Rosellinia aquila Among Fungi on Branches of Sessile Oak with Symptoms of Decline

Rosellinia aquila was found for the first time in crowns of sessile oaks, Quercus robur (Mattuschka) Liebl., with symptoms of decline. The fungus occurred mostly on diseased branches but also colonized twigs with healthy appearance. Its anamorph and teleomorph stages were produced abundantly on dead branches after long incubation in moist conditions. Colonization of oak trees by R. aquila was likely to have been facilitated by higher humidity and temperature in the oak stands.     

Ten years after: Release cutting around old oaks still affects oak vitality and saproxylic beetles in a Norway spruce stand

1. It is often suggested to release oaks (Quercus robur) from competition, to ensure their survival and boost their conservational value. However, few studies have explored how long-lasting this effect is and how it affects saproxylic beetles.
2. Ten years after cutting, we investigated effects of different release cutting levels (high, medium, and no release) around 140-year-old retained oaks in a commercial forest with Norway spruce (Picea abies).
3. We evaluated oak vitality using crown and dead wood measurements. Saproxylic beetles were caught in window traps, identified to species level, and grouped according to their association with oak and/or Norway spruce.
4. Released oaks had more light, higher temperatures, greater crown growth, and less dead wood in the crown compared to the no-release control.
5. After 10 years we still found a higher abundance of oak-associated beetles and higher overall species richness of saproxylic beetles in the released oaks. Beetle species composition significantly differed between released oaks and control.
6. We suggest avoiding planting trees beneath retained oaks when regenerating conifer forests and to proceed with conservation management during subsequent thinning by removing regeneration under the oak crowns. We emphasize the benefits of monitoring the retained oaks to maintain tree vitality, habitat quality, and insolation.

     

<Emphasis Type="Italic">Sporothrix inflata</Emphasis>, a root-inhabiting fungus of <Emphasis Type="Italic">Quercus robur</Emphasis> and <Emphasis Type="Italic">Q. petraea</Emphasis>

The anamorphic fungus Sporothrix inflata, known as a soil-borne fungus with worldwide distribution, was isolated for the first time from the cortex and central cylinder of living and dead roots of healthy and diseased oak trees (Quercus robur and Q. petraea). Isolation frequencies of S. inflata from oak roots varied according to the health status of trees, oak species, study sites, soil depth and root diameter. Colony morphology and growth rate of isolates are influenced by colony age and type of culture medium.     

Forest community structure and composition following containment treatments for the fungal pathogen oak wilt

In temperate oak forests in Ohio, USA, we examined variability in forest communities within containment treatment sites for oak wilt (Bretziella fagacearum), a fungal pathogen lethal to susceptible oak species. Containment treatments included quarantine lines in soil for limiting belowground fungal spread and sanitation cutting of 1–3 mature black oak (Quercus velutina) trees within oak wilt infection patches. At 28 sites, we compared tree structure and understory plant communities across a gradient of 1- to 6-year-old treatments and reference forest (untreated and without evidence of oak wilt). While oak seedlings were abundant, oak saplings (1–10 cm in diameter) were absent. In contrast, many native understory plant community measures were highest in oak wilt treatments. Plant species richness 100 m^?2 doubled in treatments, regardless of age, compared with reference forest. Plant cover increased with treatment age, with 6-year-old treatments exhibiting 5?×?more cover than reference forest. Non-native plants averaged only a small proportion (<?0.12) of cover across treatments and reference forest. Variability in understory communities was mostly predictable using treatment age, tree canopy cover, and geographic location, as 20 of 25 understory measures had at least 72% of their variance modeled. While oak wilt treatments did not facilitate oak regeneration nor many conservation-priority species of open savanna-woodland habitats, the treatments did diversify and increase cover of native understory communities with minimal invasion of non-native plants.

     

Facilitation of tree seedling establishment in a sand dune succession

Abstract. A nucleated pattern of establishment by pine seedlings of Pinus strobus and P. resinosa around pre-established oak trees of Quercus rubra in a sand dune succession in Ontario, Canada was examined using field observations, seed planting and habitat manipulation. Densities of young pines beneath oak canopies were approximately six times greater than in treeless areas, and densities on the north sides of the trees were significantly greater than on the south sides. However, oaks younger than 35 yr showed no preferential establishment beneath them, while the pine population structures beneath older oaks indicated single periods of successful recruitment. Pine seed planted beneath and beyond oak canopies of three sizes germinated primarily beneath the canopies of medium and large-sized oaks, but subsequent survivorship of seedlings over two growing seasons was poor. Several micro-environmental conditions were changed by oak canopies, but only shade showed a pattern closely corresponding to that of seedling establishment. A habitat manipulation experiment confirmed the primary role of shade in facilitating pine seedling establishment beneath oaks. Failure of pine to continue recruiting successfully beneath facilitating trees is tentatively attributed to intraspecific competition among pine individuals.     

