Comparative aggressiveness of standard and variant hybrid alder phytophthoras, Phytophthora cambivora and other Phytophthora species on bark of Alnus, Quercus and other woody hosts

Pathogenicity tests were carried out on the bark of Alnus glutinosa with 19 isolates of the standard (near-tetraploid) hybrid alder phytophthora, nine isolates representing its known heteroploid variants and 11 isolates of P. cambivora , a probable parent species of the hybrid. Over a 4-year period, 12 experiments were conducted on living alder logs incubated at 20°C. Most isolates of the standard hybrid and those of the 'Dutch variant' were highly aggressive to alder bark. Isolates of the 'Swedish', 'UK' and 'German variants', and of P. cambivora , were only weakly pathogenic. Also, isolates of P. fragariae , P. cinnamomi , P . sp. 'O-group', P. cryptogea , P. megasperma , P. gonapodyides and P. citricola were either weakly or nonpathogenic. Rates of lesion development were greatest on logs cut during July–October, slower on logs cut between November and March and zero on logs cut during April, indicating a strong seasonal effect. Other evidence indicated that lesion development was subject to critical thresholds of host resistance. The standard hybrid was nonpathogenic to the bark of four other hardwood and two conifer species, indicating that it is relatively host specific. In contrast, P. cambivora was an aggressive pathogen on live bark of Quercus and Castanea . The significance of these results is discussed.     

Etiology and real-time polymerase chain reaction-based detection of gremmeniella- and phomopsis-associated disease in norway spruce seedlings

ABSTRACT In spring 2002, an unusual disease outburst was recorded on Norway spruce seedlings in southeast Norway. Extensive damage was recorded on 1- and 2-year-old Norway spruce seedlings that either had wintered in nursery cold storage or had been planted out in autumn 2001. The damage was characterized by leader shoot dieback and stem necroses on the upper or lower part of the shoot from 2001. Gremmeniella abietina and a Phomopsis sp. frequently were isolated from the diseased seedlings. Internal transcribed spacer (ITS) ribosomal (r)DNA sequence analysis and random amplified microsatellites profiling indicated that the G. abietina strains associated with diseased nursery seedlings belonged to the large-tree type (LTT) ecotype of the European race of G. abietina var. abietina, and inoculation tests confirmed their pathogenicity on Norway spruce. Based on ITS rDNA sequence analysis, the Phomopsis strains associated with diseased seedlings did not represent any characterized Phomopsis spp. associated with conifers. The Phomopsis sp. was not pathogenic in inoculation tests, indicating that it may be a secondary colonizer. ITS-based real-time polymerase chain reaction assays were developed in order to detect and quantify G. abietina and Phomopsis in the nursery stock. We describe here the G. abietina-associated shoot dieback symptoms on Norway spruce seedlings and conclude that the unusual disease outburst likely was related to the G. abietina var. abietina epidemic caused by the LTT on large Scots pines in 2001.     

Real-time PCR-based monitoring of DNA pools in the tri-trophic interaction between Norway spruce, the rust Thekopsora areolata, and an opportunistic ascomycetous Phomopsis sp

The difficulty in subculturing biotrophic fungi complicates etiological studies related to the associated plant diseases. By employing internal transcribed spacer rDNA-targeted quantitative real-time polymerase chain reaction, we now show that the heteroecious rust Thekopsora areolata, commonly associated in natural conditions to sapling shoots and cones of Norway spruce and leaves of wild bird cherry, frequently infects nursery-grown seedlings of the conifer. A spatial sampling scheme was used to investigate seedlings and saplings of Norway spruce showing phloem necrosis: the highest concentration of DNA of T. areolata was recorded in the area with necrotic phloem. The separate analysis of bark and wood tissues suggested that the initial spread of the rust to healthy tissues neighboring the infection site takes place in the bark. A Phomopsis species found to coexist with T. areolata in several seedlings showed very high DNA levels in the upper part of the lesion, and even in the visually healthy proximal tissues above the lesions, which indicates that the ascomycete, most probably a secondary invader following primary infection by T. areolata, has a latent stage during early host colonization. We hypothesize that this hemibiotrophic mode of infection contributes to the successful coexistence of Phomopsis with a biotrophic rust.     

