Stalk rot resistance genetics

Corn stalk rot involves nearly all biology of the corn plant. Consequently, the genetics of resistance is complex.  The common fungi associated with stalk rot such as Gibberella zeae, Fusarium verticilloides and Diplodia zeae are often identified as the main fungi associated with destruction of stalk tissue because of their obvious symptoms but no specific genetic resistance to these fungi has been identified.  Anthracnose stalk rot, caused by Colletotrichum graminicola, is associated with a few specific resistance genes that can be identified but this has minimal effect on the overall occurrence of the corn stalk rot.
 
Resistance to premature deterioration of the corn stalk involves nearly all aspects of the plant, at least post-flowering.  Identity of the fungi most obvious in the dying stalk tissue is mostly irrelevant. Genetics of resistance involves those affecting root growth and function in that season’s environment.  This could involve resistance to feeding damage from soil insects, nematodes and pathogens.  Genes affecting the structures for water translocation to the stem or the metabolic efficiency of the living root cells influence the plant’s ability to function when under stress.
 
Photosynthesis rates during the season are affected by genetics of leaf shape and size. Leaf disease resistance is affected by both the general physiology and genes specific to each potential pathogen.  Translocation of sugars to the roots and to the grain after pollination involves many physiological and structural aspects of the corn plant, each influenced by different gene interactions.
 
Movement of sugars to the grain is influenced by the number of ovules pollinated.  Genes for establishing that number are multiple.  Rate of movement to each kernel is affected by genetics not only within the embryo but also those affecting the vascular structures to carry the sugars.  Multiple genes must be involved in the timely extension of the silks allowing successful pollination and fertilization of the ovule.
 
Successful maintenance of living pith cells in corn stalks until completion of translocation of sugars to kernels involves multiple genes affecting most parts of the corn plant in its environment.  It is unlikely that a single gene for stalk rot resistance combined with acceptable grain yield will ever be identified.  We will continue to realize that stalk rot resistance involves multiple genes influencing most of the corn plant’s biology just as does grain yield.