Plant-parasitic Nematode Populations Research Articles

Rhizobacteria with nematicide aptitude: enzymes and compounds associated.

The use of rhizobacteria to control plant parasitic nematodes has been widely studied. Currently, the research focuses on bacteria-nematode interactions that can mitigate this complex microbiome in agriculture. Various enzymes, toxins and metabolic by-products from rhizobacteria antagonize plant parasitic nematodes, and many different modes of action have been proposed. Hydrolytic enzymes, primarily proteases, collagenases and chitinases, have been related to the nematicide effect in rhizobacteria, proving to be an important factor involved in the degradation of different chemical constituents of nematodes at distinct developmental stages. Exuded metabolites may also alter the nematode-plant recognition process or create a hostile environment for nematodes in the rhizosphere. Specific bacteria strains responsible for the production of toxins, such as Cry proteins, are one of the strategies used by rhizobacteria. Characterization of the rhizobacteria mode of action could strengthen the development of commercial products to control populations of plant parasitic nematodes. This review aims to provide an overview of different enzymes and compounds produced by rhizobacteria related to the process of antagonism to plant-parasitic nematodes.

Management of Meloidogyne incognita and other phytonematodes infecting Amaranthus cruentus and Telfairia occidentalis with African marigold (Tagetes erecta) and Siam weed (Chromolaena odorata)

Field trials were conducted to investigate the effects of eight week-old seedlings of African marigold and siam weed applied as organic amendments on nematodes including Meloidogyne incognita, Helicotylenchus spp. and Dolichodorus spp. infesting Amaranthus cruentus and Telfairia occidentalis, and on leaf yield of M. incognita-infested A. cruentus and T. occidentalis. A nematode-infested plot without African marigold and siam weed served as control. There was significant reduction in population densities of M. incognita, Helicotylenchus spp. and Dolichodorus spp. in plots amended with seedlings of African marigold and siam weed compared to control treatment in both experiments. There was also a corresponding significant increase in the leaf yields of A. cruentus and T. occidentalis in the amended plots compared to control plots. The levels of total N, available P and exchangeable K increased with a decrease in pH at harvest in amended plots in both crops compared to control. The results of this study suggest that seedlings of eight week-old African marigold or siam weed incorporated into soil prior to planting has potentials to reduce plant-parasitic nematode population densities, increase soil fertility and enhance leaf yield of associated vegetable crops.

Study of plant parasitic nematode population density in Cabbage inRangareddy district, Telangana.

Study of plant parasitic nematode population density in Cabbage inRangareddy district, Telangana.

Effects of mulching on above and below ground pests and beneficials in a green onion agroecosystem

In 2013 and 2014, different mulching systems were investigated for their potential to suppress above and below ground pests, and enhance beneficial arthropods and soil health in green onion (Allium cepa) plantings. Three types of mulch systems (organic, living and solarization mulch) were evaluated and compared. Green onions were grown in four pre-plant treatments: (1) organic mulch generated by flail mowing a sunn hemp (Crotalaria juncea) cover crop (SH) followed by a no-till cropping system, (2) soil solarization (Sol), (3) sunn hemp-solarization mulch in which the sunn hemp was incorporated into the soil followed by soil solarization (SHSol), and (4) bare ground with insecticides (BG). Sol, SHSol and BG were practiced in conventional tilled system. SH (in 2013 and 2014) and SHSol (in 2014) treatments included strips of buckwheat and cowpea along the crop border to serve as living mulch or insectary plants. Green onion plants in SH had lower thrips and leaf miners damage than other treatments in both study years. When insectary borders were added to SHSol in 2014, thrips and leaf miners damages were also reduced in SHSol compared to Sol and BG. Incidence of purple blotch was reduced in SH and SHSol treatments in 2014. The SH treatment contained an increased abundance and richness of detritivores, predatory arthropods, parasitoids and beneficial free-living nematodes (particularly bacterivores and fungivores). Although weeds and initial populations of plant-parasitic nematodes were lower in solarization (Sol, SHSol) than other treatments, green onion yield was greatest in SH organic mulch systems in both study years. Overall, the integration of surface organic, living and solarization mulches into a green onion agroecosystem provided multiple ecosystem services including suppression of above and below ground pest organisms.

Compost and poultry manure as preplant soil amendments for red raspberry: Comparative effects on root lesion nematodes, soil quality and risk of nitrate leaching

