Discula quercina as a possible causal agent of dieback on oak trees in Iran

During spring and summer of 2016, dieback symptoms including blights of leaves, twigs, and acorns were observed on current year shoots of Quercus infectoria in the Zagros oak forests of Iran. The fungus isolated from damaged tissues was identified as Discula quercina based on both morphological characteristics and ITS sequencing. To fulfil the Koch's postulates, a representative isolate was inoculated onto shoots of Q. infectoria and Quercus libani in both laboratory and forest conditions. Responses of the two oak species to inoculation with D. quercina were examined under laboratory and forest conditions in a completely randomized experiment. Discula quercina was clearly involved in oak dieback, and Q. infectoria was more susceptible than Q. libani to damage by the pathogen. This is the first record of the occurrence and pathogenicity of the fungus Discula quercina on Quercus infectoria. The fungus is considered as an emerging pathogen on oak trees in Zagros forests in Iran. Furthermore, the pathogenicity of the Discula quercina on Q. libani under laboratory and forest conditions increases the potential importance of this pathogen in Zagros forests.     

Genetic diversity of European populations of the oak fine‐root pathogen Phytophthora quercina

The recently discovered oak‐specific fine root plant pathogen Phytophthora quercina is a significant factor in the current phase of European oak decline but its origins and ecology are poorly understood. A genome‐wide analysis of 260 amplified fragment length polymorphism (AFLP) markers was used to examine the genetic diversity of 72 isolates from five oak species at 28 sites in Germany (particularly Bavaria), Italy, France, Hungary and the UK. Within‐site diversity was examined at 16 sites. The limited genetic diversity (within and between sites) and lack of genetic substructuring according to geographic origin or host species suggest the rapid spread of a relatively recently introduced species. Two subgroups were distinguished and these may reflect an initial introduction of isolates of two different genetic backgrounds. The relatively low genetic diversity is probably because of the predominantly inbreeding (homothallic) nature of P. quercina. However, evidence of limited intra‐site diversity, temporal variation and the lack of clonality within the European population suggest that some diversity is being maintained by occasional outcrossing and turnover of a reservoir of long‐lived soil‐borne oospore (sexually derived) inoculum.     

Effects of oak root pruning in forest nurseries on potential pathogen infections

Despite the general practice of root pruning, little is known about the potential impact of reducing shoot/root systems of oak seedlings in this way on their future susceptibility to pathogens, for example Cylindrocarpon spp., Fusarium spp., Ilyonectria spp., Pythium spp. Phytophthora spp. or Rhizoctonia spp. In this study, root‐pruned and non‐pruned seedlings of Quercus robur grown under controlled conditions were inoculated with aggressive and less‐aggressive pathogens. Results indicated, in contrast to our initial assumption, that pathogens significantly reduced lateral root biomass more in non‐pruned seedlings, the extent of the response depending on the pathogens species. In response to pathogen pressure, pruned seedlings tended to attain a higher dry stem mass fraction, but lower dry leaf mass fraction. Pathogens also suppressed leaf mass in total root dry mass fraction (dry leaf mass/total root dry mass ratio, in g × g^?1) more in pruned than in non‐pruned seedlings. These results suggest differences in growth between non‐pruned and pruned seedlings in response to pathogen stress. In nurseries, root pruning of oak trees may enhance the reduction in leaf mass in lateral roots mass fraction resulting from pathogen infections, which may decrease seedling quality. It is therefore important to ensure a low level of inoculum of soil‐borne pathogens to minimize the risk of seedling infection.     

Physiological responses of cork oak and holm oak to infection by fungal pathogens involved in oak decline

The aim of this research was to study the changes in net photosynthesis and stomatal conductance values in 3‐year‐old cork oak and holm oak seedlings growing in natural conditions and inoculated with Apiognomonia quercina, Biscogniauxia mediterranea, Botryosphaeria corticola and Pleurophoma cava. Throughout the 4‐month experimental period, the evolution of visual external symptoms and the values of physiological variables were periodically recorded. All pathogens caused stem lesions around the infection point; however, the lesions caused by B. corticola were longer in both oak species. On cork oak seedlings, all pathogens induced a significant and gradual reduction in net photosynthesis and stomatal conductance values, whereas other physiological disturbances were induced only by B. corticola infections on holm oak seedlings.     

