A Comparative and Phylogenetic Study of the Ditylenchus dipsaci,Ditylenchus destructor and Ditylenchus gigas Populations Occurring in Poland

The genus Ditylenchus contains more than 80 recognized nematode species with a very wide host range. The most serious species are Ditylenchus dipsaci and Ditylenchus destructor. Populations of D. dipsaci species complex were collected from Allium cepa, Cichorium endivia and Phlox paniculata in Poland. The Ditylenchus gigas population was collected from Vicia faba minor, and populations of D. destructor, from Solanum tuberosum spp. tuberosum. Analyses of the rDNA sequences spanning both ITS1 and ITS2 fragment regions were carried out on the collected populations. The obtained DNA sequences were compared with those DNA sequences deposited in GenBank of populations isolated in other countries. Phylogenetic analysis was performed using the data obtained from the DNA sequence comparisons. The results indicated that there is no clear distinction between European and non‐European populations within D. dipsaci. The results also showed no clear distinction between populations isolated from different host plant species, including populations found in Poland. The populations of D. destructor described here constitute a common group together with American and Chinese populations belonging to the haplotype C of the D. destructor species. On the other hand, the D. gigas population was localized separately from those populations that have been described up until now, from Europe and Africa. This is also the first report on the occurrence of D. gigas in Poland.     

Pathological Relationship of Ditylenchus dipsaci and Fusarium oxysporum f. sp. medicaginis on alfalfa

Ditylenchus dipsaci and Fusarium oxysporum f. sp. medicaginis synergistically affected the mortality and plant growth of Ranger alfalfa, a cultivar susceptible to stem nematode and Fusarium wilt. The nematode-fungus relationship had an additive effect on mortality and plant growth of Lahontan (nematode resistant and Fusarium wilt susceptible) and of Moapa 69 (nematode susceptible and Fusarium wilt resistant). Mortality rates were 13, 16, 46, and 49% for Ranger; 4, 18, 26, and 28% for Lahontan; and 19, 10, 32, and 30% for Moapa 69 inoculated with D. dipsaci, F. oxysporum f. sp. medicaginis, and simultaneously and sequentially with D. dipsaci and F. oxysporum f. sp. medicaginis, respectively. Shoot weights as a percentage of uninoculated controls for the same treatments were 52, 84, 26, and 28%, for Ranger; 74, 86, 64, and 64% for Lahontan; and 50, 95, 44, and 39% for Moapa 69. Plant growth suppression was related to vascular bundle infection and discoloration of alfalfa root tissue. Disease severity and plant growth of alfalfa did not differ with simultaneous or sequential inoculations of the two pathogens. Fusarium oxysporum f. sp. medicaginis affected alfalfa growth but not nematode reproduction.     

Morphological and molecular characterization of two populations of <Emphasis Type="Italic">Aphelenchus avenae</Emphasis> (Nematoda: Aphelenchidae) from Iran and their phylogenetic relationships

Soil samples were collected from the rhizosphere of faba bean (Vicia faba L.) in Khuzestan province, south-western Iran. Many of the localities were positive for the presence of Aphelenchus avenae. The morphological and morphometric characters of the two Iranian populations are discussed and illustrated based on morphological and morphometrics data. Additionally, sequences of the D2-D3 expansion segments of 28S rRNA gene for two populations were used for molecular phylogenetic analysis. One population was without male and formed a separate branch in the phylogenetic tree. Results indicate high genetic variation among A. avenae populations from different geographic regions.     

A comparison of the rate of drying of four nematode species using a liquid paraffin technique

A technique of immersion refractometry has been employed to compare the rates at which four species of nematodes lose water during desiccation at 0% r.h. Panagrellus redivivus and Ditylenchus myceliophagus showed little ability to control water loss, although in the latter species coiling helped slow the rate of drying. Ditylenchus dipsaci and Anguina tritici exhibited a much greater degree of control over water loss during desiccation, A. tritici being more successful. D. dipsaci revived from ‘wool’ showed a marked decrease in ability to control water loss when compared with freshly extracted worms. The results obtained have been compared with those from work using interference microscopy, and a critical assessment of the liquid paraffin technique is presented.     

