Symptoms of southern corn leaf blight and stalk rot (Bipolaris maydis, also known as Cochliobolus heterostrophus). Image Credit: Clemson University - USDA Cooperative Extension Slide Series, via Bugwood.org used under a Creative Commons Attribution-Noncommercial 3.0 License.

Cochliobolus heterostrophus strain Hm338 is a MAT1-2, Tox1+ (ATCC 48317) field isolate, collected in New York around the time of the SCLB epidemic. Like the reference strain C4, it is a race T, T-toxin producing strain. In 1970 race T of C. heterostrophus caused the worst epidemic in US agricultural history, destroying more than 15% of the maize crop. Subsequent research demonstrated that the epidemic was triggered by the unfortunate confluence of complex DNA recombination events in both the fungal pathogen and the plant host. Before 1970, C. heterostrophus was known as an endemic pathogen of minor economic importance, first described in 1925 by Drechsler; after the appearance of race T, this race was named “race O”. Note both fungal races are pathogenic to corn, but race T is highly and specifically virulent on Texas male sterile cytoplasm (Tcms) corn.

References:

• Drechsler, C. 1925. Leaf spot of maize caused by Ophiobolus heterostrophus, the ascigerous stage of a Helminthosporium exhibiting bipolar germination. J. Agric. Res. 31: 701-726.