Southern Corn Leaf Blight: A Story Worth Retelling

1 There are few active practitioners of our profession left who recall first-hand the harsh lesson Mother Nature inflicted on agronomists and North American agriculture in 1970 and 1971. The maize disease SCLB (Bipolar maydis T.) (earlier known as Helminthosporium maydis T.) reached epidemic proportions in the United States and southern Canada, destroying an estimated 15% of the corn crop at an estimated loss of $1.0 billion at that time (Ullstrup, 1972). It was not uncommon for some growers to suffer 80 to 100% losses and some multiple county regions in the Corn Belt to have average losses ranging between 35 and 50% of their crop. In some southern states where the disease first appeared, relative losses were also high with those in Mississippi estimated to be between 30 and 40% (Moore, 1970a.) This “perfect storm” of a plant disease epidemic was a prime example of the Disease Triangle coming together in a devastating way; a relatively new race of an existing disease being introduced, a host crop of which >85% had a vulnerable common genetic background, and environmental conditions exceptionally favorable for infection and growth of the pathogen. Obviously humans have little or no control over the evolution of pathogenic organisms. Like any living thing, fungi along with all other pests, will find a way to survive and propagate. Paraphrasing the character Dr. Ian Malcom played by Jeff Goldblum in the movie “Jurassic Park” when informed that all of the dinosaurs in the park were female and through the controlled cloning program would be denied natural reproduction, Dr. Malcom warned “You can’t deny a species the ability to reproduce. Life will find a way”. Corn has always been a major feed grain in the United States since colonial times, with >80% going for livestock feed and the remainder for food and industrial products. The United States in 1969 was exporting about 15.5 Tg of corn overseas with a value of ~ $690 million. Currently exports are more than 56 Tg valued at ~ $8.7 billion (Index Mundi, 2016). The lead up to the 1970–1971 SCLB race-T epidemic had its roots with the commercialization of hybrid seed corn, and its wide acceptance by American growers. Prior to 1930, virtually all corn produced in the world utilized open-pollinated cultivars with nearly 1000 different cultivars being grown in the United States alone Southern Corn Leaf Blight: A Story Worth Retelling

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