Hosts and symptoms of Plum pox virus: woody species other than fruit and ornamental species of Prunus

The presence of Plum pox virus (PPV) in woody hosts other than in fruit and ornamental Prunus species was evaluated. PPV symptoms, and their variability and intensity, are described in leaves and fruits of Prunus cerasifera , Prunus spinosa , Ligustrum vulgare and Euonymus europaea . Juglans regia is not confirmed as a new host of PPV.     

Epidemiology of sharka disease in France

Plum pox virus was first detected in France in the 1960s. Both PPV-D and PPV-M strains are present but epidemics related to the PPV-M strain detected in the late 1980s are the most problematic. The two PPV strains have unequal distributions in peach and apricot orchards and different prevalences. More than 20 different aphid species have been identified as vectors of PPV but most of them do not colonize Prunus species. Thus, aphids involved in the spread of PPV in orchards are essentially visiting aphids. The main sources of inoculum for the vectors are leaves and fruits of infected stone-fruit trees. Spontaneous, wild and ornamental Prunus species such as Prunus dulcis , P. spinosa or P. pissardii are susceptible to PPV isolates found in France but their role as a reservoir in sharka epidemics is probably negligible. The disease spreads rapidly in orchards but the rate of progression may vary according to the identity of the PPV strain and the Prunus species. Analysis of spatial patterns of disease has shown that secondary spread by aphids frequently occurs over short distances in the orchards (aggregated patterns) but also that dissemination at longer distances (of several hundred metres) is a common event.     

Host‐range studies,genetic diversity and evolutionary relationships of ACLSV isolates from ornamental,wild and cultivated Rosaceous species

A large‐scale survey was carried out to study the host range and genetic diversity of Apple chlorotic leaf spot virus (ACLSV) in various Rosaceae species, with a special emphasis on ornamentals and wild shrubs. Samples were tested by DAS‐ELISA using two different antisera, and RT‐PCR amplification of part of the CP gene. There was generally a poor correlation between the results obtained with the two sets of serological reagents and between serological and molecular detection assays. Using a nested RT‐PCR assay developed here, ACLSV was found to be widespread among cultivated, ornamental and wild species of the Rosaceae. The virus was detected for the first time in plum, wild cherry, Crataegus monogyna, Prunus spinosa and Prunus cerasifera in Greece. Sequences of a part of the CP encoding gene and the 3′ untranslated region from ACLSV isolates originating from various wild species and ornamentals were compared to those of isolates from cultivated hosts, showing similar divergence levels. Further phylogenetic analysis using the sequenced region indicated that the isolates from wild or ornamental hosts were not more closely related to each other than to isolates from cultivated hosts. The possible role of different factors in the spread of ACLSV on cultivated, ornamental and wild species is discussed.     

Hosts and symptoms of Plum pox virus: Herbaceous hosts

Plum pox virus (PPV) is polyphagous and epidemic. Apart from cultivated and wild Prunus species, a large number of herbaceous plants can be hosts of the virus. New herbaceous host species are continuously being reported following artificial inoculation studies. Some of these herbaceous hosts, Chenopodium foetidum , Nicotiana clevelandii , N. benthamiana and Pisum sativum are very useful for concentrating and purifying the virus. The list of plants that have been found to be infected with PPV in their natural environment is shorter than the list of plants which can be experimentally infected. The role of weed species in PPV survival and spread in orchards is poorly understood. It is widely accepted that annual plants or weeds are not important in the epidemiology of PPV.     

Viruses of stone fruits in Albania

Surveys were carried out in the main stone-fruit growing areas of Albania to assess the phytosanitary status of Prunus in conimercial orchards and varietal collections. The presence of virus and virus-like diseases and their identification was ascertained through field observations, sap transmission to herbaceous hosts, graft transmission to woody indicators, ELISA and IEM tests. The mean infection level was 42%. In particular, infections in apricot and almond were 12 and 16%, respectively, i.e. lower than in plum and cherry (47 and 56%, respectively). The following viruses were identified: plum pox potyvirus (PPV). apple chlorotic leaf spot trichovirus (ACLSV). prunus necrotic ringspot (PNRSV) and prune dwarf (PDV) ilarviruses. PPV infection was very severe in plum, and limited in apricot and peach. Apple mosaic ilarvirus (ApMV), and six nepoviruses tested for (SLRV, TBRV, RRV, CLRV, ArMV and ToRSV) were not encountered in Primus.     