Oncopsis alni (Schrank) (Auchenorrhyncha: Cicadellidae) as a Vector of the Alder Yellows Phytoplasma of Alnus glutinosa (L.) Gaertn.

Alder yellows phytoplasma was detected by PCR in Alnus glutinosa trees in the Palatine and Mosel areas of Germany. The restriction profiles obtained by TaqI and AluI digestion of a PCR amplified ribosomal DNA fragment from this phytoplasma and a periwinkle isolate of alder yellows from Italy (ALY) could not be distinguished while elm yellows isolates from Europe and North America led to different fragment patterns. Different restriction profiles for ALY and the German alder phytoplasma were obtained by TruI digestion of a non-ribosomal DNA fragment. Phloem feeding insects were collected from infected alder trees. Phytoplasmas of the elm-yellows group were detected by PCR in psyllids and the leafhopper Oncopsis alni. These pathogens were indistinguishable from the phytoplasma found in alder. Only O. alni was able to transmit the pathogen to healthy alder seedlings. Thus, it is the first insect known to transmit this phytoplasma. This leafhopper could be responsible for the ubiquitous infection of Alnus glutinosa due to its close association with alder and its wide distribution in Europe.     

An unusual Phytophthora associated with widespread alder mortality in Britain

During 1993 and 1994 an unusual Phytophthora was consistently isolated from bark lesions at the stem bases of dying alder in Southern Britain. The Phytophthora resembles P. cambivora in both its gametangial and sporangial morphology. However, it is distinct from this species in being homothallic rather than outcrossing; in producing a significant proportion of small and sometimes partially developed oogonia; in having a high frequency of oosphere abortion; in having an appressed felty colony type with little or no aerial mycelium; and in exhibiting a lower optimum temperature for growth (c.22-5°C) and lower growth temperature maximum (c.29°C) on carrot agar than P. cambivora (c.27-5° and 33-5°C respectively). An inoculation test confirmed its pathogenicity to Alnus. The status of the alder Phytophthora is discussed. On the basis of its unusual characteristics and unusual host it is suggested that it might be a new or recently introduced organism rather than a previously unrecorded indigenous variant of P. cambivora.     

The Role of the Bark Beetle, Hylastes ater (Coleoptera: Scolytidae), as a Sapstain Fungi Vector to Pinus radiata Seedlings: A Crisis for the New Zealand Forestry Industry?

The role of the bark beetle Hylastes ater in the re-establishment of Pinus radiata forest in New Zealand is discussed. H. ater was found to be a dominant factor in seedlings mortality in the first year following planting. However, seedling mortality is usually relatively low. In contrast, it was found the large numbers of seedlings were sub-lethally damaged by H. ater feeding attempts, particularly in high risk sites. High risk sites were identified as sites that were harvested during March and April (autumn) when the peak flight activity of H. ater occurred, and subsequently planted with P. radiata seedlings the following winter. H. ater was found to vector sapstain fungi to seedlings during feeding attempts, and a strong relationship between the severity of damage and presence of sapstain fungi was identified. The role of H. ater as a vector of these fungi and the potential implications to the New Zealand forest industry are discussed.     

