Wageningen, Netherlands
Wageningen, Netherlands

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Biemond P.C.,International Institute Of Tropical Agriculture | Biemond P.C.,Wageningen University | Oguntade O.,International Institute Of Tropical Agriculture | Kumar P.L.,International Institute Of Tropical Agriculture | And 3 more authors.
Crop Protection | Year: 2013

Most smallholder farmers in developing countries depend on an informal Seed System (SS) for their seed. The informal SS is often criticized because farmer-produced seed samples are not tested for seed health, thus accepting the risk of planting infected seeds. Here we aimed at assessing the quality of seeds acquired from the informal SS, and compared this with the quality of seeds obtained from the formal SS. Cowpea seed production in northern Nigeria was used as a case study to evaluate the seed health of samples from farmers, seed companies, and foundation seed producers. In two years, a total of 45,500 seeds from 91 seed samples from 43 sources (farmers, seed companies and research) were tested for seed-borne bacteria and fungi by plating disinfested seed onto an agar medium. The most commonly isolated plant pathogens were Fusarium oxysporum (69% of the samples), Macrophomina phaseolina (76%) and Pseudomonas syringae pv. phaseolicola (48%). The infection incidence, the percentage of seeds infected per sample, varied from 0.2 to 75.6%. F. oxysporum had a median infection incidence of 9% in 2009 and 25% in 2010, while M. phaseolina had a median infection between 4 and 10%. On average, 8.8 species per sample were isolated from foundation seed, 9.2 from farmer-produced seed and 9.8 from seed companies' seed. No evidence was found that seed recycling in the informal SS did lead to increased levels of seed-borne pathogens. In contrast to farmers, seed companies distribute seed over large distances, and therefore form a potential threat for spreading diseases at relatively large scale. Responsible authorities are recommended to make seed dressing mandatory for all seeds sold by seed companies. © 2012 Elsevier Ltd.

Biemond P.C.,International Institute Of Tropical Agriculture | Biemond P.C.,Wageningen University | Oguntade O.,International Institute Of Tropical Agriculture | Stomph T.-J.,Wageningen University | And 3 more authors.
European Journal of Plant Pathology | Year: 2013

Many Nigerian farmers depend for their seed on seed-producing farmers, the so-called informal Seed System (SS), but seed quality of the SS is unknown. Farmers planting low quality seed risk poor field emergence and low plant vigour as a result of low physiological quality or infection with seed-borne pathogens. The objective of this research was to test seed quality of maize seed from the informal SS in north-east Nigeria. A total of 46,500 seeds (93 samples of 500 seeds each) were tested for germination, off-types and seed health. Seed pathology was quantified by plating disinfected seeds onto agar, and identifying the fungi present after 3 days incubation. Twelve seed-borne pathogens were identified including Bipolaris maydis (found in 45 % of the farmer-produced samples), Botryodiplodia theobromae (97 %) and Curvularia lunata (38 %). All samples were infected with Fusarium verticillioides, with a median infection incidence of 59 % (2009) and 51 % (2010). None of the 93 samples tested passed the demands for certified seed of the National Agricultural Seeds Council (NASC) in Nigeria, in particular the maximum limit of five off-types per kg seed sample. Based on these results, seed-producing farmers must improve the health of seed. The NASC should revise the standards for off-type seeds to minimize the time spent by farmers sorting planting material. © 2013 KNPV.

Hol W.H.G.,Netherlands Institute of Ecology | De Boer W.,Netherlands Institute of Ecology | De Boer W.,Wageningen University | Termorshuizen A.J.,BLGG Research | And 5 more authors.
Journal of Chemical Ecology | Year: 2013

