Een ziekte in erwten,veroorzaakt door het aaltje hoplolaimus uniformis thorne

Summary In some gardens on light sandy soil in Ede a poor growth and yellowing of the leaves beginning with the lowermost ones was observed in peas together with root rot and reddish discoloration of the vascular bundles. The soil was heavily infected withHoplolaimus uniformis Thorne,Pratylenchus penetrans (Cobb)Sher andAllen,P. minyus Sher andAllen and aTylenchorhynchus species.The disease symptoms described above were reproduced experimentally by growing peas in soil inoculated withHoplolaimus uniformis.The other species mentioned above did not damage peas grown in soil inoculated with numbers five times as high as in the original soil.     

Geelnervigheid,een virusziekte van luzerne

Samenvatting Door middel van de erwtebladluis (Acyrthosiphon pisum Harris) werd het topvergelingsvirus van de erwt op luzerne (Medicago sativa L.) overgebracht. De besmette planten vertoonden na verloop van tijd het verschijnsel van geelnervigheid, te weten een regelmatige, lichtgroene tot gele nerftekening op de bladeren. Dit verschijnsel blijkt veelvuldig in luzernepercelen in het zuidwesten van het land (het gebied waar topvergeling in erwt algemeen voorkomt) op te treden. Het gelukte uit vier van vijf van verschillende plaatsen van West-Brabant en Zuid-Beveland afkomstige monsters geelnervige luzerne het topvergelingsvirus te isoleren.Uit waarnemingen bij planten, groeiende in het veld en in de kas, is gebleken, dat de omstandigheden een grote invloed hebben op het te voorschijn komen van het ziektebeeld. In het voor- en najaar treedt de geelnervigheid doorgaans zeer duidelijk op; in de zomermaanden verdwijnt dit verschijnsel veelal tijdelijk bij de besmette planten en onderscheiden deze zich niet van virusvrije luzerne.In een veldproef bleek het topvergelingsvirus, gezien het voorkomen van geelnervigheid in de loop van het seizoen, vrij snel in luzerne verspreid te worden.Summary Tip yellows (leaf roll) virus of pea was transmitted to lucerne (Medicago sativa L.) by means of the pea aphid (Acrythosiphon pisum Harris). After some months the infected lucerne plants showed a regular lightgreen to yellow discoloration of the veins and the adjacent tissue (fig. 1). No differences in growth and in shape of the leaves between infected and healthy plants were found to exist.This disease—for which we have chosen the name of vein yellowing of lucerne—is very prevalent in lucerne fields in the southwestern part of The Netherlands where tip yellows is often found in peas. We succeeded in isolating tip yellows virus from four out of five samples of lucerne showing vein yellowing collected in western Brabant and Zuid-Beveland.In carrying out transmission tests, it was found that the pea aphid often hardly sucks on lucerne in the greenhouse. Although it generally is present in large numbers in lucerne fields, it refuses to feed on lucerne after having been reared on peas for a prolonged period. This behaviour of the vector impedes the experiments. It may be due to the fact that the different generations of the insect differ in host plant requirements (Evans & Gyrisco, 1956) but also to the fact that morphologically indistinguishable forms of the insect exist, which may differ in host plant preferences (Hille Ris Lambers, 1947).Furthermore, in our experiments seldom a 100% infection of pea plants was obtained, even when using pea aphids which fed on a tip yellows diseased pea plant for a period of 48 hours or longer, and using five to ten aphids per test plant.Observations on infected plants growing in the field and in the greenhouse indicate that the environment has great influence on the appearance of the vein yellowing symptom. Generally, vein yellowing occurs very strikingly during the spring-time and the late autumn but disappears in the summer months.According to observations on the rate of occurrence of vein yellowing at different times of the year in a field experiment at Wageningen (fig. 2), it appears that tip yellows virus is capable of spreading fast in a lucerne field.The experiments and observations described in the present paper confirm the idea expressed byde Fluiter & Hubbeling (1955) that lucerne fields are important as a reservoir of the tip yellows virus of pea in The Netherlands.     

