Excelling the progenitors: Breeding for resistance to Dutch elm disease from moderately resistant and susceptible native stock

Abstract

Under the continuous pressure of Dutch elm disease (DED) in Europe, increasing the genetic diversity of Ulmus minor trees resistant to Ophiostoma novo-ulmi is a priority for the species conservation and reintroduction. In this work we screened 121 U. minor genotypes for resistance to O. novo-ulmi under field experimental conditions. The genotypes had been previously obtained through controlled crosses between two moderately resistant (dams) and one susceptible (sire) genotypes. After two years of artificial inoculations with O. novo-ulmi, transgressive resistance was present but not prevalent, and a moderate relation was found between tree growth and susceptibility. Heritability estimates of DED resistance endorse significant genetic control and higher estimates for experimental blocks with milder symptoms. Three genotypes excelled for their high DED resistance, showing average foliage wilting values below 30% after the two years of inoculations. The genetic fingerprint, leaf phenology and morphology, and ornamental traits of these three genotypes were evaluated to facilitate their identification and use by stakeholders. Nuclear microsatellite profiling displayed unique barcodes for each genotype, ensuring traceability of the plant material. Morphological and phenological traits of the three genotypes are quite similar and fall within the species standards. In base of these results, three new native genotypes are proposed as basic materials for elm reintroduction in Western Europe.