Ph.D., Assistant Professor and Extension Plant Pathologist
This summer corn growers in west central and southwestern Minnesota noticed a high percentage of barren stalks and abnormal ear development in some fields. Corn growers and local seedsmen reported 30-40% barren stalks in some fields. We surveyed multiple locations for barren stalks in fields along a 50-mile path from Bunde to Madison. The fields surveyed were variety demonstration trials where hybrids from different companies could be compared side-by-side under similar field and environmental conditions. The highest percent of barren stalks observed in the survey was 17%; not as high as observed in some commercial fields in the same area. The occurrence of barren stalks was not limited to any particular company's hybrids.
Corn plants in some fields exhibited a specific set of symptoms that included reddish-purple colored leaves and stalks, barren stalks, nubbin ears, multiple ears per node (commonly 3-5 ears per node), and darkened vascular bundles running through several internodes of the affected corn stalks. The exact same set of symptoms has been attributed to a disease called Black Bundle Disease (McGee, 1988; Nyvall, 1999; and Shurtleff, 1980). The first report in the literature of black bundle disease was in 1924 (Reddy and Holbert, 1924). The researchers isolated a fungal pathogen, Cephalosporium acremonium (=Acremonium strictum), from the infected tissue and reported it as the causal agent of the black bundle disease of corn. Later work by Harris (1930) reported that he was unable to repeat the work of Reddy and Holbert, placing in question their conclusion that the symptoms were caused by C. acremonium.
We collected corn plants exhibiting multiple ears per stalk, barren stalks, and healthy plants during our survey of variety demonstration plots and from several commercial fields. Pith tissue from those plants was cultured on acidified-PDA agar to identify the organism in the affected vascular tissue. The isolated tissue produced mostly Fusarium species of stalk rotting fungus. Cephalosporium acremonium was not isolated from any of the affected stalks; thus, the condition described above was most probably not due to black bundle disease as described by Reddy and Holbert (1924).
Reddish-purple plant leaves and stalks
Figure 1. Reddish-purple discoloration of upper leaves, sheaths, and stalks of corn plants.
This condition is not uncommon in many different hybrids. Complexed sugars in the leaves and stalks of barren plants are not transported out of the tissues to the developing ear because there is no ear. As a result, when the chlorophyll in the leaves and stalks break down during senescence, the sugars remaining in the tissue express a reddish-purple color. This is similar to what occurs in tree leaves in the fall.
Barren stalks and small nubbin ears
Pollination time in much of the state this past summer was characterized by limited precipitation and by high ambient temperatures, ranging in the high 90's. It was not uncommon for poor pollination to occur, resulting in some barren stalks and nubbin ears in most, if not all corn hybrids.
Multiple ears per node on a stalk
Figure 2. Corn plants with multiple ears at a single node. Each ear contained few or no kernels.
Although this condition may be more rare (we observed it on a few hybrids), it may be partially explained by the genetics of the corn plant. According to a USDA corn breeder at the University of Illinois (M. Sachs, personal communication), some corn lines may develop a second ear if the first ear does not adequately set seed during pollination. To further extrapolate on this phenomenon, a third, fourth, and fifth ear could develop on the same node, as each preceding ear did not set adequate seed.
Darkened vascular bundles in the pith of the stalk
Figure 3. Discoloration of vascular tissue in the internode regions of the corn stalk pith.
Because different Fusarium fungi, common stalk rotting organisms, were isolated from the affected stalk tissue, the darkened bundles were possibly caused by the Fusarium infection. The root systems of some corn hybrids were compromised this year by wet soil conditions early in the growing season: root growth was probably restricted in the saturated soil. One or more high wind events later in the season caused the affected plants to lodge. This year, lodging was quite common in several corn hybrids. If you have been harvesting corn in the western portion of the state it is quite possible that you have noticed areas of lodged corn. Root tissue of wind-lodged corn is often torn open. Torn root tissue makes an excellent entry portal for soil-borne stalk rotting organisms. The fungi would then enter the plant and grow into the crown and internodal regions. Thus, the brown or black colored vascular bundles in the affected plants were probably caused by the stalk rotting fungus.
In conclusion, the above mentioned conditions, or symptoms, observed in corn this season were not the result of the disease called Black Bundle since the causal organism responsible was not found. Rather, the set of symptoms observed in corn were probably due to an interaction of corn genotype with a specific set of adverse environmental conditions. The chances that the same set of specific conditions occurring in the future are minimal. Regardless of the exact cause of the symptoms the end result was barren stalks in corn.
- Harris, M.R. 1936. The relationship of Cephalosporium acremonium to the black bundle disease of corn. Phytopathology 26:965-980.
- McGee, D. C. 1988. Maize diseases, a reference source for seed technologists. The American Phytopathological Society: St Paul, MN. 150 pp.
- Nyvall, R. F. 1999. Field crop diseases. third edition. Iowa State University Press. Ames, IA. 1021 pp.
- Reddy, C. S. and J.R. Holbert. 1924. The black-bundle disease of corn. Journal of Agricultural Research 27:177-205.
- Shurtleff, M. C. (ed.). 1980. Compendium of corn diseases, second edition. The American Phytopathological Society: St Paul, MN. 105 pp.