Cornfield battle ground

​Potential leaf pathogens of corn, feeding on bits of corn leaves or other grasses survive on ability to kill some plant tissue, dominate the dead tissue, produce large quantities of spores and spread to more live plant tissue.  The quantities of spores spread over large areas make analyses of their genetic diversity difficult because nearly any sampling system is insufficient.
 
Corn breeders can use methods to screen their new inbreds and hybrids for resistance to known variants of pathogens.  Resistance requires gene products that allow recognition of the pathogen invasion and quick response by production of pathogen-inhibiting substances by the adjacent plant cells.  Corn’s history, fueled by it cross-pollination biology and human’s transport to multiple environments has resulted in a large genetic diversity available to battle new pathogens. Problems arise with the unknown or unexpected pathogens.
 
Corn diversity also allowed selection of mitochondria with an unexpected fatal susceptibility to a race of Cochliobolus maydis, the accidental selection of the homozygous recessive gene allowing the damaging attack of race 1 of Cochliobolus carbonum.  The fungus Bipolaris turcicum did its genetic diversity part by including races of that avoided the corn Ht1, Ht2, Ht3 and HtN resistance mechanisms.
 
Multiple corn diseases have suddenly become significant in some corn growing area as the result of favoring pathogen genetics, susceptible corn defense genetics and environmental change favoring the pathogen.  With study and analysis, corn breeders have always been able to reach into corns genetic diversity to successfully limit the disease damage.
 
This battle in the cornfield will continue.