PCR-based DNA Markers for Identifying Hybrids within Phytophthora alni

Two pairs of oligonucleotide primers were designed for the polymerase chain reaction (PCR)‐based detection and differential identification of naturally occurring interspecific hybrid types (subspecies) of Phytophthora alni, all of which cause collar rot of alder trees. Primer pairs were derived from randomly amplified polymorphic DNA (RAPD) fragments that were unique to various subspecies of this alder pathogen. The primer pair set, SAP1/SAP2 (SAP), was derived from a 0.93‐kb RAPD fragment amplified from P. alni ssp. alni. The primer pair set, SWAP1/SWAP2 (SWAP), was derived from a 1.13‐kb fragment amplified from P. alni ssp. uniformis. Patterns of SAP and SWAP amplification enabled distinction among the three subspecies. No PCR products were amplified from isolates of 31 other Phytophthora spp. examined, including P. cambivora and P. fragariae, the suspected progenitors of P. alni. The SAP and SWAP primer sets were able to detect a minimum of 10 pg of DNA from pure cultures or DNA extracted from as few as 10 zoospores. Pathogen DNA could also be amplified directly from bark lesions of artificially inoculated and naturally infected common alders and from lesions developed on common cherry‐laurel leaves used in baiting the pathogen from infested soil. Direct detection of pathogen DNA from alder tissue using SAP and SWAP primer sets should prove useful in developing measures for effective quarantine and management of P. alni.     

Fusarium solani association with branch and trunk cankers on citrus weakened by cold weather in Florida

Injury or inoculation of apparently healthy citrus trunk bark and wood with Fusarium solani immediately prior to and after the December 1983 freeze resulted in cankers similar to natural branch and trunk cankers which formed on trees following the freeze. Fusarium solani was consistently isolated from active lesions of natural and induced cankered bark. Phytophora spp. were not isolated from cankered tissue. Earliest cankers appeared as a water-soaked area under the bark around the point of inoculation, later F. solani sporodochia formed on the bark surface. Older cankers became dry and cracked but produced no gum. Canker size ranged from 10–90 cm vertical diameter in spring 1984 inoculations but were only several cm diameter following late summer inoculations. Active cankers developed again after inoculation following the January 1985 freeze. Similar cankers were produced on Hamlin sweet orange stems inoculated with F. solani.     

Dieback of riparian alder caused by the Phytophthora alni complex: projected consequences for stream ecosystems

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Modeling climate impact on an emerging disease,the Phytophthora alni‐induced alder decline

Alder decline caused by Phytophthora alni is one of the most important emerging diseases in natural ecosystems in Europe, where it has threatened riparian ecosystems for the past 20 years. Environmental factors, such as mean site temperature and soil characteristics, play an important role in the occurrence of the disease. The objective of the present work was to model and forecast the effect of environment on the severity of alder Phytophthora outbreaks, and to determine whether recent climate change might explain the disease emergence. Two alder sites networks in NE and SW France were surveyed to assess the crown health of trees; the oomycete soil inoculum was also monitored in the NE network. The main factors explaining the temporal annual variation in alder crown decline or crown recovery were the mean previous winter and previous summer temperatures. Both low winter temperatures and high summer temperatures were unfavorable to the disease. Cold winters promoted tree recovery because of poor survival of the pathogen, while hot summer temperature limited the incidence of tree decline. An SIS model explaining the dynamics of the P. alni‐induced alder decline was developed using the data of the NE site network and validated using the SW site network. This model was then used to simulate the frequency of declining alder over time with historical climate data. The last 40 years' weather conditions have been generally favorable to the establishment of the disease, indicating that others factors may be implicated in its emergence. The model, however, showed that the climate of SW France was much more favorable for the disease than that of the Northeast, because it seldom limited the overwintering of the pathogen. Depending on the European area, climate change could either enhance or decrease the severity of the alder decline.     

