Naslov
First Report of Charcoal Disease of Oak (Biscogniauxia mediterranea) on Quercus spp. in Croatia

Autori
Diminić, Danko ; Kranjec Orlović, Jelena ; Lukić, Ivan ; Ježić, Marin ; Ćurković-Perica, Mirna ; Pernek, Milan

Izvornik
Plant disease (0191-2917) 103 (2019), 10; 2687-2687

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Quercus cerris, Q. pubescens, Q. ilex, perithecial stromata

Sažetak
In January 2015, an investigation of 800 ha of declining oaks in Istria and Cres (Croatian North Adriatic karst area), revealed intense dieback symptoms on Quercus cerris, Q. pubescens, and Q. ilex (Fig. 1A). Oaks make-up 82 - 100% of the trees in these stands. The disease was recorded on 357 trees/ha at the most affected site. Black stromata of various sizes were observed on branches and stems of oaks with decline symptoms. A larger percentage of Q. cerris and Q. pubescens trees were symptomatic than Q. ilex trees. Soil depth appeared to be associated with symptom severity. Oak sites revealed extensive progression of root rot and trunk decay in many trees since 2016. Examined perithecial stromata were typical for Biscogniauxia mediterranea (BM), a causal agent of charcoal disease of oak. Collected perithecial stromata are deposited in the Herbarium of the Faculty of Forestry (UNIZG). The asci were short- stipitate, 110.5 to 169.0 × 7.8 to 12.9 µm. The ascospores were ovoid, brownish-black, with roundish and narrowed ends, 12.8 to 21.6 × 6.2 to 9.6 µm. Pure fungal cultures were obtained by inoculating spores from perithecia on Potato Dextrose Agar (PDA). DNA was isolated from mycelia growing on cellophane-overlaid PDA using OmniPrep for Fungus TM (G-Bioscience) kit. The ITS1-5.8S-ITS2 region of samples, obtained in Istria from Q. cerris (45°02'54.74" N, 13°44'12.46" E), Q. ilex (45°01'32.58" N, 13°41'43.55" E) and on island Cres from Q. pubescens (45°06'32.23" N, 14°20'11.97" E), was amplified and purified PCR products were sequenced at Macrogen EU. Four obtained sequences (GenBank KU727203/4/5/6), analyzed using NCBI BLAST®, shared 99.7 - 100% identity with BM (GenBank KX611025.1, KT323196.2, KT323196.2, KM216776.1, respectively). A pathogenicity test was performed in 5-year old potted Q. ilex seedlings with mycelium plugs of a single BM isolate (GenBank MK110498 - shared 99.8% identity with BM MH754669), obtained by inoculating spores from perithecia on PDA (sampled Q. cerris). Each of 10 plants was inoculated by inserting PDA mycelium plugs in 0.5 cm circular wounds of the seedlings stem. Six control plants were inoculated only with PDA plugs. Plants were kept in a growth chamber at regulated conditions and watered once a week. Within 50 days, in 9 inoculated plants with mycelium plugs wood and bark necrosis developed (14.0 mm length +/- 2.84SE). Re- isolations after 7 months from 72 necrotic tissue samples (8 per plant) confirmed BM, recovering the pathogen from 50 samples. Isolates from 9 plants (GenBank MK208591/2/3, MK208595, MK208598/9 and MK208600/1/2) shared 99.6 - 100% identity with BM MK110498. BM was not isolated from control plants after 7 months. BM is a known endophyte in Q. cerris, Q. pubescens and Q. ilex (Luchi et al. 2005). Drought is considered the primary predisposing factor and insects a contributing factor for development of BM (Jurc & Ogris, 2006 ; Capretti & Battisti, 2007 ; Vannini et al., 2009 ; Linaldeddu et al, 2011). In the study area the symptoms appeared following several drought periods and defoliations by Lymantria dispar in 2012 and 2013. The total rainfall in June, July and August of 2012 was 27, 4 and 4% respectively of the 30-year average, while average monthly temperatures were 3.4, 3.9 and 3.5°C higher. Due to changing climatic conditions, that are known to favor the development of BM, these oak forest ecosystems are at risk of degradation.

Izvorni jezik
Engleski

Znanstvena područja
Šumarstvo

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