The Foc gene governs resistance to race 3 of Fusarium oxysporum f. sp. cucumerinum in the cucumber cv. SMR-18

Abstract

The genetics of resistance to race 3 of Fusarium oxysporum f. sp. cucumerinum (FOC race 3) in the cucumber cv. SMR-18 (P1) was investigated by crossing it with the susceptible cucumber cv. Ashley (P2) and evaluating the disease reaction in the parents, F1, F1 reciprocal, F2 and backcross (BC1P1 and BC1P2) populations. Resistance of cv. SMR-18 to FOC race 3 was consistent with that of a single dominant, nuclear gene. To study the linkage relationship between this gene and the Foc gene, which expresses resistance to both FOC races 1 and 2, 73 plants that were backcrossed to the susceptible parent (BC1P2) were self-crossed. Each resulting F2 family was evaluated for resistance or susceptibility to race 1 and race 3 by inoculating different groups of 15–20 plants with each race of the pathogen. Segregation data exhibited an absolute linkage between the Foc gene and the gene controlling resistance to race 3 of the pathogen, since no recombinants were observed and only the two parental classes at a frequency of 50% each were observed. Our data support the concept that the Foc gene, which controls resistance to races 1 and 2, also confers resistance to race 3.