Phytophthora disease of Quercus ilex in south‐western Spain

Oak decline that was affecting three holm oak sites in the province of Huelva (south‐western Spain) was studied during 1998–1999. The syndromes of dieback and sudden death have been observed and, in both cases, foliar symptoms were associated with root rot. Characterization of the fungal isolates from necrotic roots led us to identify Phytophthora cinnamomi A2 as consistently associated with the disease. The optimum growth temperatures of these isolates were very high (30°C). Inoculation tests under controlled conditions demonstrated the pathogenicity of the isolates on holm and cork oak seedlings. None of the other biotic factors of Mediterranean oak decline that have been previously described were found in the present study and so, in this case, the forest decline model does not seem to be necessary in order to explain the disease observed. The defoliation and mortality of the oaks was primarily caused by P. cinnamomi, although some abiotic factors such as alternating periods of drought and wet weather in the region may play an important role.     

Involvement of Phytophthora species in white oak (Quercus alba) decline in southern Ohio

This study was initiated to investigate the possible role of Phytophthora species in white oak decline (Quercus alba) in southern Ohio at Scioto Trail State Forest. Surveys demonstrated the presence of four species of Phytophthora including one novel species. By far, the most common species was P. cinnamomi; P. citricola and P. cambivora were isolated infrequently. In few instances, P. cinnamomi was isolated from fine roots and necroses on larger roots. No special pattern of incidence was found, but P. cinnamomi was more commonly isolated from greater Integrated Moisture Index values suggesting moist lower bottomlands favour this Phytophthora species. When tree crown condition was examined relative to the presence of Phytophthora, no significant association was found. However, roots of declining P. cinnamomi‐infested trees had 2.5 times less fine roots than non‐infested and healthy trees, which was significantly different. The population densities of P. cinnamomi from declining trees were significantly greater than from healthy trees, suggesting increased pathogen activity that has the potential to cause dieback and decline and possibly the cause of a reduced fine root amount found on declining trees.     

Phytophthora ×alni and Phytophthora lacustris associated with common alder decline in Central Portugal

Since the early 1990s, an emerging disease induced by the highly aggressive oomycete Phytophthora ×alni has caused widespread alder decline across Europe. In parallel, P. lacustris, a recently described species associated with riparian habitats, has been subject of increasing interest. A field survey conducted in 2014 showed high mortality rates in alder stands located in the riparian gallery along two rivers in Central Portugal. The pathogens isolated from necrotic alder stem base during this study were identified as P. ×alni and P. lacustris. This paper is the first to report the occurrence of P. lacustris in Portugal and presents the first finding of P. ×alni affecting mature trees in natural ecosystems located in Central Portugal.     

Field survey,isolation, identification and pathogenicity of Phytophthora species associated with a Mediterranean‐type tree species

Corymbia calophylla (marri), a keystone tree species in the global biodiversity hot spot of southwestern Australia, is suffering decline and mortality associated with a canker disease caused by the endemic fungus Quambalaria coyrecup. Phytophthora species are frequently isolated from the rhizosphere of C. calophylla, and a hypothesis is that Phytophthora root infection is predisposing C. calophylla to this endemic canker pathogen. Field surveys were conducted in both anthropogenically disturbed and undisturbed C. calophylla stands, from where a total of 100 rhizosphere soil samples, from both healthy and cankered trees, were collected. Phytophthora species were isolated from 26% of the samples collected, with Phytophthora incidence significantly higher on disturbed stands than in natural forests (73% and 27%, respectively). Five Phytophthora species were recovered, including P. cinnamomi, P. elongata, P. multivora, P. pseudocryptogea and P. versiformis. Under‐bark inoculations with the Phytophthora isolates caused significant lesion lengths in excised C. calophylla stems. Corymbia calophylla response to pot infestation trials in the glasshouse varied between Phytophthora species and isolates, with isolates of P. cinnamomi and P. multivora causing a significant reduction in seedling root volume and often leading to seedling death. This study demonstrates that root disease caused by Phytophthora species, especially P. cinnamomi and P. multivora, has the ability to adversely affect C. calophylla health. This study leads the way to do a dual inoculation trial with the canker pathogen Q. coyrecup, and different Phytophthora species to investigate if Phytophthora root infection predisposes C. calophylla to this canker disease.     

