Charcoal rot, caused by Macrophomina phaseolina, is a soil-borne fungal disease that affects many crops, including corn. The fungus causes dry-weather wilt in plants by infecting the roots and stem, leading to wilting, stunted growth, and eventual plant death. The presence of microsclerotia in infected tissue is a characteristic of the disease.
Charcoal Rot disease management in Maize
The causal organism of Charcoal Rot disease
Charcoal rot is caused by the soil-borne fungus Macrophomina phaseolina. It has a wide host range, including corn, sunflower, and weeds. The pathogen survives in host residue and dry soil and can be spread through contaminated seeds and soil.
The disease cycle of Charcoal Rot disease
The fungus Macrophomina phaseolina, which causes charcoal rot, has a wide host range, including sorghum, pearl millet, finger millet, pulses, and many other crops. It survives in infected plant debris for over 16 years and primarily infects crops through soil-borne sclerotia. The fungus is a facultative parasite and can live both as a parasite and a saprobe on dead organic tissues. Overwintering as sclerotia in the soil allows it to infect host plants at susceptible stages through their roots and then move up to the stem.
Causes/conditions favorable for Charcoal Rot disease spread in the field
- Hot and dry conditions with temperatures above 85 ºF and low soil moisture favor the proliferation of charcoal rot caused by the fungus Macrophomina phaseolina.
- Cold weather periods followed by hot conditions can preserve infected corn residue, increasing the risk of spread. Drought conditions during corn senescence can cause stress on the crop and make it more susceptible to infection.
- Tillage practices can also increase the fungus populations in the soil if susceptible hosts are grown in successive years, as the fungus can persist in soil for up to three years.
- Insect damage and plant wounding can also make plants more susceptible to fungal infection by creating openings for the fungus to enter.
Symptoms of Charcoal Rot disease
- Charcoal rot first becomes noticeable in when corn tassel stage or later and is characterized by drying out of the plant’s upper leaves.
- Infected plants have shredded stalks and completely rotted pith, with only stringy vascular strands remaining.
- The fungus’s small, black, spherical sclerotia are found on and inside the vascular strands, giving the internal stalk tissue a grey coloring.
- The growth of the fungus disrupts the translocation of water and nutrients as the hyphae grow intercellularly through the xylem and into vascular tissue.
- These fungi can grow in the lower internode stalk as the plant matures, causing premature ripening and weakening of the stalk, leading to breakage, lodging, and yield loss.