Further studies on the nature of Fusarium resistance in Tomato.
At the Department of Plant Pathology, University of Wisconsin, extracts of single-gene resistant Jefferson tomato plants failed to inhibit the growth of Fusarium oxysporum f. [F. bulbigenum var.] lycopersici [R.A.M., 33, p. 691 and next abstract] in a double-strength Czapek-Dox medium. Cuttings of both Jefferson and the susceptible Bonny Best variety reacted to treatment with culture filtrates and commercial pectinase [polygalacturonase] by the development of similar disease symptoms, so that resistance could hardly be attributed to a mechanism of detoxicification in resistant plants only. The resistance of Jefferson cuttings was broken down by treatment with the respiratory inhibitors 2, 4-D, thiourea, sodium fluoride, and sodium diethyl dithiocarbamate, which exerted no stimulatory effect on the pathogen in vitro. It is postulated, therefore, that resistance to F. b. var. lycopersici is closely associated with the metabolism of the host and is probably derived from a very labile substance continuously formed at the expense of energy obtained from respiratory processes.