Bacterial antagonists of Sunflower (Helianthus annuus L.) fungal pathogens

Bacteria isolated on nutrient agar and King's medium B from sunflower leaves, crown and roots inhibited in vitro growth of the leaf spot and wilt pathogens Alternaria helianthi, and Sclerotium rolfsii, respectively, and also the root rot pathogensRhizoctonia solani and Macrophomina phaseolina. Antagonistic bacteria from leaves were mainly actinomycetes and pigmented Gram-positive bacteria, while those from roots and crowns were identified asPseudomonas fluorescens-putida, P. maltophilia, P. cepacia, Flavobacterium odoratum andBacillus sp. In soil bioassays, when used as seed inoculum in the presence ofS. rolfsii, P. cepacia strain N24 increased significantly the percentage of seedling emergence. Bacterial strains which exhibited broad spectrum in vitro antagonistic activity were tested for colonisation of sunflower roots, when used as a seed inoculum. Good colonisers (10⁴ to 10⁶ bacteria/g root) were consistent in their ability to reduce disease and fungal wilt. A seedling having a primary root length < 5 cm with fewer lateral roots, necrosed cotyledons or crown and a wilted shoot indicated its diseased status. On an average, only 30% of seedlings were diseased when treated with the antagonistic strains, in the presence of the pathogen, while 60% of the seedlings were diseased in the presence of the pathogen alone. In microplots treated with strain N24, only 1 to 3% of the seedlings were wilted, while 14% of the seedlings were wilted in the presence of the pathogen alone. The results obtained show that bacterial antagonists of sclerotial fungi can be used as seed inocula to improve plant growth through disease suppression     

Goldspotted oak borer effects on tree health and colonization patterns at six newly‐established sites

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Long‐term and interactive effects of different mammalian consumers on growth,survival, and recruitment of dominant tree species

Throughout the world, numerous tree species are reported to be in decline, either due to increased mortality of established trees or reduced recruitment. The situation appears especially acute for oaks, which are dominant features of many landscapes in the northern hemisphere. Although numerous factors have been hypothesized to explain reductions in tree performance, vertebrate herbivores and granivores may serve as important drivers of these changes. Here, using data from 8‐ and 14‐year‐old exclosure experiments, we evaluated the individual and interactive effects of large and small mammalian herbivores on the performance of three widespread oak species in California—coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and Oregon white oak (Q. garryana). Although impacts varied somewhat by species and experiment, herbivory by black‐tailed deer (Odocoileus hemionus columbianus) reduced the height and survival of juvenile coast live oaks and altered their architecture, as well as reduced the abundance of black oak seedlings, the richness of woody species and the cover of nonoak woody species. Small mammals (Microtus californicus and Peromyscus maniculatus) had even more widespread effects, reducing the abundance of black oak seedlings and the height and cover of all three oak species. We also detected numerous interactions between small mammals and deer, with one herbivore having positive or negative effects on oak abundance and cover when the other herbivore was either present or absent. For example, deer often had negative effects on seedling abundance only when, or even more so when, small mammals were present. In summary, mammalian consumers play crucial roles in limiting oak recruitment by reducing seedling abundance, maintaining trees in stunted states, and preventing them from reaching sapling stages and becoming reproductive. Interactions between large and small mammals can also alter the intensity and direction of their effects on trees.     

Vegetation associations of birds wintering in a California oak woodland

Conditions in wintering areas can have persistent effects throughout the year for bird populations. Most studies, however, are conducted during the breeding season and the non‐breeding ecology of many species remains poorly understood. We assessed vegetation associations of birds wintering in a diverse, well‐structured oak woodland in coastal‐central California. We calculated density estimates for 20 bird species and examined correlations between bird densities and vegetation characteristics as described by a principal components analysis. Ruby‐crowned Kinglets (Regulus calendula) and Hutton's Vireos (Vireo huttoni) were positively associated with vegetation characteristic of dense, floristically diverse woodland with abundant coast live oak (Quercus agrifolia) cover and a structurally complex understory. Conversely, White‐breasted Nuthatches (Sitta carolinensis) and Western Bluebirds (Sialia mexicana) were negatively correlated with dense woodland and occurred at the highest densities on plots with large widely spaced blue oaks (Q. douglasii) and a sparse understory. Thirteen of the remaining 16 species were more abundant in dense woodland patches, but these relationships were not statistically significant. Our results are in agreement with those of previous studies and suggest that evergreen oak trees and a dense understory provide key resources (e.g., cover and food) for some bird species during the winter. However, areas with large widely spaced deciduous oaks are important habitats for other species. We therefore suggest that dense patches of live oaks and shrubs should be retained, but a mosaic of dense and sparse woodland is necessary to accommodate the entire suite of oak‐woodland birds.     

