Shoot Dieback in Thornless Blackberries in Northern Spain Caused by Diaporthe rudis and Gnomoniopsis idaeicola

Abstract

A cane disease of a non-commercial thornless blackberry cultivar (genus Rubus, subgenus Rubus Watson) obtained in a breeding program was observed in May 2021 in northern Spain during a field evaluation. Symptoms of the disease appeared in spring and firstly consisted of dark-brown lesions in the petioles, tips, and intermediate zones of the canes, finally causing the leaves, canes, and lateral shoots to die. Two strains were recovered from infected canes and identified by morphological characteristics and multigene analysis as Gnomoniopsis idaeicola (LPPAF-977) and Diaporthe rudis (LPPAF-981). Pathogenicity tests showed that both fungi caused shoot dieback when artificially inoculated, reproducing the symptoms originally observed. Moreover, tissue necrosis was enhanced when Diaporthe rudis and Gnomoniopsis idaeicola were co-inoculated. This is the first report of Diaporthe rudis and Gnomoniopsis idaeicola causing a potentially serious disease to blackberries in Spain.