Raspberry fields in the Pacific Northwest, USA and British Columbia, Canada are often prepared for replanting by fumigating with broad-spectrum biocides to control root-lesion nematodes, Pratylenchus penetrans. Nematode-suppressive organic amendments have been advocated as reduced risk alternatives to fumigation but may pose other risks to the environment. This study compared alternative pre-plant soil management practices with respect to their effects on plant-parasitic nematode populations, soil quality parameters and risk of nitrate leaching. In fall of 2009 and 2010, a mature raspberry field was mowed down and plowed, and replicate plots were randomly allocated to each of six treatments: (1) a non-amended control, (2) fumigation with Basamid®, (3) fall seeded barley cover crop, (4) recommended rate (20m3ha−1) and (5) historical “biofumigant” high rate (250m3ha−1) of spring incorporated poultry manure, and (6) spring incorporated compost (250m3ha−1). Raspberry cv Saanich was planted approximately one month after incorporation of amendments. Composite soil samples were taken from each plot at multiple times during two subsequent growing seasons and analyzed for nematode populations and soil chemical and physical properties. Primocane biomass was assessed at the end of each of the first two growing seasons as an index of crop vigor. The high poultry manure and compost treatments suppressed root-lesion nematode populations nearly as well as fumigation over two growing seasons. These treatments also improved soil bulk densities and aggregation relative to control, cover crop and fumigation treatments, while compost addition beneficially increased soil pH, CEC and Ca concentrations more than manure. Primocane production in the manure and compost treatments was greater than in the control and cover crop treatments, but less than in the fumigated treatment. Substantial nitrate accumulation in soil amended with the high rate of manure indicated that application of sufficient manure to suppress parasitic nematodes would pose a significant risk of nitrate leaching. In contrast, soil nitrate accumulation was not significantly increased in the compost amended plots. Overall, compost application reduced nematode populations, improved crop growth and did not increase the risk of nitrate leaching in the short term and may be a viable alternative to fumigation.

Incidence and population of plant parasitic nematodes in green amaranth (Amaranthus hybridus L.) (Caryophyllales: Amaranthaceae) from three selected areas in Dutsin-Ma Town, Katsina State, Nigeria

An experiment was conducted in the Department of Biological Sciences, Federal University Dutsinma, Katsina State Nigeria, between May to August, 2016. A survey was carried out from three farm areas around Dutsin-Ma Metropolis to investigate and determine the incidence and population of plant parasitic nematodes of green amaranth (Amaranthus hybridus L.). A total of 240 soil root samples from an infested A. hybridus were taken 10 cm deep from the rhizosphere of the green amaranth plant. The samples were extracted using Cobb-Seiving and Decanting Method. From the supernatants residue, a total of nine genera of plant parasitic nematodes were identified, with 6 genera in Farm 1, 8 genera in Farm 2, and 5 genera in Farm 3. The genera Meloidogyne (23.33%), has the highest incidence followed by Xiphinema (14.58%), Pratylenchus (13.33%), Heterodera (10.83%), Paratrichodorus (10.83%), Aphelenchoides (9.16%), Helicotylenchus (8.33%), Tylenchorhychus (7.92%) and Longidorus (7.08%). Data on incidence from root galling was also taken from the examined samples, with Farm 2 having highest value for moderate root gall damage. It has been deduced from the result that most of the plants with high parasitic load of the nematodes exhibit root gall, chlorotic and perforated leaves, darker weak stems, stunted growth and poor flowering. This results shows that there is a widespread distribution of plant parasitic nematodes against the A. hybridus plants in the surveyed areas (Farm 1, 2 and 3). The presence of these parasitic nematodes, even at low populations in the soil is not significant (P > 0.05) in comparison with all the root samples from the three selected farms (F = 0.12, P = 0.8803). The parasitic nematode population built up could eventually result in great reduction of the crop yield. Establishing efficient research control on the damaging potentials of these parasitic nematodes as against this vegetable crop; hence, awareness programs ought to be created for researchers, farmers and lay men.

Nematode Composition and Soil Conditions in Plots under a Wheat Crop in Colfax, Washington State

Plant parasitic nematodes have been identified as a major problem to wheat (Triticum aestivum L.) production in the Pacific Northwest (PNW) states of the USA. Nematicide control of these parasites has been successful. We were, however, interested in understanding how the soil nematode-nematode interactions and the nematode-host plant interactions affect nematode populations of different feeding groups and how the soil nematode composition could be used to elucidate soil conditions in a winter wheat crop. Our results revealed that the ratio of the plant-parasite index (PPI) to the maturity index (MI = free-living nematodes) was high, meaning we had higher populations of the herbivorous nematodes than all of the other feeding groups combined. The low populations of the free-living nematodes meant little or no nitrogen mineralization by the bacterivorous and fungivorous nematodes, and also a lack of meaningful predation of the plant-parasitic nematodes by the pest suppressive species i.e omnivores and carnivores. The high plant-parasitic nematode populations and low populations of the free-living nematodes may have also interfered with nutrient uptake by the plants and resulted in stressed soils in the plots studied. Based on our results, farming methods that will reverse the PPI/MI ratio will be a natural and ecologically friendly way of reducing populations of the parasitic nematodes in the wheat plots e.g. rotations and soil amendments. During the different sampling periods, the soil conditions changed from basal, to enriched, and then maturing, based on the nematode composition. Thus the soil nematode composition can be used for the biomonitoring of soil conditions in wheat plots.

Molecular Characterization and Phylogenetic Relationships of Plant-Parasitic Nematodes Associated with Turfgrasses in North Carolina and South Carolina, United States.