Sarcodontia pachyodon: a Canker and White‐rot Agent of Plane‐trees

Some lignivorous hymenomycete fungi are capable of causing both cankers and decay in stemwood of adult trees. Recently in Tuscany (Italy), Platanus x acerifolia trees were found colonized by Sarcodontia pachydon (Polyporales, Meruliaceae), a fungus associated with white rot and stem cankers on different host tree species. Because the relationship S. pachyodon‐plane‐tree was only preliminary studied, we decided to investigate whether isolates obtained from this host are distinct from those commonly collected from oaks. For this purpose, isolates obtained from plane‐tree and from holm oak (Quercus ilex) were compared by in vitro test and molecular markers. Results showed that fungal isolates did not differ in growth nor in wood degradation, also molecular tests revealed relative similarity among fungal samples.     

Loss of oak dominance in dry-mesic deciduous forests predicted by gap capture methods

Gap capture methods predict future forest canopy species composition from the tallest trees growing in canopy gaps rather than from random samples of shaded understory trees. We used gap capture methods and a simulation approach to forecast canopy composition in three old oak forests (Quercus spp.) on dry-mesic sites in southern Wisconsin, USA. In the simulation, a gap sapling is considered successful if it exceeds a threshold height of 13–17 m (height of maximum crown width of canopy trees) before its crown center can be overtopped by lateral crown growth of mature trees. The composition of both the tallest gap trees and simulated gap captures suggests that 68–90% of the next generation of canopy trees in the stands will consist of non-Quercus species, particularly Ulmus rubra, Carya ovata and Prunus serotina. Quercus species will probably remain as a lesser stand component, with Quercus alba and Quercus rubra predicted to comprise about 19% of successful gap trees across the three stands. Several methods of predicting future canopy composition gave similar results, probably because no gap opportunist species were present in these stands and there was an even distribution of species among height strata in gaps. Gap trees of competing species already average 11–13 m tall, and mean expected time for these trees to reach full canopy height is only 19 years. For these reasons, we suggest that dominance will shift from oaks to other species, even though late successional species (e.g., Acer and Tilia) are not presently common in the understories of these stands.     

Development of secondary pine forests after pine wilt disease in western Japan

Abstract. The development of secondary Pinus densiflora (Japanese red pine) forests after pine wilt disease was studied through phytosociological analysis, estimation of forest structure before disease and size-structure, tree ring and stem analyses. Following the end of the disease, the growth of previously suppressed small oak trees was accelerated. This is quite different from the development of forests following fire, which starts with the establishment of pine seedlings. Pine wilt disease shifted the dominance of secondary forests from Pinus densiflora to Quercus serrata oak forest. In pine forests, disturbance by fire is important for forest maintenance. In contrast, disturbance by pine wilt disease leads to an acceleration of succession from pine forest to oak forest.     

Attraction of ambrosia and bark beetles to coast live oaks infected by Phytophthora ramorum

1 Sudden oak death is caused by the apparently introduced oomycete, Phytophthora ramorum. We investigated the role of bark and ambrosia beetles in disease progression in coast live oaks Quercus agrifolia. 2 In two Marin County, California sites, 80 trees were inoculated in July 2002 with P. ramorum and 40 were wounded without inoculation. Half of the trees in each group were sprayed with the insecticide permethrin [cyclopropanecarboxylic acid, 3‐(2,2‐dichloroethenyl)‐2,2‐dimethyl‐(3‐phenoxyphenyl) methyl ester] to prevent ambrosia and bark beetle attacks, and then were sprayed twice per year thereafter. After each treatment, sticky traps were placed on only the permethrin‐treated trees. Beetles were collected periodically in 2003. 3 Inoculated trees accounted for 95% of all beetles trapped. The ambrosia beetles Monarthrum scutellare and Xyleborinus saxeseni and the western oak bark beetle Pseudopityophthorus pubipennis were the most abundant of the seven species trapped. 4 Permethrin treatment delayed initiation of beetle attacks and significantly reduced the mean number of attacks per tree. Beetles did not attack any wounded or noncankered inoculated trees. 5 Trees with larger cankers trapped more beetles early in the disease. Once permethrin lost effectiveness, the number of beetle entrance tunnels was a more reliable predictor of subsequent trap catch than was canker size. 6 Beetles were initially attracted to P. ramorum cankers in response to kairomones generated in the host‐pathogen interaction. After beetles attacked the permethrin‐treated trees, aggregation pheromones most probably were the principal factor in beetle colonization behaviour.     

