Toward dissecting naturally occurring soil suppressiveness to Ceratocystis paradoxa

Abstract: Stem bleeding caused by Ceratocystis paradoxa is of major concern to coconut production in tropical areas and no sustainable control measures are available. The exploitation of naturally occurring suppressive soils offers an unique opportunity to develop sustainable management practices. This study aimed at characterizing soil suppressiveness to C. paradoxa and determining the biological, chemical, and physical properties responsible for the suppression of the pathogen. Suppressiveness was evaluated by determining the percentage of banana peel baits colonised by the pathogen added to the soil samples. The five most suppressive and the five most conducive soils were contrasted to determine the nature of suppressiveness. Total culturable bacterial populations were the only biological property implicated in suppressiveness. Among the physical and chemical properties, soil pH, calcium content, sum of bases, effective cation exchange capacity, base saturation, and sand content were higher in suppressive soils. Aluminium and iron contents were higher in conducive soils. In conclusion, soil suppressiveness to C. paradoxa could not be narrowed down to a single factor, but the results of this study indicate that a combination of biological, physical, and chemical soil properties contribute to the phenomenon.