Pathological Studies Of Fusarium Oxysporum (Schlecht.) F.Sp. Tulipae Apt. In Tulip (Tulipa Gesneriana L.) Bulbs After Harvest

We studied the infection process and ethylene production by Fusarium oxysporum (Schlect.) f.sp. tulipae Apt. (F.o.t.) in tulip bulbs after harvest. This dissertation aimed: 1) to develop screening assays to study the infection and ethylene evolution of F.o.t. in tulip bulbs, 2) to determine the degree of resistance to Fusarium between several cutlivars, and members of lineages of cultivar sports, and 3) to generate a profile of metabolites of two cultivars (one susceptible, and one resistant) involved in the ethylene biosynthesis pathway of F.o.t., and compounds involved in confering resistance to this pathogen. Chapter 2 presents a literature review. Chapter 3 describes a multi-step procedure to isolate, characterize and identify Fusarium strains allegedly causing Fusarium rot in tulip bulbs. Chapter 4 evaluates various inoculation methods on the time course of fresh weight loss and ethylene production by F.o.t. Moist incubation conditions free of condensation led to healthy fungal development . Change in fresh weight can be used as a predictor of ethylene production by the fungus. Chapter 5 explores the correlation between ethylene evolution, visual infection rating, and FW loss of 38 cultivars and 2 species when inoculated with F.o.t. A Disease Severity Index (DSI) was developed to determine the degree of resistance to F.o.t. Cultivars and species ranged from resistant to susceptible. Time lapse videos show the infection process by F.o.t. in a susceptible cultivar and fungal growth suppression in a resistant cultivar. Chapter 6 presents the ethylene production in-vitro by F.o.t. in organs explants, and ethylene production in organs from whole inoculated bulbs. Results in organs from whole inoculated bulbs were similar to the in-vitro assay, however, biological contamination created experimental noise. Amino acid content and tulipaline-A in crude extracts from organs of two cultivars before inoculation did not correspond to ethylene production and fungal biomass of F.o.t. We postulate that tulipaline-A is a phytoanticipin in tulip bulbs, which in resistant cultivars may increase to fungitoxic levels under pathogen attack as a result of tuliposide breakdown by enzyme activity or chemical depolymerization by pH change in the tissue