Epidemiology of Pseudomonas syringae Pathovars Associated with Decline of Plum Trees in the Southwest of Germany

Plum decline was associated with Pseudomonas syringae pathovars syringae and morsprunorum in Baden‐Württemberg. The trunks of affected plum trees (Prunus domestica) were girdled by bacterial cankers resulting in sudden death of infected trees. Copper compounds that were applied extensively during leaf fall and bud burst, were not effective. A minority of P. syringae strains isolated from cankers on plum trees were moderately resistant, while most strains were sensitive to cupric ions. Invasions through blossoms, leaves and wounds during the vegetation period were limited to the infection sites and plum trees coped effectively with both P. syringae pathovars eliminating them eventually. Infections after dormancy including very rare leaf scar infections did not induce cankers on the trunk. However, infections of dormant trees through frost injuries, (pruning) wounds or non‐injurious ingress by freezing and thawing were serious, because they led to cankers girdling the trunk. Control strategies to manage plum decline have to be adapted to the disease cycle. They should concentrate on the dormant period beginning with early frosts in autumn and ending with bud burst.     

Pathogenicity of four Phytophthora Species on Wild Cherry and Italian Alder Seedlings

Inoculation tests were carried out in the greenhouse on wild cherry (Prunus avium) and Italian alder (Alnus cordata) seedlings, to determine their susceptibility to certain Phytophthora species (P. citrophthora, P. alni, P. megasperma and P. cinnamomi) that are commonly present in the soil. Host susceptibility was evaluated in accordance with a disease index, with the lesion length after stem inoculation, and with a root system disease index. Wild cherry was found to be highly susceptible to P. citrophthora, and was also found to be susceptible to P. alni, although to a lesser extent. Italian alder was very susceptible to P. alni, but had only low susceptibility to P. citrophthora. The other Phytophthora species caused only modest symptoms. The danger to alder and wild cherry is all the greater because these trees not only share the same pathogens, but also commonly planted together in mixed stands. The results will now have to be confirmed by using a more natural inoculation method.     

Nonglandular leaf trichomes as short-term inducible defense of the grey alder,Alnus incana (L.), against the chrysomelid beetle,Agelastica alni L.

Summary The grey alder compensates leaf area losses due to insect grazing by continuously producing new leaves throughout the vegetative period. Different degrees of defoliation were attained experimentally by a controlled release of the oligophagous beetle Agelastica alni on arbitrarily selected trees from a homogenous population of young alders. The reduction in leaf area per tree significantly influenced the density of leaf trichomes, assessed 10–30 days later, on newly sprouting leaves only. Cross-correlations between leaf area reduction and trichome density were strongest for leaves which completed unfolding 14–21 days after damage. Dualchoice assays suggested a negative influence of trichomes on oviposition rate of A. alni. Removal of trichomes by shaving demonstrated the highly significant effect of trichomes on feeding behavior of adults and larvae in dual-choice assays. The role of the induced increase in trichome density as a possible short-term defense reaction against herbivorous insects is discussed.     

Characterization of Alder Phytophthora Isolates from Wallonia and Development of SCAR Primers for their Specific Detection

Isolates of alder Phytophthora were collected in the southern part of Belgium on riverbanks planted with Alnus glutinosa and A. incana. They were compared with strains isolated in other European countries in terms of maximum temperature for growth, oogonia shape, pathogenicity on Alnus seedlings and genetic traits. Using both molecular techniques [random amplified polymorphic DNA (RAPD) and random amplified microsatellite (RAMS)], two groups of isolates were identified, the first group being further divided into two subgroups, Ia and Ib, using RAPD. Most of the Walloon alder Phytophthora isolates as well as the standard type from UK (formally designated P. alni subsp. alni) fell into group Ia. One isolate was classified in group Ib with the German and Dutch variants (P. alni subsp. multiformis), while three isolates were placed with the Swedish variant (P. alni subsp. uniformis) in group II. In terms of morphological properties, isolates from groups Ia and Ib developed colonies with a felt‐like appearance and usually produced numerous oogonia, varying from wavy to warty after 1 week (group Ia) or 2–3 weeks (Ib) in darkness. In contrast, colonies from group II isolates were generally irregular, and smooth oogonia were produced in low quantities after approximately 1 month in culture. A polymerase chain reaction (PCR) using sequence‐characterized amplification region (SCAR) primers derived from a polymorphic amplification product generated with a RAPD primer was developed for the specific detection of alder Phytophthora. The specificity and sensitivity of this test are discussed here.     

