Isolation of antagonistic bacteria of Mycosphaerella fijiensis Morelet and growth promoters in banana (Musa AAA)

Abstract

The Black Sigatoka Disease (BSD) is caused by the ascomycete Mycosphaerella fjiensis Morelet, a highly virulent pathogen in triploid banana plantations (Musa AAA). Management of the BSD is mainly achieved by weekly-aerial sprayings of chemical fungicides that provoke environmental pollution and potential hazardous effects on human health. There are reports about of the potential of plant-associated microorganisms (leaf, fruit, stem and root-associated) as candidate biocontrol agents of phytopathogens and as biofertilizers. In this work we isolate banana phyllosphere and rhizosphere-associated bacterial strains in salt broth M9 + colloidal chitin, to test their ability to produce indol- acetic acid (IAA) and to evaluate the antifungal activities of the bacterial chitinolytic culture supernatants on M. fijiensis ascospore germination. Three chitinolytic bacterial strains were isolated, one phyllosphere-associated (Res F) and two rhizospheric (Res R-01, Res R-02) strains. The chitinolytic culture supernatants of the three isolates failed to inhibit ascospore germination but showed a germ tube inhibition of 75.7%, 76.8% and 61.5%, respectively, as compared to untreated M. fijiensis ascospores. Only strain Res F produced IAA from L-tryptophan. The three chitinolytic bacterial strains isolated from banana phyllosphere and rhizosphere have the potential as biocontrol agents, as function of their in vitro antifungal activities against M. fijiensis. Moreover, due to its ability to synthesize IAA, strain Res F is also a candidate as plant growth promoter in banana plants.