Macrophomina phaseolina, an internationally distributed fungus, causes a disease known as "charcoal rot" (also known as dry-weather wilt and summer wilt) which clogs vascular tissue and produces yellow, wilted plants with visible fungal sclerotia. Primarily acting in dry, hot conditions it inflicts massive economic losses in Midwestern crops such as soybean, alfalfa, sorghum and cotton. In the southern 16 states was ranked the 2nd most damaging disease from 1990-1994 and caused an estimated 4.7 X105 metric tons of soybean loss from 1999-2002. By subjecting the model legume Medicago truncatula to a series of ecotype and mutant screens, it is hoped that altered susceptibility (AS- either unusual susceptibility or resistance), may be found. Once encountered, further analysis should reveal altered molecular pathways in the host-fungus interaction which are key to understanding resistance.