Aboveground and belowground herbivore species modify plant defense responses differently. Simultaneous attack can lead to non-additive effects on primary and secondary metabolite composition in roots and shoots. We previously found that aphid (Brevicoryne brassicae) population growth on Brassica oleracea was reduced on plants that were infested with nematodes (Heterodera schachtii) prior (4 weeks) to aphid infestation. Here, we examined how infection with root-feeding nematodes affected primary and secondary metabolites in the host plant and whether this could explain the increase in aphid doubling time from 3.8 to 6.7 days. We hypothesized that the effects of herbivores on plant metabolites would depend on the presence of the other herbivore and that nematode-induced changes in primary metabolites would correlate with reduced aphid performance. Total glucosinolate concentration in the leaves was not affected by nematode presence, but the composition of glucosinolates shifted, as gluconapin concentrations were reduced, while gluconapoleiferin concentrations increased in plants exposed to nematodes. Aphid presence increased 4-methoxyglucobrassicin concentrations in leaves, which correlated positively with the number of aphids per plant. Nematodes decreased amino acid and sugar concentrations in the phloem. Aphid population doubling time correlated negatively with amino acids and glucosinolate levels in leaves, whereas these correlations were non-significant when nematodes were present. In conclusion, the effects of an herbivore on plant metabolites were independent of the presence of another herbivore. Nematode presence reduced aphid population growth and disturbed feeding relations between plants and aphids. © 2013 The Author(s).

Kohl J.,Wageningen UR Plant Research International | de Jong P.-F.,WageningenUR Applied Plant Research PPO Fruit | Kastelein P.,Wageningen UR Plant Research International | Groenenboom-de Haas B.H.,Wageningen UR Plant Research International | And 3 more authors.
European Journal of Plant Pathology | Year: 2013

Brown spot disease on pear caused by Stemphylium vesicarium may affect leaves and fruits. Inoculum sources present on orchard floors play an important role in the epidemiology of pear brown spot. The pathogen can overwinter on plant residues and multiply and spread on the residues during the growing season. In the Netherlands, brown spot characteristically occurs only in a fraction of the orchards per season. Until now, no tools are available for Dutch pear growers to predict the risk of brown spot in specific orchards. As a consequence, preventive fungicide sprayings are common. The concentration of DNA of pear-pathogenic S. vesicarium was quantified by a specific TaqMan-PCR assay for various types of plant residues present on orchard floors to evaluate their importance as potential inoculum source. The pathogen was often found in residues of pear leaves, grasses and weeds, but only occasionally in mummies and prunings. Studies of the population dynamics showed that S. vesicarium decreased in dead pear leaves during early winter whereas pathogen populations developed with irregular pattern during the growing season on residues of weeds and grasses. Based on DNA concentrations of S. vesicarium in plant residue samples taken in 78 to 106 orchards in the springs of 2010, 2011 and 2012, the risk of brown spot development could be predicted for individual orchards. Such a risk prediction will allow growers to adapt their fungicide spray schedules to avoid unnecessary sprays in low-risk orchards. © 2013 KNPV.

Ali M.,Wageningen University | Ali M.,Wageningen UR Livestock Research | Van Duinkerken G.,Wageningen UR Livestock Research | Cone J.W.,Wageningen University | And 6 more authors.
Animal | Year: 2014

Several in situ studies have been conducted on maize silages to determine the effect of individual factors such as maturity stage, chop length and ensiling of maize crop on the rumen degradation but the information on the relationship between chemical composition and in situ rumen degradation characteristics remains scarce. The objectives of this study were to determine and describe relationships between the chemical composition and the rumen degradation characteristics of dry matter (DM), organic matter (OM), CP, starch and aNDFom (NDF assayed with a heat stable amylase and expressed exclusive of residual ash) of maize silages. In all, 75 maize silage samples were selected, with a broad range in chemical composition and quality parameters. The samples were incubated in the rumen for 2, 4, 8, 16, 32, 72 and 336 h, using the nylon bag technique. Large range was found in the rumen degradable fractions of DM, OM, CP, starch and aNDFom because of the broad range in chemical composition and quality parameters. The new database with in situ rumen degradation characteristics of DM, OM, CP, starch and aNDFom of the maize silages was obtained under uniform experimental conditions; same cows, same incubation protocol and same chemical analysis procedures. Regression equations were developed with significant predictors (P < 0.05) describing moderate and weak relationships between the chemical composition and the washout fraction, rumen undegradable fraction, potentially rumen degradable fraction, fractional degradation rate and effective rumen degradable fraction of DM, OM, CP, starch and aNDFom. © The Animal Consortium 2014.