Oak decline: Aerobic bacteria associated with declining Quercus cerris in Central Italy

Declining Turkey oaks (Quercus cerris) in Central Italy were studied. Bacteria were isolated from woody tissues between necrotic areas and healthy tissues beneath the bark, from apparently healthy tissues and from exudates oozing from the trunk in spring. A total of 98 bacterial isolates were collected. The determination of the bacteria was by fatty acid profiling and biochemical tests. Erwinia herbicola was frequently found both in necrotic and healthy tissues. Ice-nucleation active species were present. None of the species isolated was considered responsible for the decline     

Susceptibility of the Quercus rubra root system to Phytophthora cinnamomi; comparison with chestnut and other oak species

The susceptibility of oak seedlings (Quercus palustris, Quercus robur, Quercus rubra) and chestnut seedlings (Castanea sativa) to Phytophthora cinnamomi was tested. The dynamics of infection was examined in plant material raised in a rhizotron. In the oak species, primary root tissues were susceptible whereas secondary cortical tissues showed some resistance to P. cinnamomi. Secondary cortical tissues of the tap root in C. sativa were susceptible. Inoculations with P. cinnamomi were performed both in situ and on excised roots of mature Q. rubra. In both cases, the resistance of Q. rubra roots and shoots was negatively correlated with diameter at the inoculation point. Small roots (l–5-cm diameter) were resistant, whereas collar and trunk were susceptible. In contrast to oak, small excised roots of mature C. sativa (0.7–2-cm diameter) were susceptible to P. cinnamomi. This may explain why P. cinnamomi does not induce a decline of the attacked oaks, but rather a trunk canker.     

Stand factors influencing Pinus halepensis decline in north‐western Spain

Although decline of Aleppo pine was observed long ago and several climatic and biotic factors have been previously associated with this complex process, site factors involved in this decline remain poorly understood. The objective of the work described here was to identify site factors associated with canopy condition. Canopy condition was estimated both by a visual estimation of defoliation, and by an indirect estimation of leaf area index (LAI) and other stand‐ and light‐related parameters through the analysis of hemispherical photographs. A high percentage of damaged trees (81%) along with high levels of defoliation in plots (up to 53%) and trees (up to 85%) were recorded. Regression models showed that the site factors associated with defoliation were basal area, age, crown depth and elevation, while those associated with LAI were diameter at breast height, tree density and canopy openness. Analysis of hemispherical photographs proved to be a useful method for LAI estimation, but not for estimation of defoliation due to heterogeneous defoliation patterns caused by fungal pathogens detected in the study area. Soils and climatic conditions were common to all plots, so their influence could not be tested, but poor soil conditions and climatic restraints are known in this area, including low soil productivity, frequent summer droughts and high numbers of frost days. The results obtained suggest that several factors were associated with the decline of Pinus halepensis, including age, basal area, canopy openness, diameter, height and tree density. These factors can influence canopy condition, and thus, they might be acting as predisposing factors for the decline. The modulation of these factors is possible if suitable forest management strategies are applied, which could lead to a decrease of the decline incidence.     

Phytophthora species associated with dieback of sweet chestnut in Western Turkey

Sweet chestnut (Castanea sativa) is an important tree species in the Marmara and Aegean regions of Turkey as these two regions produce the great majority of edible nuts, especially those used for marron glacé production. Chestnut forests and orchards in these regions showing severe dieback symptoms not associated with chestnut blight were investigated to determine the role of Phytophthora spp. in the decline syndrome. Soil samples were collected from around 108 symptomatic chestnut trees at 29 sites and Phytophthora spp. isolated using soil baiting technique and selective medium. Species isolated were identified by cultural characteristics and ITS sequencing. Phytophthora x cambivora was the dominant species detected in 13 sites, followed by P. cinnamomi (5 sites), P. plurivora (3 sites) and P. cryptogea (1 site). Phytophthora x cambivora was present in both regions, while P. cinnamomi was found only in the Marmara region in coastal areas around Istanbul. When inoculated at the stem bases of 3‐year‐old chestnut saplings, P. cinnamomi produced significantly longer necrotic lesions (7.8–12.0 cm) than P. x cambivora (2.6–6.3 cm) by 12 days after inoculation. Phytophthora plurivora was the least aggressive species causing only small lesions. Phytophthora cryptogea, which represents the first record on chestnut in Turkey, produced intermediate sized lesions in between P. x cambivora and P. plurivora. These results indicate that P. x cambivora and in some areas P. cinnamomi play major roles in the observed dieback of sweet chestnut in western Turkey.     

