Characterisation and pathogenicity of fungal species associated with branch cankers and stem-end rot of avocado in Italy

Abstract

Branch cankers and stem-end rot are two of the most important threats to avocado production. During the autumn of 2013, sampling was conducted in the main avocado growing area in eastern Sicily to study the occurrence and establish the causal agents of branch canker and stem-end rot. A total of 94 fungal isolates, recovered from four avocado orchards, were identified by morphological characterisation, DNA sequencing and phylogenetic analyses as belonging to the genera Colletotrichum, Neofusicoccum or Diaporthe. The majority of the isolates were identified as Neofusicoccum parvum (70.2 %), with the remaining isolates being Colletotrichum gloeosporioides or C. fructicola (16 %), and Diaporthe foeniculacea or D. sterilis (13.8 %), respectively. Pathogenicity tests showed N. parvum was the most virulent species (P = 0.05), whereas Diaporthe isolates were the least so. An intermediate virulence was observed for C. gloeosporioides and C. fructicola, which were associated only with stem-end rot of fruit. Regarding cultivar susceptibility of fruit to these pathogens, ‘Hass’ was more susceptible to infection by C. fructicola and D. foeniculacea compared with ‘Bacon’ whereas no significant differences were detected for the remaining pathogens. To our knowledge, this is the first account of the pathogens causing branch canker and stem-end rot of avocado in Italy, and the first studies comparing the relative virulence of each species involved.