樟子松幼苗水力结构参数和生长特征对模拟降水梯度的响应

水分是影响樟子松生长和存活的关键因素,为弄清樟子松幼苗对水分胁迫的响应过程,采用人工控制降水处理方法 (105%年均降水量：500 mm,无干旱; 74%年均降水量: 350 mm,轻度干旱;42%年均降水量: 200 mm,干旱),监测了2 a生樟子松幼苗水力结构和生长特征对降水处理的响应。结果表明：随着降水量减少,幼苗水分饱和亏缺没有发生显著变化;轻度干旱下幼苗组织密度显著增加,干旱下幼苗失水系数显著降低;表明樟子松幼苗的保水、抗旱能力随干旱胁迫程度增强而增加。干旱胁迫显著降低了株高、基径和各器官生物量的增加量,轻度干旱胁迫下幼苗根重比和根冠比显著增加,表明轻度干旱胁迫改变了生物量分配格局,促使幼苗向有利于水分维持方向的发展策略;与轻度干旱相比,干旱胁迫下幼苗生物量分配策略并没有发生明显变化。樟子松幼苗可以通过改变水力结构特征和生物量分配策略来适应轻度干旱;而在干旱下幼苗仅改变水力结构特征,不利于其在干旱环境下生存。     

松烂皮病内生拮抗细菌的筛选、生防效果及华山松的生理响应

为探究内生细菌对华山松烂皮病的生防效果及其生理响应,采用平板涂布法和对峙培养法从健康华山松树皮上分离筛选抗烂皮病菌Cenangium ferruginosum的拮抗菌株,运用形态学、生理生化及分子生物学对其进行鉴定;并利用喷雾法研究其对华山松苗烂皮病的盆栽防治效果及苗木各生理指标的变化,观测其对田间发病华山松病斑的防治效果.结果显示,分离得到具有优良拮抗效果的菌株Ba4,经鉴定为解淀粉芽胞杆菌Bacillus amyloliquefaciens;其发酵原液盆栽防治效果可达90.15%,稀释至10⁵防治效果也有17.77%,发病率和病情指数均下降.接种病原菌30 d后,不同浓度Ba4菌剂处理的苗木丙二醛含量均减少,木质素、可溶性蛋白和可溶性糖含量均增加;丙二醛含量与发病率和病情指数呈显著正相关,与防治效果呈显著负相关;木质素、可溶性蛋白和可溶性糖含量则与其相反.田间试验中原液和稀释倍液(10、10²和10³)的病斑治愈率均超过80%.表明菌株Ba4对松烂皮病有良好的防治效果,能调节华山松抗性物质的合成.     

Chemical control of vascular-streak dieback disease of cocoa in Papua New Guinea

High-volume foliage sprays of 18 compounds including 13 systemic fungicides in field trials at 4-week intervals did not control vascular-streak dieback (VSD) of cocoa caused by Oncobasidium theobromae in Papua New Guinea. Soil drenching with carbendazim and other systemics was also ineffective, possibly because insufficient carbendazim may have been taken up into the xylem to inhibit the fungus. Stem paints with four systemic fungicides in aqueous formulations were also ineffective, but 4-weekly stem painting of the hardened bark of young seedlings with 10 g/l propiconazole in 25% white oil caused a highly significant reduction in VSD incidence under field conditions. The treatment had no curative effect. Some phytotoxicity was observed but this was not apparent when the concentration of propiconazole was doubled and the treatment interval lengthened to 8 weeks. The ineffectiveness of systemic fungicides as soil drenches and foliage applications was probably due to failure of these compounds to accumulate at the shoot apex where infection occurs. A stable and non-toxic formulation containing surfactants was developed which may improve control by aiding bark penetration by propiconazole or related compounds.     

Dieback and death of larch caused by Ceratocystis laricicola sp. nov. following attack by Ips cembrae

Circumstantial and experimental evidence suggests that the bark beetle Ips cembrae acts as a vector for Ceratocystis laricicola sp. nov. which it introduces into larches during breeding attacks. The fungus kills bark and cambium, and invades the sapwood causing the formation of areas of 'blue stain' surrounded by dry wood. Multiple inoculations resulting from numerous beetle attacks may totally disrupt conduction causing dieback and death of whole trees. Attacks seem frequently to be associated with drought and other forms of stress. Trees damaged by I. cembrae and C. laricicola may be attacked subsequently by the woodwasp Urocerus gigas which introduces a sapwood decay fungus, Amylostereum chailletii.
This is the first record of an association between I. cembrae and a species of Ceratocystis and the first record of dieback in larch caused by I. cembrae and C. laricicola. I. cembrae was introduced into Britain from mainland Europe and a similar association may occur there.     

