First report of Diplodia seriata causing dieback on Quercus coccifera in Tunisia
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First report of Diplodia seriata causing dieback on Quercus coccifera in Tunisia Sawssen Hlaiem 1,2 & Meriem Zouaoui Boutiti 1 & Mohamed Lahbib Ben Jamaa 1 Received: 31 August 2019 / Accepted: 3 March 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Keywords Symtoms of diseases . Kermes oak . Diplodia seriata
In 2017, dieback symptoms were observed on Quercus coccifera L. (kermes oak) in the mixed forest of Rimel (37°17′48”N; 10°0′2″E; alt. 41 m), located in the Northest of Tunisia. 30% of kermes oak trees showed cankers on the branches often associated with gummy exudates; twigs dieback was also observed and dark brown to black pycnidia emerged through the bark. To identify the causal agent, 30 small pieces (3 × 3 mm) of infected stem tissues were surface-disinfected with 3% sodium hypochlorite for 20 s, washed in sterile distilled water, plated onto potato dextrose agar (PDA) and incubated at 25 °C for 3 days in darkness. Seventeen identical isolates were obtained. To induce sporulation, sterile pine needles were placed over actively growing cultures incubated under ultraviolet light at 25 °C. Colonies on PDA were fluffy white at first, covered the entire plates within 5 days becoming dark grey with abundant aerial mycelium. After one week of incubation, all isolates produced dark brown to black pycnidia, 300–550 um in diameter. No perithecia were observed in culture. Conidiogenous cells measuring 3 to 5 × 8 to 14.5 μm were cylindrical, hyaline, thin-walled and smooth, proliferating internally giving rise to periclinal thickenings and produced a single conidium
* Sawssen Hlaiem [email protected] 1
Institute National of Research Rural Engineering, Water and Forests, University of Carthage, B.P. N°10, 2080 Ariana, Tunisia
2
National Agronomic Institute of Tunisia, 43 street Charles Nicolle, 1082 Tunis, Mahrajene, Tunisia
at the tip. Conidia were first hyaline becoming dark brown, before discharge from pycnidia. They were aseptate, ovoid, apex obtuse, widest in the middle, base truncate or rounded with thick melanised cell walls and 20 to 27.4 × 9.8 to 13.7 μm in size. Based on macroand micro-morphological characters of colonies, the fungus was identified as Diplodia seriata De Not. (Phillips et al. 2007). Molecular identification was performed by sequencing the internal transcribed spacer (ITS)-rDNA using the primers ITS1 and ITS4, part of the translation elongation factor 1-α (EF1-α) region using the primers EF1-688F and EF1-986R and the β-tubulin genes using the primers Bt2a and Bt2b. BLAST searches of the ITS (GenBank Accession No. MN318471), elongation factor EF-1-α (MN373270) and β-tubulin (MN373271) sequences, revealed 99% (MK370087), 99% (MK370088) and 98% (HQ660477) identity with reference sequences of D. seriata strains (PPO-46524 and GA-422). Pathogenicity assay was made according to Linaldeddu et al. (2014) by inoculating the mycelial plugs in a shallow wound (3 mm) made by a scalpel on five excised Q. coccifera shoots from healthy-looking tree which were then cov
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