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Histopathology of Fleck and Lesion Symptoms on Blueberry Infected with Gloeosporium minus. R. D. Milholland, Associate Professor of Plant Pathology, North Carolina State University, Raleigh 27607; Phytopathology 63:320-323. Accepted for publication 9 September 1972. DOI: 10.1094/Phyto-63-320.

Host-pathogen relationships of Gloeosporium minus were studied histologically in infected blueberry leaves. Penetration of the leaf tissue was directly through the cuticle. Appressoria were formed 48 hr after inoculation and were unicellular, generally spherical to obovate, and measured 2 to 4 µ in size. Penetration hyphae enlarged within the epidermal cell into broad primary hyphae ca. 2 µ in diam which invaded adjacent cells intracellularly. Addition of glucose to the inoculum increased spore germination, appressoria formation, and hyphal growth prior to penetration. Infected epidermal cells located near the center of the lesion were filled with pseudoparenchyma. In several instances, infection of the hydathode tissue resulted from germ tube growth through the broken cuticle without appressoria formation. All leaf tissues from the lower epidermis to the upper epidermis, including the vascular tissue, were invaded by the fungus. Twenty-four days after inoculation, the hydathode and infected leaf tissues were completely disorganized and necrotic, and mature acervuli had developed. The resistant fleck symptom apparently is a hypersensitive reaction.