The Mediterranean coastal region is considered a "hot spot" of both biodiversity and climate change, as global average air temperatures and atmospheric CO2 concentrations are increasing with subsequent impacts on regional precipitation patterns. The main goal of this study, performed in the largest Mediterranean holm oak forests (Sardinia Island, Italy), was to verify whether the vitality of root tips and the composition of the ectomycorrhizal community of holm oak change with the altitudinal gradient. The results demonstrated that the altitude does not significantly affect the vitality and the degree of ectomycorrhization of the root tips, while significant differences were observed in the ectomycorrhizal community composition, correlated with both the altitude and the Southward exposition of the root systems, both associated to the increase of xeric and drought conditions at the soil level. This study should help to integrate the understanding of forest ecology and forecast modelling, to improve the management strategies of the Mediterranean oak forests in the future.
From the culture filtrates of Diaporthella cryptica, an emerging hazelnut pathogen, 2-hydroxy-3-phenylpropanoate methyl ester and its 3-(4-hydroxyphenyl) and 3-(1 H-indol-3-yl) analogues, named crypticins A-C, were isolated together with the well-known tyrosol. Crypticins A-C were identified by spectroscopic (essentially nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry) methods. The R absolute configuration (AC) of crypticin A was determined by comparing its optical rotation and electronic circular dichroism (ECD) spectrum with those of papuline, the methyl ester of (-)( S)-phenyllactic acid isolated as the main phytotoxin of Pseudomonas syringae pv. papulans, responsible for apple blister spot. The ACs of crypticins B and C were determined by time-dependent density functional theory calculations of their ECD spectra. Papuline and the new metabolites herein isolated, except tyrosol, were tested at 1 mg/mL on cork oak, grapevine, hazelnut, and holm oak leaves using the leaf puncture assay. They were also tested on tomato cuttings at 0.5 and 0.05 mg/mL. In the leaf puncture assay, none of the compounds was found to be active. Crypticin C and papuline were active in the tomato cutting assay. Additionally, crypticin C displayed moderate inhibitory effect against Phytophthora cambivora.
The black-banded oak borer, Coraebus florentinus, is an emerging pest of oak trees in the western Mediterranean region. Larvae of the insect are xylophagous and progressively excavate an annular gallery that interrupts sap flow, resulting in the death of the attacked branches. Until now, limited information has been available regarding the ecological interactions between C. florentinus and the main plant pathogenic fungi involved in the etiology of oak decline. Knowledge of these interactions is important in understanding their impact in natural ecosystems and developing appropriate management strategies. Therefore, in this study, we characterized the fungal communities occurring in the exoskeleton of adults and larvae of C. florentinus and associated with the necrotic wood tissues surrounding the branch galleries of declining oak trees. A total of 29 fungal species were identified based on DNA sequence data and morphological features, of which 14 were from symptomatic woody tissues, six from insect exoskeleton, and nine from both insects and symptomatic wood tissues. The most frequent fungal species, Cryphonectria naterciae (15.9% of isolates), Dothiorella iberica (11.3%), and Diplodia corticola (9.9%), were isolated from both insect and gallery systems. All three species are well-known oak pathogens and are reported here, for the first time, to be associated with C. florentinus. At the same time, 89.6% of the fungal taxa were isolated from one or two sites, highlighting the site-dependence of fungal community assemblages.
Large, open, irregularly shaped cankers on trunks and twigs of 4- to 12-year-old Crataegus monogyna Jacq. in a mixed oak forest in northern Italy were observed in 2001. Radial sections through the cankers, which often occurred at sites of hail damage from the previous year, showed a brown discoloration in the xylem. Foliage distal to the cankers became chlorotic, wilted, and finally died. When the disease was severe, the entire top of the plant died, and epicormic shoots developed below the cankers. Fruiting bodies were not present on the canker surface, and symptoms were not observed on root collars or roots. Microscopic examination of cankers showed that vessels frequently contained mycelium. Five symptomatic plants were selected, and from each of these plants isolations were made from one canker. Two chips, 3 mm wide, were cut from the necrotic margin of each canker, superficially sterilized with sodium hypochlorite, rinsed, plated on potato dextrose agar (PDA), and incubated at 20 ± 1°C for 8 days in the dark. Among a variety of microorganisms isolated from the necrotic tissues, Fusarium solani (Mart) Sacc. and Coniothyrium sporulosum (Gams & Domsch) van der Aa (1,2) were isolated from 70 and 100% of the chips, respectively. Artificial inoculations were made on 3-year-old, container-grown Crataegus monogyna seedlings obtained from the same seed stock using two isolates each of the two fungi. Where the stems measured 5 mm in diameter, the bark was surface sterilized with sodium hypochlorite, rinsed, wounded with a 2-mm-diameter cork borer, inoculated with a PDA disk containing mycelium and spores, and the wound sealed with Parafilm. Controls were treated the same but using sterile discs of PDA. Each treatment was replicated on five seedlings, incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12-h natural light per day) for 60 days. After 20 days, the 10 plants treated with C. sporulosum showed small necrotic lesions, which developed into small patches of dead bark that cracked and formed spindle-shaped cankers. Radial sections through the stem at the canker site from four of the inoculated plants showed the presence of mycelium in the vessels, and C. sporulosum was reisolated from the infected tissue. After 60 days, the cankers measured as much as 22 mm, and the microscopic observations on the remaining six plants confirmed the presence of the fungus. No disease symptoms or mycelium in the inner tissues were observed for control plants, or plants inoculated with Fusarium spp. The present work adds the genus Crataegus to the wide list of hosts (e.g., Rubus, Malus, Quercus, Picea, Taxus, Juniperus, Chamaecyparis, Cupressocyparis, and Mahonia) susceptible to C. sporulosum, which may act as an important pathogen under forest conditions, in orchards, and in breeding programs. References: 1) W. Gams and K. H. Domsch. Nova Hedwigia, 18:1, 1969. 2) I. Vegh and A. Le Berre. Pepinieristes Hort. Maraich. Rev. Hortic. 331:11, 1992.
Summary In the past few decades, economic interest in the cultivation of chestnuts for both timber and nut production has resurfaced in the Mediterranean area. However, chestnut cultivation has suffered in recent years from the spread of exotic pests, such as the gall wasp Dryocosmus kuriphilus , and from the resurgence of previously present diseases, most likely due to anomalous climate dynamics. This is the case with chestnut ink disease, caused by the soilborne pathogens Phytophthora cinnamomi and P. cambivora . Scientific and technical support in monitoring and management, that utilizes new forecasting approaches incorporating related environmental variables, is therefore essential. The main aim of this study was to develop a mathematical model assessing the potential for the establishment of chestnut ink disease at a large scale. Towards this goal, fuzzy rule‐based theory was applied to the environmental variables associated with host presence, pathogens' ecological niches and ink disease symptoms expression. The effectiveness of the rule‐based modelling outcomes, provided with uncertainty maps to facilitate their correct interpretation, was confirmed by detailed field data collected from a large chestnut‐growing area where ink disease has been increasing in recent years. The final model gave consistent predictions for disease presence. For this reason, it represents a flexible and valuable decision‐support tool to forecast which sites are at risk from CID .
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