Insecticidal effects of some biological agents on Agelastica alni (Coleoptera: Chrysomelidae)

The alder leaf beetle (Agelastica alni L., Coleoptera: Chrysomelidae) causes approximately 10% of total economic damage to hazelnut product per year in Turkey. A. alni larvae are susceptible to several pathogens indigenous to the area in which these insects occur in Turkey. In the present study, in order to find a more effective and safer biological control agent against this common pest, we evaluated the various biological agents’ insecticidal activity during the four hazelnut seasons from 2002 to 2005 on the larvae of the alder leaf beetle collected from the vicinity of Trabzon, Turkey. The tested agents are 25 insect-originating bacteria, 2 bacterial toxins and 1 viral preparation. The results showed that the highest insecticidal activity was obtained by bacterial isolates at 1.8 × 10⁹ bacteria/mL dose, within ten days on the larvae of A. alni. These are 90% for Bacillus thuringiensis biovar tenebrionis (4AA1), Bacillus sphaericus (Ar4, isolated from Anoplus roboris L., Col.: Curculionidae), and Bacillus thuringiensis (Mm2, isolated from Melolontha melolontha L., Col.: Scarabaeidae). Our results indicate that these isolates may be valuable as biological control agent.     

Dependence of the cellulosolytic activity in the lichen <Emphasis Type="Italic">Hypogymnia physodes</Emphasis> (L.) Nyl. on the substrate

Samples of the lichen H. physodes were collected from bark of living trees (pine, spruce, birch, alder, rowan, and willow); from the wood of these trees and of juniper; from bark of dead spruce, alder, and rowan trees; and from the moss Hypnum pallescens. Thalli of this lichen were placed onto medium with carboxylmethyl cellulose (CMC) (water being used as a control). Output of sugars was determined using the Nelson-Somogyi technique. Cellulosolytic activity of samples from the bark of pine and birch was higher than that of samples from the bark of spruce. In thalli of the lichen from wood, from moss, and from bark of living alder and rowan trees, the output of sugars on the medium with CMC was similar to that in the control. The cellulosolytic activity was revealed in samples from the lichen from bark of dead rowan and alder trees. In the lichen from spruce bark, the output of sugars on the medium with CMC was higher in samples from dead trees in comparison with living trees. The results are discussed.     

Identification of deep bark canker agent of walnut and study of its phenotypic,pathogenic, holotypic and genetic diversity in Iran

The deep bark canker of the walnut is a serious threat to walnut plants that had an increasing verge since recent years. This disease is caused by Brenneria rubrifaciens bacteria. Therefore, this research was carried out with an aim to identify the deep bark canker agent. The suspected samples having symptoms were collected from the bark and branches of walnut trees. After purification, the phenotypic and biochemical specification of separations was assessed. Even the genetic diversity of pathogen population was conducted with BOX-polymerase chains reaction (PCR) technique and BOXAIR primer. Based on the phenotypic and biochemical specifications, 30 isolates were identified as B. rubrifaciens. In PCR reaction, the specific amplicons of size 537 and 671?bp in the case study strains were amplified via specific primer pairs. The present study is a prime report on outbreak of this disease in Iran and bacterial pathogenicity evidence of B. rubrifaciens on fruit in the world.     

