Osmotic Potential Effects on In Vitro Growth, Morphology and Pathogenicity of Macrophomina phaseolina

The influence of osmotic potential (Ws) on in vitro growth and morphology of four isolates of Macrophomina phaseolina was studied using potato-glucose-agar adjusted to different osmotic potentials with KCl, NaCl and sucrose. The effect of NaCl on M. phaseolina pathogenicity in common bean was determined and then related to the pathogenicity of each isolate on seeds of 12 differential common bean cultivars. The three sources of Ws reduced M. phaseolina growth under in vitro conditions, whereby NaCl caused the highest negative effects. The high solute concentrations reduced the synthesis of mycelial pigments and the size and shape of microsclerotia. Pathogenicity of M. phaseolina in common bean seeds was reduced by high concentrations of NaCl but no relationship was found between the tolerance to high Ws concentrations under in vitro conditions and M. phaseolina pathogenicity in common bean seeds