Corn plants are most vulnerable to premature wilting during the period of 40 to 60 days after flowering. This sudden change in the plant appearance is due to depravation of sugar to roots because of competition with grain in plants with insufficient photosynthate to meet metabolic needs of the roots and the translocation pull to the grain. Each factor is a complex genetically involving physiology of photosynthesis, morphology and disease resistance of leaves, root structure, rate of translocation of sugars to each kernel and number of kernels. Environmental influences such as plant spacing, moisture influencing kernel numbers, daily light intensity and pest and disease pressure.
Wilting, commonly known as premature death, occurs scattered within a corn field as majority of plants maintain normal green and turgid leaves as they continue to move sugars to the kernels while maintaining enough root tissue functions for water absorption and movement to the leaves. The wilted plants show the outside appearance of gray leaves and ears turning downwards. Wilting causes major internal changes in the corn plant. Physical strength of the stalk is reduced by 1/3rd as the pith tissue is withdrawn from the outer rind tissue, essentially changing the strength of a solid rod to that of a tube. This is even before fungi begin to digest the cell walls of the stalk. Most cell metabolism is halted within a few days because of dependency on water. This includes translocation of sugars to the kernels, resulting in light kernel weight, compared to kernels on plants that continue to function for the usual 60 days after pollination. Kernels of affected plants form an abscission layer (black layer) within a few days after plant wilting although kernels on most non-wilted plants delay the abscission layer formation until normal grain fill is finished.
Individual plants with wilting symptoms have lighter kernels than most plants in the field because of this shortened grain filling period. If these plants did not have unusual environmental stress such as leaf disease or insects causing upper stalk breakage, they probably had more kernels than the adjacent, green plants. A study published in 1980 (Phytopathology 70:534-535) showed that wilted plants with no obvious leaf damage had 10% more kernels than adjacent non-wilted plants. The individual plants may have nearly identical total grain weight, depending upon the timing of plant wilt in relation to normal grain-filling period. A few wilted plants within a field can indicate that near maximum yield was obtained for that hybrid in that season’s environment. However, the ensuing effect on lodging detracts from that optimistic view and is the subject of the next Corn Journal issue.
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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.