Decline‐associated Phaeoacremonium species occurring on forest trees in the north of Iran

Between 2013 and 2015, several surveys were conducted throughout forest areas in the north of Iran with the aim of isolating and identifying fungi present on trees showing decline symptoms. Fungal species, isolated from symptomatic wood tissues of various tree genera, including Zelkova, Acer, Parrotia, Quercus, Diospyros, Fagus, Fraxinus, Populus, Pinus, Pterocarya, Gleditsia, Carpinus, Ulmus, Crataegus, Alnus, Mespilus, Punica, Cydonia, Cupressus and Prunus, were morphologically identified and characterized. A molecular identification based on comparisons of DNA sequences of the β‐tubulin gene allowed us to identify seven species belonging to Phaeoacremonium; namely, Phaeoacremonium parasiticum, Pm. alvesii, Pm. minimum, Pm. iranianum, Pm. scolyti, Pm. fraxinopennsylvanicum and Pm. croatiense were isolated and identified. Phaeoacremonium minimum was the most common species and isolated from Gleditsia caspica, Parrotia persica, Cydonia oblonga and Alnus glutinosa. Pathogenicity on selected plants using a mycelium plug inoculation method revealed that most of these species are pathogenic to all the tested trees, with Pm. parasiticum and Pm. minimum being the most pathogenic species. According to host plant species and geographical distribution, the majority of Phaeoacremonium species found represent new records. This is also the first report of Pm. croatiense in Iran and outside Croatia.     

Canopy species composition drives seasonal soil characteristics in a Mediterranean riparian forest

European Journal of Forest Research - Mediterranean riparian ecosystems provide key ecosystem services, such as climate regulation, water quality, and flood protection. Forest degradation and...     

Spatial associations among tree species in a temperate forest community in North-western Spain

Analyzing spatial patterns in plant communities may provide insights in the importance of different processes for community assembly and dynamics. We applied techniques of spatial point pattern analysis to data from a fully mapped plot of a temperate forest community (Corylus avellana, Crataegus monogyna, Fagus sylvatica, Ilex aquifolium and Taxus baccata) in North-western Spain to conduct a community wide assessment of the type and frequency of intra and interspecific spatial association patterns. We first explored the overall intra and interspecific patterning, and then classified the types of association patterns at various neighbourhoods. By conditioning on the larger scale pattern we then explored small-scale (0–15 m) intraspecific and interspecific patterns. Association patterns varied from strong positive association at small scales to, as a by-product, repulsion at intermediate scales. Surprisingly, there were no negative associations at small scales, but trees were arranged in multi-species clumps, up to 2.5 m in diameter and comprising a few individuals. Ilex and Corylus, the understorey species, were frequently involved in the clumps, showing positive small-scale association with the other tree species. Our analyses highlighted that animal mediated seed dispersal, interspecific facilitation and perturbation processes may operate successively to shape tree distributional patterns, although their relative importance vary among species. Given the complexity of the patterns described and the current threats to some of the species studied, directed experiments in the field are needed to further elucidate some of the hypotheses derived.     

