Effect of solid culture media and cultural or morphological variability among different isolates of Macrophomina phaseolina stem and root rot of sesame (Sesamum indicum)

Five isolates of Macrophomina phaseolina (Tassi) Goid. namely, AUMP-1, AUMP-2, AUMP-3, AUMP-4 and AUMP-5 were isolated and identified morphologically. Variability among these isolates of M. phaseolina was determined using growth parameters and sclerotial body formation criteria. Based on the virulence study on the susceptible host (VRI-1) it was identified that AUMP-1 was the most virulent with (53.60% of disease severity) and AUMP- 2 was the least. Optimum growth of the M. phaseolina was observed at 30 °C temperature and observed maximum mycelial growth (90.00 mm) under in vitro conditions. Cultural and morphological studies revealed that the mycelium of M. phaseolina initially appeared as dirty white then turned to fluffy white to black with minute dark black sclerotia on the PDA medium. The hyphal branches were at dense and feathery angles with constriction of hyphal branches at their point of origin with the closed septum. The microsclerotia were dark black in colour and varied in size from 70.27 to 99.00 μm. The highest radial growth and excellent sclerotial formation were obtained on PDA media (90.00 mm) and proved best for growth followed by Richard’s Agar media (83.63 mm) for growth of M. phaseolina.