Detection of the endophyte Discula umbrinella in buds and twigs of Fagus sylvatica

Endophytic fungi have been isolated from buds and twigs of beech trees collected at four different sites in Switzerland. Discula umbrinella. was recovered at high frequencies from the bud scales and the twig pieces contiguous to the buds, but was virtually absent from the rolled up leaves enclosed by the scales. In addition to infection by air-borne inoculum, thalli of D. umbrinella may grow from the twigs into the leaf tissues.     

Viability of thinning sessile oak stands by girdling

The effects of girdling were analysed in a sessile oak (Quercuspetraea Matts. Leibl.) forest with an 80-year-old coppice withstandard structure in northern Spain. The study evaluated theviability of girdling as an alternative to felling trees duringcrown thinning. Eighty-four direct competitors of selected futurecrop trees were girdled by double notching and peeling. Threeyears after girdling, 100 per cent of the treated trees haddied. Approximately half of the girdled trees did not resprout.The occurrence of basal sprouting was very low, and more than35 per cent of the sprouts had very low vigour. No correlationwas found between sprouting and the diameter of the girdledtrees or the distance to their nearest neighbour. A negativerelationship between the diameter of the girdled tree and thestage of decline was recognized. Girdling is an economic alternativeto non-commercial thinning in oak stands and can be seen asan effective structural enrichment treatment.     

利用柞蚕蛹人工繁育白蛾周氏啮小蜂

为了达到以虫制虫、无污染、无公害生物防治的目的,利用白蛾周氏啮小蜂寄生美国白蛾蛹,能达到很好的生物防治效果。该文论述了选用优质的柞蚕蛹人工繁殖白蛾周氏啮小蜂的方法。采用“三刀削茧法”,将柞蚕茧有蚕蒂的一端两侧用刀削两个孔口,另一端削一个孔口,孔口直径1.5~2cm为宜,削口时不能破蛹,削口不宜过小,能使种蜂进入。人工繁育和释放周氏啮小蜂,增加了林间蜂种的种群数量,提高了对美国白蛾蛹的寄生率,增强了自然界小蜂持续控灾的能力,有效恢复和改善了林间生态环境。     

A new method to detect Lonsdalea quercina in infected plant tissues by real‐time PCR

Presymptomatic and accurate diagnoses of pathogens are essential for disease prediction and the timely application of bactericide. The bacterium Lonsdalea quercina (=Brenneria quercina) has been reported as the causal agent of drippy nut and bark canker disease on oak in California (US) and Europe. In recent years, it is also found on Populus × euramericana trees in Henan province of China. This bacterium causes longitudinal cankers of a few centimetres in size on the bark surface of the upper trunk. In this study, we developed two species‐specific PCR assays using primer pairs LqfF/LqfR and LqgF/LqgR for the rapid and accurate detection of the pathogenic bacteria in diseased plant tissues. The results show that the LqfF/LqfR primers amplified only a single PCR band of approximately 382 bp and the LqgF/LqgR primers yielded a PCR product of approximately 286 bp. The two primers were successfully adapted to real‐time PCR based on SYBR Green I used with the ABI 7500 system. The detection limit of the reaction was 0.1 pg genomic DNA per 20 μl PCR reaction volumes. The pathogen was mainly detected in the phloem of cankers as well as in the exudates of diseased trees, but was not found in the xylem or leaves. The size of pathogen in distribution was larger than the lesion. The results demonstrate that real‐time PCR assays can be used to detect the pathogen by extracting DNA directly from infected plant tissues. This method is a rapid, reliable method for the presymptomatic and accurate detection of L. quercina, providing a useful insight into epidemiological studies.     

