Diversity of fungal species causing apple canker disease in India using multigene characterization

Abstract

Apple canker diseases are significant threats to the global apple industry, causing extensive damage, including shoot blights, stem cankers, and internal wood discoloration. This study aimed to investigate the symptomatology, disease incidence, and diversity of pathogens associated with apple cankers in three major apple-growing regions of India including the states of, Uttarakhand, Himachal Pradesh and Jammu & Kashmir (J&K). The survey revealed that canker symptoms typically begin as sunken spots on shoots and stems, which can progress to bark cracking and internal wood discoloration Disease incidence and severity varied across regions, with J&K showing the highest levels, particularly in Shopian (37.10 % incidence; 20.85 % severity). Himachal Pradesh also exhibited significant disease prevalence, with Shimla recording the highest severity (23.15 %). In Uttarakhand, Almora had the highest incidence (27.52 %) and severity (13.89 %). Isolations provided 38 isolates of Diplodia and Botryosphaeria spp., which were classified into four morpho-groups based on morpholo-cultural characteristics. Molecular analyses using the internal transcribed spacer region (ITS), beta-tubulin (β-tubulin) gene and translation elongation factor 1 subunit alpha (EF1-α), gene sequences identified four pathogenic species, namely, Diplodia bulgarica, Diplodia seriata, Diplodia mutila, and Botryosphaeria dothidea. Phylogenetic studies grouped these species into distinct clades with high bootstrap support. Pathogenicity tests demonstrated their role in causing canker symptoms under favourable conditions. This study presents regional variability in disease prevalence and identifies key pathogens responsible for apple cankers in India and highlights the need for development of effective management strategies.