Chlorate reaction in different isolates of Macrophomina phaseolina and its relationship with pathogenicity

Eleven isolates of Macrophomina phaseolina, isolated from various hosts (soybean, sunflower, cantaloupe, muskmelon, wheat) in different provinces were assayed for reaction to potassium chlorate on nutrient medium. The isolates were grown on minimal medium amended with 120 mM potassium chlorate. The results showed that isolates were separated into two groups of which 54.5 % were chlorate-resistant and showed dense phenotype. The results of pathogenicity tests on soybean plants in green house showed that there was positive correlation between soybean root rot and reaction to potassium chlorate. The M-21 and M-30 isolates with chlorate-resistant reaction and dense phenotype were recognized as the most virulent isolates.