Phytophthora alticola and P. boodjera associated with decline of young Eucalyptus smithii trees in Uruguay

Eucalyptus production mainly destined to cellulose pulp production has expanded strongly in the last 30 years in Uruguay. Eucalyptus smithii has recently emerged as a promising species for cellulose pulp production. However, an average of 40% of young trees die during the first and second summer of post-planting. In this study, 32 Phytophthora isolates were obtained from 132 E. smithii young trees with root and collar rot symptoms, confirming the association of Phytophthora to E. smithii decline. Based on phylogenetic analysis of ITS, TUB2, cox1 and HSP90 gene regions and phenotypical characteristics, two species belonging to the genera Phytophthora clade 4 were identified, P. alticola (96%) and P. boodjera (4%). Tested isolates of both species significantly reduced both shoot and root dry weights of inoculated E. smithii seedlings compared to control plants. To our best knowledge, this is the first time that P. alticola and P. boodjera are recovered from young symptomatic E. smithii trees in commercial plantations as well as the first time these species are found in the Americas.     

Phytophthora pseudosyringae associated with the mortality of Nothofagus obliqua in a pure stand in central‐southern Chile

Mortality of Nothofagus trees in the southern‐central Chile region has been observed for over 30 years. A field survey conducted in 2013 detected partial defoliation and bleeding cankers on Nothofagus obliqua in a pure stand in the Nahuelbuta coastal ranges of the Biobío region. A Phytophthora sp. was isolated from stem cankers and soil samples around symptomatic N. obliqua trees: All isolates were identified as Phytophthora pseudosyringae. These isolates were pathogenic on 1‐year‐old N. obliqua and Nothofagus alpina, and on detached twigs of adult N. obliqua and Nothofagus dombeyi trees. This paper is the first to report association and pathogenicity of P. pseudosyringae with N. obliqua, N. alpina and N. dombeyi native to the Biobío region of Chile. The potential of P. pseudosyringae to cause damage in natural Nothofagus stands in Chile must be determined.     

Rapid diagnosis of pathogenic Phytophthora species in soil by real‐time PCR

Real‐time PCR assays based on the TaqMan system and using ITS sequences were developed for the identification of Phytophthora species, including P. cactorum, P. megasperma, P. plurivora, P. pseudosyringae and P. quercina, all of which are currently causing significant damage to roots of forest trees in both managed stands and natural ecosystems. Total genomic DNA was extracted from mycelia of aforementioned Phytophthora isolates. Species‐specific primers for P. cactorum, P. megasperma, P. plurivora, P. pseudosyringae and P. quercina were designed based on ITS sequences of rDNA. The amplification efficiency of target DNA varied from 93.1% (P. pseudosyringae) to 106.8% (P. quercina). The limit of the detection was calculated as 100 – 1,000 fg DNA, depending on the Phytophthora species. In mixed soil samples, all Phytophthora species were detected for Ct values shifted by 0.7 – 2.1 cycles. Based on these real‐time PCR assays we were able to identify the five Phytophthora species. These techniques will be of value in the identification of these pathogens, which may cause up to 80 – 90% fine root loss in oak stands.     

Multinomial logit estimation of a diameter growth matrix model of two Mediterranean pine species in Spain

• Introduction   

Understanding diameter growth of the Mediterranean pine species is fundamental for evaluating and making appropriate strategic decisions in forest management. A matrix diameter growth model for two Mediterranean pine forest ecosystems in Spain has been developed.     

Seasonal changes in the temperature response of photosynthesis in canopy leaves of Quercus crispula in a cool-temperate forest

Understanding seasonal changes in photosynthetic characteristics of canopy leaves is indispensable for modeling the carbon balance in forests. We studied seasonal changes in gas exchange characteristics that are related to the temperature dependence of photosynthesis in canopy leaves of Quercus crispula Blume, one of the most abundant species in cool-temperate forests in Japan. Photosynthetic rate and ribulose-1,5-bisphosphate (RuBP) carboxylation capacity (V(cmax)) at 20 degrees C increased from June to August and then decreased in September. The activation energy of V(cmax), a measure of the temperature dependence of V(cmax), was highest in summer, indicating that V(cmax) was most sensitive to leaf temperature at this time. The activation energy of V(cmax) was significantly correlated with growth temperature. Other parameters related to the temperature dependence of photosynthesis, such as intercellular CO(2) partial pressure and temperature dependence of RuBP regeneration capacity, showed no clear seasonal trend. It was suggested that leaf senescence affected the balance between carboxylation and regeneration of RuBP. The model simulation showed that photosynthetic rate and its optimal temperature were highest in summer.     

