Two genes for resistance to Fusarium oxysporum f. sp. radicis-cucumerinum in melon (Cucumis melo, Cucurbitaceae)

Abstract

Fusarium oxysporum f. sp. radicis-cucumerinum (fusarium crown rot, Forc) is an emerging pathogen of melons, Cucumis melo. Forc incites rotting of the plant crown, causing the plants to die prematurely. Most melon accessions are susceptible to this pathogen but the cantaloupe ‘Hemed’ is highly resistant. ‘Hemed’ was crossed with the susceptible muskmelon ‘Dulce’ to ascertain the mode of inheritance of resistance to Forc. Parental-, filial-, and backcross-generation plants were grown under controlled conditions and inoculated with Forc by using a root-dip methodology. Plants were scored as resistant or susceptible at 18 days post inoculation (dpi), when all plants of the susceptible parent ‘Dulce’ were dead or showed severe disease symptoms. At 18 dpi, plants of ‘Hemed’, the F1, and the backcross to ‘Hemed’ were resistant. The F2 population segregated in accordance with a 13:3 ratio, deviating significantly from a 3:1 ratio of resistant to susceptible. The backcross to ‘Dulce’ segregated in accordance with a 1:1 ratio of resistant to susceptible. These results indicate that ‘Hemed’ carries two genes for resistantance to Forc, one dominant and one recessive, which are herein designated, respectively, as Forc-1 and forc-2. Resistance to Forc is not co-inherited with resistance to F. oxysporum f. sp. melonis (fusarium wilt, Fom) races 0, 1, and 2, as both ‘Hemed’ and ‘Dulce’ are resistant to Fom races 0 and 2 and susceptible to Fom race 1.