Vascular Fungi Associated with Branch Dieback of Olive in Super-High-Density Systems in Southern Spain

Abstract

Symptoms of branch dieback of olive with internal longitudinal dark streaking were observed during routine surveys in super-high-density systems in southern Spain. Nineteen fungal isolates recovered from wood samples showing internal discoloration and necrotic xylem vessels were selected. Multilocus alignments of the internal transcribed spacer, 28S ribosomal RNA, β-tubulin, or actin were performed, and the following species were identified: Acremonium sclerotigenum, Cadophora luteo-olivacea, Paracremonium sp., Phaeoacremonium italicum, P. minimum, P. scolyti, and Pseudophaeomoniella oleicola. Colony color, mycelial growth, conidial characteristics, and production were defined on potato dextrose agar, malt extract agar (MEA), and oatmeal agar. Phenotypic characteristics and conidial production varied depending on the isolate and culture media. The effect of temperature on mycelial growth was evaluated on MEA. The isolates showed slow mycelial growth (0.5 to 2.0 mm day−1), with the optimum temperature ranging from 23.2 to 33.9°C. Pathogenicity tests were conducted on 9-month-old olive potted plants (Arbequina) inoculated with mycelial plugs. C. luteo-olivacea, Phaeoacremonium minimum, and Phaeomoniella chlamydospora isolates from grapevine were included in the pathogenicity tests for comparative purposes. Prior to inoculation, the effect on the infection by inoculation with conidial suspensions or mycelial plugs was evaluated, with the second method being the most effective. C. luteo-olivacea was the fungus most aggressive to olive, followed by Phaeoacremonium minimum.