Twenty-five almond cultivars were assessed for susceptibility to Diaporthe amygdali, causal agent of twig canker and shoot blight disease. In laboratory experiments, growing twigs were inoculated with four D. amygdali isolates. Moreover, growing shoots of almond cultivars grafted onto INRA 'GF-677' rootstock were used in 4-year field inoculations with one D. amygdali isolate. In both types of experiments, inoculum consisted of agar plugs with mycelium, which were inserted underneath the bark, and the lesion lengths caused by the fungus were measured. Necrotic lesions were observed in the inoculated almond cultivars in both laboratory and field tests, confirming the susceptibility of all evaluated cultivars to all inoculated isolates of D. amygdali. Cultivars were grouped as susceptible or very susceptible according to a cluster analysis. The relationship between some agronomic traits and cultivar susceptibility was also investigated. Blooming and ripening times were found to be relevant variables explaining cultivar performance related to D. amygdali susceptibility. Late and very late blooming and early and medium ripening cultivars were highly susceptible to D. amygdali. Our results may provide valuable information that could assist in ongoing breeding programs of this crop and in the selection of cultivars for new almond plantations.
Keywords: almond breeding; blooming time; fungi; nut crops; pathogenicity; ripening time.