and Jennifer Shike
Some destructive events are so monumental that we never forget the fear. For farmers and those involved in hybrid seed production, such a time came when blight blew across the Corn Belt in the summer of 1970.
A disease known as Southern corn leaf blight (SCLB) ravaged an estimated 25% of the nation’s corn crop that season. The epidemic is still considered by many to be the most economically devastating field crop disease of any developed area in the world during the 20th century, says Jerald Pataky, University of Illinois plant pathologist.
Now, 40 years after three University of Illinois researchers led the race to unlock the disease’s secrets, it remains as testimony to the need for diversity. Scientists Art Hooker, Dave Smith and Sung Lim determined the U.S. corn crop was susceptible because most of the seed was then produced on inbred parents with Texas male-sterile cytoplasm.
In the spring of 1970, Hooker wrote a prophetic statement: "Although many different inbred lines are used, thus giving genetic variability among the different hybrids in the U.S., the cytoplasm of the American corn crop
is essentially uniform. A majority of America’s most valuable crop is now uniformly susceptible and exposed to
a pathogen capable of developing in epiphytotic proportions."
The solution to the problem was detasselling. In fact, Pataky says, it is because of SCLB that decades worth of teens have been employed with the hot job of pulling tassels.
In 1970, seed companies avoided detasselling through the use of malesterile inbred parents. Although there are several sources of cytoplasmic male sterility, the T source became popular because it didn’t break down in hot weather.
Terry Williams had just taken his first job that summer as a Pioneer Hi-Bred research scientist. "We called the disease ‘Race T blight,’" Williams recalls. "About 80% of the seed in the U.S. was being grown that way.
"Pioneer had a brand new hybrid (3369A) that hadn’t been put in T cytoplasm. That summer, I gave my dad enough to plant 15 acres of it on the home farm near Vincennes, Ind. It so stood out on the landscape that farmers drove from all over to see that field and find out what he did different," he says.
Williams says SCLB lesions started on the leaves, attacked the husk and would ultimately impact the grain. "Fields with poor drainage that lacked air circulation or in river bottoms were particularly susceptible," he recalls. "Yields of 10 bu. to 15 bu. per acre weren’t unusual in those fields."
The industry emerged in 1971 with enough resistant and partially resistant seed within its inventories to plant about one-half of a crop. Williams recalls that some farmers were forced to plant F2 seed or bin-run seed. That year, new resistant hybrids went to farmers’ fields without the lengthy testing that customarily occurs before commercialization.
"Prior to this blight, seed corn sold for $20 per bag and industry profit margins were thin," Williams notes. Added costs came with the need to detassel. There was more winter production. On the flip side, the disease brought new meaning to the science of plant pathology and caused seed banks to be organized.
Hooker noticed SCLB symptoms in the fall of 1969, but seed corn was already in the bin. Still, the Illinois scientists made history by not waiting until the disease reached catastrophic levels before starting research. Their swift actions reduced lag time to find a solution in about a year. By the 1972 planting season, SCLB caused by Race T was a thing of the past.
"SCLB caused the seed and agricultural industry to understand that without diversity, we are vulnerable," Pataky notes.