Identification of Plum pox virus Determinants Implicated in Specific Interactions with Different Prunus spp

ABSTRACT The characterization of pathogenic properties of two infectious clones of Plum pox virus (PPV) isolates, pGPPV (D group) and pGPPVPS (M group), was investigated in their woody hosts (seedlings of Prunus spp.). The two clones differed in their ability to infect plum and peach cultivars, from no infection to local and systemic infection. The phenotype determinants were located with a set of chimeric viruses from the two clones. In plum, determinants of systemic infection were located in a genomic fragment encoding the P3 and 6K1 proteins, which might influence genome amplification or virus movement. The capacity of pGPPVPS to induce stable local and systemic infections in peach was not located accurately and might be influenced by multiple determinants carried by different regions of the genome, excluding those encoding the protein 1, the majority of helper component, nuclear inclusions a and b, and coat protein. We conclude that PPV infections of plum and peach are governed by different determinants.     

Variation for pathogenicity among isolates of bean common mosaic virus in Africa and a reinterpretation of the genetic relationship between cultivars of Phaseolus vulgaris and pathotypes of BCMV

Bean common mosaic virus (BCMV) isolates were collected from crops of Phaseolus vulgaris (bean) and from wild legume species in 13 African countries. Isolates of pathotype VIa from both beans and wild legume species were predominant in central, eastern and southern Africa. Isolates of pathotypes I, III, IVa, IVb and Va were also found. Some isolates did not conform to previously published pathotypes, and therefore represent records of novel pathotypes. The susceptibility of various wild legume species to BCMV was investigated and isolates of the virus obtained from Crotalaria incana, Rhynchosia sp., Macroptilium atropurpureum and Cassia occidentalis (synonym Senna occidentalis) were aphid-transmitted both from P. vulgaris to their original host species and to P. vulgaris. Isolates of BCMV from wild legume species were seed-transmitted in bean and in several other legume species. The natural occurrence of BCMV in wild legume species in Africa is probably a significant factor in the ecology and epidemiology of the virus and possibly the evolution of isolates of the 'A' serotype which induce necrotic reactions in cultivars carrying the I gene for resistance. The occurrence of viruses other than BCMV from P. vulgaris and other legume hosts is also reported. The gene-for-gene model described by Drijfhout (1978) is reinterpreted to explain the variation for pathogenicity, and it is proposed that there may be genes which control the temperature sensitivity of necrosis in combination with the I gene.     

Phytophthora ramorum and Phytophthora kernoviae on naturally infected asymptomatic foliage

Phytophthora ramorum and Phytophthora kernoviae are recently discovered invasive Phytophthoras causing leaf necrosis and shoot tip dieback mostly on ornamental and forest understorey species, but also cause bleeding cankers on stems of a wide range of tree species. Sporulation occurs only on infected shoots or fruits and foliage so foliar hosts are central to the disease epidemiology. In field trials to assess infection in trap plants exposed to natural inoculum of P. ramorum and P. kernoviae on rhododendron in south west England, it was discovered that leaves of the trap plants ( Rhododendron 'Cunninghams White') and holm oak ( Quercus ilex ) were asymptomatically infected and supported sporulation of both pathogens. More than half the rhododendron trap plants exposed to inoculum of P. kernoviae became infected compared with approximately a third of those exposed to P. ramorum in a natural situation. Approximately one third of the infections were detected from asymptomatic foliage for both pathogens. The significance of these findings for plant health regulation based on visual inspection as a measure to prevent introduction and dissemination of both these pathogens is explored and research gaps identified.     

