Theses and Dissertations

Issuing Body

Mississippi State University


Allen, Thomas Ward, Jr.

Committee Member

Brown-Johnson, Ashli

Committee Member

Golden, Bobby

Committee Member

Tomaso-Peterson, Maria

Committee Member

Lu, Shien

Date of Degree


Original embargo terms

MSU Only Indefinitely

Document Type

Dissertation - Campus Access Only


Plant Pathology

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology


Charcoal rot of soybean is an important disease affecting soybean. Charcoal rot is caused by the ubiquitous soilborne fungus Macrophomina phaseolina (Tassi) Goid. The fungus infects over 500 plant species. Although charcoal rot occurs primarily under drought-like conditions, it has also been reported in high-yield irrigated soybean environments. Symptoms of charcoal rot on soybean include wilting, stunting, and premature death. Management options to reduce charcoal rot-associated losses are limited. The objective of this research was to reduce M. phaseolina colonization of soybean by supplementing with secondary nutrients, specifically calcium and magnesium; therefore, reducing the concentration of the associated toxin, and determine if isolates of M. phaseolina from non-soybean hosts are pathogenic on soybean and rotational hosts. Between 2014 and 2016, non-irrigated, M. phaseolina-inoculated field and field replicate greenhouse experiments evaluated applications of 1,120 kg/ha of Ca and Mg alone and in combination at pre-plant, at-plant, and pre-plant followed by at-plant compared with an inoculated and non-inoculated. Disease ratings were visually assessed from roots collected at R3, R5, R7, and R8. Colony forming units (CFU) were used to quantify fungal colonization in root tissue. Gas chromatography mass spectrometry was used to quantify the concentration of botryodiplodin, a toxin previously associated with charcoal rot from root tissue. An application of calcium applied pre-plant provided the greatest numerical reduction, 39.7%, in toxin concentration and also reduced disease severity by 1.0% and CFUs by 15.4% when compared to the inoculated control in a moderately resistant cultivar. Although numerical benefits were observed, these data do not support applications of Ca and Mg as a charcoal rot management option. Numerical differences were observed between rotational hosts and isolates in pathogenicity studies. The greatest numerical reduction of 34% in soybean dry plant weight was observed with the corn isolate when compared to the non-inoculated control. Macrophomina isolates from corn had up to an 8% greater colonization in soybean than corn or cotton plants. Although no significance was observed between isolates with regard to dry plant weight and colonization, colonization occurred regardless of treatment; suggesting crop rotation should not be a stand-alone charcoal rot management option.



charcoal rot||macrophomina phaseolina