Lucio Montecchio

Vertical distribution of the ectomycorrhizal community in the top soil of Norway spruce stands

The vertical distribution of the ectomycorrhizal (ECM) community was studied in four old high-mountain Norway spruce (Picea abies [L.] Karst.) stands in northern Italy. The aim was to verify if the variability in the community structure could be explained by characteristics of the organic and mineral soil horizons. The community structure was evaluated in terms of both fungal species and their ability to explore soil (exploration types). From the 128 humus profiles sampled over the two study periods, 31 ECM species were recorded. The study demonstrated that the number of both non-vital tips and vital non-mycorrhized tips decreases with soil depth, from organic to mineral horizons, while the number of ectomycorrhizal tips mainly increases with soil depth. A preference was found of some ECM species and exploration types for specific organic or mineral soil layers and their features, especially moisture and available nitrogen. These results can help in understanding how the functional role of the single consortia and the ecological features determining this “adaptive diversity” in ectomycorrhizal communities could be of major importance to assess the resilience in forest soil ecosystems.

Changes in ectomycorrhizal diversity in a declining Quercus ilex coastal forest

Oak decline is generally accepted to be the result of a dynamic interaction between oaks and a mix of abiotic and biotic causes, within which environmental stresses (drought, salinity, frost, low fertility) may be important as predisposing factors. As a result of these interactions, trees gradually begin to show symptoms of general suffering, which below ground consist of functional and anatomical modifications to the rootlets and changes in the ectomycorrhizal status. The present study was performed in a coastal Quercus ilex forest, where decline symptoms appeared after heavy land reclamation in the adjoining areas, which caused a rapid lowering of the ground water level and the underground intrusion of seawater from the neighbouring Adriatic Sea into the forest itself. A forest survey including examination of rootlet features from asymptomatic and declining trees suggested that drought and salinity were involved in this decline. The relative frequency of the most recurrent ectomycorrhizal morphotypes distinguished clearly between asymptomatic, weakly declining and strongly declining trees, suggesting that the occurrence and distribution of only a limited number of morphotypes can give an indication of the severity of the decline. Moreover, of all the morphotypes observed only one third were found in all three decline classes, while the remaining two thirds were gradually replaced by others as the proportion of declining trees increased, where the number of morphotypes was greater. The hypothesis of an adaptive response of the ectomycorrhizal community to decline or to the predisposing factors of decline is discussed.

The ectomycorrhizal community structure in high mountain Norway spruce stands

The species composition of ectomycorrhizal (ECM) fungal communities can be strongly influenced by abiotic and biotic factors, which determine interactions among the species such as resource partitioning, disturbance, competition, or relationships with other organisms. To verify whether ectomycorrhization of the root tips and composition of the ECM community in Norway spruce vary according to site features and if ECM species peculiar to these environmental variables can be detected, ten comparable stands differing in bedrock pH and exposure were selected and studied. The results demonstrated that tips vitality and ectomycorrhization degree do not change significantly either on the same tree, or among trees growing in the same stand, whereas they differ greatly with bedrock pH and exposure, even if no spatial or temporal trend were found. ECM species composition revealed instead a significant connection with the two environmental features, with a few species significantly associated to them. The results suggest that pH/exposure patterns play a primary role in the adaptive selection of ECM species constituting the consortium.

A geostatistical model to describe root vitality and ectomycorrhization in Norway spruce

Abstract The spatial distribution of vital root tips and ectomycorrhizal (ECM) communities in forest soils is characterized by patchiness at a microscale level, mostly related to the distribution patterns of biotic and abiotic factors. A geostatistical model was applied to verify if spatial analyses could be useful in identifying an appropriate sampling method to study root tip vitality, ectomycorrhization and the ECM community. Root samples were collected from two high mountain Norway spruce forests (Trentino province, Italy) following a geometrical design. Laboratory microscopic and geostatistical ordinary kriging analyses were used to map tip vitality and ectomycorrhization degree, ECM richness and distribution grouped in “exploration types” (amount of emanating hyphae or presence and differentiation of rhizomorphs). Spatial gradients of the examined features existed at plant level, associated to the up-downslope direction (root tip vitality and ectomycorrhization, ECM richness) and distance from the stem base (ECM exploration types). The effectiveness of the geostatistical model used demonstrates that a geometrical sampling design, associated to spatial mapping techniques, can be useful in research where the tree, and not the forest, is the subject (mycological and phytopathological studies).

The ectomycorrhizal community in Mediterranean old-growth Quercus ilex forests along an altitudinal gradient

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.

