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A Single Gene Cluster Controls Incompatibility and Partial Resistance to Various Melampsora larici-populina Races in Hybrid Poplars

First author: Institut National de la Recherche Agronomique (INRA), Unité de Recherches Forestiéres Méditerranéennes, av. A. Vivaldi, F-84000 Avignon, France; and second, third, and fourth authors: Institut National de la Recherche Agronomique (INRA), Station d'Amélioration des Arbres Forestiers, F-45160 Ardon, France

Complete cosegregation for race-specific incompatibility with three Melampsora larici-populina rust races was observed in five F₁ hybrid progenies of Populus, with different patterns among the various progenies. A single gene cluster could explain these segregations: one locus with multiple alleles or two tightly linked loci controlling complete resistance to E1 and E3, and two tightly linked loci for E2. The random amplified polymorphic DNA marker OPM03/04_480 was linked to that cluster in all families (<1 cM). This marker accounted for more than 70% of the genetic variation for field resistance in each family (heritability ≈ 0.40). The same marker accounted for up to 64% of the clonal variation for growth in the nursery under natural inoculum pressure; the weak tolerance to rust of F₁ interspecific hybrids was attributed to a genetic background effect. Partial resistance was split into epidemiological components (heritability ranged from 0.35 to 0.87). Genotypic correlations among resistance traits for the different races were high (0.73 to 0.90). However, correlations among different resistance components for a single race were not all significant. A major quantitative trait locus for all components of partial resistance to E2 was associated to the cluster controlling incompatibility to E1 and E3 and marked by OPM03/04_480 (R²from 48 to 68%).

Additional keywords: leaf-disk bioassay , quantitative resistance .