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Fusarium Wilt Resistance in Sweet Potatoes. W. W. Collins, Graduate Student, Department of Plant Pathology, North Carolina State University, Raleigh 27607; L. W. Nielsen, Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27607. Phytopathology 66:489-493. Accepted for publication 6 October 1975. DOI: 10.1094/Phyto-66-489.

Experimental sweet potato clones were indexed for disease reaction to the wilt fungus Fusarium oxysporum f. sp. batatas. The clones exhibited a wide range of reactions with disease indices well correlated between tests (r = .94). Initial uptake of bud-cells of the fungus was similar in resistant and susceptible clones and not correlated with the disease index (r = 0.2). Distribution of bud-cells in the stems of resistant and susceptible cuttings was discontinuous, but they often reached a level of 15 cm 15 minutes after inoculation. When resistant stems were serially sectioned at 1-cm intervals after 6 days of incubation, Fusarium was recovered from about 50% of the sections and was still present after 48 days of incubation; but susceptible clones were completely invaded and often dead after 6-9 days. Development of tyloses in inoculated plants exceeded that in healthy plants. Tyloses were more abundant in inoculated resistant plants than in susceptible plants, but they rarely blocked all vessels completely. Although tyloses may function in resistance, they did not appear to be the primary resistance mechanism.