Comparative host suitability to Meloidogyne spp. and Pratylenchus vulnus in Myrobalan plum (Prunus cerasifera)

Nine Myrobalan plum clones ( Prunus cerasifera ) obtained from in vitro propagation were tested for host suitability to four root-knot nematode (RKN) isolates ( Meloidogyne incognita (2), M. javanica (1), and M. hispanica (1)) and one root-lesion nematode (RLN), Pratylenchus vulnus , isolate. The clones are characterized according to the Ma major resistance genes that control resistance to M. arenaria , M. incognita and M. javanica and are categorized into five resistant (R) and four host (H) clones to these RKN species. As expected, the clones ranged, regardless of the RKN species or isolate, into the same distinct R (P.2175, P.1079, P.2980, H.17 and H.21) and H (P.2794, H.18, H.23 and P.16.5) groups for RKN resistance. The P. vulnus tests showed that all the clones had higher final populations than initial populations ( P _f :  P _i > 1) and that P _f :  P _i ratios were equivalent in each RKN resistance group (R or H). Consequently, resistant alleles of RKN Ma genes in Myrobalan plum have no major effect on RLN multiplication. Our data must be taken into account for breeding strategies aimed at incorporating multiple resistance to both RKN and RLN in Prunus spp.     

不同杀线剂对穿刺短体线虫的杀灭效果研究

为寻找杀灭短体属线虫有害生物的有效药剂,以穿刺短体线虫为供试线虫,测定了5种不同杀线剂对该线虫的杀灭效果。结果表明,5种供试杀线剂分别处理该线虫0.5h、1h和24h后,对该线虫均有一定的杀灭效果,顺序依次为:阿维菌素﹥噻唑磷﹥灭线磷﹥丁硫克百威﹥棉隆,其中阿维菌素和噻唑磷对穿刺短体线虫的杀灭效果较好,可作为备选药剂进一步研究。     

Detection of the root lesion nematode Pratylenchus penetrans in potato tubers

The root lesion nematode Pratylenchus penetrans parasitizes a wide range of economically important crops, including potato (Solanum tuberosum). Damage by P. penetrans impacts not only the potato yield but can also reduce the tuber quality. Detailed information on tuber infection by P. penetrans is scarce for most cultivars and molecular detection of nematodes from infected tubers is needed. The objective of this study was to assess tuber symptomatology due to P. penetrans infection in 10 potato cultivars and to provide an accurate molecular methodology for nematode detection using tuber peels. Sprouts of certified potato seed from cultivars Agata, Agria, Camel, Désirée, Dirosso, Kennebec, Laura, Picasso, Royata, and Stemster were planted in 2 L pots, and soil was inoculated with 4 P. penetrans/g of soil. Sixty days after inoculation, tubers were harvested, inspected for lesions, and the number of nematodes/g of potato peel assessed. Observations of tubers with symptoms showed the presence of P. penetrans in superficial layers of peels around the lenticels and injured necrotic tissue. Different nematode stages were detected in tubers of all inoculated cultivars, varying from 4 to 46 nematodes/g of potato peel. Species-specific primers showed suitable sensitivity and reproducibility for the detection of P. penetrans in tuber potato peel samples. The molecular detection of P. penetrans directly from tuber peels can facilitate routine nematode inspections of potato seed tubers or cull potatoes for nematode detection, and prevent further dissemination of this species.     

Quantitative detection of the root-lesion nematode, Pratylenchus penetrans, using qPCR

Pratylenchus penetrans is one of the most economically damaging plant-parasitic nematodes and is found on a wide variety of crops. Correct identification and quantification of this nematode are necessary for providing advice to farmers, but are not easily obtained with the traditional way of microscopic observation. We developed a qPCR assay to detect and quantify P. penetrans in a short but accurate manner. A qPCR primer set, including two primers and a TaqMan probe, was designed based on the sequence of the β-1,4-endoglucanase gene. The assay was optimized by using the primers in a qPCR assay with SYBR green I dye and setting the qPCR program to different annealing temperatures ranging from 60 °C to 64 °C. Based on the Ct-values, we retained the program with an annealing temperature of 63 °C. The assay with the probe was very sensitive as it was able to detect a single individual of P. penetrans, even when mixed with up to 80 individuals of P. thornei. The specificity of the reaction was confirmed by the lack of amplification of DNA from 28 populations of 18 other Pratylenchus species and from plant-parasitic nematodes from nine other genera. DNA from 21 different isolates from P. penetrans was amplified. DNA extraction from 80 individuals and quantification by qPCR was repeated four times; Ct-values showed consistent results (Ct?=?24.4?±?0.4). A dilution series from DNA of P. penetrans resulted in a standard curve showing a highly significant linearity between the Ct-values and the dilution rates (R²?=?0.99; slope?=??3.23; E?=?104 %). The tests showed a high correlation between the real numbers of nematodes and the numbers detected by the qPCR. The developed qPCR assay provides a sensitive means for the rapid detection and reliable quantification of individuals of this pest. This method does not require expertise in nematode taxonomy and morphology, and can be used as a rapid diagnostic tool in research, as well as in diagnostic labs and extension services advising farmers for pest management.     

