Evaluation of resistance to Phomopsis amygdali in almond

The disease caused by the fungus Phomopsis amygdali (Del.) Tuset & Portilla is, today, one of the most important in almond growing, since the main commercial cultivars are susceptible to this pathogen. In Algarve (Portugal), the disease has been causing severe damage to introduced foreign commercial cultivars while traditional cultivars are not significantly affected. Field observations have led to the identification of 'Barrinho Grado' as a local cultivar that has shown non-susceptible behaviour in a heavily infected orchard. Inoculation tests with Phomopsis amygdali isolates were performed on young trees obtained from open-pollinated seeds of 'Barrinho Grado' (resistant) and 'Ferragnes' (susceptible). The 'Barrinho Grado' progeny showed higher resistance to the disease than the population descended from 'Ferragnes'. In order to study the inheritance of resistance to this fungus several controlled crosses were performed involving susceptible and resistant cultivars and the respective progeny plants were inoculated with fungus isolates in order to ascertain their phenotype. Moreover, to evaluate genetic variability of parents involved in the crosses, preliminary studies using isozymes, microsatellites, RAPD and ISSR markers were performed. Genetic similarities between these cultivars were established and suitable molecular markers for genomic mapping were selected. Hybrid populations will be used to construct genetic maps and to identify molecular markers closely linked to the resistance gene(s)