Antagonistic effect of fluorescent pseudomonads against Macrophomina phaseolina that causes charcoal rot of groundnut.

Maximum colony growth inhibition was observed due to Pseudomonas PS2 (74%) as compared to PS1 (71%) on trypticase soy agar (TSM) plates after 5 days of incubation. Light and scanning electron microscopic examination showed hyphal coiling, vacuolation, coagulation and granulation of cytoplasm resulting in lysis of hyphae of M. phaseolina by pseudomonads. Cell free culture filtrates of strains PS1 and PS2 restricted the growth of mycelium of M. phaseolina. PS1 and PS2 caused maximum colony growth inhibition by 57 and 61% respectively at 20% concentration of culture filtrate after 4 days of incubation. Volatile substances produced by PS1 and PS2 also inhibited the colony growth of M. phaseolina by 25 and 32%, respectively. Inhibitory effect of volatile substances, however, decreased with advancing in incubation period. Colony growth of M. phaseolina was significantly decreased by PS1 and PS2 as compared to control both in iron- sufficient and iron-deficient conditions. PS2 showed higher antagonistic activity than PS1, as evidenced by pronounced colony growth inhibition.