Distribution and impact of virus associated diseases of common bean (Phaseolus vulgaris L.) in northern Iran

Different viral diseases infect common bean crops in Iran. A total of 248 symptomatic samples were collected from common bean fields throughout main growing fields of Guilan province in Iran during the summer of 2006. Eight viruses were detected using double antibody-sandwich – enzyme-linked immunosorbent assay (DAS-ELISA). Bean common mosaic virus – BCMV (1%), Bean leaf roll virus – BLRV (9%), Cowpea mild mottle virus – CpMMV (6%), Southern bean mosaic virus – SBMV (3%), Cucumber mosaic virus – CMV (15%), Bean golden mosaic virus – BGMV (2%), Bean common mosaic necrosis virus – BCMNV (1%) and Bean yellow mosaic virus – BYMV (1%) were detected. Comparatively CMV (15%) was found to be more prevalent in Guilan province. Multiple infections of viruses were recorded in many samples. Weed species belonging to Chenopodiaceae, Solanaceae, Malvaceae and Amaranthaceae families were also found to be infected with the viruses.     

Cold tolerance of an Antarctic nematode that survives intracellular freezing: comparisons with other nematode species

Panagrolaimus davidi is an Antarctic nematode with very high levels of cold tolerance. Its survival was compared with that of some other nematodes (P. rigidus, Rhabditophanes sp., Steinernema carpocapsae, Panagrellus redivivus and Ditylenchus dipsaci) in both unacclimated samples and those acclimated at 5°C. Levels of recrystallization inhibition in homogenates were also compared, using the splat-cooling assay. The survival of P. davidi after the freezing of samples was notably higher than that of the other species tested, suggesting that its survival ability is atypical compared to other nematodes. In general, acclimation improved survival. Levels of recrystallization inhibition were not associated with survival but such a relationship may exist for those species that are freezing tolerant.     

Association of two groups of phytoplasma with various symptoms in some wooden and herbaceous plants

During 2015–2016, wooden and herbaceous plants growing in parks, boulevards, fields, gardens and forests in Khuzestan province, southwestern Iran, were visually inspected for symptoms resembling phytoplasma. Fifty‐one symptomatic samples from nine different species and one symptomless sample from each plant were collected. Leaf midribs, petioles and the parts of stem cambium were separated and freeze‐dried. Total DNA was extracted using CTAB‐based method and tested for phytoplasma using a nested PCR assay. The expected size amplicons of 16S rDNA were sequenced and compared to those of reference phytoplasmas by BLASTn search and phylogenetic analysis. The consensus 16S rDNA sequence of the detected phytoplasma in narrow cattail related to reference phytoplasma group 16SrVI, “Candidatus Phytoplasma trifolii” while in the other plants were related to reference phytoplasma subgroup 16SrII–D, “Candidatus Phytoplasma aurantifolia.” All isolates showed 98%–99% sequence identity to members of their reference groups. To our knowledge, this is the first report of “Candidatus Phytoplasma aurantifolia”‐related strains infecting the plants of Acacia salicina, Alternanthera ficoidea, Melaleuca citrine, Citrus aurantium throughout the world and Celosia christata in Iran. Furthermore, this study is the first to report the association of a “Candidatus Phytoplasma trifolii”‐related strain with Typha angustifolia worldwide.     

Resistance and tolerance of potato varieties to potato rot nematode (Ditylenchus destructor) and stem nematode (Ditylenchus dipsaci)