Ecological dynamics of Quercus dominated woodlands in California and southern Spain: a state-transition model

There are many similarities between Spanish and Californian Quercus woodlands and savanna. Both are located in Mediterranean climate zones, and are used predominantly for livestock grazing. The Californian overstory is dominated by one or a combination of five Quercus species and their hybrids: Quercus douglasii H.&A., Q. agrifolia Nee., Q. wislizenii A.DC., Q. lobata Nee., and Q. englemennii Greene (blue, coast live, interior live, valley, and Englemann oaks). In southern Spain and Portugal, Quercus woodland overstory is predominantly one or a combination of two Quercus species, Quercus ilex L. (holm oak) and Quercus suber L. (cork oak). The underlying natural and semi-natural ecological dynamics of the Quercus woodlands of Spain and California are different, and it follows that the management practices employed also differ. The greatest point of contrast between California and Spain is in the intensity and diversity of management goals and practices. A state-transition model for comparing the ecological dynamics of Quercus woodlands and savanna in California and southern Spain is developed and examined. The highly simplified model is an analytic tool of use in organizing research and developing management practices. States are reached and maintained in different ways in Spain and California, but their appearance and their function in each landscape are quite similar.     

Spread and potential host range of the invasive oak lace bug [Corythucha arcuata (Say, 1832) – Heteroptera: Tingidae] in Eurasia

1. The North American oak lace bug feeds on leaves of ‘white oaks” in its native range. In Europe, it was first discovered in northern Italy in 2000. In recent years, it has subsequently spread rapidly and population outbreaks have been observed in several European countries. In the present study, we summarize the steps of its expansion.
2. To predict its potential host range, we checked 48 oak species in 20 sentinel gardens in seven countries between 2013 and 2018.
3. In total, 27 oak species were recorded as suitable hosts; 13 of them are globally new ones, 23 out of the 29 in section Quercus (～ white oaks, an intrageneric taxonomic unit within genus Quercus), including Asian oaks, native to Japan, Korea and China, and four out of five in section Cerris (another intrageneric unit of the same genus), were accepted as hosts. None of the species in section Lobatae (red oaks) or in the Ilex group was accepted.
4. Host records were also collected in forest stands of 10 countries. We found 11 oak species that were infested. Outbreak populations were most commonly found on Quercus robur, Quercus frainetto, Quercus petraea and Quercus cerris, comprising widespread and outstandingly important oaks species in Europe.
5. Based on our findings, we conclude that suitable hosts for oak lace bug are present in most of Europe and Asia. This means that a lack of hosts will likely not restrict further range expansion.

     

Fungal Endophytic Communities in Healthy and Declining Quercus robur L. and Q. cerris L. Trees in Northern Italy

Healthy and declining English oak (Quercus robur) and Turkey oak (Q. cerris) in north‐western Italy, in a plain oak forest showing decline for oak puzzle disease, were tested to assess possible variations in the composition of their fungal endophytic communities and their relation to the health status of trees. Samples collected in spring (buds) and in autumn (leaves, annual shoots and twigs) were surface‐sterilized, cut into fragments and placed on potato dextrose agar for a month; 26 fungal species were isolated, the most frequent being Tubakia dryina, Dendrodochium sp., Eutypella sp. and a sterile mycelium. Correspondence analysis showed significant qualitative differences between assemblages inhabiting twigs and herbaceous tissues that were due to the low frequency of Tubakia dryina in twigs and its higher frequency in buds, leaves and shoots. Tubakia dryina was isolated more frequently from leaves of declining oaks and from buds of healthy oaks; Monochaetia monochaeta showed a preference for healthy trees, especially leaves and buds. According to the Shannon–Wiener index, endophytic fungal communities of leaves, twigs and buds of declining English oak were poorer than those of declining Turkey oak, but there were no significant differences between healthy hosts.     

