April, 2004

Identification of Fungi and Fungal Pathogens Associated with Hypolixus haerens and Decayed and Cankered Stems of Amaranthus hybridus. J. T. Blodgett, former Post-Doctoral Fellow, and W. J. Swart, Professor, Department of Plant Science, and S. vdM. Louw, Professor, Department of Zoology & Entomology, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa. Current address of J. T. Blodgett: USDA-Forest Service, Forest Health Management, 1730 Samco Rd., Rapid City, SD 57702. Plant Dis. D-2004-0127-02R, 2004 (online). Accepted for publication 29 October 2003.

Smooth amaranthus (Amaranthus hybridus) is a nutritious leafy vegetable well suited for cultivation in semiarid regions throughout the world. Discoloration, cankers, and decay in branches, stems, and root collars of smooth amaranthus were observed in Bloemfontein, South Africa. Examination of symptomatic stems revealed larval galleries of the pigweed weevil (Hypolixus haerens). Therefore, we identified the most common fungal species associated with this disease and the associated pigweed weevils. The objectives of our study were to test if the associated fungi can cause the stem canker disease observed in the field, and to determine if the adult pigweed weevil might transport the disease-causing fungi. Three of the seven most common fungal species produced cankers following inoculation, with Fusarium sambucinum and F. oxysporum being the most aggressive. Results suggest that pigweed weevils might be vectors of the Fusarium disease. There is significant potential for yield loss associated with this disease. The identification of this insect–fungal association and the pathogens involved in disease sets the stage for further research on the management of this important insect–fungal relationship.