Ditylenchus destructor and Ditylenchus dipsaci are economically important plant‐parasitic nematodes, affecting potato production mostly in temperate climates. Management through crop rotation is not feasible because of their wide host range. These nematodes are listed as quarantine pests in many countries. Limited information exists on the resistance and tolerance of currently cultivated potatoes to D. destructor and D. dipsaci. Two greenhouse experiments were conducted to screen 25 potato varieties for resistance to and tolerance for D. destructor and D. dipsaci infections. Reproduction factor (RF) and relative susceptibility (RS) were used to evaluate resistance, while potato tuber damage and tuber weight reduction was used to evaluate tolerance. Based on the RF, 16 varieties were evaluated as susceptible (S) while 5 varieties were evaluated as resistant (R) to D. destructor; varieties ‘Innovator’, ‘Aveka’ and ‘Spunta’ were resistant to D. dipsaci based on RF. ‘Désirée’ was observed to be highly susceptible to D. destructor and D. dipsaci in both experiments and was used as the standard susceptible control variety for the calculation of RS. A scale of 1–9 was used to classify RS of the potato varieties to D. destructor and D. dipsaci, where 9 indicated the highest level of resistance. All classes of resistance to D. destructor and D. dipsaci were observed in the potato varieties tested in the experiments. Six varieties had significantly lower RS to D. dipsaci than the standard susceptible control variety. Tolerant to highly sensitive potato varieties to both nematodes were also observed. RS and external potato tuber damage were identified as suitable methods for resistance and tolerance determination, respectively. This study provides essential information on the status of resistance and tolerance in potato varieties against D. destructor and D. dipsaci but needs to be confirmed under field conditions.     

Stem Nematode-Fusarium Wilt Complex in Alfalfa as Related to Irrigation Management at Harvest Time

A high moisture level in the top 10 cm of soil at time of cutting of alfalfa increased the incidence of plant mortality and Fusarium wilt in soil infested with Ditylenchus dipsaci and Fusarium oxysporum f. sp. medicaginis in greenhouse and field microplot studies. Ranger alfalfa, susceptible to both D. dipsaci and F. oxysporum f. sp. medicaginis, was less persistent than Moapa 69 (nematode susceptible and Fusarium wilt resistant) and Lahontan alfalfa (nematode resistant with low Fusarium wilt resistance). In the greenhouse, the persistence of Ranger, Moapa 69, and Lahontan alfalfa plants was 46%, 64%, and 67% respectively, in nematode + fungus infested soil at high soil moisture at time of cutting. This compared to 74%, 84%, and 73% persistence of Ranger, Moapa 69, and Lahontan, respectively, at low soil moisture at time of cutting. Shoot weights as a percentage of uninoculated controls at the high soil moisture level were 38%, 40%, and 71% for Ranger, Moapa 69, and Lahontan, respectively. Low soil moisture at time of cutting negated the effect D. dipsaci on plant persistence and growth of subsequent cuttings, and reduced Fusarium wilt of plants in the nematode-fungus treatment; shoot weights were 75%, 90%, and 74% of uninoculated controls for Ranger, Moapa 69, and Lahontan. Similar results were obtained in the field microplot study, and stand persistence and shoot weights were less in nematode + fungus-infested soil at the high soil-moisture level (early irrigation) than at the low soil-moisture level (late irrigation).     

Irish faba beans (Fabales: Fabaceae) depend on wild bumblebee pollination for marketable yields

1. Quantifying the contributions of insect pollinators to crops provides insight into how pollination services should be managed and protected into the future.
2. Faba bean, Vicia faba var minor (Linneaus), is a widely grown crop globally that can benefit from pollinator visitation, but only from species that are morphologically compatible with the plant's long-corollae flowers. Here, we rank insect pollinators in terms of their potential importance to faba bean pollination and quantify the economic value of pollination for Irish faba beans.
3. Our findings demonstrate that bee pollination contributes significantly to the pod set of faba beans, and, consequently, the crop's production value. We find that pollination services account for almost half of Ireland's total faba bean market value, with the pollinator contribution estimated at almost €4,000,000 per year.
4. We estimate that, relative to other pollinators, wild bumblebees contribute to approximately 70% of the economic value of pollination services in faba bean fields, driven mainly by the contributions of a long-tongued bumblebee species, Bombus hortorum (Linneaus; Hymenoptera: Apidae).
5. Based on these results, we suggest that B. hortorum populations be encouraged on farmland through appropriate management to ensure the continued delivery of pollination services to Irish faba beans.

