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First Report of Phomopsis vexans on Apricot in the Americas

Prunus armeniaca L. plants with blight symptoms on leaves and twigs were observed near La Plata (Argentina) in 1999. On leaves, symptoms ranged from small (up to 4 mm diameter) and dispersed brown circular spots to irregular blighted areas with numerous pycnidia. Twig blight developed initially on buds as necrosis that expanded and caused shoots to wilt. A Phomopsis sp. was isolated from necrotic tissues. Pathogenicity was assessed by inoculating healthy mature leaves with a spore suspension (1 × 10⁶ conidia per ml). Detached sterile twigs were placed in Roux tubes with water (1) and were infected by needle-stab inoculation. Controls were treated with sterile water. Inoculated leaves and controls were left in bags for 48 h. After 5 to 14 days, symptoms were similar to those described for field samples. The Phomopsis sp. was reisolated from necrotic lesions and characterized as identical to the original isolates. On potato dextrose agar, the fungus had white floccose mycelium and produced numerous black, globose to irregular pycnidia (up to 300 µm). Alpha-conidia were one-celled, hyaline, and ellipsoidal (4.5 to 10.3 µm long × 1.8 to 2.1 µm wide); beta-conidia were one-celled, hyaline, filiform, and straight or curved (16.8 to 27.5 µm long × 1.0 µm wide). A pure culture was identified as Phomopsis vexans (Sacc. & Syd.) Harter based on morphology and host specificity. This is the second report of P. vexans on apricot since the disease was cited in Algeria (2).

References: (1) T. A. Gally. Fitopatologia 10:87, 1975. (2) D. V. Narendra et al. FAO Plant Prot. Bull. 27:132, 1979.