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New Zealand Plant Protection 66 (2013): 223-228

Sweetpotato cultivar susceptibility to postharvest soft rot caused by Rhizopus stolonifer

S.L. Lewthwaite, P.J. Wright and C.M. Triggs

ABSTRACT

Infection by the fungal pathogen Rhizopus stolonifer causes a postharvest disease in sweetpotato (Ipomoea batatas) roots known as soft rot. In recent years, due to changes in legislation prescribing acceptable agrichemical residues, post-wash applications of the fungicide dicloran can no longer be used on exported sweetpotato roots. An important component of any alternate disease control system is cultivar resistance. This study examined the range of responses within artificially inoculated roots of various cultivars, under different wounding regimes. While none of the cultivars evaluated was immune to infection, they differed in their degree of susceptibility (P<0.001). Cultivars also differed in their response to the type of wound they received at inoculation (P<0.001). The internationally recognised cultivar, 'Beauregard', was vulnerable to infection through piercing wounds, but showed relatively less susceptibility when the wound was a bruise. Disease evaluation using both piercing and bruising wounds appears necessary in characterising sweetpotato germplasm.

Keywords: kumara, fungus, disease, resistance, wound.

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