Evaluation of Culture Filtrates of Endophytic Microorganisms from Tomato against Ralstonia solanacearum

A novel approach to biological control using endophytes has gained immense potential in disease management. The endophytes constitute a valuable source of secondary metabolites such as alkaloids, terpenoids, sterols and phenolic compounds which play a major role in plant defense mechanisms. Therefore an experiment was carried out to study the effect of secondary metabolites of endophytes from tomatoes against the bacterial wilt pathogen Ralstonia solanacearum both in vitro and in vivo conditions using their culture filtrates. In vitro evaluation of the culture filtrates of the endophytes was carried out by inoculating the pathogen on a five per cent culture filtrate amended Potato Dextrose Agar medium. Complete inhibition of the pathogen was observed in all endophytes indicating the inhibitory effect of their culture filtrates. In order to study the effect of secondary metabolites of endophytes on R. solanacearum under in planta conditions, culture filtrates along with culture suspensions for comparison were used. The tomato seedlings dipped first in culture filtrate/suspension then in bacterial ooze showed lowest wilt incidence and among the two, seedling dip in filtrate was the effective one. The minimum wilt incidence was noticed with seedlings dipped first in culture filtrate of endophyte Trichoderma viride-2 recording 10.92, 15.68 and 19.84 per cent followed by T. harzianum-1 and Bacillus subtilis, which showed 12.5, 16.67 and 22.22 per cent at 7, 10 and 14 days after inoculation respectively. Thus the above findings clearly indicated the inhibitory effect of secondary metabolites of the endophytes on bacterial wilt pathogen.