Forest stand dynamics and sudden oak death: Mortality in mixed-evergreen forests dominated by coast live oak

Sudden oak death (SOD), caused by the recently discovered non-native invasive pathogen, Phytophthora ramorum, has already killed tens of thousands of native coast live oak and tanoak trees in California. Little is known of potential short and long term impacts of this novel plant–pathogen interaction on forest structure and composition. Coast live oak (Quercus agrifolia) and bay laurel (Umbellularia californica) form mixed-evergreen forests along the northern California coast. This study measured tree mortality over a gradient of disease in three time periods. Direct measurements of current mortality were taken during 2004, representing a point-in-time estimate of present and ongoing mortality. Past stand conditions, c. 1994, were estimated using a stand reconstruction technique. Future stand conditions, c. 2014, were calculated by assuming that, given a lack of host resistance, live trees showing signs of the disease in 2004 would die. Results indicate that coast live oaks died at a rate of 4.4–5.5% year⁻¹ between 1994 and 2004 in highly impacted sites, compared with a background rate of 0.49% year⁻¹, a ten-fold increase in mortality. From 2004 to 2014, mortality rates in the same sites were 0.8–2.6% year⁻¹. Over the entire period, in highly impacted sites, a 59–70% loss of coast live oak basal area was predicted, and coast live oak decreased from 60% to 40% of total stand basal area, while bay laurel increased from 22% to 37%. Future stand structures will likely have greater proportions of bay laurel relative to coast live oak.     

Responses of oaks and tanoaks to the sudden oak death pathogen after 8 y of monitoring in two coastal California forests

Sudden oak death, caused by Phytophthora ramorum, is widely established in mesic forests of coastal central and northern California. In 2000, we placed 18 plots in two Marin County sites to monitor disease progression in coast live oaks (Quercus agrifolia), California black oaks (Q. kelloggii), and tanoaks (Lithocarpus densiflorus), the species that are most consistently killed by the pathogen in these areas. Through early 2008, the numbers of newly infected trees increased for all species. The infection rate for trees that were asymptomatic in 2000 was 5.0% y⁻¹ for coast live oaks, 4.1% y⁻¹ for black oaks and 10.0% y⁻¹ for tanoaks. Mortality rates were 3.1% y⁻¹ for coast live oaks, 2.4% y⁻¹ for black oaks, and 5.4% y⁻¹ for tanoaks. Mortality not attributed to P. ramorum was 0.54% y⁻¹ for coast live oaks, and 0.75% y⁻¹ for tanoaks. Weibull survival models of trees that were asymptomatic in 2000 provided overall median survival times of 13.7 y for coast live oaks, 13.8 y for black oaks, and 8.8 y for tanoaks. Survival of infected (bleeding) trees declined to 9.7 y for coast live oaks, 6.2 y for black oaks, and 5.8 y for tanoaks. Ambrosia beetle attacks on bleeding trees further reduced modeled survival times by 65–80%, reaffirming the earlier finding that beetle attacks on bleeding cankers considerably reduce survival. Across all plots, the modeled time for 90% of trees that were asymptomatic in 2000 to become infected is 36.5 y for coast live oaks and 15.4 y for tanoaks. There was a trend toward higher infection rates as tree diameter increased. Greater than 90% of living coast live oaks that failed during the study had extensive beetle tunneling at the site of the break. Disease intensity in coast live oaks at the plot level was positively associated with bay laurel (Umbellularia californica) basal area and negatively associated with Pacific madrone (Arbutus menziesii) basal area. This study demonstrates the use of survival modeling to characterize the effects of epidemic disease on different species and to project the future of forests infected with tree pathogens.     

