Endophytic-Host Selectivity of Discula umbrinella on Quercus alba and Quercus rubra Characterized by Infection, Pathogenicity and Mycelial Compatibility

The fungal endophytic–host relationships of Discula umbrinella and two oak species, Quercus alba and Quercus rubra, were characterized on the basis of endophytic infection, pathogenicity, and mycelial compatibility. Isolates of D. umbrinella were cultured from leaves of Q. alba and Q. rubra collected from a hardwood forest located in Patuxent Wildlife Research Center in Laurel, Maryland, USA. Endophytic infection was observed on sterile leaf discs and living 2-month-old seedlings of Q. alba and Q. rubra. Fungal-host reciprocal inoculations revealed the presence of conidiomata on both hosts but conidiomata production was more abundant on Q. alba. Isolates from Q. rubra produced milder disease symptoms on both oak species. Mycelial compatibility studies identified seven different MCG groups. MCG groups 1–3 contained isolates from both oak species whereas MCG groups 4–7 contained host specific isolates. Field studies monitored the seasonal appearance of the sexual fruiting structures, perithecia, as a possible source of new genetic variation that might alter host specificity/pathogenicity of the D. umbrinella isolates on Q. alba and Q. rubra hosts. Only 1–2% of the leaves contained perithecia throughout the sampling period (April–September). Isolates collected from Q. alba differed from those collected from Q. rubra in endophytic infection, pathogenic response, and perithecia production. The results of this study suggest that the endophyte–host relationship is one of host selective preference for Q. alba, but that the endophyte has the ability to maintain the endophytic/pathogenic life cycle on the less preferred host species, Q. rubra.     

PM 8/5 (1) Quercus

Specific scope

The purpose of the EPPO Standard on Quercus is to recommend to EPPO Member Governments the phytosanitary measures which they should use or require for Quercus plants and plant products moving in international trade to prevent the introduction and spread of quarantine pests. Some of these recommendations are addressed to all EPPO Member Governments, others are addressed only to countries considered to face a certain level of risk from the introduction and spread of the regulated pests concerned. All these recommendations were derived from:

• EPPO Standards PM 1/2 (EPPO A1 and A2 lists) and the former EPPO Standards PM 2 (pest‐specific phytosanitary measures), or
• Pest Risk Analysis (PRA) carried out or reviewed by EPPO, or
• the Working Party on Phytosanitary Regulations.

For wood packaging material, recommendations are based on ISPM 15 Regulation of wood packaging material in international trade.

Specific approval and amendment

First approved in 2010‐09 as PM 8/3 Quercus and Castanea. Revised and approved as a separate Standard PM 8/5 in 2017‐09     

微生境对辽东栎幼苗生长的影响

以早期辽东栎（Quercus wutaishanica）实生幼苗个体为研究对象,探讨影响辽东栎幼苗生长的关键微生境因子。采用典型样线调查法,对子午岭马栏林区1～3龄的辽东栎实生幼苗的生长指标和幼苗所处的微生境变量进行了调查分析。结果表明：3龄幼苗的株高、基径、芽数目与1、2龄幼苗有显著性差异,随着龄级的增长幼苗的生长率逐渐降低,影响幼苗生长的微生境变量呈增加趋势,对微生境做出响应的生长指标也呈增加趋势,暗示着微生境对幼苗生长的影响具有时滞效应。枯落物是限制幼苗生长的重要因素之一,乔木层的适度遮荫是1、2龄幼苗生长的最佳光照环境,3龄幼苗生长的最佳环境则是林隙,可见辽东栎幼苗要成功定居必须等待林窗的出现。     

Untersuchungen zum Erreger der Ringfleckigkeit an Stieleichen (Quercus robur)

