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Fusarium Wilt of Susceptible and Resistant Tomato Isolines: Spore Transport. M. E. Mace, Plant Pathologist, Disease Resistance Investigations, Crops Research Division, ARS, USDA, Beltsville, Md. 20705; J. A. Veech(2), and F. Hammerschlag(3). (2)(3)Plant Physiologist, and Plant Pathologist, respectively, Disease Resistance Investigations, Crops Research Division, ARS, USDA, Beltsville, Md. 20705. Phytopathology 61:627-630. Accepted for publication 15 December 1970. DOI: 10.1094/Phyto-61-627.

The effects of the length of the inoculation period, inoculum concentration, and host plant age on spore uptake and distribution were determined for Fusarium wilt-susceptible and -resistant isolines of tomato. Stained spores were introduced directly into the shoot vascular system through a transverse cut in the hypocotyl 2 cm below the cotyledons. Within 15 min, the bulk of the spores was distributed over a 2.3-cm distance. The rate of transport then leveled off, and after a 90-min inoculation period, the bulk of the spores was distributed over a 3.2-cm distance. A similar, but more sensitive, experiment using unstained, viable spores and a bioassay procedure to measure transport distances indicated that some spores were transported up to 5 cm. Factors such as host plant age and inoculum concentration were investigated to determine their effect on spore transport. We conclude that morphological features of the stem xylem in the two cultivars affect spore distribution similarly, and that resistance is not manifested in the ability of the resistant cultivar to inhibit physically the systemic distribution of pathogen spores.