Weed suppression in mixed cropped grain peas and false flax (Camelina sativa)

Mixed cropping peas with false flax, a brassica oil seed crop, in additive arrangements had a significant suppressive effect on weed coverage (63% in 2003 and 52% in 2004), compared with the monocropped pea plots. Weed suppression by false flax was apparently restricted to the establishment phase, because effects were significant against the key annuals Fallopia convolvulus, Sonchus oleraceus and Matricaria recutita, but ineffective towards the major perennials Cirsium arvense and Elytrigia repens. Relatively higher yields in mixed stands with calculated land equivalent ratios (LER) of 1.43 (2003) and 1.98 (2004) were the result of low monocrop yields mainly related to weed pressure not only in pea but also in false flax. Partial LERs were in favour of peas, demonstrating a balanced but asymmetric complementarity of the components, with peas as the main and false flax as the minor crop component. The role of false flax in row‐cropped peas can be characterized as both a smother crop and weed antagonist with no obvious indications for allelopathic traits. Weed suppression was probably achieved by a mutually enhanced competitiveness of both crop components, indicating a mechanism based on resource allocation, but further research is needed for a better understanding of weed‐suppressive traits in pea–false flax mixed cropping systems.     

Prediction of yield loss caused by Orobanche spp. in carrot and pea crops based on the soil seedbank

Root parasites of the genus Orobanche cause serious losses in many subtropical crops. Direct control options are very limited and crop yield loss can reach 100%. Prediction of potential damage in a crop before sowing or planting would support farmers in their choice of crop. This paper discusses the relationship between the number of Orobanche spp. seeds in the field and yield loss in peas (Pisum sativum L.) and carrots (Daucus carota L.) in Israel. Yield loss due to Orobanche crenata Forsk. in peas was 100% at high infestations, whereas in carrots when O. crenata and O. aegyptiaca were present it stabilized at about 50% for moderate infestations of 200 seeds per kg of soil. Statistical analyses related the yield loss from parasitism in peas and carrots to the numbers of Orobanche seeds remaining in the soil. A rectangular hyperbolic model, previously applied to competition data, fitted the data well. Confidence intervals for per cent yield loss were calculated using the bootstrap method. The practical applications of these models in predicting yield loss are discussed.     

Pathogenic fungi involved in root rot of peas in the Netherlands and their physiological specialization

Research on root rot pathogens of peas in the Netherlands has confirmed the prevalence ofFusarium solani, F. oxysporum, Pythium spp.,Mycosphaerella pinodes andPhoma medicaginis var.pinodella. Aphanomyces euteiches andThielaviopsis basicola were identified for the first time as pea pathogens in the Netherlands. Other pathogens such asRhizoctonia solani andCylindrocarpon destructans were also found on diseased parts of roots. F. solani existed in different degrees of pathogenicity, and was sometimes highly specific to pea, dwarf bean of field bean, depending on the cropping history of the field.A. euteiches was specific to peas, whereasT. basicola showed some degree of physiological specialization.     

Occurrence and distribution of ‘Candidatus Phytoplasma trifolii’ associated with diseases of solanaceous crops in Lebanon

A survey for phytoplasma diseases in tomato and pepper fields in Lebanon was conducted during 2003 and 2004. Tomato plants with stunting, yellowing or purplish leaves, proliferation of laterals buds, hypertrophic calyxes and virescent flowers were found in 25% of the tomato fields surveyed, where they represented 2–8% of the plants. Pepper plants displaying stunting and yellowing of leaves, were found in 27% of the fields and 1–4% of the plants were affected. Phytoplasmas infecting tomato and pepper had identical 16S-rDNA RFLP profiles and sequences. A phytoplasma isolate named PTL was transmitted by dodder from a diseased tomato plant to a periwinkle (Catharanthus roseus) plant in which it induced leaf yellowing, virescence and phyllody. 16S-rDNA phylogenetic analysis classified PTL as a strain of ‘Candidatus Phytoplasma trifolii’.     

The Problem of Protecting Crops Against Harmful Birds in Poland

From the point of view of Polish agriculture, the rook (Corpus frugilegus L.) causes the most damage. Jackdaws (C. monedula L.) usually forage together with rooks and are equally abundant as a breeding species in the southern and central regions of Poland. Fields under spring oats, barley, wheat, maize, peas and winter wheat are the main feeding grounds of rooks and jackdaws. Unlike the corvine birds, starlings (Sturnus vulgaris L.), in Poland, only cause damage to cherry orchards, although in certain areas they also attack strawberries and currants. The house sparrows (Passer domesticus L.) cause considerable damage to ripening crops of wheat, barley, and sunflowers. Domestic pigeons cause considerable damage to crops of peas, wheat and maize grown within a 50 km radius of a town.     

