# Study on the Susceptibility of Some Almond (Prunus dulcis) Cultivars to the Pathogen Diaporthe amygdali

## TL;DR

This study identifies almond cultivars resistant to a damaging fungus and finds the best method to test for susceptibility.

## Contribution

The study introduces a reliable mycelial plug method for testing almond resistance and identifies highly resistant cultivars.

## Key findings

- Four almond cultivars showed high resistance to Diaporthe amygdali, while others were highly susceptible.
- The mycelial plug method was found to be the most consistent and reliable for field inoculation testing.
- Genetic resistance in 'Ferrastar' and 'Ardèchoise' was confirmed across various growing conditions.

## Abstract

Diaporthe amygdali Delacr. is a phytopathogenic fungus of considerable agronomic importance, responsible for branch canker in almond (Prunus dulcis [Mill.] D.A. Webb) and peach (Prunus persica L.) trees. It represents a major phytosanitary threat to almond cultivation in Europe, particularly in Mediterranean regions. Almond is currently among the most rapidly expanding perennial crops, with cultivated areas increasing as a result of the introduction of new cultivars and the adoption of improved agronomic practices. The objectives of this study were to isolate and identify fungal pathogens from infected almond samples collected in France through multilocus phylogenetic analyses (ITS, tef1-α, his3, tub2, cal genes) combined with morphological characterization; evaluate the susceptibility of 18 almond genotypes, using ‘Ferragnès’ and ‘Texas’ as reference standards for susceptibility and tolerance, respectively; and compare three field inoculation methods. All isolates were identified as D. amygdali. The varietal screening identified marked differences in resistance among the tested cultivars. In particular, ‘Ferrastar’, ‘R1877’, ‘R1413’, and ‘R1542’ exhibited high levels of resistance, whereas ‘Tuono’, ‘Guara’, and ‘R1568’ showed susceptibility comparable to that of ‘Ferragnès’, which was used as the susceptible control. Among the inoculation methods evaluated, the mycelial plug technique proved to be the most consistent and reliable, outperforming both conidial suspension inoculation and the toothpick method coated with mycelium. These findings further confirm the genetic resistance of the cultivars ‘Ferrastar’ and ‘Ardèchoise’ to branch canker across different growing conditions, supporting their suitability for use in breeding and genetic improvement programs.