Mit einer visuellen Bonitur konnte das Vorkommen von Eichen mit virusverdächtigen chlorotischen Ringflecken an den Blättern in einem Forstbereich Berlins, dem Spandauer Forst, gezeigt werden. An Blattproben bonitierter Eichen wurden Untersuchungen zur Virusreinigung und zum Virusnachweis vorgenommen. Eine visuelle elektronenoptische Darstellung sowie eine mechanische Übertragung des Erregers der chlorotischen Ringfleckigkeit an Eichen auf ausgewählte krautige Indikatorpflanzen gelang nicht.Mit Hilfe spezifischer Primer zum Nachweis des Erregers der Ringfleckigkeit an Ebereschen konnte gezeigt werden, dass der Erreger der Ringfleckigkeit an Eichen mit diesem nicht identisch ist. Aus dem Blattmaterial erkrankter Eichen konnten DNA-Fragmente von ca. 150 bzw. 550 bp amplifiziert werden. Das aus dem Blattmaterial kranker Ebereschen amplifizierte DNA-Fragment hat eine Größe von 224 bp. Die beiden aus erkranktem Eichenblattmaterial amplifizierten Fragmente sind vermutlich auf eine unspezifischen Anlagerung der Primer zurückzuführen.     

Real-time PCR identification and detection of Fuscoporia torulosa in Quercus ilex

Fuscoporia torulosa is the causal agent of white alveolar wood decay on several species including a large number of forest trees. Early detection of the fungus is essential to identify diseased trees before spread occurs to healthy plants. However, current detection methods based on isolation from infected tissues on semi-selective media are laborious, time consuming and require expertise in identifying the pathogen after isolation. In the present study, a rapid and reliable Scorpion-PCR based molecular method to identify and detect F. torulosa in planta was developed in a highly polymorphic portion of the internal transcribed spacer (ITS) regions. Specificity of primers and probe was assessed by means of both BLAST analyses and by using genomic DNA from 131 F. torulosa isolates and 43 other fungi and oomycetes from different hosts and geographic areas. In Scorpion-PCR the limit of detection was 1 pg of total DNA and a high correlation ( r ² = 0·996) was achieved between target DNA quantity and cycle threshold (Ct). Real-time PCR combined with effective procedures for DNA extraction enabled the detection of F. torulosa from naturally infected tissues of oaks with and without fruit bodies in approximately 6 h. Comparative testing showed that detection of F. torulosa in wood samples is more sensitive and reliable with real-time PCR than with conventional isolation.     

Untersuchungen zum Erreger der Ringfleckigkeit an Stieleichen (Quercus robur)

Oak trees showing leaves with chlorotic ring spots have been observed in an area of Berlin (Spandau Forest). Leaves from infested trees were used for investigations on virus purification and mechanical transmission. Electron microscopic visualisation of the virus particles was unsuccessful, as was their mechanical transmission to herbaceous indicator plants. The use of specific primers to detect ring spot disease on mountain ash showed that both ring spot disease forms do not stem from the same causal agent. Whilst the amplified DNA fragment of mountain ash consists of 224 bp, those of diseased oak trees had lengths of 150 bp and 550 bp. These two fragments amplified in diseased oak leaf tissue probably result from an unspecific reaction of the primers with the cDNA. Further investigations are considered necessary.     

PM 8/3 (1): Quercus and Castanea

Specific scope

The purpose of the EPPO Standard on Quercus and Castanea is to recommend to EPPO Member Governments the phytosanitary measures which they should use or require for Quercus and Castanea plants, and plant products moving in international trade, to prevent the introduction and spread of regulated pests. Certain of these recommendations are addressed to all EPPO Member Governments, others are addressed only to countries considered to face a certain level of risk from the introduction and spread of the regulated pests concerned. All these recommendations are derived:

• ? from the EPPO Standards PM 1/2 (EPPO A1 and A2 lists)
• ? from the former EPPO standard PM 2 (pest‐specific phytosanitary measures) (which was withdrawn in 2006 by the Working Party on Phytosanitary Regulations)
• ? from Pest Risk Analysis
• ? from the Working Party on Phytosanitary Regulations
• ? from the ISPM n°15 ‘Guidelines for regulating wood packaging material in international trade’.