Meyer K.M.,Netherlands Institute of Ecology | Meyer K.M.,University of Gottingen | Vos M.,University of Potsdam | Vos M.,Netherlands Institute of Ecology | And 6 more authors.
PLoS ONE | Year: 2012

In the light of ongoing land use changes, it is important to understand how multitrophic communities perform at different land use intensities. The paradox of enrichment predicts that fertilization leads to destabilization and extinction of predator-prey systems. We tested this prediction for a land use intensity gradient from natural to highly fertilized agricultural ecosystems. We included multiple aboveground and belowground trophic levels and land use-dependent searching efficiencies of insects. To overcome logistic constraints of field experiments, we used a successfully validated simulation model to investigate plant responses to removal of herbivores and their enemies. Consistent with our predictions, instability measured by herbivore-induced plant mortality increased with increasing land use intensity. Simultaneously, the balance between herbivores and natural enemies turned increasingly towards herbivore dominance and natural enemy failure. Under natural conditions, there were more frequently significant effects of belowground herbivores and their natural enemies on plant performance, whereas there were more aboveground effects in agroecosystems. This result was partly due to the "boom-bust" behavior of the shoot herbivore population. Plant responses to herbivore or natural enemy removal were much more abrupt than the imposed smooth land use intensity gradient. This may be due to the presence of multiple trophic levels aboveground and belowground. Our model suggests that destabilization and extinction are more likely to occur in agroecosystems than in natural communities, but the shape of the relationship is nonlinear under the influence of multiple trophic interactions. © 2012 Meyer et al.

Kosten S.,Wageningen University | Kosten S.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Vernooij M.,Wageningen University | Vernooij M.,BLGG Research | And 4 more authors.
Freshwater Biology | Year: 2012

1.The alternative state theory claims that shallow lakes may have either clear water, and be dominated by submerged macrophytes, or turbid water and be dominated by phytoplankton. Most evidence for this theory comes from studies in temperate or boreal regions of Europe. Because of differences in the strength of trophic interactions, such as in the pressure of zooplankton grazing on phytoplankton, this influential theory might not apply elsewhere. 2.Here, we test the theory for South American lakes, combining field data and Landsat satellite data. We studied the frequency distribution of primary producers and water transparency, looking for potential bimodality separating clear and turbid lakes. A bimodal distribution might be observed if there are indeed alternative states, although would not itself be sufficient evidence for the theory. Possible shifts between alternative states were analysed by comparing satellite data from 1987 to 2005. 3.In our field data, there was a bimodal pattern in phytoplankton abundance and possibly in the abundance of submerged macrophytes, but not in water transparency. Analyses of the larger satellite data set revealed bimodality in lake transparency in 2005, but less so in 1987. In 1987, the lakes were generally clearer, and the transition to higher turbidity was more gradual than in 2005. The stronger bimodality in the more recent data, and the overall lower transparency, could have been caused by an increase in fertiliser use and subsequent eutrophication but also by differences in hydrology. Further, 1987 was much wetter than 2005, which could have caused dilution of suspended particles, leading to clearer water. 4.While a bimodal distribution in the abundance of primary producers and water clarity is not decisive evidence for or against the theory of alternative states, our data clearly fail to refute it. © 2012 Blackwell Publishing Ltd.

Reijneveld A.,BLGG AgroXpertus | Termorshuizen A.,BLGG Research | Vedder H.,BLGG Research | Oenema O.,Wageningen University
Communications in Soil Science and Plant Analysis | Year: 2014

