First report of Fusarium proliferatum causing rot of garlic bulbs in North America

Abstract

In September 2001, bulbs of garlic (Allium sativum cv. Italian Red) rotted in a drying shed at the Plant Introduction farm in Pullman, Washington. Softened cloves displayed water-soaked, tan lesions, often with white mycelium near the bulb axis. Similar symptoms were noted in the same cultivar commercially grown in Idaho, 10 km from Pullman, and purchased at a retail outlet in July 2002. In each case, surface-disinfested tissue plated on agar produced a Fusarium sp. with catenate microconidia borne on polyphialides. Pathogenicity tests were conducted using eight garlic plants (W6-672) grown in the glasshouse. Three plants and a control were used for each of two replications. For each treated plant, six injections of 25 µL of isolate AsatF1 (106 conidia mL−1 in nutrient yeast extract broth) were delivered to developing cloves. Controls received sterile broth only. At 55 days, tissue was dissected from cloves in each replicate, disinfested (15 s in 70% ethanol, 3 min in 0.5% v/v NaOCl) and plated on antibiotic malt extract agar for recovery of fungi. The experiment was repeated once. Subsequent experiments employed cured garlic (cv. Italian Red grown in California) with five garlic bulbs inoculated with AsatF1 and five serving as controls. Treatments were replicated and the inoculations repeated, but substituting isolate AsatF8 for AsatF1 Conidia (106 mL−1 in sterile H2O) were injected into each bulb at three sites, while sterile H2O was injected into controls. After 11 weeks bulb tissue was disinfested as above, and portions of tissue incubated on nutrient agars. Every bulb injected with AsatF1 in greenhouse experiments displayed rot corresponding to material rotted in the drying shed. No controls displayed symptoms. Tissue excised from garlic cloves with symptoms and plated on agar produced Fusarium isolates indistinguishable from AsatF1. The fungus did not grow from controls. All cured garlic bulbs injected with isolates AsatF1 or AsatF8 developed symptoms. Internal tan rot progressed from injection sites toward the clove apex, with occasional white mycelium in rot cavities. Fusarium isolates indistinguishable from isolates AsatF1 or AsatF8 were isolated from all treatment bulbs. No controls developed symptoms, or produced Fusarium when tissue was incubated on agar. Isolates were identified as Fusarium proliferatum (Nelson et al., 1983; Nirenberg & O’Donnell, 1998). Previously, F. proliferatum has been reported on onion in the north-western USA (Mohan et al., 1997), and isolates AsatF1 or AsatF8 were also pathogenic to onion (data not shown). This is the first report of a Fusarium in section Liseola attacking garlic in North America. Seefelder et al. (2002) have reported F. proliferatum and fumonisins in garlic bulbs in Germany.