More on new corn disease occurrences

The recent issue of Plant Disease http://apsjournals.apsnet.org/toc/pdis/100/4 includes studies of Goss’ wilt that illustrates how new distributions of corn diseases occurs. There are three studies published in that issue that do advance our knowledge of this disease but one, http://apsjournals.apsnet.org/doi/full/10.1094/PDIS-04-15-0486-RE , typifies the difficulty of detecting or predicting new problems.  Susceptible and resistant hybrids were planted in ground that had not been in corn during previous years.  There were three treatments: (1) plants inoculated after plant tissue was injured with a strain of the Goss bacteria that could be identified as distinct from the wild type, (2) Plants not inoculated but seedlings surrounded with dried leaf tissue infected with Goss from the previous year and (3) non-inoculated plants with no infected debris.
 
All of the wounded, inoculated plants on the susceptible hybrid showed typical symptoms by midseason. A few of the residue infected plants showed symptoms and even a few of the non-inoculated,  non-residue plants had symptoms.  That is consistent with my observations in our Goss inoculation field trials in which there would be a few plants near the inoculated plants that would show symptoms.  This disease is so closely linked to fields damaged by hail that I think we assumed that this was the only method of infection.  I hypothesized that insects may have carried the bacteria but another paper, http://apsjournals.apsnet.org/doi/full/10.1094/PDIS-08-15-0923-RE , by the same authors offers that infection could be occurring through open stomata or hydathodes near the margins of leaves.
 
This research supports the concept that a disease is not actually new by the time it is discovered. It arrives in a field through seed or wind or transitions from another grass to a corn variety previously unknown to be susceptible and slowly increases until it's noticed.  Good that we have many hybrid genetics available, that we have plant pathologists to try to figure out these dynamics and that we have people looking closely at our crop while it is growing.