AbstractThe host-parasite of citron (Citrus medica L.) and the fungus Sphaeropsis tumefaciens, causal organism of the citrus knot disease, were studied. Conidial germination was observed 4 hours after inoculation. Initial movement through the cortex occurs by mechanical action of the germination tube. Knot development started 25 days after inoculation. Hyperplasia and hypertrophy of cells in the deformed area were observed. Invasion of tissues by the pathogen is indiscriminate in all stem tissues, with inter- and intracellular penetration of cells in the infected areas. All tissues invaded by the fungus appeared completely necrotic 75 days after inoculation.
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