     

Cold tolerance in nematodes

Summary The nematodesTrichostrongylus colubriformis (J3),Ditylenchus dipsaci (J4) andPanagrellus silusae (adults) are freezing-susceptible but can avoid freezing by supercooling. Their mean supercooling points were –30.0±0.7°C forT. colubriformis, –21.7±0.7°C forD. dipsaci and –20.7±0.84°C forP. silusae. T. colubriformis andD. dipsaci could prevent seeding by external ice butP. silusae could not. The glycerol concentrations of these nematodes are considered to be too low to have a significant antifreeze effect.Abbreviations J3 3rd-stage juvenile - J4 4th stage juvenile - SEM standard error of the mean - T ₅₀ 50% survival temperature     

Aggregated distribution of Ditylenchus dipsaci on broad bean seeds

The distribution of Ditylenchus dipsaci (Kühn) Filipjev between seeds in infested samples of broad bean seed was skewed so that the nematodes were concentrated on a few seeds. Such aggregation increases the likelihood of reproduction by the nematodes in infested plants and the consequent establishment of foci of infestation in the soil. These foci will be small and scattered giving the nematode the best chance of a finding a favourable environment in the field. The numbers of foci of infestation introduced by seed tend to be nearly constant, independent of the numbers of nematodes on the seed and therefore provide a stable unit of population.     

Separation of Three Species of Ditylenchus and Some Host Races of D. dipsaci by Restriction Fragment Length Polymorphism

This study examined the ribosomal cistron of Ditylenchus destructor, D. myceliophagus and seven host races of D. dipsaci from different geographic locations. The three species showed restriction fragment length polymorphisms (RFLPs) in the ribosomal cistron, the 18S rDNA gene, and the ribosomal internal transcribed spacer (ITS). Southern blot analysis with a 7.5-kb ribosomal cistron probe differentiated the five host races of D. dipsaci examined. Polymerase chain reaction (PCR) amplification of the ITS, followed by digestion with some restriction endonucleases (but not others), produced restriction fragments diagnostic of the giant race. Because the PCR product from D. myceliophagus and the host races of D. dipsaci was about 900 base pairs and the ITS size in D. destructor populations was 1,200 base pairs, mixtures of populations could be detected by PCR amplification. ITS fragments differentiated between D. dipsaci and Aphelenchoides rhyntium in mixed populations. This study establishes the feasibility of differentiation of the host races of D. dipsaci by probing Southern blots with the whole ribosomal cistron.     

Detection and molecular characterization of phytoplasmas associated with vegetable and alfalfa crops in Qassim region

During a survey conducted in Qassim province, Saudi Arabia, in the year in 2015, 120 samples of carrot (Daucus carota subsp. sativus), onion (Allium cepa), faba bean (Vicia faba), green mustard (Brassica juncea) and alfalfa (Medicago sativa) plants displaying symptoms reminiscent of phytoplasma diseases were collected and tested for phytoplasma infection. Phytoplasma-specific PCR products were only amplified from symptomatic plants by nested-PCR. Disease incidence ranged from 3.14% in alfalfa crop fields 1 year after cultivation to 77.48% in 3-year-old fields. In the five carrot fields sampled in this study, the incidence changed from 3.2% to 100% after 7 months of cultivation. Phylogenetic analysis revealed that all Qassim phytoplasma isolates belong to the 16SrII group. Most of them shared 100% identity with papaya yellow crinkle (16SrII-D Y10097). The results from phylogenetic and virtual restriction fragment length polymorphism analyses of the 16S rRNA gene sequence confirmed that the phytoplasma of Qassim isolates under study is a member of 16SrII-D subgroup. To the best of my knowledge, the onion and green mustard are considered new hosts for the 16SrII group; therefore, this is the first report on the association of phytoplasma with diseases of faba bean, onion, carrot, mustard and alfalfa in Qassim province, Saudi Arabia.     

Occurrence of Didymella fabae,the Teleomorph of Ascochyta fabae,on Faba Bean Straw in Spain

Pseudothecia of Didymella fabae, the teleomorph of Ascochyta fabae, were first observed on faba bean (Vicia faba) debris in Spain during autumn 1995. Most pseudothecia were mature by December–February. The ascospores gave rise to typical cultures of A. fabae, and conidia from these cultures caused ascochyta blight symptoms on inoculated faba bean plants. Placing straw‐bearing pseudothecia over the plants to allow ascospore discharge also resulted in typical ascochyta blight symptoms. Pseudothecia maturity and discharge of ascospores from the infested faba bean straw overlapped with the vegetative stage of the faba bean crop, which occurs in southern Spain during winter as the crop is sown in autumn and harvested in spring. These observations indicate that ascospores may serve as primary inoculum for the disease.     

