By Charmain Tan Courcelle

MISSISSIPPI STATE -- Mississippi Agricultural and Forestry Experiment Station researchers are determining whether fungi are responsible for some of the seedling diseases and low grain yields seen in Mississippi.

Larry Trevathan, MAFES plant pathologist, is identifying fungal species common to corn production systems in Mississippi and looking for a link between fungal occurrence in the roots of this crop and subsequent seedling disease.

Plant-infecting fungi are found commonly in agricultural soil where they use crop residue as a source of nutrition during the winter and between crops. These fungi can also be found in untreated seed. While fungicides have been somewhat effective as control agents, their success depends on timely and accurate diagnosis of a fungal disease -- a task made difficult by the similarity of symptoms for different diseases.

"We initially wanted to identify fungal pathogens that are most active under the corn production systems found in the state," Trevathan said. "A second goal was to find fungal species that might be useful in the future as agents of biological control."

One challenge facing researchers is that fungus-infected plants do not always show outward signs of disease.

"In most cases, you find visually discernible symptoms of a fungal infection," Trevathan said. "But sometimes you don't see symptoms at all, and you're left with the question, 'is this variety growing and producing yields to its full potential or is it infected with a fungal species that is not causing symptoms but is affecting plant productivity?'"

In a three-year study, Trevathan looked at the effect of tillage systems (no-till and conventional), soil types (silty clay and silt loam soils) and planting date on the population and variety of fungal species found in corn. He also collected corn seedlings at three, 10, 17 and 28 days after planting to determine which fungal species are important disease agents at different times in the seedling stage of the plant life cycle and the effect infecting fungi have on subsequent grain yield.

"We found Fusarium species consistently in Mississippi soils and most frequently in silty clay. This is important because members of the Fusarium genus are some of the most serious seedling disease pathogens in the state," Trevathan said. "Trichoderma species were another well-represented class of fungi."

Results from this study showed a correlation between the incidence of fungal root infection and seedling disease severity. Trevathan also saw the highest incidence of seedling disease in tilled plots planted on the latest corn-planting date in silty clay soil.

He did not find a connection between root infection and yield or between disease severity and yield. Instead, corn grain yields appeared to be most affected by the tillage system used. No-till systems produced consistently higher grain yields on the silty clay and silt loam soils.

The researcher said his most significant finding, however, was the presence of fungi that have both disease-causing and nonpathogenic members in his samples.

"That means there's the potential to characterize both fungal pathogens and control agents out of the same population," he said.

Some species of fungi could be used to competitively exclude or displace disease-causing members from crops, Trevathan said. They could also "prime" a plant's antifungal defenses.

For the next phase of his studies, Trevathan will determine whether the presence of seedling disease fungal pathogens influences the development of stalk rot, a disease of mature corn that reduces yields and can result in plant death. He said work in other states suggests some fungal species that cause seedling disease have roles in stalk rot, but such a connection has not been investigated in Mississippi corn production systems.

Another question that Trevathan would like to answer is related to the role of environmental stress on plant pathogen infection. Moisture is the No. 1 limiting factor to corn production in Mississippi. One management strategy that has been adopted to address this problem is early planting, he said.

"But if you plant early, there is more stress on the plant from the cool to cold, moist to wet soil conditions. We want to know whether this stress provides an advantage to plant pathogens that would be removed if planting is accomplished at a later date."

Trevathan said he believes the results from this and future studies will help producers develop improved pest management practices for fungi and give them confidence to make adjustments in production practices.

Contact: Dr. Larry Trevathan, (662) 325-2588