Three Macrophomina phaseolina isolates from bean, cotton, and peanut (MP7, MP9, and MP14) were used to inocilate four, cotton cultivars (Stoneville 825, CABCS-1-81, LE(2)BOS-1-81 and Tamcot CAMD-E) to identitify their pathogenicity. All four cotton cultivars were infected by the M. phaseolina from peanut (MP14) was more pathogenic on the four cotton cultivars. Infected cotton seedlings were shorter than healthy ones Mechanical wounding was not necessary for infection to occur. Tamcot was not necessary for infection to occur. Tamcot CAMD-E and CABCS-1-81 were more susceptible to isolate MP14 and Stoneville 825 was more resistant than the other three cultivars in the seedling stage. Differential responses of cultivars and M. phaseolina isolates occurred.

Dead cotton plants, with unshed leaves, were found in a field west of Buckholts, Texas. The roots appearance to be normal without any external damage or lesions. The stele portion of the tap root and the pith in the lower portion of the main stem and root were discolored. The color varied from rust brown to black. Sclerotia of M. phaseolina were found in the pith and the organism was isolated from the stele.