Sapling architecture and growth in the co-occurring species Castanopsis cuspidata and Quercus glauca in a secondary forest in western Japan

This study quantitatively compared the sapling (height 62–289cm) architecture and growth of Castanopsis cuspidata and Quercus glauca, both of which are major components in the temperate zone of western Japan, under shaded light conditions in secondary forest. When the sapling architectures were compared at the same support mass (trunk + branch mass), C. cuspidata had a larger crown area but a smaller height gain than did Q. glauca owing to the allocation of more biomass to lateral branches in C. cuspidata. The above-ground relative growth rate (RGR) of C. cuspidata (0.442gg^–1 year^–1) was nearly twice that of Q. glauca (0.256gg^–1year^–1), primarily as a result of a greater total leaf area per above-ground biomass (LAR) in C. cuspidata (56cm²g^–1) as compared to Q. glauca (33cm²g^–1). Because it has a disadvantage in height gain, related to its allocation pattern of biomass, C. cuspidata realized the same height growth (RGR_H) as Q. glauca, despite the large biomass production. The great potential for photosynthesis in C. cuspidata, which results from its vigorous lateral spreading, is presumed to give it a long-term advantage over Q. glauca in the shaded forest understory. Q. glauca invests preferentially in trunk biomass, possibly giving it an advantage in sunny sites as opposed to a shaded forest understory.     

Nutrients return from leaves and litterfall in a mediterranean cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) forest in southwestern Spain

The knowledge of the cycle of nutrients is fundamental for the correct comprehension of the tree–soil relationship and for an adequate forest management. In order to analyse the nutrients return from leaves and litterfall in a Mediterranean cork oak forest in southwestern Spain, 12 trees were randomly selected and litterfall collected for 2 years. Samples were taken monthly and separated in different fractions (leaves, twigs, catkins, acorns and miscellaneous), then leaves nutrients were analyzed. Simultaneously, we analyzed the nutrient content of living leaves from the same trees in each season during 1 year. The analyzed nutrients were C, N, P, K, Ca, Mg, Fe, Mn, S, Cu, Zn and Mo. Annual patterns of each nutrient in fallen leaves were characterized and compared with seasonal values of these nutrients in living leaves. Leaves fall has two annual maximum, first and most important in spring around April coinciding with renewal of foliar cover and second around October. Main concentration patterns of N, P and K are related with phenological patterns, in consequence minimum concentration in leaves fall were obtained in periods of growing and maximum litterfall. Concentrations of Ca, Fe and Mn increase with the age of the leaves and maximum concentrations were obtained before periods of maximum litterfall while concentrations of Cu, Mo and Mg stay stable. Seasonal analysis of nutrients in living leaves collected from the same trees in four different periods of the year allowed to corroborate the patterns of leaves fall and the probable osmotic function of K.     

Biotic interactions in a Mediterranean oak forest: role of allelopathy along phenological development of woody species

Plant–plant chemical interactions in forests can have a strong impact on the biodiversity and dynamics of these ecosystems, particularly in Mediterranean forests where plants exhibit a high secondary metabolite diversity. Allelopathic interactions in Mediterranean ecosystems have been mostly studied in the first stages of ecosystem dynamics, shrublands and pine forests, but little is known about these interactions in mature oak forests. In this study, the allelopathic effect of three main woody species of downy oak forests (Quercus pubescens, Acer monspessulanum and Cotinus coggygria) on germination and growth of two herbaceous species (Festuca ovina and Linum perenne) was tested through aqueous extracts obtained from different leaf phenological stages (green, senescent and litter). The germination velocity of the two target species was inhibited by the aqueous extracts of senescent leaves from all the woody species. The growth of F. ovina seedlings was affected by aqueous extracts of green leaves of all the woody species, while the growth of L. perenne was only affected by aqueous extracts of green leaves of A. monspessulanum. This shows that (i) allelochemicals released by leaf leachates of the dominant woody species could control the dynamic of the herbaceous species, and then their potential competition with trees and (ii) allelopathic effects of woody species are related to their phenological stage and seem consistent with the development stage of target species.