Dynamics of this disease serves as a reminder of the complexity of host resistance, environment and pathogen biology are common with agricultural crops. Although the disease had been identified before 1970 it was not regarded as damaging to the corn. Host and environments in USA changed in the 1970’s. Conservation tillage allowed more corn leaf and stalk debris left on the soil surface and wide use of the inbred B73 as a female parent changed in favor of the fungus (Colletotrichum graminicola). It had difficulty surviving when buried in soil but has special sporulation advantages over other organisms with survival of winter stresses when on surface of soil. This allowed for early infection of seedling leaves. Infected leaf debris continues to produce spores during the season. Although most corn genotypes are somewhat resistant to older leaf infection, presence of this fungus and its spores allowed for eventual infection of the stalk rind cells. A few hybrids are susceptible enough to be actively killed by infection in the root and stalk but this fungus is mostly an aggressive invader of senescing cells in the mature plant.
The B73 connection was linked to its contribution of high yields in hybrids. Some of that high yield component was tendency to produce large deposits of carbohydrates in the grain, sometimes at the sacrifice of adequate reserves for maintenance of living cells in the stalk and root tissues. Colletotrichum graminicolais favored in the environment of senescing cells, often speeding to the death of these tissues.
Reducing the infected corn debris by deep tillage or crop rotation can greatly reduce the disease but reducing the environmental stress is also important. Breeders affected this reduction by selecting hybrids with less grain fill per plant and, perhaps, more net photosynthesis per plant. This effectively lengthened the time of vigorous cells in corn stalks with ability to hold off this fungus until harvest. Anthracnose remains present in USA corn fields but damage is less now than 30 years ago.
Like much in agriculture, corn disease development is the result of a complexity of factors. It is human nature to want simple explanations but each of the factors, like those mentioned in this brief blog have sub-factors. Fortunately, human and government problems are not complex so politician’s simple answers surely will solve all of them (L.O.L.).
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.