Abstract

The virulence of the 25 geographical isolates of Macrophomina phaseolina significantly varied for their disease incidence. The isolate Mp8 collected from Kovilpatti was the most virulent with maximum (88.3%) incidence of charcoal rot while Mp27 from Sankarankoil was the least virulent with the minimum (38.3%) diseases incidence. The most virulent isolate showed significant faster growth (41.3 mm) on PDA even 24 hours after inoculation while the least virulent isolate exhibited slowest growth (19.7 mm). Thus the virulence of the isolates was directly correlated with the initial growth rate of the isolates.

Keywords: Macrophmoina phaseolina, Virulence, Sunflower