Single cross corn hybrids are made by crossing two homozygous inbreds, in theory, resulting in each plant of such a hybrid being genetically identical. A few mutations along the way and a few impurities occurring during seed increases and hybrid production are probable, but most of the 32000 genes in each plant of a single cross hybrid are identical to the adjacent plant.
Close observation during the season shows slight differences in growth among those plants. Not each one emerged from the soil at the same time. Perhaps this was due to planting depth, or soil consistency or differences in individual seed germination quality. Each plant may not reach exactly the same plant height due to differences in soil water or nutrient supply. Slight differences in silk growth and timing is especially obvious if the field had moisture stress. Most of these differences are easily observed during the growing season when comparing regions or pockets of the field and are associated with soil differences.
It becomes a little more confusing when one plant suddenly wilts while adjacent plants are still green. Seemingly same genetics in what would seem the same environment as the plants are a few inches away but one dead and one alive. The wilted plant gains a gray appearance, with all leaves, including the ear husks turned downwards. The change in the affected plant’s appearance occurs within a few days. A few days later the stalk outer color changes from green to yellow and then brown. Adjacent plants maintain green leaves and green stalk color. The dead plant’s inner stalk tissue becomes separated from the outer rind as the pith cells shrink from desiccation.
It is tempting to blame the problem on one of the fungi found in the deteriorating cell tissue. We can call it Fusarium, Gibberella, Diplodia or Anthracnose stalk rot but still why that plant and not the adjacent ones. These fungi are ubiquitous in a corn field with near uniform exposure to each plant. The plants are genetically the same with the same exposure to potential pathogens.
Dead plants, usually, have more kernels than adjacent plants. This is most obvious with the 2-earred plants near a plant gap on outside rows of a field but also can be clear when counting kernels of single eared plants. All plants were genetically alike but some had a slight environmental advantage resulting in additional number of kernels. If the later environment, or stress, did not allow sufficient fulfillment of the daily demand for movement of sugars to the developing kernels, the root cells of that plant died from starvation. When the roots could no longer transport enough water from the soil to meet the water loss via transpiration from the leaves, the continuous chain of water in xylem tissue was broken and the plant wilted. What was an advantage of a favorable environment for that individual plant becomes a disadvantage. It has a larger ‘sink’ for carbohydrates but if not sufficient photosynthesis to fill the sink, the resulting kernels will not be completely filled for the 50-60 days after pollination. Additionally, this weakened stalk will probably lodge. All plants of the single cross hybrid may have the same genetics but not exactly the same environment.
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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.