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)xVanda' (pollen donor). A single molecular marker-genotyped F-1 hybrid plant was selfed and individual plants of a segregating F-2 population as well as 63 families F-2:F-3 were inoculated with a FOLac race 1 isolate by using the root-dipping method (3x10(6)conidia/ml). Our results confirmed the high levels of resistance of Vanda' even under very harsh experimental conditions. Overall, the reaction of the F-1 plants and the segregating patterns of the F-2 population (n=82) and of the F-2:F-3 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.