Complex seed environment

Most corn seed planted in the USA has a seed treatment that includes at least one fungicide intended to reduce damage from Pythium.  But effectiveness is complicated by differences among Pythium species and environments.  A very recent publication in Plant Disease (http://dx.doi.org/10.1094/PDIS-04-15-0487-RE) indicated that 3 of the 4 species isolated from Iowa fields in 2014 were favored by lower temperatures (55-62°F) but one species favored a little warmer temperature of 73°F.  Although the fungicides were generally effective there were situations in which the pathogen still effectively infected the seed or seedling root.
 
It has to be complicated down there. There are the dynamics of the biology of a germinating seed, with some less vigorous than others, soils with varying water holding capacities and organic matter, and competing microorganisms.  The latter generally produce chemicals to ward off others as well.  Cell contents are leaked into the environment surrounding the seed as the seed swells and begins germination, attracting not only the zoospores of Pythium species but also numerous fungi.  The plant responds to invaders by producing phenols that can stop or slow down further invasion.  The fact that the germinating seed environment has many complicated interactions makes any attempt to give exact characterizations is difficult and contradictions to conclusions are often seen.
 
With favorable temperatures, moisture and oxygen levels, we know high quality corn seed generally overcome the potential problems with fast root and shoot growth.  We also know that every seed can be slightly different in cell membrane status because factors that includes genetics, maturity, drying, handling, and storage conditions.  Field conditions vary in soil type, temperatures and moisture levels. Pathogen intensity and seed treatment effectiveness may vary with all of the above conditions.  It is a wonder that we actually usually get 90+% stands in the fields.  It is to the credit to everyone from the corn breeder, seed producer, seed quality workers, public and private researchers and the grower that this happens.