Isolation and Characterization of Rhizobacteria Antagonistic to Macrophomina phaseolina (Tassi) Goid., Causal Agent of Alfalfa Damping-Off

Alfalfa (Medicago sativa L.) is affected by several pathogens; however, those that attack crown and roots, such as Macrophomina phaseolina , directly define the longevity or productive period of the plant. Use of microorganisms with biological control capacity constitutes an alternative to chemical products. In this chapter, we have gathered some studies on this subject; in addition, we contribute data from our own researches on in vitro and in vivo antifungal activity of rhizobacteria isolated from alfalfa rhizosphere against the causal agent of damping-off, M. phaseolina. In vitro tests consisted in culturing a bacterium and the pathogen on Potato Dextrose Agar (PDA) medium. In vivo tests were carried out in pots containing soil infested with M. phaseolina sclerotia. Alfalfa seeds were inoculated with each selected isolate (single inoculation treatments) or co-inoculated with Sinorhizobium meliloti strain B399 (mixed inoculation treatment); also, non-inoculated seeds were sown in infested soil (control treatment). Experiments were conducted in a growth chamber for 30 days and the evaluated parameters were: germination percentage, damping-off at 5 and 8 days, number of surviving plants at 15 and 30 days, and number of nodules.