Diversity Benefits

Corn’s history of genetic diversity has saved us from crop disaster from disease many times.  Although there have a few years of damage as a ‘new’ disease appears, the diversity available among corn breeding stock has always come to the rescue.  It is ironic that nearly all cases, the problem initially arises because of uniformity of the crop, for a few years combined with environments favorable to the disease.  Once recognized and main factors understood, seed suppliers select resistant genotypes, and that disease is reduced in significance.
 
Southern Corn Leaf Blight, caused by Bipolaris maydis race T, was the most significant in USA and elsewhere in 1969-70.  Genetic mutants of cellular mitochondria (the site of energy transformation in each cell) which allowed for cost-efficient seed production was not expected to be susceptible to a toxin produced by a strain of a fungus that was normally controlled by chromosomal genetics of corn.  Once recognized, however, the seed industry was able to switch to the resistant cytoplasm. It was very unusual that most of the industry was using the same source of genetic vulnerability, of course, but it was also relatively easy for everyone to switch within 2 years.
 
Most often the outbreaks have been much more limited to only a few genetic sources and the diversity already in corn breeding programs allows for adjustments once the source of susceptibility is understood.  With each the solution has come through good diagnosis by public and private plant pathologists, analysis of sources of susceptibility and recognition of sources of reasonable levels of resistance from current supplies of corn genetics. Not each experience has been exactly identical but in near future blogs I intend to review several of these ‘new’ diseases.
 
One of the good aspects of the southern corn leaf blight was it convinced corn seed companies that they should hire plant pathologists at the time I was looking for a job.  So, in 1972, I got lost in the corn field and have yet to find a way out.