Woodland canopy structure and the light response of juvenile Quercus lobata (Fagaceae)

I investigated competition for light between canopy plants and juvenile valley oaks (Quercus lobata Nee) in a mixed-broadleaf woodland of California's northern Coast Ranges. Canopy effects on understory light supply were separated among the overlying adult valley oak, the adult's woody understory, and neighboring trees and shrubs through a series of light sampling surveys and measurements of the number, size, and spatial distribution of neighboring plants. Light supply in the understory was primarily influenced by neighboring plants, with no detectable effect of the overlying adult valley oak. Light supply in the understory averaged 25% full sun due to a high frequency of canopy gaps and a typically open understory. Seedling response to understory light supply was investigated in an experimental sunfleck gradient (10%, 19%, and 100% full sun). Between 10% and 100% full sun, seedling growth increased by 90% and the shoot:∗∗∗root ratio changed from 1.561 to 0.607. Shade seedlings were also taller and produced fewer, larger, and thinner leaves than seedlings grown in full sun. A field survey of the spatial distribution and crown morphology of saplings and young adults found 1) the distance between young valley oaks and neighboring overstory trees to increase with neighbor size, and 2) crowns of the young oaks to be skewed away from neighbors. Although shading by the canopy was only moderate, canopy effects on understory light supply may restrict juvenile recruitment of valley oak in this woodland.     

Changes in ectomycorrhizal community structure on two containerized oak hosts across an experimental hydrologic gradient

Shifts in ectomycorrhizal (ECM) community structure were examined across an experimental hydrologic gradient on containerized seedlings of two oak species, Quercus montana and Quercus palustris, inoculated from a homogenate of roots from mature oak trees. At the end of one growing season, seedlings were harvested, roots were sorted by morphotype, and proportional colonization of each type was determined. DNA was subsequently extracted from individual root tips for polymerase chain reaction, restriction fragment length polymorphism, and rDNA sequencing of the ITS1/5.8S/ITS2 region to determine identities of fungal morphotypes. Twelve distinct molecular types were identified. Analysis of similarity showed that ECM fungal assemblages shifted significantly in composition across the soil moisture gradient. Taxa within the genus Tuber and the family Thelephoraceae were largely responsible for the changes in fungal assemblages. There were also significant differences in ECM community assemblages between the two oak host species. These results demonstrate that the structure of ECM fungal communities depends on both the abiotic and biotic environments and can shift with changes in soil moisture as well as host plant, even within the same genus.     

Are climatic factors responsible for the process of oak decline in Poland?

Oak decline, a complex process leading to increased mortality of this species, has been observed in Europe for many years. Previous studies suggest that climate conditions, especially drought, may be one of the most important factors that trigger this phenomenon. The paper investigates the radial growth and wood anatomy features of pedunculate oak (Quercus robur) trees of various health status as well as their response to climate conditions. Wood samples including all annual increments were taken at two sites (western and central Poland, 15 trees each). Based on the crown defoliation level, three health groups (healthy, weakened and dead oaks) were distinguished. Cross-sections were prepared with sliding microtome and Cell P image analysis software was used for the measurements. Tree-ring width (TRW), earlywood vessels density (VDen) and non-weighted vessels diameter (VD) were determined and correlated with mean monthly values of temperature, precipitation, vapour pressure, and Palmer Drought Severity Index (PDSI). Radial increment and anatomical parameters were significantly higher for the healthy oaks than for the weakened and the dead trees. TRW showed smaller dependence on climate than analysed anatomical attributes. No obvious pattern of relationship was found between oak radial growth and climate regarding tree health status. Our results revealed that the drought has a weak impact on the process of oak decline on investigated sites in Poland.     

Real-time PCR detection of Biscogniauxia mediterranea in symptomless oak tissue

AIMS: Real-time PCR, based on TaqMan chemistry, was used to detect Biscogniauxia mediterranea, a fungal pathogen that after a long endophytic phase may cause charcoal disease in oak trees. METHODS AND RESULTS: Specific primers and probe were designed and tested on axenic cultures of B. mediterranea and other fungi commonly colonizing oaks. Twig samples were collected in Tuscany from apparently healthy oaks (Quercus cerris, Quercus ilex and Quercus pubescens) growing near trees infected with the fungus. Twigs were divided into two groups: one for isolation in agar plates, and one for real-time PCR after DNA extraction. The detection limit of the assay was 0.01 pg/DNA, whereas the amounts of fungal DNA detected in asymptomatic tissue were >0.5 pg microg(-1) total DNA extracted. In the apparently healthy twigs the frequency of isolation found on agar was 25.0%, much lower than that with real-time PCR (96.4%). CONCLUSIONS: Real-time PCR is a sensitive and fast technique able to specifically detect and quantify the DNA of B. mediterranea in oak tissue. SIGNIFICANCE AND IMPACT OF THE STUDY: This diagnostic method is a precise tool to localize fungi in symptomless plant tissues and promises to advance our understanding of fungal infection during their latent phase.