Breeding for resistance: breeding for Plum pox virus resistant plums (Prunus domestica L.) in Germany

In German plum breeding programmes new varieties tolerant to Plum pox virus (PPV) were initially obtained by selecting hybrids originating from crossings between tolerant old varieties while, later on, sharka tolerant varieties bred in Čačak, Serbia were used as crossing partners. Varieties released from these programmes replaced the sensitive ones in all sharka infected regions in Germany. While all the new tolerant varieties can be infected by the virus, PPV symptoms on the fruits are acceptable. However, environmental factors can weaken the plant, causing them to suffer more from PPV infections and to display worse symptoms on fruits, as did occur during some recent very dry and warm years. A breeding programme at the University of Hohenheim is tackling this problem with genotypes that show a hypersensitive response after infection. These genotypes are completely field resistant to PPV, remaining virus free in the field since they cannot be infected via aphid transmission. They are able to isolate the virus after infection. The first hypersensitive variety was 'Jojo'. Many seedlings originating from crossings with at least one hypersensitive parent are under evaluation. Since the inheritance of the trait 'hypersensitivity against PPV' is very good, combining hypersensitivity with excellent fruit quality and good cropping capacity will be possible soon. In 2005, a breeding programme for hypersensitive Prunus genotypes began at the Technical University of Munich.     

The sympatric Ascochyta pathosystems of Near Eastern legumes,a key for better understanding of pathogen biology

The primary and secondary centres of origin of domesticated plants are often also the places of origin of their pathogens. Therefore, the Near Eastern cradle of agriculture, where crop plants, their wild progenitors, and other con-generic taxa grow sympatrically, may hold some clues on the biology of the pathogens of the respective crops. Unlike the situation in the well-studied Near Eastern cereals and their important diseases, hardly any data are available on basic questions regarding grain legumes. What is the role of genetic diversity at resistance loci of the wild hosts and is it greater compared with the cultigens? Are populations of Ascochyta pathogens infecting wild legumes genetically distinct from populations infecting their domesticated counterparts, and if so, is this differentiation related to differences in host specialization or to adaptation to different ecological conditions? Do isolates originating from wild taxa exhibit a similar level of aggressiveness and have different aggressiveness alleles compared with those originating from domesticated grain legumes? In this review we propose an experimental framework aimed at gaining answers to some of the above questions. The proposed approach includes comparative epidemiology of wild vs. domesticated plant communities, co-evolutionary study of pathogens and their hosts, phenotypic and genetic characterization of fungal isolates from wild and domesticated origins, and genetic analyses of pathogenicity and parasitic fitness among progeny derived from crosses between isolates from wild and domesticated hosts.     

Viruses and viroids of stone fruits in Syria

Field surveys were carried out in the main stone fruit-growing areas of Syria to evaluate the sanitary status of mother blocks, varietal collections and commercial orchards. The presence of virus and virus-like diseases was checked by enzyme-linked immunosorbent assay (ELISA), sap transmission to herbaceous hosts, testing on the woody indicators Prunus persica cv. GF 305 and Prunus serrulata cv. Kwanzan and dot-blot hybridization tests. A total of 1337 samples was tested by ELISA (444 apricot, 283 peach, 246 cherry, 222 almond and 142 plum). The overall mean infection rate was 13%, and the percentage infection level of single species was: peach 24%, cherry 16%, almond 13.5%, apricot 6%, plum 5%. The following viruses and viroids were detected: PNRSV, PDV, ACLSV, PPV, ApMV, PLMVd and HSVd ¹ .     

Detection ofplum pox virus in ornamentalPrunus cerasifera

Plum pox virus (PPV) is the causal agent of sharka disease. It is a serious threat for temperate fruit, mainly apricots, plums and peaches. In order to study the ability ofPPV to infect wild and ornamentalPrunus species, several wild, native ornamental stone fruits and weeds were analyzed as possible reservoirs ofPPV. Five species of ornamental stone fruits and 24 species of weeds were evaluated between 2000 and 2004. The virus was not found in the weeds but was detected in one species of ornamental stone fruit, purple cherry-plums (Prunus cerasifera Pissardii). ThePPV strain M was identified by DASI-ELISA and confirmed by IC-RT-PCR. Additionally, mealy plum aphid (Hyalopterus pruni) was determined as a vector ofPPV inP. cerasifera. This is the first report on the reservoir potential of ornamental stone fruit trees and weeds forPPV in Turkey. http://www.phytoparasitica.org posting July 19, 2006;     