Physiological and phenological responses of oak seedlings to oak forest soil in the absence of trees

Established trees influence the growth and physiology of seedlings by altering above- and belowground conditions; however, tree influences on seedling physiology via belowground interactions are not well understood. We used soil transfers to an open field to examine the belowground influences of a Quercus ellipsoidalis E.J.Hill dominated forest on Q. ellipsoidalis seedling mycorrhizal infection, nutrient uptake, growth and photosynthesis over three years. After two years, seedlings planted with large quantities of forest soil (HF treatment) had greater leaf mass and foliar N concentrations than seedlings receiving smaller quantities of forest soil (LF) and control treatments. Mycorrhizal infection was greater in the HF treatment after one year compared with the LF and control treatments, with a positive correlation of foliar N and mycorrhizal infection in Year 2. There were marked effects of treatments on seedling spring phenology with HF seedlings breaking bud up to 17 days earlier than seedlings in the other treatments. The HF seedlings also had more rapid leaf expansion and larger leaves, and an increase in net photosynthetic rates. These results highlight complex linkages between above- and belowground physiology: forest soil had substantial effects on seedling physiology, including traits such as phenology that have previously been considered to be under aboveground control. Belowground influences of trees on conspecific seedlings may play a critical role in early seedling establishment.     

Spatial pattern dynamics of oak mortality and associated disease symptoms in a California hardwood forest affected by sudden oak death

Sudden oak death is a disease affecting coastal forests in California and southern Oregon. The spatial pattern of disease dynamics is important for forest and landscape pathology; in this work we investigated the interaction across landscape scales of disease symptomology in coast live oaks, Quercus agrifolia, (trunk bleeding, presence of beetles, and presence of the fungus Hypoxylon thouarsianum) and tree mortality through time. We used two-dimensional spatial analysis tools with data gathered in point-centered-quarter format in 2001 and 2004 to quantify the population density of the disease through time; to examine the spatial pattern of tree mortality across scales through time; and to examine the spatial co-occurrence of disease symptoms with crown mortality through time. Early in the study period dead trees were strongly clustered at smaller scales (~300 m) and after three years this clustering was less pronounced. Bleeding on trees occurred in clusters away from dead trees, particularly in 2004, likely indicating a new cohort of infected trees. The presence of H. thouarsianum was strongly related to overstory mortality through time. Beetle-infested trees co-occurred with mortality in 2001. By 2004, they occurred throughout the forest, and were less strongly correlated with overstory tree mortality, suggesting a future peak of tree mortality.     

Effects of hot water treatment,biocontrol agents,disinfectants and a fungicide on storability of English oak acorns and control of the pathogen,Ciboria batschiana

Eight biological control agents (BCAs; Clonostachys rosea, Trichoderma harzianum, Trichoderma polysporum, Phlebiopsis gigantea, Bacillus subtilis, Pseudomonas chlororaphis, Streptomyces griseoviridis), five disinfectants and a fungicide (Prochloras‐Mangan^TM) were evaluated for the control of harmful mycoflora on Ciboria batschiana‐infected English oak (Quercus robur) acorns during storage at ?1°C. All treatments were tested on both hot water‐treated (HW) and untreated acorns. HW‐treated acorns generally stored better than untreated acorns as a result of elimination of C. batschiana. The HW treatment increased the germination percentage before storage from 60 to 85%. Germination of HW‐treated acorns decreased from 85 to 40% after 16.5 months of storage, whereas germination of untreated acorns decreased from 60 to 20% after a similar time. Ciboria batschiana infection of untreated acorns increased from 14% before storage to 55% after 16 months of storage. All disinfectants and BCAs had a positive effect on viability and particularly on control of C. batschiana in untreated acorns. Best control of C. batschiana occurred with C. rosea, Mycostop^TM (S. griseoviridis), Binab TF^TM (T. polysporum + T. harzianum), and P. chlororaphis. For HW‐treated acorns, there was only a small effect of BCAs on acorn viability while the fungicide and the disinfectants had no effect. Treatments also affected the saprophytic mycoflora with the HW treatment reducing the frequency of Cladosporium spp. and Papulaspora spp., but enhancing Alternaria spp., Mucoraceae and Penicillium spp. However, when combined with HW treatment, several BCAs significantly reduced the prevalence of these fungi. Also, C. rosea reduced the growth of Fusarium spp. Significant negative correlations (p < 0.001) were found between acorn germination and certain storage fungi such as Acremoniella atra, Cladosporium spp. and dematiaceous mycelia.     

