Morphological and molecular characterization of Diplodia spp. associated with apple canker disease in India

In recent years, the incidence of apple canker disease is increasing and assuming an epidemic in major apple growing parts of Jammu and Kashmir. During 2017-18, canker disease incidence was observed in all the apple growing regions surveyed, with characteristic symptoms of smoky canker. Total 40 samples were collected from regions of north, central and south Kashmir from three different varieties, Red Delicious, Royal Delicious and Golden Delicious. Among 40 samples collected total 20 isolates representing all the three varieties and regions were maintained for morpho-molecular characterization. Based on cultural and morphological characteristics, the fungus was identified as genus Diplodia with two morphological groups. Sequence based analysis of the internal transcribed spacer region (ITS) and elongation factor (EF1) gene confirmed the species as Diplodia bulgarica and Diplodia seriata. The Diplodia bulgarica was found predominant species in all the three regions surveyed. The phylogenetic analysis of both the genes clustered the two species in two different groups. The pathogenicity was confirmed on two-year-old potted plants of apple cv. Red Delicious. This study would help in better understanding the role of Diplodia species on symptom development, epidemiology and formulation of improved disease management strategies against apple canker.