Greenhouse and field evaluations of commonly occurring weed species for their host suitability to Meloidogyne species

Since weeds serve as hosts for nematode pests, the host status of 20 weed species (commonly occurring in fields of developing farmers) to Meloidogyne incognita and M. javanica, respectively, were investigated. Greenhouse studies showed that seven weed species had Rf values >1 for both nematode species indicating susceptibility, while 13 had Rf values ≤ 1 indicating resistance. Greenhouse results showed that Hibiscus trionum and Amaranthus tricolor were identified as the most susceptible and Chenopodium carinatum and Datura ferox the poorest hosts for M. incognita and M. javanica. For field experiments at Kuruman, Solanum retroflexum was the most susceptible weed to a M. javanica population, while the same was evident for H. trionum at Nelspruit, where a mixed population of M. incognita and M. javanica occurred and at Potchefstroom, where a population of M. incognita was present. Results from this study indicated that certain weed species are highly susceptible to root-knot nematodes and should be removed timely and effectively to prevent population level increases of root-knot nematode pests in the fields of farmers.     

Synergism of Pratylenchus penetrans and Verticillium dahliae Manifested by Reduced Gas Exchange in Potato

ABSTRACT The effects of solitary and concurrent infection by Pratylenchus pene-trans and Verticillium dahliae on gas exchange of Russet Burbank potato (Solanum tuberosum) were studied in growth chamber experiments. Treatments were P. penetrans at low, medium, and high density; V. dahliae alone at one initial density; the combination of the nematode at these three densities and V. dahliae; and a noninfested control. Gas exchange parameters of leaf cohorts of different ages in the different treatments were repeatedly measured with a Li-Cor LI-6200 portable photosynthesis system. At 45 days after planting, joint infection significantly reduced net photosynthesis, stomatal conductance, and transpiration of 1- to 25-day-old leaf cohorts. Intercellular CO(2) levels were significantly increased by co-infection, especially in older leaves. The synergistic effect of co-infection on gas exchange parameters was greater in the oldest cohort than in the youngest cohort. No consistent effects on leaf gas exchange parameters were observed in plants infected by the nematode or the fungus alone. The relationship between the assimilation rate and stomatal conductance remained linear regardless of solitary or concomitant infection, indicating that stomatal factors are primarily responsible for regulating photosynthesis. The significant reduction of gas exchange in leaves of co-infected plants without reduction in intercellular CO(2) concentrations suggests that nonstomatal factors also play a role when both organisms are present.     

Vertical Distribution of the Plant-Parasitic Nematode, Pratylenchus penetrans, Under Four Field Crops

ABSTRACT The vertical distribution of Pratylenchus penetrans was monitored in four fields cropped with maize, black salsify, carrot, or potato. Soil samples were collected at 21-day intervals from May 2002 until April 2003 from five plots (2 x 5 m(2)) per field. Per plot, 15 cores were taken to a depth of 70 cm and split into seven segments of 10 cm each. Within the plots, segments from corresponding depths were pooled. After mixing, 200-g subsamples were taken and nematodes were extracted by zonal centrifugation from the root fraction and the mineral soil fraction separately. In most crops, the root fraction contained more than 50% of the total number of P. penetrans. Because the ratio between the numbers of nematodes in the root fraction and mineral soil fraction changes during the growing season, numbers of P. penetrans found in the mineral soil fraction cannot be used to estimate the total number in the soil. Therefore, both fractions have to be processed to obtain a reliable estimate of the density. No nematodes were recovered below 50 cm soil depth, except in the maize field where nematodes were found at 70 cm. The optimum sampling depth for maize, black salsify, carrot, and potato was 45, 25, 25, and 35 cm, respectively. The percentage of nematodes per soil layer was independent of the sampling date, indicating that a defined optimum sampling depth will be applicable throughout all seasons. The cumulative vertical distribution, modeled with a logistic equation, can be used to estimate the sampling error when samples are collected at different depths.     

