| The colonization of vascular tissues of the stem by Fol races 1, 2, or 3 and non-pathogenic Fusarium oxysporum f.sp. cubense (Foc) and Fusarium oxysporum f.sp. pisi (Fop) was examined in a highly susceptible tomato cultivar, and in polygene- and single-dominant-gene resistant cultivars. Tomato plants of all cultivars localized the non-pathogenic fusarial Foc or Fop within initially infected vascular tissues. Single-dominant-gene resistant cultivars showed no symptoms four weeks after inoculation with the corresponding avirulent race of Fol. The colonization of vascular tissues was localized in the lower part of plants and further fungal spread in vessels was not detected. Plants of highly susceptible Bonny Best uniformly showed yellowing and wilting symptoms three weeks after inoculation with Fol races 1, 2, or 3. A large number of vessels were infected and the fungus was detected at the top of each plant. In polygenically resistant cultivars inoculated with Fol races 1, 2, or 3, disease severity varied among individual plants in each cultivar. The extent of fungal spread in the vertical direction was correlated with disease severity of the individual plants. More vessels were infected in plants showing severe symptoms than in symptomless plants and in plants showing slight symptoms.; Polygenically resistant Marglobe tomato plants were vegetatively propagated and clones with low or high levels of resistance to Fol race 1 were selected. The colonization ratio was greater and the rate of fungal spread in vascular tissues was faster in susceptible clones than in resistant clones. Petiolar infection was related to the foliar symptom expression.; Polygenically resistant Marglobe plants responded to infection with Fol race 1 by developing vessel wall coating, producing tyloses, and accumulating secretion materials in vessel lumens. The coating response levels were significantly higher in resistant clones than in susceptible clones. The production of tyloses and accumulation of secretion materials was faster and significantly higher in resistant clones than in susceptible clones. |
