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New Zealand Plant Protection 63 (2010): 276

Kumara root resistance to Ceratocystis fimbriata

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

ABSTRACT

The fungal pathogen Ceratocystis fimbriata causes a disease of the kumara (Ipomoea batatas or sweetpotato plant) known as black rot. The fungus was first recorded in New Zealand in 1907 and by 1947 black rot had become a significant problem for the kumara industry. The pathogen spread to most kumara production areas, causing severe or occasionally complete crop loss. The industry only survived this period by adopting strict hygiene practices, as the pathogen is highly transmissible. While the fungus may spread in propagation beds and within crops in the field, it is during storage and bulk handling of roots that most cross-infection occurs. Infection by C. fimbriata may stimulate the kumara root to respond by producing phytoalexins, which are toxic and bitter in taste. Although there have been no reports of human poisoning, there have been cattle deaths as a direct consequence of consumption of infected kumara roots. One approach to limiting disease spread is through using resistant cultivars. A laboratory bioassay was developed to distinguish levels of cultivar storage root resistance to C. fimbriata infection. The traditional and modern cultivars assessed showed a range (P<0.001) of responses to pathogen infection by point inoculation.

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