Interaction of spatially separated Pratylenchus penetrans and Verticillium dahliae on potato measured by impaired photosynthesis

Experiments were conducted under growth-chamber conditions to determine if Pratylenchus penetrans systemically alters light use efficiency (LUE) of Russet Burbank potato infected by Verticillium dahliae. Pathogen separation was achieved by inoculating potato roots with the nematode prior to injecting fungal conidia into the stem vasculature. Treatments were P. penetrans alone, V. dahliae alone, nematode and fungus together, and a no-pathogen control. Gas exchange was repeatedly and nondestructively measured on the fifth-youngest leaf with a Li-Cor LI-6200 portable photosynthesis system. By 16 and 20 days after stem injection with the fungus, LUE was synergistically impaired in jointly infected plants. Transpiration in plants infected with both pathogens was significantly reduced. However, the combined effect of nematode and fungus was synergistic in one experiment and additive in the other. Stems were destructively harvested when LUE was synergistically impaired. Coinfected potato plants contained more colony-forming units (CFU) of V. dahliae in stem sap than those infected by the fungus alone in one experiment. Evidence is provided that infection of Russet Burbank roots by P. penetrans systemically affects disease physiology associated with stem vascular infection by V. dahliae . The findings indicate that the role of the nematode in the fungus/host interaction is more than simply to facilitate extravascular and/or vascular entry of the fungus into potato roots.     

Manipulating inoculum densities of Verticillium dahliae and Pratylenchus penetrans with green manure amendments and solarization influence potato yield

We used cover crops with demonstrated efficacy against Verticillium dahliae and Pratylenchus penetrans in combination with the biocidal practice of solarization to determine the importance of targeting both organisms for managing potato early dying, an issue relevant to the search for alternatives to soil fumigation. Two experiments were conducted in commercial fields using a split-plot design with cover crop treatments of rapeseed, marigold, forage pearl millet, sorghum-sudangrass, and corn as the main plot factor and solarization as the subplot factor. Cover crops were grown and solarization applied in year one, followed by potato in year two. The main effect of solarization was significant for reduced inoculum levels of both organisms in year two and increased tuber yields. The main effect of cover crop was also significant with lower population densities of P. penetrans following the marigold and millet treatments and of V. dahliae following rape and sorghum-sudangrass. The cover crop treatments influenced yield in only one of the experiments in the absence of solarization. The combinatorial effect of cover crops and solarization resulted in a wide range of pathogen population densities. Mean soil inoculum levels were negatively related to yield for V. dahliae in experiment 1, and for P. penetrans and the P. penetrans × V. dahliae interaction in both experiments.     

Disease Progress Based on Effects of Verticillium dahliae and Pratylenchus penetrans on Gas Exchange in Russet Burbank Potato

ABSTRACT The interactive effects of concomitant infection by the nematode Pratylenchus penetrans and the fungus Verticillium dahliae on symptom expression in Russet Burbank potato was studied in growth chamber experiments. Treatments were P. penetrans at three initial densities, V. dahliae at one inoculum density, the combination of the nematode at these three densities and the fungus, and a noninfested control. Gas exchange was measured nondestructively in leaf cohorts of different ages, one to three times weekly, with a LI-COR portable photosynthesis system. The single-pathogen treatments had no effect on assimilation or transpiration rates, but joint infection had a significant impact. In concomitant infection, photosynthesis was impaired more than transpiration, so estimates of leaf health were based on carbon assimilation rates only. Reductions in assimilation rate were apparent before the onset of visual symptoms. Assimilation rates decreased as much as 44% in the top, and newest, leaves of concomitantly infected plants, compared to rates in control plants. Even so, the health of newly produced leaves did not become progressively worse through time. With light use efficiency less than 0.20 mol of CO(2) fixed per mol of photosynthetically active radiation used as the criterion for disease incidence, disease progressed acropetally from the oldest to the youngest leaves. In plants infected with P. penetrans (0.8 nematodes per cm(3) of soil) in combination with V. dahliae, all leaves in cohorts 1 and 2 were symptomatic by 45 days after planting, and leaves in cohorts 3 to 6 became symptomatic at weekly intervals thereafter. For the control and single-pathogen treatments, the first time that light use efficiency fell below 0.20 in all leaves in cohort 1 was 71 days after planting. Concomitant infection reduced leaf life span by about 3 weeks. Both visual and physiological symptom expression were invariant to differences in initial nematode inoculum densities ranging from 0.8 to 2.5 nematodes per cm(3) of soil in one experiment and from 1.3 to 4.1 nematodes per cm(3) of soil in a second experiment.     

Additive effect of the root-lesion nematode Pratylenchus penetrans and the fungus Rhizoctonia solani on potato yield and damage

Journal of Plant Diseases and Protection - The significance of nematodes for disease development caused by other soil-borne pathogens has been demonstrated in many crops throughout the world and...     