Risk of Natural Spread of Hymenoscyphus fraxineus with Environmental Niche Modelling and Ensemble Forecasting Technique

Ash dieback, caused by the ascomycete Hymenoscyphus fraxineus, is rapidly expanding over large geographical areas in Europe. A myriad of factors influence pest invasions and long-term establishment, i.e., species’ life stage, the availability of suitable hosts and the suitability of the environment. This paper examines the principal environmental features that characterise naturally infected zones in order to forecast the potential distribution of the pathogen within the ranges of European ash species by means of Species Distribution Modelling and an ensemble forecasting technique. Furthermore, a network analysis permitted dispersal dynamics to be included in order to obtain realistic risk predictions for the natural spread. The multi-modelling procedure allowed the most endangered regions to be identified as the central and eastern Alps, Baltic States, southern Finland and the area encompassing Slovakia and southern Poland, whereas most marginal regions of the study area appeared less suitable for the natural establishment and spread of the disease. Statistical model predictions were highly correlated with abundant summer precipitation, high soil moisture and low air temperature. A novel approach to the ensemble forecasting technique in epidemiological modelling of plant pathogens is suggested as a tool to aid the survey of this infectious disease. Moreover, the final potential distribution maps may promote discussions about the control of the disease and the risks associated in the trade or movement of ash species.

A sampling method to describe the Norway spruce ectomycorrhizal community at plant level

Abstract To verify the possibility of developing a sampling method to accurately describe the Norway spruce ectomycorrhizal community at plant level, research was conducted in four comparable monospecific forests on healthy, mature and coeval Norway spruce trees. The results showed that the lowest number of tips per root core can characterize the community changes from site to site, with tree species, age and sampling design being constant. This highlights the importance of ectomycorrhizal species distribution, which is not an intrinsic character of ectomycorrhizal species, and probably changes with the environmental and fungal community features. The research demonstrated, in accordance with a theoretical ectomycorrhizal distribution, the effectiveness of an encoded geometrical sampling design consisting of the collection of 24 root samples from each of the four unrelated plants, along four perpendicular directions and at six fixed distances from the collar, and with the observation of 10 randomly selected ectomycorrhizal tips per sample.

Damping-off of beech seedlings caused by Fusarium avenaceum in Italy.

During May of 2004, damping-off of an estimated 70% of beech (Fagus sylvatica L.) seedlings was observed in a bare-root forest nursery located in northern Italy. Twenty-eight days after sowing, cotyledonary leaves were chlorotic, wilted, and occasionally desiccated; stem and collars appeared stunted and discolored with yellowish gray-to-brownish longitudinal streaks arising from the foot region, and rootlets were partially to completely rotten. No fruiting bodies were present on or near the damaged regions. Seedling establishment was poor within the disease foci that gradually increased in size. Longitudinal sections through the damaged stems showed dark brown streaks in the vascular tissue, and microscopic examination revealed that vessels frequently contained mycelium. Ten symptomatic plants were selected, and isolations were made from the necrotic margins of stems previously surface sterilized with 1% sodium hypochlorite and thoroughly rinsed, longitudinally cut into two parts 5-mm long, placed on potato dextrose agar (PDA), and incubated at 22 ± 1°C for 5 days in the dark. Although a variety of microorganisms were isolated, Fusarium avenaceum (Fr.:Fr.) Sacc. (1) was always recovered. Artificial inoculations with the fungus were made on 20-day-old, container-grown beech seedlings. The epidermis surrounding the collar was surface sterilized with 1% sodium hypochlorite, rinsed, and gently scraped with a sterile scalpel. After masking the rest of the plant with a plastic sheet, the wound was sprayed with a conidial suspension containing 103 macroconidia per cm3 in water and sealed with Parafilm. Controls were treated the same way but with sterile water. Each treatment was applied to 10 seedlings and incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12 h of natural light per day). After 20 days, wounds treated with F. avenaceum showed necrotic lesions that developed into small patches of dead epidermis. Radial sections through the stem 2 cm above the inoculation site from five plants showed the presence of mycelium in the vessels, from which the fungus was reisolated. Thirty days postinoculation, the remaining five plants showed the same symptoms observed in the nursery, and microscopic observations confirmed the presence of the fungus. No disease symptoms or mycelium were observed in the inner tissues of control plants. The pathogenicity test was repeated twice with the same results. The fungus was not detected by culturing 100 surface-sterilized seeds from the same stock that had been sown in the nursery. F. avenaceum has a broad host range including angiosperms and gymnosperms, and the described symptoms are fairly typical (2). To our knowledge, this is the first report of this disease in Italy. Further research on fungal survivability in nursery soil and plant debris is in progress. The isolate is preserved in the Centraalbureau voor Schimmelcultures (NL) collection as no. 115957. References: (1) C. Booth. Fusarium. Commonwealth Mycological Institute, Kew, UK, 1977. (2) H. Butin. Tree Diseases and Disorders. Oxford University Press, New York, 1995.

