Factors leading to deterioration of corn stalks are complex, as discussed previously. In most cases the direct loss of strength comes from premature death of the plant in which it suddenly wilts before completion of grain fill. This is preceded with destruction of roots by soil fungi due to reduction of cellular resistance. This happens when the upper plant cannot adequately supply carbohydrates for maintenance of those root cells as sugars are also moved to the grain.
The wilting of plant results in withdrawal of the pith tissue from the rind, essentially changing the strength of the stalk from a rod to a tube. Stalk cell death also reduces the resistance to the fungi feeding on the cellulose and pectin of the rind, further weakening the stalk strength.
Fungicides could be affecting those stalk invading fungi but also could be reducing leaf pathogens during the grain fill period and therefore reducing loss of photosynthesis. This would potentially provide more carbohydrates to the roots and therefore avoiding the premature death and wilting that started the stalk strength weakening. It would be interesting to see that hypothesis tested.
Grain farmers are finding varying corn grain drying challenges in the wild, summer 2019 USA weather. Late plantings, varying wet conditions extending into the harvest time have made for confusing grain drying to avoid mold developments while stored. Moisture reduction in grain is due to evaporation as water must move through the pericarp basically as a physical phenomenon of water moving from higher to lower concentration. Warmer air absorbs more water than cooler air, and consequently prime field drying after black later is best with warm, dry winds. Open leaves surrounding the kernels on the ear, increases access to that warm dry air. Plants reaching black layer after the warmer days of late summer, are likely to have less field drying than normal seasons, and thus slower natural drying in the field.
Corn hybrid maturity classifications are often determined with some classification based upon moisture contents at time of harvest. 2019 data may not be a good year to make those classifications.
Seed breeding and production groups may have a more difficult time than most this year as well. Field variability probably was greater than normal due to excessive rain interacting with soil variability. Later planted test sites may have harvest moistures not typical for a given hybrid or predictive of performance in future seasons.
Drying seed is an art that includes manipulating air flow and temperatures in drying bins. It includes consideration of outside relative humidity. As moisture is withdrawn from the seed, cellular membranes, including those of mitochondria, are potentially damaged. Rehydration of seed for germination tests after drying can be the first indication of potential problems but often damage from does not become evident for some months later.
We all want to return to a normal season but what is that?
Among the contradictions in corn culture is the need to have corn stalks maintaining upright plants through harvest but rapid deterioration in soil between seasons and /or efficient decomposition for fermentation to recover the carbon in ethanol or energy for cattle. Primary strength during the growing season is derived from a combination of the tight connection of the pith cells to the outer rind cells, fibers and near the outer rind and thick cell walls of the outer rind cells.
Stalk components after harvest range among hybrids. About 50% of the solid weight is composed of carbon but most of it is involved in complex molecules such as cellulose, hemicellulose and lignin. Although lignin composition is only about 7% of the stalk, it is the most difficult to digest and often is wrapped around the more easily decomposed cellulose molecules.
Multiple fungal species in the soil produce enzymes capable of breaking and modifying the lignin molecules. Tree wood, mostly composed of lignin, is slowly destroyed by fungi specializing in production of lignocellulolytic enzymes. These initial wood rotting species are succeeded by other fungal species that enzymatically degrade the cellulose into its components. Genetic variation among fungi and competitive pressure for obtaining the energy locked up in corn stalks provides multiple sources to break down the complex carbon compounds that provided strength for the corn stalk previous to harvest.
Among the challenges for all interested in corn is to identify hybrids that produce stalks that remain upright through harvest but can be efficiently digested by cows, fermentation and soil organisms.
Published in Corn Journal 11/1/2018
The fungal genus Fusarium is a ubiquitous inhabitant of corn and other grasses. Several species of Fusarium are also associated with their sexual stage of the genus Gibberella. Fusarium is recognized microscopically by the shape of their asexually produced spores (conidia) that are produced in abundance and dispersed by wind currents. Distinction between Fusarium species requires specific lab methods but quick microscopic exam for the curved, multicellular, hyaline conidia leads to a quick analysis as Fusarium.
Fusarium species do not tend to be aggressive pathogens of vigorous, living corn tissue but almost more of an inhabitant, not actively killing cell tissue but more of a scavenger of dying or dead tissue. Some Fusarium species such as F. verticillioides (formerly named F. moniliforme not only produce multicell conidia but are known to produce single cell microconidia that apparently can move in the vascular system of a corn plant. Ease of movement within and outside of the corn plant and the ability to infect weakened and dead corn tissue allows for this fungus to be found in nearly all dead corn tissue. This can include leaf tissue injured by insects, hail or other physically injury. Active leaf pathogens such as Exserohilum turcicum (cause of northern leaf blight, apparently ward off Fusarium invasion via antibiotics.
Nearly every dead stalk will have a Fusarium species among its inhabitants. If the dead tissue includes the more easily identified symptoms of Gibberella zeae (the sexual stage of Fusarium graminearum) the diagnosis will be Gibberella stalk rot. If black streaks typical of the anthracnose that will be the announced cause. Diplodia maydis, now called Stenocarpella maydis, is distinguished by its symptoms as well. If none of these symptoms are evident, the ever-present Fusarium, is diagnosed as the cause of Fusarium stalk rot.
The actual cause of death of the stalk tissue is the complex interactions of photosynthesis and distribution of carbohydrates during grain fill of the corn plant. The fungi present are able to digest the dying and dead tissue. If none of the easily identified fungi associated with stalk rot are found, there is always Fusarium stalk rot. The ease of identifying a fungus in the tissue, implying the case of the early death of the plant, can lead to avoiding the diagnosis of why the plant died before completion of grain fil.
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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.