寄主植物对烟粉虱后代种群抗性相关酶活性的影响

比较了取食不同寄主植物的烟粉虱后代羧酸酯酶和乙酰胆碱酯酶的活力。结果表明:寄主植物对烟粉虱羧酸酯酶和乙酰胆碱酯酶(AChE)活力影响显著,取食不同寄主植物的烟粉虱后代羧酸酯酶和AChE活力差异显著。在试验的甘蓝、花菜、小白菜和苘麻4种寄主中,取食小白菜、甘蓝的烟粉虱后代种群羧酸酯酶的酶活力显著高于取食花菜和苘麻的,取食小白菜的酶活力最高,是取食苘麻的3.90倍。取食甘蓝的后代种群AChE的酶活力最高,取食苘麻的后代种群酶活力最低;取食花菜与小白菜、小白菜与苘麻之间没有明显差异,但甘蓝与其他寄主上的烟粉虱后代种群之间的差异均达到了极显著水平。取食甘蓝、花菜、小白菜的后代AChE OD值分别为取食苘麻的2.85、2.39倍和1.07倍。     

Variability of some plant species from different origins and their suitability for virus work

Plants of four species obtained from various sources were raised and compared for their suitability as test plants for a number of viruses. The species comprisedChenopodium amaranticolor (local lesion host of red clover mottle virus),Nicotiana glutinosa (local lesion host of tobacco mosaic virus (TMV)),N. rustica (systemic host of TMV, cucumber mosaic virus and tomato spotted wilt virus) andN. tabacum ‘White Burley’ (systemic host of TMV). Some sources proved to be more attractive as test plants or experimental hosts because of, e.g., production of more local lesions per unit of leaf area (C. amaranticolor andN. glutinosa), distinctness of lesions (C. amaranticolor), development of more pronounced systemic symptoms (N. rustica andN. tabacum ‘White Burley’), better growth characteristics (particularlyC. amaranticolor andN. rustica), smoother leaves being easier to rub (N. glutinosa) or more and bigger leaf formation (particularlyN. rustica). The implications for the interpretation of host range studies and the quest for propagation and assays hosts are discussed.     

Epitrix similaris and Epitrix cucumeris in Portugal: damage patterns in potato and suitability of potential host plants for reproduction

The potato flea beetle species Epitrix similaris and Epitrix cucumeris were identified in mainland Portugal in 2009. This was the first finding of the species E. similaris in the EPPO region, and the first report of the species E. cucumeris, established in the Atlantic Islands of Azores (Portugal) for three decades, in the mainland EPPO zone. Preliminary information on the damage patterns caused by E. similaris and E. cucumeris on potato and their host plant preferences is provided. Leaf feeding by the adults causes the characteristic shot‐hole pattern common to flea beetles. The larvae of both species develop on the root system and cause damage to the tubers. In field experiments, tuber damage by E. similaris presented three patterns: superficial tracks (serpentines), black splinters, and shallow holes. In the laboratory E. cucumeris was observed to be able to feed on very small immature tubers, causing serpentines and holes as well. However, in some cases it developed exclusively on roots. The adults of both Epitrix species hardly fed and reproduced on sweet pepper plants but fed and reproduced on the remaining five solanaceous plants tested (aubergine, Datura stramonium, tomato, potato and Solanum nigrum). E. similaris produced a much higher number of progeny on potato and on S. nigrum than on the other host plants. E. cucumeris produced more offspring on S. nigrum than on the other host‐plants.     

Field Response to Pratylenchus Thornei of a Wheat Line with the CreAet Gene for Resistance to Heterodera Avenae

The gene CreAet for resistance to Heterodera avenae, transferred from Aegilops triuncialis to Triticum aestivum introgression line TR-353, was assessed for responses to Pratylenchus thornei under field conditions. After 2.5 months, P. thornei infestation on TR-353 was similar to those on its progenitors (T. aestivum H10-15, T. turgidum H1-1 and A. triuncialis A-1) and on the cultivar Capa. After 5 months, TR-353 hosted significantly more P. thornei per plant than A. triuncialis, T. aestivum H10-15 or cultivar Rinconada, being very close to the maximum value obtained from T. turgidum. The final infestation of line TR-353 by H. avenae was significantly lower than on the other plants, except for A. triuncialis. In addition, at 2.5 months, the abundance of P. thornei on TR-353 was intermediate between the introgression wheat line H93-8 (Cre2 gene) and the cultivar Loros (Cre1 gene), but the final number of P. thornei per plant on TR-353 was significantly greater than on Loros. Line TR-353 was not able to control P. thornei in the field, but it confirmed its resistance to H. avenae, which was significantly lower than those due to Cre1 and Cre2 genes. No competition was observed between P. thornei and H. avenae populations on line TR-353 or A. triuncialis.