First Report of Thielaviopsis basicola on Cool-Stored Carrots in New Zealand. L. H. Cheah, New Zealand Institute for Crop & Food Research Limited, Private Bag 4005, Levin, New Zealand . A. P. Marshall, and D. W. Brash, New Zealand Institute for Crop & Food Research Limited, Private Bag 4005, Levin, New Zealand. Plant Dis. 80:821. Accepted for publication 17 April 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0821A.
Fresh carrots have become one of the promising new export crops from New Zealand to Asia. Export value has risen from NZ$1M in 1993 to about NZ$4.3M in 1995. Quality deterioration and storage rots have become constant problems during cool storage. In 1995, a trial was carried out to check cool-stored (0 to 10°C) carrots for quality and storage rots at monthly intervals up to 3 months. During the trial, a black storage rot was frequently observed on carrots that had been cool-stored for 2 to 3 months. This rot accounted for up to 5% of crop losses. The initial sign was a fine growth of mold that later became black. Lesions were black, large (1 to 2 cm) and irregular, and were frequently associated with senescent leaves or plant debris attached to the root. Isolation from diseased tissue and from single spores onto potato dextrose agar (PDA) consistently yielded black colonies with dark gray mycelium. On close examination the fungus was found to produce two types of spores: hyaline conidia, produced within a conidiaphore, and brown-walled chlamy-dospores. The fungus was identified as Thielaviopsis basicola (Berk. & Broome) Ferrarisp. Pathogenicity was proven by inoculating carrots with spores and mycelium from a 7-day-old culture. Ten carrots were artificially wounded by rubbing with stainless steel wool along one side of the root and then inoculated with culture plugs. Control carrots were treated with agar plugs without the fungus. Inoculated carrots were placed in sealed containers and incubated at 20°C. The experiment was conducted three times. Signs and symptoms developed 6 days after inoculation and were identical to those observed in natural infection. The fungus was readily reisolated on PDA from artificially inoculated carrots. T. basicola has been reported on carrots in the U.S. (1), but this is the first report of T. basicola on carrots in New Zealand.Reference: (1) B. A. Friedman et al. Plant Dis. Rep. 38:855, 1954.