Induced systemic resistance could explain the reduction in the incidence of black sigatoka (Mycosphaerella fijiensis) in banana plants inoculated with bacteria isolated from banana tree roots in the Dominican Republic

Abstract

Black sigatoka caused by Mycosphaerella fijiensis (Morelet) is one of the main diseases affecting banana trees worldwide, resulting in a reduced fruit yield. Banana is a major export crop in many tropical and subtropical countries, and many farmers have decided to shift to an organic production system for produce that is destined for the international market. Induced systemic resistance (ISR) protects plants against disease-causing pathogens, and this mechanism can be triggered by some bacteria associated with plant roots. The inoculation of plant roots with bacteria able to induce systemic resistance in plants has been proposed for disease control in organic agriculture as an alternative to chemicals. Fifty-six nonpathogenic and endophytic strains isolated from roots of banana trees cv. Cavendish in organic systems from four regions of the Dominican Republic were the starting point for the present work. We used 26 of them to inoculate the root systems of banana plants, the leaves of which were inoculated with M. fijiensis inoculum, in order to analyse their effect on the control of black sigatoka under growth chamber conditions. The selection of the 26 strains to be tested in plants was based on the following plant growth-promoting (PGP) traits: production of siderophore (17 strains), production of IAA (two strains) and ACC deaminase activity (two strains); the remaining five showed low values for all of the PGP traits. The best controllers of sigatoka were five strains from the genus Bacillus (related to B. licheniformis, B. siamensis and B. subtilis ssp. inaquosorum) and one Rhizobium massiliae. With the six strains, the severity index (SI) of the plants coinoculated with the bacteria and the pathogen did not differ from the noninoculated control. The sigatoka control observed has been tentatively assigned to ISR phenomena, which is discussed in the chapter. The six selected strains could be used in the short term to control black sigatoka in organic banana production systems in the Dominican Republic.