A single dominant gene/locus model for control of Fusarium oxysporum f. sp. lactucae race 1 resistance in lettuce (Lactuca sativa)

Fusarium oxysporum f. sp. lactucae (FOLac) is responsible for significant economic losses across major lettuce-producing regions around the world. Thus far, only FOLac race 1 isolates have been reported associated with Fusarium wilt outbreaks in Brazil. The most sustainable strategy for disease control is the pyramidization of race-specific resistance factors in lettuce cultivars. The loose-leafy cultivar ‘Vanda’ was found as one of the most promising sources of resistance to FOLac race 1. The genetic basis of this resistance was determined by analyzing the reaction to this pathogen of segregating populations derived from the cross ‘Gisele’ (susceptible) × ‘Vanda’ (pollen donor). A single molecular marker-genotyped F1 hybrid plant was selfed and individual plants of a segregating F2 population as well as 63 families F2:F3 were inoculated with a FOLac race 1 isolate by using the root-dipping method (3 × 106 conidia/ml). Our results confirmed the high levels of resistance of ‘Vanda’ even under very harsh experimental conditions. Overall, the reaction of the F1 plants and the segregating patterns of the F2 population (n = 82) and of the F2:F3 families (n = 838 plants) fit a single dominant gene/locus model. However, the phenotypic expression of resistance might suffer effects of additional genetic factor(s) (e.g., locus dosage, minor modifying genes, and incomplete penetrance). Notwithstanding, the high levels of FOLac race 1 resistance and its relatively simple genetic control makes ‘Vanda’ a major germplasm source for lettuce-breeding programs aiming to incorporate this trait in a wide array of elite lines from distinct varietal groups.