GENETICS OF TOMATO RESISTANCE TO THE FUSARIUM-VERTICILLIUM COMPLEX

In the Fusarium-Verticillium wilt disease complex on tomato, Fusarium-resistant tomato cultivars become relatively resistant to Verticillium. This induction of resistance by Fusarium oxysporum f. sp. lycopersici (F) against Verticillium albo-atrum (V) was evaluated genetically by testing F1, F2 and testcross progenies derived from VFN-8 × Bonny Best tomato cross. The segregating progenies were tested singly (F or V) and simultaneously (F+V). Two independent dominant genes for resistance were identified-one effective against Fusarium race 1 (FIR1) and the other against Verticillium (VaR1). Fusarium-resistant but Verticillium-susceptible tomato genotypes also exhibited a resistance response to Verticillium when tested simultaneously with both fungal pathogens. As a result, the dihybrid ratio (9 : 3 : 3 : 1) observed from single infections (i.e. F or V) was modified to an epistatic ratio 12 : 3 : 1 corresponding to resistance to both, to one or to none of the two pathogens, respectively. This ratio is characteristic of dominant epistasis. Implications of such genetic modifications in disease complexes for plant breeding are discussed. © 1979.