The role of weeds in the epidemiology of pospiviroids

Many weeds that are closely associated with horticultural activities are known as natural reservoirs of plant viruses. However, whether these weeds can also serve as hosts of pospiviroids is not well known. Pospiviroids are naked, non‐coding RNA pathogens that cause severe economic damage in many solanaceous crops. In this study, we examined the overall risk of pospiviroid spreading from weeds to economically important crops, by combining the results from previous inoculation studies with new results coming from a survey, a contact experiment and an inoculation experiment. A survey of commercial ornamental glasshouses revealed that ornamental plants mainly belonging to the Solanaceae harbour pospiviroids, in contrast to weed species sampled in the same places. No new weed hosts could be identified after testing weeds that grew in contact with Tomato apical stunt viroid (TASVd)‐infected plants of tomato (Solanum lycopersicum) and jasmine nightshade (Solanum jasminoides) in an experimental glasshouse. Finally, in mechanical inoculation experiments with TASVd, none of the six tested weed species were determined to be a host at 6 weeks after inoculation. Commonly occurring weed species therefore do not appear to play a significant role as reservoir hosts for pospiviroids. This does not rule out other potential weed hosts that have not yet been tested. Inoculation studies should include rigorous experimental protocols with a sufficient number of replicated as well as adequate positive controls. The information gained through this study may prove useful in future risk assessments for the pospiviroid group.     

Unravelling the Prunus/Plum pox virus interactions

Plum pox virus (PPV) belongs to the genus Potyvirus that contains the largest number of virus species infecting plants. Its virus genome has been extensively characterised and sequenced. However, few data are available on its interactions with woody host plants. We therefore focused, in the past 4 years, both on the cellular and molecular aspects of the compatible and incompatible Prunus /PPV interactions. GFP (Green fluorescent protein)-tagged PPV and in situ hybridisation were used to compare the localization of viral particles in stems and leaves of susceptible and resistant apricot cultivars. In parallel, molecular tools were developed through the cloning and characterization of polymorphic, homologous resistance genes and of candidate genes involved in the expression of Prunus /PPV interactions. Candidate genes are currently used to target genomic regions involved in resistance or susceptibility and to identify molecular markers indispensable for further marker assisted selection for resistance to sharka disease.     

Epidemiology of sharka disease in Spain

PPV was first detected in Spain in 1984 in Japanese plum ( Prunus salicina Lindl) cv. Red Beaut and spread very quickly to other Japanese and European plums and apricot cultivars but left peach cultivars unaffected. In the years following the detection of PPV, the predominant aphid species visiting Prunus orchards in Mediterranean areas were Aphis gossypii followed by Aphis spiraecola , the latter being the main aphid species found at present. Both species are considered to be the main vectors of PPV in Spanish early Prunus growing areas. Spatial analysis of the spread of PPV-D in Japanese plum and apricot trees confirmed the lack of significant association between immediately adjacent trees. The observed spatial pattern of sharka suggests a lack of movement of PPV-viruliferous aphid vectors to immediately adjacent trees and indicates their preferential movement to trees several tree spaces away. PPV-D is the only type currently present in Spain, with the exception of a PPV-M outbreak that was detected in and successfully eradicated from Aragón in 2002. The short-distance spread of PPV-M infection occurred as far as 12 m along the rows of peach trees. However, PPV-D has not been observed to spread through peach cultivars, despite being grown in the vicinity of heavily infected plots of apricot or Japanese plum trees.     

