Elucidating the almond constriction canker caused by Diaporthe amygdali in Sicily (South Italy)

The almond (Prunus dulcis) constriction canker caused by Diaporthe amygdali is considered one of the most important diseases of this crop in the European continent, especially in the Mediterranean countries. Field surveys conducted in Sicily, Italy, revealed the occurrence of almond trees severely infected by the disease. Symptoms of twig canker, shoot blight and gummosis were widely distributed in almond orchards grown with both local and international cultivars. The highest disease incidence and severity (DI and DS) were observed in the orchards grown with ‘Ferragnes’, ‘Supernova’ and ‘Tuono’ cultivars, whereas those grown with local sicilian cultivars such as ‘Pizzuta’ and ‘Romana’ showed the lowest DI and DS. Laboratory isolations yielded a total of 58 Diaporthe-like isolates. Morphological observations and molecular analysis based on sequencing and phylogenetic analyses of ITS, tef1-α and tub2 gene regions of representative isolates identified the causal agent as D. amygdali. The effect of temperature (5, 10, 15, 20, 25, 30 and 35 °C) was evaluated on mycelial growth rate on PDA and on lesion development in inoculated detached shoots, with the isolates tested showing an optimum growth temperature around 25 and 20 °C, respectively. Pathogenicity tests were conducted by means on detached almond shoots and on potted almonds plants. Results showed that all the isolates were pathogenic in all tissues evaluated showing significant differences in aggressiveness among the isolates. According to our results, this is the most updated study of constriction canker in Italy, including a molecular characterization of D. amygdali, since its first identification in 1936.