Soil phosphorus (P) tests are used for P fertilization recommendations, environmental evaluations, and occasionally for legislation purposes. The basis of fertilization recommendation as function of soil P status was established in the 1950s-1960s. Since then the agroeconomic environment has altered: Environmental protection became increasingly important and P rock resources for fertilizers appeared exhaustible. Also, new insights in soil testing and fertilization recommendations reflecting more efficient use of P became available. However, these new insights seem hard to implement into agricultural practice, to a large extent because replacing existing soil tests and recommendations would imply a very significant effort with respect to introducing new tests and recommendations by fertilization trials in practice. The same would apply for environmental evaluations. Here, a novel, three-step schedule for introducing new soil tests is proposed: (1) establishing new promising soil tests, (2) creating regression models between the old and new soil tests, and (3) implementing the new soil test stepwise by fertilization trials. In this way, the knowledge based on the old soil tests can be used until the new soil tests and their subsequent crop responses are validated sufficiently. As a novel P test we considered combining soil P intensity [as reflected by P-calcium chloride (CaCl2)] with P capacity [as reflected by P-ammonium lactate (Al)] and P-buffering capacity (as reflected by P-Al/P-CaCl2 ratio) characteristics. Researchers tested whether this novel soil test can predict P water (Pw), P-calcium lactate / acetate (CAL), and P-Olsen values. To test the hypothesis, four datasets were used (two with Pw, one with P-CAL, and one with P-Olsen). In all datasets additional soil characteristics were available including soil type. Regression models with Radj 2 from 0.80 to 0.93 were obtained by using P-Al, P-CaCl2, and soil type. It can be concluded that these regressions can be used as a helpful intermediate instrument when introducing fertilization recommendations based on new soil tests. Predicting one soil P test out of other soil characteristics, analogous to the predicted Pw, P-CAL, and P-Olsen, could also be helpful in comparing P statuses of agricultural land in different nations. © 2014 Taylor and Francis Group, LLC.

Reijneveld J.A.,BLGG AgroXpertus | Abbink G.W.,BLGG AgroXpertus | Termorshuizen A.J.,BLGG Research | Oenema O.,Wageningen University
European Journal of Agronomy | Year: 2014

It is reasonable to expect that compliance with grassland fertilization recommendations in the long run results in optimal soil fertility, and subsequent herbage quality. Here, we evaluate the development of soil, herbage and manure characteristics and their relation over the last decades. We hypothesized that herbage and manure quality are related with soil fertility. We used a large database with results of soil tests, spring forage quality characteristics, and manure analyses, which were made on demand of dairy farmers. We considered the Netherlands as a whole and three selected regions with contrasting soil types (sandy soil, riverine clay, and peaty marine clay). Effects of soil fertility on herbage quality were evident when comparing farms. Farms higher in soil P and K generally have correspondingly higher contents in forage. On average, soil fertility and herbage characteristics were within or just above the agronomical optimal range during the last decades. Herbage crude protein content decreased in all regions during last two decades, which is likely an effect of legislative measures on decreasing the application of N. Selenium (Se) and sulphur (S) contents increased sharply on sandy soils, likely because of increased use of Se and S containing fertilizers. Manure composition did not differ between soil types. In conclusion, at farm level, the element composition of herbage reflected the soil fertility status. The contents of S, P, K, Na, Mg, and Ca in the herbage were all significantly influenced by soil fertility characteristics. Our results emphasize the importance of maintaining soil fertility for high quality roughage production. © 2014 Elsevier B.V.

Termorshuizen A.J.,BLGG Research | Jeger M.J.,Imperial College London
Acta Horticulturae | Year: 2014

Inoculum of a pathogen is its biomass available for infection. Inoculum density (ID), usually expressed per unit of volume or (dry) weight of soil, is the common measure to evaluate the effect of soil disinfestation. Interpretation of ID of a given pathogen depends on the sampling and detection procedures. For example, soil drying and sieving selects for relatively large surviving propagules, and ID only reflects the density of these surviving structures. Factors affecting the reliability of the prediction of future damage based on ID include: no more than one type of surviving propagule; absence of a saprophytic phase; strong sensitivity to fungistasis; high survival capacity; and availability of validated sampling and detection methods. The efficacy of soil disinfestation is often determined rapidly after finishing the disinfestation treatment. If that is the case, certain detection methods may lead to false positives. The perspective of a given soil disinfestation method not only depends on the relationship between ID and disease incidence/severity, but also on the initial ID prior to treatment. For a given soil disinfestation method there is, theoretically, a threshold initial ID, above which the method leads to a final ID that is higher than the damage threshold; if no other methods are available, a switch to resistant crops may be the only other control alternative. In soil disinfestation experiments, scientists can choose between a natural level of infestation or introduce inoculum. In the first case, spatial variation of inoculum has to be dealt with, while in the second case, care has to be taken that the introduced inoculum must have the same properties such as persistence and germinability as the inoculum occurring naturally.

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