Phenology and growth of Orobanche crenata Forsk (broomrape) in four legume crops

Studies were conducted in the field in 2 years comparing the phenology and growth of Orobanche crenata (Forsk) (crenate broomrape) in lentils (Lens esculenta L.) cv. Castellana, peas (Pisum sativum L.) cv. Orix, vetch (Vicia sativa L.) cv. comun and broadbean (Vicia faba L. cv. Alameda. First attachment of O. crenata to these crops took place 9–14 weeks after mid-November planting and earlier after later plantings, Differences in the first O. crenata attachment dates and in the duration of the underground growth period of O. crenata were much greater between years for any given crop than between crops in a given year: both attributes were apparently affected more by seasonal climatic conditions than by crop species, Furthermore, there was no consistent relationship found between crop growth stages and time after first attachment of the parante. This occurred in lentils and vetch while they were vegetative, in peas at late vegetative-early flowering stages, and at widely varying growth stages in broadbean, depending on planting dates and years. The maximum number of O. crenata plants successfully attached to each individual crop plant decreased in the order: peas > broadbean > lentil > vetch, with 21, 14, 10 and 8 per plant, respectively, averaged over the two seasons. Similarly, plant parasites: host dry weight ratio were 1.0, 0.7, 0.3 and 0.2 For each of these crops, respectively.     

Transmission of the agent causing a melon yellowing disease by the greenhouse whitefly Trialeurodes vaporariorum in southeast Spain

The agent causing a yellowing disease of melon (Cucumis melo), which results in severe losses in crops under plastic on the coastal plains of southeast Spain, was shown to be transmitted in a semipersistent manner by the greenhouse whitefly (Trialeurodes vaporariorum Westwood). The agent was transmitted by grafting, but not by mechanical inoculation or through seeds. The agent was acquired in the minimum period tested (2 h) and could infect plants in an infection feeding interval of 6 h. Capsella bursa-pastoris, Cucumis melo, C. sativus, Cucurbita moschata, Cichorium endivia, Lactuca sativa andTaraxacum officinale were found susceptible.Results suggest that the yellowing disease affecting melon crops in the southeast of Spain is due to a pathogen similar to beet pseudo yellows virus, but this has to be confirmed by serology.     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.     

High diversity,expanding populations and purifying selection in phytoplasmas causing coconut lethal yellowing in Mozambique

In this study, the putative phytoplasma species causing coconut lethal yellowing disease in Mozambique and Tanzania were characterized. The 16S rRNA and secA genes were sequenced. Phylogenetic analysis revealed that Mozambican coconut phytoplasmas belong to three different types: ‘Candidatus Phytoplasma palmicola’ 16SrXXII‐A, a second strain that was previously isolated in Tanzania and Kenya (16SrIV‐C), and a third strain that was different from all known lethal yellowing phytoplasma species. The third strain potentially represents a novel species and is closely related to pine phytoplasma. Co‐infection with ‘Ca. Phytoplasma pini’‐related and ‘Ca. Phytoplasma palmicola’ 16SrXXII‐A strains was observed. Furthermore, sequence variation in ‘Ca. Phytoplasma palmicola’ at the population level was consistent with purifying selection and population expansion.     

Host range and molecular analysis of Beet leaf yellowing virus,Beet western yellows virus-JP and Brassica yellows virus in Japan

Beet western yellows virus (BWYV; genus Polerovirus, family Luteoviridae) is one of the most important viruses causing yellowing disease of many field and vegetable crops. This study isolated different poleroviruses from sugar beet, spinach, radish and brassica in Japan, and identified them as BWYV-JP, Beet leaf yellowing virus (BLYV), Brassica yellows virus (BrYV) and BrYV-R (radish strain) based on host range and molecular analysis. Among over 100 plant species from 19 families inoculated with the vector Myzus persicae, about half of the species in 13 families were infected with some of these viruses. BLYV shared a similar host range to Beet mild yellowing virus (BMYV). These had a much more limited host range than BWYV-JP, which resembled BWYV-USA. The host range of BrYV was similar to that of Turnip yellows virus (TuYV). Phylogenetic analyses at the 5′ portion (replication-related gene) of the genome showed that BLYV, BMYV, BWYV (-JP and -USA) and Cucurbit aphid-borne yellows virus (CABYV) formed one large group, whereas BrYV and TuYV were grouped together. BLYV and BWYV were most closely related to each other, and were more closely related to CABYV than to BMYV. However, at the 3′ end (coat protein gene), BLYV and BWYV-JP formed a distinct group, separated from the BrYV group, which in turn was more closely related to BWYV-USA, BMYV, TuYV and Beet chlorosis virus, a group originating from outside Asia. Thus, this study presents host range differences and phylogeographical relationships of BWYV-like poleroviruses that are distributed worldwide.     

