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Polygenic Inheritance of Partial Resistance to Fusarium oxysporum f. sp. melonis Race 1.2 in Melon

Fusarium oxysporum f. sp. melonis is responsible for Fusarium wilt of melon. Race 1.2 strains overcome two dominant resistance genes (Fom-1 and Fom-2) and are further divided into two types depending on the symptoms they cause, yellowing or wilting. Partial resistance to F. oxysporum f. sp. melonis race 1.2 was studied by using a recombinant inbred line (RIL) population that was developed by single seed descent from an F₁ hybrid between ‘Isabelle’, a partially resistant line, and a susceptible line, ‘Védrantais’. Artificial inoculations were performed with a yellowing strain (TST) and a wilting strain (D'Oléon 8) and replicated in six locations. Disease reactions of the parental lines, controls, and RILs were scored using a 1-to-5 scale and by using the area under the disease progress curve (AUDPC). Phenotypic correlations were highly significant between the different locations and experiments. The heritability of the resistance was high, from 0.72 to 0.96, and 4 to 14 genetic factors were estimated to confer resistance to F. oxysporum f. sp. melonis race 1.2. Thirteen other strains were tested with an RILs subset. Some small strainspecific effects may be involved. These results contribute to a better understanding of the polygenic inheritance of the partial resistance to F. oxysporum f. sp. melonis race 1.2.