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First Report of Fusarium Wilt of Babaco (Carica × heilbornii var. pentagona) in Ecuador

Babaco, Carica × heilbornii V.M. Badillo var. pentagona (Heilborn) V.M. Badillo, is a fruit native to Ecuador that has great potential as a cultivated crop. Local market demand and strong potential as an export crop have greatly increased interest in babaco production in Ecuador. Although the crop can be produced in open fields, the majority of crop production is in plastic greenhouses. In 1996, a serious wilt disease developed on babaco in several greenhouses, resulting in up to 100% loss of plants. Symptoms first appeared as chlorosis of the lower leaves, followed by defoliation progressing up the stem until the entire plant was defoliated. When cut in cross section, vascular discoloration was observed in the stem. Eventually necrosis and soft rot of the stem occurred and entire plants collapsed. Fungal isolations were conducted from fine feeder roots of diseased plants by soaking root pieces (2 cm long) in a 0.5% solution of sodium hypochlorite for 3 min. Root pieces were cut into smaller sections and placed on potato dextrose (PDA) or corn meal (CMA) agar in petri dishes. Isolations from larger roots, crowns, stems and fruits were made by soaking tissue sections of each plant part in a 2.87% solution of sodium hypochlorite for 3 min. Tissue sections were rinsed three times in sterile distilled water. Smaller tissue sections (≈0.125 cm³) were cut from surface-disinfested pieces and placed on PDA and CMA in petri dishes. Cultures were incubated at 20°C. A fungus resembling Fusarium sp. was isolated consistently from infected tissues from all infected plant parts. Based on the morphology of the fungal colony and conidia from monosporic isolations, the fungus was identified as Fusarium oxysporum Schlechtend:Fr. (1). Pathogenicity tests were conducted by growing babaco plants in pots containing an equal mixture of sterilized soil, compost, and sand in the greenhouse. Eight 7-month-old plants were inoculated by placing 40 ml of a suspension (10⁶ conidia per ml) of F. oxysporum in four plastic straws placed in the soil (5 cm depth) at equal distances (5 cm) from the base of each plant. Straws around noninoculated control plants received sterile water. Plants were watered with 400 ml of sterile water daily. Pathogenicity tests were repeated once as described. All inoculated plants developed typical wilt symptoms within 45 days after inoculation. No symptoms developed on uninoculated control plants. F. oxysporum was successfully reisolated from infected stem tissues of inoculated plants. Incidence of Fusarium vascular wilt of babaco has continued to increase since 1996 and is currently the major constraint to production.

References: (1) P. E. Nelson et al. 1981. Fusarium: Diseases, Biology, and Taxonomy. The Pennsylvania State University Press, University Park.