Selection of a compatible biocontrol strain mixture based on co-cultivation to control rhizome rot of ginger

Rhizobacteria and Trichoderma spp. that were antagonistic against Fusarium oxysporum f.sp. zingiberi and Pythium splendens inciting rhizome rot disease of ginger were identified. In vitro assays identified positive interactions for growth, antifungal and chitinase gene expression between antagonistic TEPF-Sungal (Burkholderia cepacia) and S2BC-1 (Bacillus subtilis) with S17TH (Trichoderma harzianum), and vice versa. In comparison with the other strains and strain mixtures, one strain mixture, TEPF-Sungal + S17TH, recorded a maximum rhizome production of 84% efficiency with less incidences of yellows and rhizome rot at an 84.2 and 79.7% reduction over the pathogen control, respectively, in a polyhouse with a challenge inoculation with the pathogens. Inoculation of the mixture of biocontrol agents was associated with an increase in known defence gene products such as chitinase etc., so we speculate that these are involved in the mechanism of disease suppression. In field experiments, the strain mixture reduced yellows and rhizome rot to 45.9 and 49.3% over the untreated control, respectively, which is comparatively better than that produced with fungicide (44.3 and 45.3%, respectively). The treatment also produced an increased rhizome yield with an average increase of 60.0% relative to the control.

► Compatible combinations of antagonistic bacteria with Trichoderma harzianum were identified in vitro.
► Talc-based formulation of a combination of Burkholderia cepacia + T. harzianum significantly reduced rhizome rot of ginger.
► Reduction in rhizome rot was associated with enhanced rhizome production and defence enzyme activities.