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Resource competition and antagonism in natural soil suppressive to Bayoud disease on date palm (Phoenix dactylifera) in Morocco

Adil Essarioui: INRA

<div>Date palm cultivation in Morocco suffers from Bayoud, a vascular disease caused by the soilborne fungus <em>Fusarium oxysporum</em> f. sp. <em>albedinis</em>. Some soils are naturally suppressive to the disease, but we have limited knowledge of how this occurs. To improve our understanding of mechanisms by which Bayoud is suppressed, we characterized functional traits of <em>Fusarium</em> isolates and the composition of bacterial and fungal communities in one suppressive and two conducive soils. Thirty saprophytic <em>Fusarium</em> isolates were randomly selected from each soil sample. <em>In vitro</em> inhibitory activity of every isolate against the Bayoud pathogen was assessed and isolate growth on 95 carbon substrates was evaluated using Biolog plates. The composition and diversity of fungal and bacterial communities were analyzed in each soil sample by sequencing the internal subscribed spacer (ITS1) and the ribosomal (16S) genes, respectively. <em>Fusarium </em>isolates from one conducive soil had the greatest antagonistic activity, but the slowest growth, suggesting tradeoffs between inhibition and growth. However, <em>Fusarium</em> isolates from the second conducive soil showed the lowest frequency and intensity of antagonism with growth efficiency that was comparable to that of the pathogen. Isolates from the suppressive soil displayed intermediate antagonism but the greatest growth. Sequence data revealed greater microbial diversity in the suppressive compared to the conducive soils with enrichment in microbial taxa known for their prolific production of antimicrobial compounds including <em>Fusarium</em>, <em>Aspergillus</em>, and diverse Actinomycetes. Microbial antagonism and resource competition may jointly contribute to Bayoud disease suppression in the suppressive soils in Morocco.</div>

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