Sudden death of cocoa in Papua New Guinea associated with Phytophthora palmivora cankers invaded by bark beetles

An extensive survey in 1976-82 indicated that sudden death of cocoa was widespread in Papua New Guinea with losses up to 1% per month in trees over 10-yr-old, especially in neglected plantations. Over 95% trees affected had large Phytophthora palmivora canker lesions and over 90% of the cankers were invaded by bark beetles. In an intensive single year survey of one plot 18-8% of 69 healthy trees died. Ambrosiella spp., P. palmivora and Fusarium solani were isolated from wood surrounding beetle tunnels but only the last two caused extensive lesions when inoculated into the xylem of healthy trees. The evidence obtained indicated that the sudden death syndrome is initiated by P. palmivora cankers on trunks and main branches but bark beetles are a major contributory factor and fungi associated with their tunnels may contribute to the problem. There is a risk of further outbreaks of the disease as cocoa cultivars susceptible to P. palmivora continue to be planted.     

Widespread Distribution of Fungivorus Aphelenchoides spp. in Blight Cankers on American Chestnut Trees

Previously we showed in laboratory studies that the fungivorus nematode, Aphelenchoides hylurgi, was attracted to and fed upon the chestnut blight fungus, Cryphonectria parasitica, from American chestnut bark cankers and was a carrier of biocontrol, white hypovirulent C. parasitica strains. In the present field study, we recovered Aphelenchoides spp. in almost all (97.0 %) of 133 blight canker tissue assays (three 5-g samples each) from four eastern states. High mean population densities (227 to 474 nematodes per 5 g tissue) of Aphelenchoides spp. were recovered from cankers in Virginia, West Virginia, and Tennessee but not from New Hampshire (mean = 75 nematodes per 5 g tissue). Overall, most canker assays yielded population densities less than 200 nematodes per 5 g tissue. All of 12 very small or young cankers yielded a few to many Aphelenchoides spp. Regression analysis indicated greatest recovery of Aphelenchoides spp. occurred in the month of May (r = 0.94). The results indicate that Aphelenchoides spp. appear to be widespread in blight cankers on American chestnut trees and could play a role in biocontrol of chestnut blight.     

Defoliation of alders (Alnus glutinosa) affects herbivory by leaf beetles on undamaged neighbours

The effects of defoliation of alder (Alnus glutinosa) on subsequent herbivory by alder leaf beetle (Agelastica alni) were studied in ten alder stands in northern Germany. At each site, one tree was manually defoliated (c. 20% of total foliage) to simulate herbivory. Subsequent damage by A. alni was assessed on ten alders at each site on six different dates from May to September 1994. After defoliation, herbivory by A. alni increased with distance from the defoliated tree. Laboratory experiments supported the field results. Not only leaf damage in the field, but also the extent of leaf consumption in laboratory feeding-preference tests and the number of eggs oviposited per leaf in another laboratory test were positively correlated with distance from the defoliated tree. Resistance was therefore induced not only in defoliated alders, but also in their undamaged neighbours. Consequently, defoliation of alders may trigger interplant resistance transfer, and therefore reduce herbivory in whole alder stands.     

Egg distribution and mortality in the alder aphid, Pterocallis alni

Alder aphid oviparae produced 14 eggs at constant temperature but in the field the average was 6. Favoured oviposition sites were bud axils and bark crevices. Summer pruning of host trees reduced the availability but not the choice of site. Oviparae reared on leaf regrowth of summer pruned alder were smaller and contained fewer eggs than those on mature leaves. Winter pruning resulted in the loss of 41% buds and 25% eggs. Total winter egg mortality was 65%, being greatest in early winter due to insect predation. Spring egg hatch was synchronised with bud burst and both were affected by temperature.

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Distribution des oeufs et mortalité Pterocallis alni

Résumé Les ovipares de P. alni ont pondu 14 oeufs à température constante mais dans la nature la moyenne n'était que de 6. La taille estivale a réduit les disponibilités, mais n'a pas modifié le choix des lieux de ponte. Les ovipares élevés sur feuilles de repousses estivales d'aulnes taillént plus petits et contenaient moins d'oeufs que ceux élevés sur feuilles adultes. La taille hivernale a provoqué la perte de 41% des bourgeons et 25% des oeufs. La mortalité hivernale totale des oeufs a été de 65%, la partie la plus importante, due à la prédation par les insectes, ayant eu lieu au début de l'hiver. L'éclosion des oeufs au printemps était synchronisée avec l'éclatement des bourgeons, tous les deux étant conditionnés par la température.