Parasitic weeds of the Orobanchaceae family and their natural hosts in Jordan

A field survey of the Orobanchaceae family members and their hosts in Jordan was carried out from 2003 to 2007. The intensity of parasite infection on different hosts and the severity of the infestation were evaluated. The results showed the presence of seven species of Orobanche and three species of Cistanche . The Orobanche species were found parasitizing 86 plant species belonging to 24 botanical families. Most of the species attacked by Orobanche were from the Compositae (20 species), Solanaceae (11 species), Leguminosae (nine species), Umbelliferae (seven species), Cruciferae (seven species), Cucurbitaceae (four species), Labiatae (four species), and Rosaceae (four species) families. Other families were represented by one-to-three species. Cistanche attacked 20 species of forage wild shrubs, fruit trees, and forest trees of seven families, mostly belonging to the Chenopodiaceae (seven species) and Leguminosae (three species) families. Previously unreported hosts for both genera include: Amygdalus communis , Olea europaea , and Quercus coccifera , which were parasitized by Orobanche palaestina ; A. communis , O. europaea , Prunus armeniaca , and Prunus persica , which were parasitzed by Orobanche cernua ; O. europaea and A. communis , which were parasitzed by Orobanche schultzii ; Haloxylon persicum , which was parasitzed by Cistanche lutea ; Punica granatum , Alhagi maurorum , Casuarina equisetifolia , Centaurea postii , and Prosopis farcta , which were parasitzed by Cistanche tubulosa ; and Achillea spp., Anabasis syriaca , H. persicum , Haloxylon salicornicum, Suaeda spp., and Zilla spinosa , which were parasitzed by Cistanche salsa . Certain Orobanche species were completely destructive to the cultivated crops. The results indicated the high potential of both parasitic genera to spread and to attack new hosts, while the threat they impose to agriculture in Jordan will probably result from poor management and deficiences in farmers' training.     

Transmission of plum pox potyvirus in Spain1

Transmission tests were conducted in the laboratory to determine which are the aphid species responsible for the great natural spread of plum pox potyvirus (PPV) observed in the field in Spain. Woody hosts were used in these tests and different transmission techniques were compared. The aphid species tested were Myzus persicae, Aphis gossypii, A. spiraecola, A. fabae, Hyalopterus pruni and Brachycaudus prunicola. Although the transmission rates obtained were, in general, quite low, it can be stated that, except for B. prunicola (pending confirmation of results), all species tested transmitted PPV under the conditions of the trial.     

Potential role of almond in sharka epidemics: susceptibility under controlled conditions to the main types of plum pox potyvirus and survey for natural infections in France 1

The changes in cropping conditions of almond and the development of efficient tools for the detection and characterization of plum pox potyvirus (PPV) populations have led us to reassess the potential susceptibility of this species to sharka disease and its role as a virus reservoir. The susceptibility of almond cv. Aï to nine isolates, representative of the known diversity among PPV populations, was assessed under controlled conditions. Most isolates were able to infect almond, by graft or aphid inoculation, causing generalized stable infections without any obvious sharka symptoms. These infected almonds were found to constitute a potential source of virus for aphid vectors, mainly in the case of M isolates. Surveys were carried out in the south of France, in foci of M and D strains of PPV, to evaluate the presence of natural infections of almond. No typical symptoms were observed and the virus was never detected. It can be assumed that the actual limited prevalence of PPV in France does not lead to a sufficiently high inoculum pressure to allow almond trees to be infected.     

Viruses and viroids of stone fruits in Jordan

Field surveys were carried out in the main stonefruit-growing areas of Jordan to assess the sanitary status of varietal collections, mother plant blocks and commercial orchards. The presence of virus and virus-like diseases was determined by ELISA, sap transmission to herbaceous hosts, graft transmission to Prunus persica cv. GF 305 and P. serrulata cv. Kwanzan, and molecular hybridization tests. A total of 1312 samples was tested by ELISA (531 peach, 361 plum, 218 apricot, 135 almond and 67 cherry trees). The overall mean level of infection was about 14%, indicating an acceptable sanitary status as a whole, considering that no sanitary selection has ever been carried out in Jordan. The infection level of different species was: peach (18%), cherry (15%), almond (14%), apricot (11%) and plum (10%). The following viruses and viroids were identified: Plum pox potyvirus (PPV), Prunus necrotic ringspot ilarvirus (PNRSV), Prune dwarf ilarvirus (PDV), Apple mosaic ilarvirus (ApMV), Apple chlorotic leaf spot trichovirus (ACLSV), Hop stunt viroid (HSVd) and Peach latent mosaic viroid (PLMVd). Most of these agents (ApMV, ACLSV, PLMVd and HSVd) are reported for the first time from Jordan.