Characterising the Influence of First-Year Wheat Cultivar on Pseudomonas Selection and Function in a Take-All Infected Field

Wheat, the world’s most widely cultivated crop, is highly susceptible to Take-all disease caused by the soil ascomycete fungus Gaeumannomyces tritici (Gt). Crop rotations using different wheat cultivars can influence Take-all build up (TAB) in the following year’s wheat crop. The exact mechanism for this is unknown, but there may be a bacterial biocontrol component associated with TAB control. We cultured and characterised Pseudomonas isolates from the rhizosphere and endosphere of second-year field-grown wheat, in plots which, in the previous season, had been used to culture High-TAB cultivar Hereward or Low-TAB cultivar Cadenza. Analysis of two bacterial loci, wsm and fecB, showed that these genes were significantly and differentially associated with first-year wheat-planting regime: wsm was more abundant within the High-TAB Hereward-derived isolates, while fecB was more prevalent within the Low-TAB Cadenza-derived isolates. These findings were supported by a gyrB phylogenetic analysis and an in vitro Gt antagonism assay. These data show that the wheat cultivar grown in the first year plays an especially important role in the selection of the associated Pseudomonas spp. found in the second-season wheat-root environment, emphasising the importance of understanding agronomic practice in improving plant health and food security.