A reanalysis of Parabuthus (Scorpiones: Buthidae) phylogeny with descriptions of two new Parabuthus species endemic to the Central Namib gravel plains,Namibia

Two new thick‐tail scorpions in the genus Parabuthus Pocock, 1890 are described from the gravel plains of the Central Namib Desert, Namibia: Parabuthus glabrimanus sp. nov. ; Parabuthus setiventer sp. nov. The two new species occupy discrete distributional ranges, allopatric with the closely related species Parabuthus gracilis Lamoral, 1979 and Parabuthus nanus Lamoral, 1979. The distributions of the four species are mapped and a key provided for their identification. Revised diagnoses are provided for P. gracilis and P. nanus. The two new species are added to a previously published morphological character matrix for Parabuthus species and their phylogenetic positions determined in a reanalysis of Parabuthus phylogeny. Parabuthus setiventer sp. nov. is found to be the sister species of P. nanus, whereas P. glabrimanus sp. nov. is sister to a monophyletic group comprising P. gracilis, P. nanus, and P. setiventer sp. nov. The discovery of two new scorpion species endemic to the Central Namib gravel plains contributes to a growing body of evidence that this barren and desolate region is a hotspot of arachnid species richness and endemism. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 673–710.     

Effects of mycorrhizae and chitin-hydrolysing microbes on Vicia faba

The effect of Streptomyces albovinaceus (S-22) and Bacillus sp. (B1) on the growth response, nodulation, nutrition and nitrogenase activities of faba bean (Vicia faba) varieties infected with Glomus mosseae under pot conditions in sterile soil amended with chitin was studied. The growth, nodulation, nutrients content and nitrogenase activity of mycorrhiza-treated plants of Giza-667 were significantly increased compared to untreated ones. Such increases were related to the increase in mycorrhizal root infection. Amendment of soil with chitin alone reduced the growth, nodulation, total nitrogen contents and nitrogenase activities of mycorrhiza-treated faba bean plants (Giza-667) compared to untreated plants. Inoculation of plants with S. albovinaceus or Bacillus sp. significantly increased the level of mycorrhizal roots infection, but addition of chitin to the soil in combination with Bacillus sp. reduced the mycorrhizal infection of faba bean roots. Highest phosphorus contents of faba bean Giza-667 were recorded after G. mosseae inoculation in the presence of all treatments. Similar results were observed for the other varieties. The microbial populations were significantly increased in rhizospheres amended with chitin. Such increases were not in response to the mycorrhizal inoculation. Generally, the microflora of faba bean rhizospheres was increased after treatment with G. mosseae in the absence of chitin amendment alone compared with non-mycorrhizal rhizospheres.     

Interaction of Ditylenchus dipsaci and Meloidogyne hapla on Resistant and Susceptible Plant Species

Numbers ofDitylenchus dipsaci or Meloidogyne hapla invading Ranger alfalfa, Tender crop bean, Stone Improved tomato, AH-14 sugarbeet, Yellow sweet clover, and Wasatch wheat from single inoculations were not significantly different from numbers by invasion of combined inoculations. D. dipsaci was recovered only from shoot and M. hapla only from root tissue. Combined inoculations did not affect reproduction of either D. dipsaci or M. hapla. D. dipsaci suppressed shoot growth of all species at 15-30 C, and M. hapla suppressed shoot growth of tomato, sugarbeet, and sweet clover at 20, 25, and 30 C. There was a positive correlation (P < 0.05) between shoot and root growth suppression by D. dipsaci on all cultivars except wheat at 20 C and tomato at 30 C. M. hapla suppressed (P < 0.05) root growth of sugarbeet at 20-50 C and wheat at 30 C. Growth suppression was synergistic in combined inoculations of sweet clover shoot growth at 15 C and root growth at 20-30 C, wheat root growth at 15 and 20 C, and tomato root growth at 15-30 C (P < 0.05) D. dipsaci invasions caused mortality of alfalfa and sweet clover at 15-30 C and sugarbeet at 20-30 C. Mortality rates of alfalfa and sweet clover increased synergistically (P < 0.05) from combined inoculations.