Penetration and colonization of oak roots by Armillaria mellea in Wisconsin

The level of Armillaria mellea activity on root systems of living and herbicide-killed oâks was assessed. Epiphytic rhizomorphs were almost always present on living and dead oak roots. After an oak was killed or completely defoliated, A. mellea usually penetrated directly through the root-collar bark and spread rapidly in the cambium. Sapwood in the root collar and main lateral roots was colonized within 2 years. The production of thizomorphs from this region was assessed on trees that had been killed by herbicide sprays 2 to 14 years before sampling.     

Observations on the colonization of oak wilt mats (Ceratocystis fagacearum) by Pesotum piceae

Subcortical mats of Ceratocystis fagacearum were found to become readily overgrown by Pesotum piceae. Thus by reducing the chance of contamination of insect vectors with spores of the pathogen P. piceae is likely to contribute to the low efficiency of oak wilt transmissions.     

Steaming effects on selected wood properties of Turkey oak by spectral analysis

Turkey oak (Quercus cerris L.) is characterized by some technological and aesthetical factors limiting its market value from its great potential. In this study, the effect of direct and indirect steaming on reduction in equilibrium moisture content (EMC) and colour variations was evaluated using a hyperspectral radiometer. Steaming treatments were carried out at 80°C for 48?h, and 120°C for 18 and 24?h, showing a reduction in EMC in the order of 8.1, 28.5 and 13.5, respectively, as well as very significant lightness (L^*) and hue (h°) modifications in comparison with untreated specimens. The spectral signature analysis confirmed that hydrothermal treatments modify wood sensibility to the light source in the entire spectrum range. The study supports the validity of hydrothermal treatments for improving technological and aesthetical properties of Turkey oak.     

Survival of the oak wilt fungus in air-dried lumber

The survival of the oak wilt fungus, Ceratocystis fagacearum (Bretz) Hunt, in air-dried red, white, and scarlet oak lumber was studied in South Carolina and West Virginia. The position of boards in the piles did not have a significant effect on culture recovery of C. fagacearum. The fungus was not recovered after the initial sample at set-up time in the summer harvested oaks in South Carolina nor beyond 28 days in West Virginia. In autumn harvested material recoverability was slightly longer, 28 days in South Carolina with one positive recovery at 70 days, and much longer in West Virginia with some recovery of C. fagacearum occurring at 140 days. Recovery of C. fagacearum from white oak at both locations was generally much lower than from red or scarlet oak during any given sample period.     

Dutch elm disease pathogen transmission by the banded elm bark beetle Scolytus schevyrewi

Dutch Elm Disease (DED) is a vascular wilt disease of Ulmus species (elms) incited in North America primarily by the exotic fungus Ophiostoma novo‐ulmi. The pathogen is transmitted via root grafts and elm bark beetle vectors, including the native North American elm bark beetle, Hylurgopinus rufipes and the exotic smaller European elm bark beetle, Scolytus multistriatus. The banded elm bark beetle, Scolytus schevyrewi, is an exotic Asian bark beetle that is now apparently the dominant elm bark beetle in the Rocky Mountain region of the USA. It is not known if S. schevyrewi will have an equivalent vector competence or if management recommendations need to be updated. Thus the study objectives were to: (i) determine the type and size of wounds made by adult S. schevyrewi on branches of Ulmus americana and (ii) determine if adult S. schevyrewi can transfer the pathogen to American elms during maturation feeding. To determine the DED vectoring capability of S. schevyrewi, newly emerged adults were infested with spores of Ophiostoma novo‐ulmi and then placed with either in‐vivo or in‐vitro branches of American elm trees. The inoculation of trees via feeding wounds was successful 30% of the time for in‐vivo trials and 33% for in‐vitro trials. Although the infection rate of DED has declined in Colorado over the past 10 years, the disease is still present in urban elms. While it appears that S. schevyrewi is another vector of the DED pathogens, it appears that S. schevyrewi is no more efficient than S. multistriatus. Thus, management programs that remove elm bark beetle breeding sites, rapidly remove DED‐infected elms and include the planting of DED‐resistant elms should continue to be effective management tactics.