Interpretation of Resistance to Fusarium Wilt in Tomato

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Abstract
Bonnie Best and Pan America tomato plants were inoculated when 6 wks. old by cutting through the lower taproot under a spore suspension of Fusarium oxy-sporum f. lycopersici. The spores began growth in the vascular elements of the root into which they were originally drawn, and the mycelium grew up into the stem. Foliage symptoms appeared rapidly on Bonnie Best but in only a few plants of Pan America. Fungus in the xylem was demonstrated equally in both plants by cultures and microsc. exam. The number of vessels infected in Pan America was much less than in Bonnie Best. An inhibitory subst. is not present in xylem fluid. The fungus grew comparably in vitro in liquid from resistant and susceptible plants. Xylem fluid is also not inhibitory in vivo. Resistance in Pan America may be physiological in nature, is present but not localized in the root system, and does not operate in the xylem.