     

Ceratocystis species on Quercus robur with oak decline symptoms in southern Poland1

In southern Poland during 1986–1989, six species of Ceratocystis were found on sick and dead Quercus robur. The frequency of their occurrence in above-ground portions and roots of trees is given. The possibility is discussed whether oak decline, caused by a complex of abiotic and biotic factors, is intensified when trees are colonized by Ceratocystis.     

Seasonal changes in susceptibility of Quercus suber to Botryosphaeria stevensii and Phytophthora cinnamomi

Monthly inoculations of both intact plants and excised shoots of Quercus suber with the pathogenic species Botryosphaeria stevensii and Phytophthora cinnamomi were performed to investigate seasonal changes in susceptibility of this forest tree species in relation to environmental parameters and plant water status. Infection symptoms were mainly detected on seedlings inoculated from spring to autumn (April through October) with either pathogen. Mean canker sizes also showed a seasonal pattern, the higher values being recorded in the same period as above. Lesion lengths were significantly ( P  < 0·001) related to environmental minimum temperature. Mean daily minimum temperatures within the range of 5–12°C clearly inhibited lesion development of P. cinnamomi , whereas B. stevensii showed a less pronounced decrease in canker expansion at the same temperature range. In excised shoots of Q. suber inoculated monthly with B. stevensii , a negative linear relationship was found between the studied range of plant relative water content (81–91%) and canker length. In contrast, the lesions caused by P. cinnamomi were not significantly ( P  = 0·32) related to any seasonal change in water content. Some control measures for the diseases caused by both pathogens are discussed on the basis of the seasonal changes in host susceptibility observed in this study.     

Histopathology of infection and colonization of Quercus ilex fine roots by Phytophthora cinnamomi

Quercus ilex is one of the European forest species most susceptible to root rot caused by the oomycete Phytophthora cinnamomi. This disease contributes to holm oak decline, a particularly serious problem in the ‘dehesas’ ecosystem of the southwestern Iberian Peninsula. This work describes the host–pathogen interaction of Q. ilex and P. cinnamomi, using new infection indices at the tissue level. Fine roots of 6‐month‐old saplings inoculated with P. cinnamomi were examined by light microscopy and a random pool of images was analysed in order to calculate different indices based on the measured area of pathogen structures. In the early stages of invasion, P. cinnamomi colonizes the apoplast and penetrates cortical cells with somatic structures. On reaching the parenchymatous tissues of the central cylinder, the pathogen develops different reproductive and survival structures inside the cells and then expands through the vascular system of the root. Some host responses were identified, such as cell wall thickening, accumulation of phenolic compounds in the middle lamella of sclerenchyma tissues, and mucilage secretion blocking vascular cells. New insights into the behaviour of P. cinnamomi inside fine roots are described. Host responses fail due to rapid expansion of the pathogen and a change in its behaviour from biotrophic to necrotrophic.     

陕西地区栓皮栎种群统计特征的区域变异性研究

种群统计是种群生态学研究的核心 ,主要研究种群在时间和空间上的数量变化规律。本文通过样方法对陕西不同地区栓皮栎的年龄结构、大小结构、密度结构和组成构件四个方面探讨栓皮栎种群的区域变异性规律。结果表明 ,从分布中心到分布边缘 ,沿生境梯度栓皮栎种群年龄结构呈现出不均匀分布 ,绝大部分样地幼苗和幼树的个体数量偏少 ,但栓皮栎种群能顺利通过瓶颈。不同样地不同年龄的栓皮栎种群的大小结构分布不一 ,种群中胸径小的个体与胸径大的个体数量比较少 ,中等大小的个体数量较多 ,种群表现出增长的趋势。不同样地的密度随径级的变化特点是低径级的密度高 ,高密度的径级小 ,密度在不同样地平均径级上的分布呈现出明显的负相关。不同样地的栓皮栎叶面积指数的变化 ,反映出栓皮栎种群的生长活力。     