     

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.     

Control of apple canker using fungicidal paints and gels

Paints containing mercuric oxide or thiophanate-methyl were applied to either scraped or unscraped cankers caused by Nectria galligena on apple trees at two sites. Three gel formulations (carbendazim/triadimefon in alginate or xanthan and carbendazim/imazalil in xanthan) and a solvent-based PP969 formulation were applied to unscraped cankers only. Assessments were made 9 and 21 months after treatment. Mercuric oxide was more effective than thiophanate-methyl after 21 months on both scraped and unscraped cankers. All gel formulations reduced spore production and fungitoxicant could still be detected in bark and wood after 21 months. The solvent-based PP969 formulation did not perform as well as the gels.     

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.     

Occurrence and Characterization of the Bacterial Spot Pathogen Xanthomonas euvesicatoria on Pepper in Iran

We report in this study for the first time the occurrence of bacterial spot of pepper in Iran and both phenotypic and genetic characterization of its causal agent, Xanthomonas euvesicatoria. Pepper plants grown in 15 of 30 surveyed private gardens and commercial fields were infected by the pathogen in Marand County, East Azerbaijan Province, north‐western Iran. The obtained strains of X. euvesicatoria had different amylolytic and pectolytic activities compared with those reported for this species elsewhere. Pathogenicity tests showed that strains isolated from diseased pepper are able to infect tomato, in addition to pepper. Host range of the pathogen was assessed on eight annual plant species including crops and weeds by measuring the population dynamics. The host range assessment showed that in addition to pepper and tomato, known hosts of X. euvesicatoria, the Iranian strains were able to colonize a number of new hosts such as nightshade and common bean. In contrast, none of them were able to build up their population on cowpea, eggplant, bindweed and zucchini. All X. euvesicatoria strains obtained in this study were sensitive to copper sulphate and streptomycin at concentrations higher than 20 and 50 mg/l, respectively. Phylogenetic analyses of the strains using the sequences of gyrB and hrpB genes confirmed their species as X. euvesicatoria. Given a direct commercial trade of fresh solanaceous vegetables between Iran and Turkey, it is hypothesized that the pathogen entered north‐western Iran from eastern parts of Turkey through infected plant materials. Finally, the role of prevention – based on the use of healthy planting materials and resistant and/or tolerant plant varieties – to contain the potential disease epidemics is discussed.     

The ecology of Erwinia rubrifaciens and the development of phloem canker of Persian walnut

A requisite for development of bacterial phloem canker caused by Erwinia rubrifaciens is the presence of the highly susceptible Hartley cultivar; when interplanted with Hartley, the Franquette and Payne cultivars are sometimes attacked by the disease. The recently developed cultivars, Gustine and Howe, developed active cankers when inoculated, but not as extensive as those in Hartley. The age of the plant part is important in the disease. One-year-old Hartley trees and twigs of the current season on mature trees did not develop active cankers. The complete disease syndrome occurs only on trunks and primary (scaffold) branches. Extension of the cankers was most rapid during the summer when the temperature was high. This was correlated with the effect of temperature on growth of the bacterium in culture. At midday in summer the temperature of the cambial area of a shaded trunk was as much as 10d?F (5.6 d?C) below ambient temperature but it was commonly a few degrees above ambient at night. Breaks in the thick phelloderm of the trunks and branches are necessary for penetration of the pathogen to the inner bark. Of the several types of breaks commonly occurring, those produced by mechanical harvesting equipment and by sap-sucking birds were found to be infection sites. Bacteria occur in large numbers in a slimy substance which exudes through cracks and accumulates on the bark of infected trees. They survived for at least 123 days in the exudate and were disseminated laterally as far as 20 ft (6.1 m) in wind-blown rain. Bacteria were also transmitted from tree to tree in exudate contaminating the pads of mechanical harvesting equipment.