Infection process of Entomosporium mespili on leaves of saskatoon, Amelanchier alnifolia

Abstract

The infection process for Entomosporium leaf spot of saskatoon (Amelanchier alnifolia) was evaluated with scanning electron microscopy. Following treatment with a conidiospore suspension of Entomosporium mespili, detached leaves of saskatoon cultivars were fixed at various times during disease development (2, 5, 8, and 12 days postinoculation). Scanning electron microscopy showed that conidiospore germination occurred rapidly, usually by the extrusion of a single major germ tube from the larger of two body cells. Fungal penetration of the host cuticle involved appressoria, produced directly below the germinating spore or at germ tube termini. Subspore appressoria were most common and resulted in the earliest formation of leaf acervuli. Conidiospore germination and penetration occurred more rapidly on leaves of the susceptible cv. Buffalo, than on leaves of resistant cv. Success. At 2 days postinoculation, 43% of germinating conidiospores had penetrated the leaf surface of cv. Buffalo, compared with 12% on leaves of cv. Success. Acervuli bearing large quantities of conidiospores, were produced as the result of conidiogenesis from a subcuticular stroma of hyphae. Acervuli formed on leaves of all saskatoon cultivars, but cultivars differed in acervulus surface area and number of acervuli per leaf.

Keywords:

• Amelanchier alnifolia
• Entomosporium mespili
• infection process