Cryptogein and capsicein promote defence responses in Quercus suber against Phytophthora cinnamomi infection

The decline of cork oak (Quercus suber) stands in Iberian Peninsula is associated with infection by Phytophthora cinnamomi. Most Phytophthora species secrete elicitins, which can enhance defence reactions against some pathogens. Here cytological and physiological effects of the elicitins cryptogein and capsicein on cork oak root infection by P. cinnamomi were evaluated. The progression of the pathogen in root tissue and its effects on total fatty acid (TFA) composition of roots and leaves were analysed in seedlings. Net photosynthesis (P _n ), stomatal conductance (g _s ), chlorophyll a fluorescence measurements (quantum yield of linear electron transport ? _e , photochemical quenching q _P, non-photochemical quenching NPQ) and carotenoid determinations were carried out in well established (4?months) plants. In elicitin-treated roots, 2?days after inoculation, the pathogen which presented loss of viability and membrane degradation was mainly restricted to the intercellular spaces of the cortical parenchyma, and did not reach the vascular cylinder. Electron dense materials accumulated in the intercellular spaces of the cortex next to disorganized hyphae, suggested to be related with defence reactions. Cryptogein (or its interaction with P. cinnamomi) induced enhanced lipid synthesis in leaves, which may contribute to preserve membrane stability. P. cinnamomi decreased P _n , g _s , ? _e , and q _P, whereas elicitin-treated plants displayed values similar to controls. Overall, the results indicated a resistance response of cork oak against this oomycete, induced by the elicitins.     

Biological Control of Sclerotinia pseudotuberosa and Other Fungi During Moist Storage of Quercus robur Seeds

The fungal pathogen Sclerotinia pseudotuberosa is a major cause of deterioration during storage of Quercus robur seeds (acorns) and along with other, mainly saprotrophic fungi, contributes to the decline of viability and vigour in the acorn population. Hot-water thermotherapy (HWT; 41 °C for 2.5 h) killed the fungal pathogen S. pseudotuberosa and prolonged the storage life of acorns. The addition of the systemic fungicide benomyl to the HWT and/or the broad-spectrum fungicide thiram as a seed dressing further enhanced the storage life of acorns. Three fungal antagonists, Coniothyrium minitans, Trichoderma sp. (KW3) and Trichoderma virens (G20), were also applied as a film-coating to acorns using a polyvinylacetate sticker achieving ca. 10⁷–10⁸ viable conidia per acorn. The biological treatments provided protection against infection and the spread of infection of S. pseudotuberosa and other fungi on the acorns during storage over several months. All treated and stored acorns grew normally following sowing in seedbeds. The Trichoderma species were more effective than C. minitans, with T. virens being the most effective. T. virens reduced pathogen spread from acorns infected with S. pseudotuberosa to `clean' acorns when T. virens coated infected and 'clean' acorns were mixed together. However, T. virens was less effective than HWT at preventing the proliferation of this pathogen within individual acorns that were infected before coating. A combination of HWT and subsequent coating with T. virens provided a more effective control against both S. pseudotuberosa and saprotrophic fungi than when either treatment was applied alone.     

Relationships between health of Quercus robur, occurrence of Phytophthora species and site conditions in southern Sweden

The effect of Phytophthora species, soil chemistry, precipitation and temperature on the vitality of oak was evaluated in 32 oak stands in southern Sweden. In addition, the relationship between the occurrence of Phytophthora species and soil conditions was determined. The results showed that there was a weak association between the presence of P. quercina , the most frequently recovered Phytophthora species in southern Sweden, and the vitality of the oak stands (determined from estimates of crown defoliation of individual trees). The pathogens occurred more frequently in clayey and loamy soils that were less acidic and which had higher base saturation. However, they were found in all but the most acidic soils (pH < 3·5). In stands where Phytophthora species were not present, positive correlations between the average crown defoliation and proportion of damaged trees with average summer precipitation and average annual precipitation were found. There were no significant differences in soil chemistry between healthy and declining stands included in this study, and no significant correlations were found between any soil parameter and crown vitality. Based on the results from these 32 oak stands, it is likely that the decline of oaks in southern Sweden can be attributed to several different site-specific factors, such as infection by P. quercina or unusual weather events, which interact with a number of biotic and abiotic factors, leading to oak decline.     