Rode verkleuringen,waargenomen bij erwten en bonen

Summary Pink discoloration, observed by growers in Holland and England in peas and beans (Phaseolus), is caused byBacterium rubefaciens. Presumably the infection of the seeds had taken place during unfavourable weather at harvest-time. The bacterium can not be considered as a plant pathogen. The pink colour is soluble in water.     

Tomato chlorosis virus in pepper: prevalence in commercial crops in southeastern Spain and symptomatology under experimental conditions

Tomato chlorosis virus (ToCV), a member of the genus Crinivirus (family Closteroviridae), has been present in Spain since at least 1997, causing annual epidemics of yellowing in protected tomato crops. In 1999, sweet pepper plants exhibiting stunting and symptoms of interveinal yellowing and mild upward curling in the leaves, were found to be infected with ToCV in a greenhouse heavily infested with the whitefly Bemisia tabaci in the province of Almería, southeastern Spain. This study investigated the prevalence of ToCV in tomato and pepper crops in the major growing areas of southeastern Spain (Murcia, Almería and Málaga provinces) over a 3‐year period. In addition, an experimental system was developed for ToCV inoculation using B. tabaci as a vector, which allowed analysis of susceptibility of different pepper cultivars to the virus. The disease syndrome and yield losses induced by ToCV in pepper were also studied under experimental conditions, confirming severe yield reduction in infected plants.     

Cucumber mosaic virus isolated from Aconitum spp. in Japan

Viruses were isolated from leaves of plants of Aconitum species with symptoms such as mottling and yellowing in Hokkaido and Gunma prefectures in Japan. These viruses were identified as Cucumber mosaic virus (subgroup II) based on particle morphology, host range, aphid transmission, and serology.     

De invloed van enkele milieufactoren op de vatbaarheid van erwten voor Botrytis cinerea

In a temperature and nutrient experiment with Rondo peas marked differences were observed in the degree of infection of the plants byBotrytis cinerea. After harvesting the ripe plants these differences were clearly expressed in the percentage of seeds with a chalky appearence, due to invasion by the mycelium ofB. cinerea. Comparatively high percentages of chalky peas were found when the plants were grown at a temperature of 20°C during the day and 15°C during the night. Omitting calcium or magnesium from the nutrient solution did not significantly influence the percentage of chalky peas, but omitting potassium from two weeks before flowering until the end of ripening increased the percentage of chalky peas significantly. This suggests that potassium deficiency before and during flowering makes the plant more susceptible toB. cinerea infection.Samenvatting In een temperatuur- en voedingsproef met Rondo erwten werden opvallende verschillen waargenomen in aantasting van de planten doorBotrytis cinerea. Na het oogsten van de rijpe planten kwamen deze verschillen duidelijk tot uiting in het percentage kalkerwten; dit zijn zaden die door het mycelium vanB. cinerea zijn doorwoekerd. Er werden relatief hoge percentages kalkerwten gevonden bij een temperatuur van 20°C overdag en 15°C's nachts. Het weglaten van calcium of magnesium uit de voedingsoplossing had geen betrouwbare invloed op het percentage kalkerwten, maar het weglaten van kalium vanaf 14 dagen voor de bloei tot het einde van de afrijping verhoogde het percentage kalkerwten zeer belangrijk. Dit wijst er op dat kaliumgebrek vóór en tijdens de bloei de planten vatbaarder maakt voorB. cinerea.     

