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Pathological Histology of Four Onion Cultivars Infected by Fusarium oxysporum f. sp. cepae. G. S. Abawi, Former Research Assistant, now Research Associate, Department of Plant Pathology, Cornell University, Ithaca, New York 14850; J. W. Lorbeer, Associate Professor, Department of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 61:1164-1169. Accepted for publication 26 April 1971. DOI: 10.1094/Phyto-61-1164.

Onion (Allium cepa) cultivars differentially tolerant or susceptible to basal rot caused by Fusarium oxysporum f. sp. cepae were equally susceptible to root and stem plate infection by the pathogen. Anatomical differences between the cultivars Treasure, Autumn Spice Improved, Grandee, and Elba Globe which could account for their different bulb decay reactions to the pathogen were not detected. The pathogen invaded roots by both direct penetration and/or through wounds. Invasion of the stem plate was by growth of the pathogen from infected roots and/or through natural wounds in the lower portion of the stem plate area. Invasion of the fleshy leaf bases of the bulb in either tolerant or susceptible cultivars usually was from the stem plate, but occasionally it occurred through the lower portions of leaf bases below the soil surface when propagule levels in the soil were high. The pathogen at first grew in the intercellular spaces of the root or the stem plate, but soon invaded cells. Tylose formation and occlusion of xylem vessels were observed equally in the stem plate tissues of the four cultivars. Chlamydospores formed in the cortex and vascular tissues of the root but not in the stem plate.