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Soil-borne diseases identified as key yield-limiting factors in potato crops

Richard Falloon: The New Zealand Institute for Plant & Food Research Limited

<div>The climate in Canterbury, New Zealand, supports potato yields of 90 t/ha in most growing seasons, as indicated by a verified simulation model. However, current yields from processing (French fry) potato crops are 50-60 t/ha. Soil-borne diseases, particularly <em>Rhizoctonia</em> stem canker and <em>Spongospora</em> root galling, were identified in a previous survey as commonly occurring yield-limiting factors in potato crops. Three irrigated crops (each ≅ 25 ha, but with different soils and cropping histories) were intensively monitored (2014/15 growing season) to determine causes of this “yield gap”. At eight sites in each crop, selected to represent local soil variability, observation plots (eight rows by 10 m) were marked, and plants were assessed at 10 to 14 d intervals for potential yield-limiting factors and tuber yields. In one crop, where little soil- or seed tuber-borne disease occurred, measured yields approached potential (mean = 78 t/ha). In the second crop, yields were slightly reduced (mean = 72 t/ha), where <em>Rhizoctonia</em> stem canker developed late in the growing season, and <em>Spongospora</em> root galling was slight (mean = 6-8 galls/plant) and also late-developing. Yields from the third crop averaged 55 t/ha, where <em>Rhizoctonia</em> stem canker was severe, killing many plant stems, and <em>Spongospora</em> galling developed early and was severe on roots and underground stems. This study, of three contrasting potato crops, highlights the need for effective strategies to reduce soil-borne diseases, to obtain yields from intensively managed potato crops that approach their modelled potential.</div>