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Seasonal and potato cultivar effects on common scab causing Streptomyces spp. and bacterial communities

Claudia Goyer: Agriculture and Agri-Food Canada

<div>Pathogenic <em>Streptomyces</em> spp. cause common scab (CS) of potato resulting in significant economic losses. How potato cultivar can influence the abundance of pathogenic <em>Streptomyces</em> spp. is unclear. This study evaluated the effects of potato cultivar on pathogenic <em>Streptomyces</em> spp. abundance and diversity of bacterial communities in three spatial locations: bulk soil (BS), rhizosphere (RS) and geocaulosphere (GS) over the growing season. The experiment was conducted in a naturally common scab infested field located in Fredericton, NB, Canada in 2013 and 2014. Two tolerant (Gold Rush, Hindenburg) and two susceptible cultivars (Green Mountain, Agria) were tested. Soil samples were collected from BS, RS and GS soils. When averaged over time, the abundance of pathogenic <em>Streptomyces </em>spp. measured using quantitative polymerase chain reaction, was significantly greater in GS for susceptible than for tolerant cultivars. The abundance of pathogenic <em>Streptomyces</em> spp. increased in BS, RS and GS for susceptible cultivars at 90 days after planting compared with other dates, whereas no changes over time were observed for tolerant cultivars. Principal coordinate analyses indicated that pH, extractable organic carbon, ammonium and nitrate concentrations explained 68 and 76% of the variability in BS among cultivars in 2013 and 2014, respectively, and 69% of the variability in RS among cultivars in 2013. This finding suggests that the cultivars influenced the soil chemical properties in BS and RS. Alpha- diversity of bacterial communities was significantly different among BS, RS and GS, but was not significantly different among potato cultivars. Thus, differences in growth of pathogenic <em>Streptomyces</em> spp. among cultivars may reflect cultivar-specific effects on soil chemical properties rather than effects on soil bacterial communities.</div>