Susceptibility of common herbaceous crops to Phytophthora cinnamomi and its influence on Quercus root rot in rangelands

The susceptibility to Phytophthora cinnamomi of four crops (wheat, oat, vetch, and yellow lupin) commonly planted in rangeland ecosystems in southern Spain was evaluated. By means of in vitro infection experiments, the presence of the pathogen into the roots of yellow lupin (symptomatic) and vetch (asymptomatic) was observed, but never into wheat and oat roots (asymptomatic). It was also demonstrated that yellow lupin stimulated the production of zoospores of P. cinnamomi. Vetch, wheat and oat did not stimulate zoospore production. Under controlled conditions, only yellow lupin induced an increase in the number of viable chlamydospores in the soil. We concluded that the culture of wheat, oat, and vetch in rangelands did not influence the epidemiology of the Quercus root disease, even when asymptomatically-infected vetch is grown, and these crops can constitute an alternative to the culture of yellow lupin in rangeland ecosystems affected by Quercus root rot.     

Comparison of the Susceptibility of Quercus petraea, Q. robur and Q. rubra to Collybia fusipes

Collybia fusipes is the cause of a root rot of Quercus petraea (sessile oak), Q. robur (pedunculate oak) and Q. rubra (red oak). This parasite is often reported to cause problems in stands of red oaks and field evidence suggests that this North American oak species is more susceptible than the two European oak species. Young saplings of the three oak species and of chestnut, Castanea sativa, in the glasshouse, and also mature sessile and red oaks growing in the same stand were inoculated with C. fusipes to compare their susceptibility. Red oak, both as young seedlings and mature trees, was more susceptible to C. fusipes than sessile oak. Chestnut seedlings were as susceptible as sessile oak. Susceptibility of pedunculate oak seedlings was intermediate between red oak and sessile oak. In one experiment this species was significantly less susceptible than red oak, and in the other it was as susceptible.     

黄土高原子午岭辽东栎（Quercus liaotungensis）幼苗动态生命表及生存分析

在子午岭马栏林区3种生境（辽东栎林、油松林、灌草丛）中通过野外播种,建立辽东栎（Quercus liaotungensis）幼苗同生群,根据3年观测数据,编制动态生命表,绘制存活曲线、死亡曲线、生存率函数曲线、死亡率函数曲线及危险率函数曲线,分析辽东栎幼苗同生群在不同生境的动态变化。结果显示：辽东栎幼苗存活曲线接近De...     

Le problème de Phytophthora cinnamomi sur le chêne rouge (Quercus rubra)1

L'encre du chêne rouge (Quercus rubra) provoquée par Phytophthora cinnamomi est connue en France depuis 1948. L'auteur en décrit les symptômes et indique que ses conséquences sont essentiellement d'ordre technologique (dépréciation de la bille de pied). La maladie est localisée dans le sud-ouest de la France. La comparaison entre la répartition actuelle et celle connue dans les années 50 ne permet pas de conclure à une extension de la maladie. La question de l'extension potentielle mérite une attention particulière, car le chêne rouge est une espèce utilisée de façon croissante; il paraît cependant vraisemblable que des barrières de nature climatique (température) peuvent limiter le développement géographique de la maladie. Par ailleurs, les programmes d'amélioration de l'espèce faisant appel, entre autres, à la sélection clonale, se trouvent confrontés au problème de la résistance individuelle.