Characterization and pathogenicity of Diplodia, Lasiodiplodia and Neofusicoccum species causing Botryosphaeria canker and dieback of apple trees in central Chile

Abstract

In recent years, the number of apple trees affected by Botryosphaeria cankers and dieback has considerably increased in central Chile. This study aimed to identify the species of Botryosphaeriaceae associated with canker and dieback symptoms, estimate disease incidence and distributions, and study their pathogenicity and virulence on apple and other fruit crops. A field survey of 34 commercial orchards of apple (7-to 30-year-old) was conducted in 16 localities obtaining 270 symptomatic branches and trunks samples in 2017 and 2018 growing seasons. The incidence of Botryosphaeria canker and dieback ranged between 5 and 40%, and a total of 255 isolates of Botryosphaeriaceae spp. were obtained from 238 cankers. Morphological identification along with phylogenetics studies of the internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2) of the rDNA, part of the translation elongation factor 1-α (tef1-α), and part of the beta tubulin (tub2) genes allowed to identify Diplodia mutila (n = 49 isolates), D. seriata (n = 136 isolates), Lasiodiplodia theobromae (n = 16 isolates) and Neofusicoccum arbuti (n= 54 isolates). L. theobromae was isolated mainly of apple dieback from northern localities. All pathogens tested were pathogenic, causing canker and dieback symptoms on lignified twigs of apple, pear, walnut, and green grapevine shoots in the field. Isolates of N. arbuti were the most virulent by reproducing more severe cankers on lignified tissues inoculated. This study reports D. mutila and L. theobromae for the first time associated with Botryosphaeria canker and dieback in Chile, and it is the first description of N. arbuti causing apple dieback worldwide.