Archivio Journal of Plant Pathology

Abstract:

From January to April 2014, sixteen pecan (Carya illinoinensis) orchards in southern Brazil were surveyed to determine the causal agent of a small black circular leaf spot disease. Forty isolates obtained on potato dextrose agar (PDA) were identified on the basis of morphological features and sequence analysis of the translation elongation factor 1-α gene (Bensch et al., 2012). Morphological features and sequence homology confirmed the isolates to be either Cladosporium cladosporioides, C. pseudocladosporioides or C. subuliforme, all species included in the C. cladosporioides complex. On PDA, C. cladosporioides (2/1PR, GenBank accession No. KT991541) and C. pseudocladosporioides (11RS, KT991560) both produced colonies of greenish-gray pigmentation with velvety and floccose aerial mycelium, whereas C. subuliforme (16/2RS, KT995114) produced colonies with similar pigmentation but more abundant aerial mycelium. Isolates 2/1PR, 11RS and 16/2RS produced on average colonies that were 72.2, 68.1 and 74.6 mm in diameter, respectively; conidia were 5.1 × 2.6 μm, 5.7 × 2.5 μm and 5.3 × 2.9 μm in length; ramoconidia were 23.7 × 4.2 μm, 22.5 × 2.8 μm and 16.0 × 4.3 μm in length. To confirm pathogenicity, young detached leaflets were inoculated with twenty-six isolates. One-tenth ml of conidial suspension (1 × 106 conidia ml-1) divided into six individual drops was applied on each leaflet surface with eight replicates. Leaflets receiving only sterile distilled water served as a non-inoculated control. Black leaf spots were observed after 22 days on all inoculated leaflets. The original Cladosporium species was re-isolated from inoculated leaflets. To our knowledge, this is the first report of C. cladosporioides, C. pseudocladosporioides and C. subuliforme causing pecan leaf spot in Brazil as well as in the world.