Southern corn leaf blight (SCLB) is a fungal disease of maize caused by the plant pathogen Bipolaris maydis (also known as Cochliobolus heterostrophus in its teleomorph state).
[1] Corn plants with T-cms cytoplasm have maternally inherited the gene T-urf 13, which encodes for a protein component of the inner mitochondrial membrane.
[4] In a similar manner, Race C is only pathogenic to hosts with cytoplasm male-sterile C.[3] Bipolaris maydis can also infect sorghum and teosinte.
Later on, lesions have red to dark brown borders and can spread to all other above-ground parts of the plant including the stem, sheath, and ear.
SCLB affected kernels will be covered in a felty, black mold, which may cause cob rot.
SCLB lesions are more parallel sided, lighter, and smaller in comparison to NCLB [9] The disease cycle of Cocholiobolus heterostrophus involves the release of either asexual conidia or sexual ascospores to infect corn plants.
Once conidia have landed on the leaf or sheath of a healthy plant, Bipolaris maydis will germinate on the tissue by way of polar germ tubes.
[1] The term 'favorable conditions' implies that water is present on the leaf surface and temperature of the environment is between 60 and 80 degrees Fahrenheit.
[10] The fungus overwinters in the corn debris as mycelium and spores, waiting once again for these favorable spring conditions.
An environment with warm temperatures (68 to 90 degrees Fahrenheit) and a high humidity level is particularly conducive to SCLB.
[3] Farming practices and optimal environmental conditions for the propagation of B. maydis in the United States led to an epidemic in 1970.
In the early 1960s, seed corn companies began to use male sterile cytoplasm so that they could eliminate the previous need for hand detasseling to save both money and time.
[15] This seed was eventually bred into hybrid crops until there was an estimated 90% prevalence of Texas male sterile cytoplasm (Tcms) maize, vulnerable to the newly generated Race T. The disease, which first appeared in the United States in 1968, reached epidemic status in 1970 and destroyed about 15% of the corn belt's crop production that year.
This was due to the return usage of normal cytoplasm corn, not as conducive weather, residues being buried, and planting early.
[10] The SCLB epidemic highlighted the issue of genetic uniformity in monoculture crops, which allows for a greater likelihood of new pathogen races and host vulnerability.
[1] In the present day, there are many management methods and better education practices but the disease can still be an issue in tropical climates, causing devastating yield losses up to 70%.