The necrotrophic soil-borne fungus Macrophomina phaseolina (Tassi) Goid (M. phaseolina) causes the disease charcoal rot in a wide range of plant species worldwide. Many of these species are agronomically important. Attempts to control the disease have been met with little success. Expression of auxin-regulating GH3 genes have been shown to be up-regulated in Medicago plants upon infection with M. phaseolina. Other studies have shown that GH3 knockout mutants have increased resistance to necrotrophic fungal pathogens such as Botrytis cinerea. Based on our previous research, we hypothesized that mutations in GH3 genes in the plant host Arabidopsis thaliana (A. thaliana) would decrease the aggressiveness of M. phaseolina. The research presented here investigates this interaction in an attempt to elucidate the importance of GH3 genes in the disease response pathway. To assess this, available insertion mutants for seven group II GH3 genes of A. thaliana were included in this study. Since GH3 is a multi-gene family and some genes may have functional redundancy, double mutants for two pairs of closely related genes were generated. Homozygous mutants for four of the seven insertion lines were established. Despite being prevalent in other research, homozygosity was unattainable for three of the mutant lines (gh3.2, gh3.4, and gh3.6). The gh3.6 line was found to have an inverted tandem repeat of the T-DNA insert. Although obvious phenotypic differences were present for all the lines, three of the four homozygous lines produced their respective mRNA based on RT-PCR; therefore, they are most likely not a knockout of their perspective gene. The disease phenotypes of these mutant lines were compared to that of the wild type. With three repeats of inoculation, it was concluded that these lines showed no increased resistance to M. phaseolina. Given the data presented here, it is likely GH3 genes play no major role in the pathogenicity of M. phaseolina on the model plant A. thaliana.