Diversity and occurrence of chickpea chlorotic dwarf virus on legumes from Iran

Chickpea chlorotic dwarf virus (CpCDV; genus Mastrevirus, family Geminiviridae) is one of the most important legume-infecting viruses with a wide host range and geographic distribution in Africa and Asia. In Iran, CpCDV is common in chickpea (Cicer arietinum), but there is limited information about diversity and infections in plants of other legume species. In the current study, a total of 1671 leaf samples from different pulse crops with symptoms were collected in nine provinces of Iran, and the CpCDV infection status was tested by PCR and/or rolling circle amplification (RCA), resulting in the detection of CpCDV in samples of chickpea, lentil (Lens culinaris) and faba bean (Vicia faba) from different regions. Sequence analysis of complete genomes of 18 isolates recovered by digestion of RCA products revealed infection with isolates of the strains CpCDV-A and CpCDV-F in chickpea, lentil and faba bean. Phylogenetic analysis showed that the Iranian isolates of CpCDV were closely related to previously sequenced isolates of CpCDV-A and CpCDV-F. To the authors' knowledge, this is the first report of CpCDV-F in Iran. Using agroinoculation with infectious clones for one isolate each of CpCDV-A and CpCDV-F, infectivity was confirmed in both faba bean and chickpea, with plants developing leaf curling and/or yellowing. Both infectious clones also successfully infected Nicotiana benthamiana resulting in mild yellowing and intensive leaf curling for CpCDV-A, and dark-green mosaic, dwarfing and mild leaf curling for CpCDV-F.     

<Emphasis Type="Italic">Cucurbit aphid-borne yellows virus</Emphasis> in Egypt

During 2010, yellowing symptoms were frequently observed in cultivated squash fields in Egypt. A total of 717 symptomatic squash leaf samples were collected from four regions where squash cultivation is of economic importance for the country: Kafrelsheikh, El-Behira, El-Sharkia and El-Ismailia. Serological analysis showed that 95.6% of the symptomatic squash samples were infected by Cucurbit aphid-borne yellows virus (CABYV), and visual estimation of the incidence of yellowing symptoms suggested a very high incidence of CABYV in the fields. Twelve CABYV isolates were characterized by sequencing two regions of the viral genome, open reading frame (ORF) 3 and ORFs 4/5. Overall, Egyptian isolates were very similar among them, and had higher similarity values with a French than with a Chinese isolate. The average nucleotide diversity for ORF 3 was significantly higher than for the other two regions, indicating that variability is not evenly distributed along the viral genome. The ratios between nucleotide diversity values in non-synonymous (d _N ) and synonymous (d _S) positions (d _N /d _S) for each ORF showed that the three ORFs are evolving under different pressures, although predominantly under purifying selection. Phylogenetic analyses revealed that these Egyptian isolates, with only one exception, shared the same clade with a French isolate. Moreover, these analyses suggested that Egyptian isolates belong to the Mediterranean group described previously.     

Dispersion patterns and sampling plans for the pea aphid,Acyrthosiphon pisum (Harris), on grass pea,Lathyrus sativus L.

From 2009/2010 to 2010/2011, flight patterns and spatial distribution of pea aphids were studied in northwestern Ethiopia. Yellow traps were used and legume fields sampled. Trap catches varied between years (lower in 2009/2010 than in 2010/2011), locations and months in the growing season. At Woreta, peaks were observed in January (20–70 per trap) and at Wondata in October and November (60–80 per trap). Also, pea aphid numbers were more on fallow land than on other land-use systems (a maximum of 41,000 in December 2010/2011 and 25,000 in January 2009/2010 per 100 plants). Taylor's power law coefficients, i.e., b values, were significantly greater than 1 on grass peas planted after fallow; the corresponding r² values ranged between 0.87 and 0.94. Coefficients were inconsistent on grass peas planted after teff and undersown in maize. The optimum sample size n (number of yellow traps) required in relation to the mean densities of the pea aphid was more or less the same for the three levels of accuracy (D = 0.2, 0.3 and 0.5). At D = 0.5, numerical sample size curves showed 10 traps as mean number of aphids per trap approached 4 or 5, which is practical and affordable. Some additional work at more locations may be required to validate these sampling plans before wider use.     

First report of <Emphasis Type="Italic">Candidatus</Emphasis> Phytoplasma asteris associated with yellowing and rosetting of Japanese spurge in Korea

Phytoplasma-induced leaf yellowing, stunting and rosetting were observed on Japanese spurge (Pachysandra terminalis) in Jung-gu of Daegu city, Korea. Molecular analyses based on PCR–RFLP and 16S rDNA sequences indicated that the phytoplasma associated with Japanese spurge yellows disease is a new strain of Candidatus Phytoplasma asteris. This report is the first on the occurrence of phytoplasma disease on Japanese spurge in Korea.