干旱胁迫对胡杨和灰叶胡杨光合作用及叶绿素荧光特性的影响

采用盆栽试验,研究正常供水(土壤相对含水量70%～80%)、轻度干旱胁迫(50%～60%)和重度干旱胁迫(30%～40%)条件下2年生胡杨(Populus euphratica)和灰叶胡杨(P. pruinosa)的光合作用及叶绿素荧光特性.结果表明:在干旱胁迫进程中,轻度和重度干旱胁迫下胡杨、灰叶胡杨的净光合速率经历了急剧下降--缓慢回升--下降3个阶段.在相同的干旱胁迫处理下,光合作用及叶绿素荧光参数Pn,Gs,Ci,WUE,Fv/Fm,Fv/Fo,qP和NPQ胡杨明显高于灰叶胡杨,表明胡杨比灰叶胡杨对干旱胁迫具有更强的适应性.     

猕猴桃采后病害鉴定和侵染规律研究

 猕猴桃果实在0℃贮藏4周后开始出现腐烂,贮藏19周,腐烂率高达50%以上。腐烂部位几乎都在果蒂和花端两点以外的果身上,极少数是蒂腐和花端腐烂。病原菌有7种,其中Botrytis cinerea,Penicillium sp.和Phomopsis sp.3种为优势菌。病原菌主要通过采收运输时造成的机械伤口侵染,未发现在果实过熟衰老前直接侵染。     

Pathogenicity of fungi affecting black locust(Robinia pseudoacacia) in Greece

The main fungi affecting black locust(Robinia pseudoacacia L.) were recorded during a survey which took place in northern Greece in 1997. It was found thatPhomopsis oncostoma (Thüm.) v. Höhn,Aglaospora profusa (Fr.) de Not. andCucurbitaria elongata (@#@ Fr.) Grev. cause necroses of twigs, branches and even entire trees. The pathogenicity of these fungi was confirmed by inoculation experiments in which typical disease symptoms appeared with re-isolation of the respective fungi from the inoculated plants.     

Assessing the virulence of four bark beetle-associated bluestain fungi using Norway spruce seedlings

The virulence of two isolates of each of four different bark beetle-associated bluestain fungi was evaluated by wound-inoculating 2- and 4-year-old Norway spruce seedlings. One isolate of Ceratocystis polonica killed 40% of the 2-year-old plants and 20% of the 4-year-old plants, whereas the other fungi ( Ophiostoma piceae , Ophiostoma sp., an unidentified fungus with dark sterile mycelium) and the control treatments (inoculation with sterile agar and unwounded plants) did not kill any plants during the 11-week incubation period. Only C. polonica and the Ophiostoma sp. caused any bluestain of the sapwood. The two C. polonica isolates caused significantly deeper bluestain penetration into the sapwood and longer necrotic lesions on the sapwood surface than all other isolates. The symptoms caused by the other fungi were similar to those on the sterile inoculated control plants. The virulence of the fungal isolates tested in this study agrees largely with results from a previous mass inoculation study using the same isolates inoculated into 40-year-old Norway spruce trees. Thus, inoculation of seedlings seems to be a reliable, inexpensive and convenient bioassay for determining the virulence of bark beetle-associated bluestain fungi.     

