after thegreat famine (Smart and Fry, 2001). Since susceptiblepotatoes are widely planted in many areas of the world, thecrop cannot be grown without frequent fungicideapplication. The disease has reached epidemic proportions inNorth America, Russia, and Europe due to the developmentof resistance to the phenylamide fungicide metalaxyl inpopulations of the pathogen and the widespread occurrenceof new and more virulent genotypes (Drenth et al, 1994;Kadish and Cohen, 1995). Some strains including the Ib orUS-1 clonal lineage are sensitive to the fungicide metalaxyland mefenoxam, while many other strains have developedresistance to these fungicides.More fungicides are used onpotato worldwide, than any other food crop, largely becauseof late blight. The cost of fungicide use by US potato growersexceeds 3 billion dollars annually. The disease can bedevastating in the developing world where fungicides areoften not affordable or available.