Macrophomina phaseolina

Macrophomina phaseolina is a Botryosphaeriaceae plant pathogen fungus that causes damping off, seedling blight, collar rot, stem rot, charcoal rot, basal stem rot, and root rot on many plant species. Culture of Macrophomina phaseolina on a PDA plate. Source: Photchana Trakunsukharat, Department of Agriculture, Thailand. One of the most harmful seed and soil borne pathogens, Macrophomina phaseolina is a fungus that infects nearly 500 plant species in more than 100 families. The hosts include: peanut, cabbage, pepper, chickpea, soybean, sunflower, sweet potato, alfalfa, sesame, potato, sorghum, wheat, and corn, among others. The identification of isolates of M. phaseolina is usually based on morphology and efforts to divide the pathogen into subspecies, but because there are wide intraspecific variations in the phenotype of the isolates, these criteria are often not reliable. The failure to correctly detect and identify M. phaseolina using conventional culture-based morphological techniques has led scientists to develop nucleic acid-based molecular approaches, such as highly sensitive and specific polymerase chain reaction-based methods. Researchers have also recently created species-specific oligonucleotide primers and digoxigenin-labeled probes in hopes of better identifying and detecting M. phaseolina. The pathogen M. phaseolina affects the fibrovascular system of the roots and basal internodes of its host, impeding the transport of water and nutrients to the upper parts of the plant. As a result, progressive wilting, premature dying, loss of vigor, and reduced yield are characteristic symptoms of M. phaseolina infection. The fungus also causes many diseases like damping off, seedling blight, collar rot, stem rot, charcoal rot, basal stem rot, and root rot. Although brown lesions may form on the hypocotyls or emerging seedlings, many symptoms occur during or after flowering, including grey discoloration of the stem and taproots, shredding of plant tissue in the stem and top of the taproot, and hollowing of the stem. Small black dots may form beneath the epidermis of the lower stem and in the taproot, giving the stems and roots a charcoal-sprinkled appearance. When the epidermis is removed, small and black microsclerotia (a sign of the disease) may be so numerous that they give a greyish-black tint to the plant tissue. In addition, reddish-brown discoloration and black streaks can form in the pith and vascular tissues of the root and stem. Pycnidia and sclerotia of Macrophomina phaseolina on mung bean. Source: Photchana Trakunsukharat, Department of Agriculture, Thailand. M. phaseolina has a monocyclic disease cycle.