First report of Neodidymelliopsis ranunculi causing foliar black spot on citrus leaves in orchards of Algeria

Abstract

During pest and disease surveys in summer 2017, severe leaf drops were observed in four citrus orchards, two sweet orange (cvs Thompson Navel and Washington Navel) and two mandarin (cvs Nova and Oro Grande) orchards, located in Chlef, one of the most important citrus region in Algeria. Visual inspection of green dropped leaves and leaves on tree canopy revealed unusual symptoms consisting of greasy black protuberant spots on the abaxial side and yellowing on the adaxial surface. A quick survey was conducted to determine the incidence of the disease. The proportions of trees affected by the disease were 50 and 35% for the sweet orange and mandarin orchards, respectively. The incidence of the diseased leaves ranged from 30 to 60% for sweet orange, while 50–70% of leaves were symptomatic in the mandarin orchards. Morphological identification and a multi-locus sequencing approach associated this disease to the fungus Neodidymelliopsis ranunculi. Koch's postulates also confirmed N. ranunculi to be the causal agent. This is the first report of black spot symptoms caused by N. ranunculi on citrus in Algeria. The rapid spread of the disease since its first detection, poses a serious threat to the sustainability of citrus production in Algeria and calls for the implementation of urgent management actions.