Diseases of the kumara crop

Abstract

The predominant diseases of the commercial kumara (Ipomoea batatas) or sweetpotato crop are caused by fungal pathogens The field disease pink rot results from infection by the fungus Sclerotinia sclerotiorum Lesions form on vines but may spread down stems to the roots The widespread nature of this disease in sweetpotato appears peculiar to New Zealand Scurf is a disease caused by Monilochaetes infuscans which occurs in the field but may proliferate amongst stored roots The disease causes a superficial discolouration of the root surface which is mainly cosmetic but can also increase root water loss in storage Infection by Ceratocystis fimbriata produces a disease known as black rot The disease can be transmitted amongst plants at propagation but is particularly rampant amongst roots in storage This disease is readily transmitted and can cause severe economic loss Fusarium oxysporum causes surface rots in stored roots characterised by light to dark brown lesions that tend to be firm dry and superficial The lesions may be circular and centred on wounds caused by insects or mechanical damage at harvest Soft rot caused by Rhizopus stolonifer generally occurs in roots after they are washed and prepared for the market Fungal infection occurs through wounds or bruised tissue producing distinctive tufts of white fungal strands and black spores