Standard and Swedish variant types of the hybrid alder Phytophthora attacking alder in Hungary

A new Phytophthora disease of common alder (Alnus glutinosa) similar to that previously reported in several countries in Europe has been observed in Hungary. Based on these earlier studies, the alder Phytophthora was considered likely to be a hybrid between P cambivora and a P fragariae-like species: across Europe a range of new alder Phytophthora is spreading that comprise a range of heteroploid hybrids including a 'standard' hybrid type and several other hybrid types termed 'variants'. Phenotypic and molecular features of the pathogen in Hungary were characterised and compared with isolates from elsewhere. The morphologies of five isolates from one region (Hévíz) resembled the common, 'standard' type, whereas the three isolates from another region (Hanság) exhibited traits similar to those of one of the 'variant' types, ie the Swedish 'variant'. Molecular markers of these two groups of Hungarian isolates also represented a good fit to those of the standard type and the Swedish variant, respectively. Isozyme patterns and profiles of restriction fragments of the entire internal transcribed spacer (ITS) region or mitochondrial DNAs and of RAPD-PCR products did not differ within a group, but distinct polymorphisms were exhibited between the two groups of isolates. Southern analysis of random amplified polymorphic DNA (RAPD) revealed the homologous nature of co-migrating bands of P cambivora and the isolates of alder Phytophthora. Furthermore, restriction fragment profiles of the ITS region of ribosomal DNAs and the mtDNAs were consistent with reported biparental origin of alder Phytophthora. The hybrid status of these continuously evolving pathogens raises many issues and challenges concerning efficient control measures.     

Virulence of the invasive ash pathogen Hymenoscyphus fraxineus in old and recently established populations

Following its introduction from Asia in the 1990s, the ascomycete Hymenoscyphus fraxineus has caused a severe dieback of Fraxinus excelsior in Europe. In this study, the virulence of 200 H. fraxineus isolates were assessed and compared. These isolates equally represented (i) two geographically distant populations with a different disease history (Switzerland, recently established populations at the epidemic front versus Lithuania, old established populations), and (ii) isolates from two different types of host tissue (necrotic bark lesions as dead‐end tissue versus fallen leaf petioles as primary host tissue). Inoculations conducted on 3‐year‐old F. excelsior seedlings showed that the vast majority of the isolates (98%) were able to induce necrotic bark lesions after 10 months. Although a high variation in virulence was observed among isolates, no significant differences were detected between the older and the epidemic‐front populations. Decline in virulence of populations of invasive organisms is generally assumed with increasing age of epidemics. However, this does not appear to hold true for H. fraxineus. Either the Lithuanian population is still too young (15 to 20 years old) to show a decline in virulence, or the size of the host population may still not be critical for pathogen survival. Given that bark lesions represent an epidemiological dead end and do not benefit the survival of H. fraxineus, a trend towards reduced ‘bark virulence’ of isolates originating from leaf petioles compared to isolates from the bark lesions was expected. However, such a trend was observed neither in old, nor in recently established populations.     

Macropsis mendax as a vector of elm yellows phytoplasma of Ulmus species

A 3-year study was carried out in north-east Italy, the site of recent elm yellows epidemics, to identify vectors for the elm yellows phytoplasma. Using PCR analysis, Ulmus minor and Ulmus pumila , each with and without symptoms, were positive for the elm yellows phytoplasma. Macropsis mendax , a univoltine and monophagous leafhopper, was shown to be the vector of the elm yellows-associated disease agent. PCR analyses demonstrated that the insect was infected both in natural conditions and in the screenhouse after acquisition-feeding on infected elm plants. Groups of M. mendax , collected from naturally infected elm trees, transmitted elm yellows phytoplasma to elm test plants. In nature, Alnus glutinosa trees affected by alder yellows were found in the surroundings of yellows-affected elm trees; the associated disease agent of alder yellows was transmitted under controlled conditions from alder to elm test plants by grafting.     