A Twig Canker on Russian Olive Caused by Phomopsis arnoldiae in Italy

In June 2002, open, irregularly shaped cankers on stems and twigs of Russian olive (Eleagnus angustifolia L.) were observed in central Italy in two neighboring experimental walnut timber plantations (i.e., Juglans regia L. or J. nigra L. grown with Alnus glutinosa L. and E. angustifolia as nitrogen-fixing plants). Foliage distal to the cankers appeared chlorotic and wilted and occasionally desiccated. No fungal, fruiting bodies were present on or near the canker surface, nor were symptoms were observed on root collars or roots. Radial sections through the cankers revealed dark brown discoloration of xylem, and microscopic examination showed that vessels frequently contained tyloses and mycelium. Four symptomatic plants were selected, and from each of these plants, isolations were made from one canker. From the necrotic margin of each canker previously surface-sterilized with 2% sodium hypochlorite and rinsed, two chips, 3-mm-wide, were placed on potato dextrose agar (PDA) and incubated at 20 ± 1°C for 8 days in the dark. Among a variety of microorganisms isolated were Coniothyrium fuckelii Sacc., Penicillium spp., and Phomopsis arnoldiae B. Sutton (3). Artificial inoculations were made on 3-year-old, container-grown E. angustifolia seedlings using two isolates each of the three fungi. Where the stems measured 5 mm in diameter, the bark was surface sterilized with 2% sodium hypochlorite, rinsed, wounded with a 3-mm-diameter cork borer, inoculated with a PDA disk containing mycelium and spores, and the wound sealed with Parafilm. Controls were treated the same way but with sterile disks of PDA. Each treatment was replicated with 10 seedlings and incubated in the greenhouse (20 ± 2°C, 80% relative humidity, and 12 h of natural light per day) for 60 days. After 30 days, wounds treated with P. arnoldiae showed necrotic lesions that developed into small patches of dead bark that cracked forming cankers. Radial sections through the stem at the canker site from 10 plants (five per isolate) showed the presence of mycelium in the vessels, from which P. arnoldiae was reisolated. After 60 days, the cankers on the remaining 10 plants measured 8 to 14 mm long, and microscopic observations confirmed the presence of the fungus. No disease symptoms or mycelium in the inner tissues were observed in the control plants or in the plants inoculated with the other fungi. The pathogenicity test was repeated twice with the same results. Detailed descriptions of both fungal features in vitro (1,3) and symptoms on larger plants are available (2). To our knowledge, this is the first report of this disease in Italy. Further research is in progress since Russian olive in Italy is frequently grown in the nursery for agronomic purposes because of its nitrogen-fixing ability. Cultures of our isolates of P. arnoldiae, the identification of which was confirmed by the Centraal Bureau voor Schimmelcultures (Utrecht, the Netherlands), are preserved in the herbarium L. Montecchio (LMPa1 and LMPa2) in Padova. References: (1) R. H. Arnold and J. C. Carter. Mycologia 66:191, 1974. (2) W. A. Sinclair et al. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY, 1987. (3) B. C. Sutton. The Coelomycetes. Commonwealth Mycological Institute, Kew, UK, 1980.

An enhanced trunk injection formulation of potassium phosphite against chestnut ink disease

Abstract Chestnut ink disease, caused by Phytophthora cinnamomi and P. cambivora, is one of the most destructive diseases affecting Castanea sativa. Currently, disease control requires careful integrated chemical and agronomic measures. Trunk injection with potassium phosphite was proven to be effective in reducing symptoms but little is known about the ideal formulation. In this research, potassium phosphite at different concentrations and with some other bio stimulants was injected into sweet chestnuts which had been inoculated with a local strain of P. cinnamomi. The most effective formulation, potassium phosphite mixed with a micronutrient solution, was then tested with a preventive approach; as a result, the trunk injection treatments completely ceased the development of the disease in planta in most cases. In order to consider the importance of each component of the solution, potassium phosphite and the bio stimulant elements were tested in vitro singly and in an isobolographic analysis of interactions. The results broaden the knowledge base on endotherapic treatments as an effective measure for the management of chestnut ink disease with potential for many other diseases.