The relationship between soil inoculum and the development of Fusarium dry rot in potato cultivars Asterix and Saturna

A glasshouse experiment was carried out with the aim of quantifying the relative contribution of seed- and soil-borne inoculum of three Fusarium spp. (F. coeruleum, F. sambucinum and F. avenaceum) in causing dry rot in two potato cultivars, Asterix and Saturna. Different concentrations of inoculum; control (water only), low (102 conidia ml−1) and high (105 conidia ml−1) were used to inoculate seed and infest soil and disease severity on progeny tubers was subsequently assessed following an 8-week post-harvest storage period. Overall, F. sambucinum caused significantly (P < 0.05) larger rots than F. avenaceum, with the severity of rots caused by F. coeruleum being intermediate, and disease severity was greater in cv. Asterix than cv. Saturna (P < 0.01). None of the seed inoculation treatments resulted in dry rot development on progeny tubers. In contrast, soil infested with Fusarium species resulted in significantly more severe tuber rots on progeny tubers compared with controls (P < 0.01). Soil infested with F. sambucinum (low and high levels) resulted in significantly more severe rots than control treatments (P < 0.001), whilst only high levels of F. avenaceum soil inoculum increased the severity of tuber rots compared with control treatments (P < 0.05). Increased disease severity observed as a result of the addition of inoculum of F. coeruleum to soil was not significant.