Pathogenicity of Marssonina betulae and other fungi on birch

Marssonina betulae , Discula betulina , Melanconium bicolor and Fusarium avenaceum were inoculated onto shoots of 1- and 2-year-old seedlings of Betula pendula and B. pubescens and symptom development monitored over several seasons. Marssonina betulae caused disease on B. pendula , but not on B. pubescens . On B. pendula symptoms included discrete lesions, which often girdled, causing dieback of inoculated leading shoots, and the development of secondary sunken cankers on the main stems, which were usually centred around a dead sideshoot. Cankers on the main stems expanded during subsequent growing and dormant seasons, and often coalesced, girdling stems and causing the death of some seedlings. All isolates of M. betulae caused disease on B. pendula and conidia were able to infect young shoots in early flush without requiring a wound. Discula betulina caused lesions and dieback on B. pendula and B. pubescens within 3 months of inoculation, but disease did not progress thereafter and all inoculated seedlings recovered. Melanconium bicolor and F. avenaceum caused very little disease on either birch species. This study showed that M. betulae is an aggressive pathogen on B. pendula , causing sunken stem cankers and progressive crown dieback, which are symptoms commonly observed on young, planted birch at field sites across Scotland.     

Fungi as potential factors limiting natural regeneration of pedunculate oak (Quercus robur) in mixed-species forest stands in Poland

Dieback of young Quercus robur seedlings can limit natural regeneration in mixed-species forest stands in Poland. The aim of this study was to examine the role of fungi in the dieback of oak seedlings in central Europe. Fungi were isolated from the stems and roots of Q. robur, from both healthy seedlings and seedlings with symptoms, that were sampled from four stands in Poland. In total, 111 distinct taxa were identified. Ascomycota was dominant, representing 95.6% of the isolates. Among the taxa identified, Alternaria alternata, Colletotrichum fioriniae, Colletotrichum godetiae, Coniella quercicola, Diaporthe eres, Gnomoniopsis paraclavulata, Ilyonectria rufa, Mucor genevensis, Penicillium glandicola, Tubakia dryina, and Umbelopsis changbaiensis were most frequently isolated, and were consistently found in stems and roots of both healthy and diseased plants. The community compositions of fungi in healthy and diseased stems were similar, although Fusarium species, especially Fusarium sp. 1 (FTSC 5) and F. sporotrichioides, were found mainly in seedlings with symptoms. The pathogenicity of the most consistently isolated species from stems and roots of diseased seedlings was tested on Q. robur seedlings. F. sporotrichioides caused the largest lesions on inoculated seedlings. Six weeks after inoculation, D. eres, C. fioriniae, G. paraclavulata, T. dryina, and F. sporotrichioides killed 0%–18.8% of seedlings, while I. rufa and Ilyonectria pseudodestructans did not cause any lesions or other symptoms. This study is the first comprehensive report suggesting that massive fungal attack can lead to oak seedling dieback in mixed-species forest stands in central Europe.     

Effects of Moderate Water Stress on Disease Development by Sphaeropsis sapinea on Red Pine

ABSTRACT The aggressiveness of Sphaeropsis sapinea isolates was compared on water-stressed and nonstressed 3-year-old red pines (Pinus resinosa) in greenhouse and growth chamber experiments. Water was withheld from stressed seedlings to achieve mean predawn needle water potentials (psi(PD)) above -1.9 MPa. The lowest mean psi(PD) of well-watered seedlings was maintained at or above -0.8 MPa. Young shoots were inoculated by placing colonized agar plugs on wounds made by removing a needle fascicle. Two isolates of each recognized morphotype (A and B) were used in the greenhouse experiment and two isolates of morphotype A were used in the growth chamber experiment. After 4 weeks, isolates of morphotype A caused more severe symptoms and could be recovered farther from the inoculation site on water-stressed than on nonstressed trees in both experiments. In the greenhouse experiment, isolates of mor-photype A also caused more severe symptoms and could be recovered farther from the inoculation site than isolates of morphotype B, regardless of watering regime. These results indicate that water stress at levels observed typically in the field can result in increased disease development by isolates of S. sapinea morphotype A on red pine. The reduction of water stress of red pines in the field may reduce losses due to Sphaeropsis shoot blight.