The near-full-length 18S ribosomal DNA (rDNA) gene and internal transcribed spacer 1 region were amplified and sequenced from 52 nematode populations belonging to 28 representative species in 13 families recovered from turfgrasses in North Carolina (38 populations) and South Carolina (14 populations). This study also included 13 nematode populations from eight other plant hosts from North Carolina for comparison. Nematodes were molecularly characterized and the phylogenetic relationships were explored based on 18S rDNA sequences. Phylogenetic analysis using Bayesian inference was performed using five groups of the plant-parasitic nematode populations Tylenchids, Criconematids, Longidorids, Xiphinematids, and Trichodorids. The 65 nematode populations were clustered correspondingly within appropriate positions of 13 families, including Belonolaimidae, Caloosiidae, Criconematidae, Dolichodoridae, Hemicycliophoridae, Hoplolaimidae, Heteroderidae, Longidoridae, Meloidogynidae, Paratylenchidae, Pratylenchidae, Telotylenchidae, and Trichodoridae. This study confirms previous morphological-based identification of the plant-parasitic nematode species found in turfgrasses and provides a framework for future studies of plant-parasitic nematodes associated with turfgrasses based upon DNA sequences and phylogenetic relationships.

Effects of organic and conventional pesticides on plant biomass, nematode diversity and the structure of the soil food web

Due to the uncertain future of the soil fumigants most commonly used in the EU, there is a need to develop new integrated pest management programmes to control crop diseases. Different nematode management practices, such as solarisation and the use of ecological nematicides, including nematophagous fungi, are used to control populations of plant-parasitic nematodes, one of the most common pests affecting crops. The objective of this study was to determine the effects of organic (neem seed paste and a mixture of nematophagous fungi) and conventional (oxamyl and fenamiphos) nematicides on soil physical chemical properties, soil biodiversity and plant biomass. Such effects were investigated in two types of habitats: low diversity soils from an agricultural farm and high diversity soils from a natural vegetation area. The greater effect was observed with the neem treatment, which induced a large boost of dauer juveniles in the nutrient-depleted soil, while the same treatment induced an increase of populations of less opportunistic, generalist bacterivore nematodes in the pine forest soil, rich in organic matter. We have studied the effects of different biological and chemical nematicides on the whole soil nematode community through ecological indices and their relationship with plant biomass, but further research is needed to improve understanding of the effect of these products on nematode assemblages.

Diagnóstico y dinámica poblacional de nematodos fitoparásitos en dos sistemas de cultivos de piña en Costa Rica

<p class="p1">La presente investigación determinó la presencia de géneros, densidad de población y dinámica poblacional de nematodos fitoparásitos en plantaciones de piña (<em>Ananas comosus, </em>var. <em>comosus</em>) en dos sistemas de cultivos en Costa Rica, período 2006-2008.</p> <p class="p1">El estudio comprendió un diagnóstico a nivel de suelo y raíz en plantas de dos a doce meses de edad que permitiera la determinación de la dinámica poblacional de los nematodos en los diferentes lotes cultivados de piña, durante el lapso de tiempo señalado en sistemas de cultivos convencionales y orgánicos en las regiones Huetar Norte y Huetar Atlántica de Costa Rica. Se seleccionaron lotes comerciales, los cuales fueron muestreados una vez al mes durante febrero a diciembre en los años 2006-2008. Se caracterizaron y cuantificaron los géneros de nematodos encontrados.</p> <p class="p1">El diagnóstico permitió la identificación de siete géneros a nivel de suelo: <em>Helicotylenchus </em>spp., <em>Meloidogyne </em>spp., <em>Pratylenchus </em>spp., <em>Tylenchus</em>, <em>Tylenchorhychus</em>, nematodos depredadores y de vida libre, donde el género <em>Helicotylenchus </em>spp. el que se indentificó con más frecuencia. La mayor población de nematodos fitoparásitos fue observada a nivel de suelo y correspondió a los géneros <em>Pratylenchus </em>spp. y <em>Helicotylenchus </em>spp.</p> <p class="p1">Los nematodos más frecuentemente observados en raíces de plantas de piña bajo técnicas orgánicas fueron: <em>Criconemella </em>spp., <em>Helicotylenchus </em>spp., <em>Pratylenchus </em>spp.; en el suelo se presentaron <em>Helicotylenchus </em>spp., y <em>Pratylenchus </em>spp., con frecuencias del 100%. En raíz y suelo de plantas de piña bajo técnicas convencionales el género <em>Helicotylenchus </em>spp. ,fue el más frecuente. El género <em>Pratylenchus </em>spp. presentó la densidad poblacional promedio más alta en la raíz en sistemas orgánicos y convencionales con 1.009,83 y 1.075,22 ind/100 g de raíz, respectivamente.</p> <p class="p1">En las áreas de manejo orgánico se presentó una mayor diversidad de géneros de nematodos en la raíz de la piña, los nueve géneros fitoparásitos que se observaron fueron: <em>Pratylenchus </em>spp., <em>Helicotylenchus </em>spp., <em>Meloidogyne </em>spp., <em>Haplolaimus </em>spp., <em>Tylenchus </em>spp., <em>Criconemella </em>spp. y <em>Xiphinema </em>spp. y nematodos de vida libre, en comparación con muestras de raíz de plantas con manejo convencional donde se presentaron seis géneros fitoparásitos (<em>Pratylenchus </em>spp., <em>Helicotylenchus </em>spp., <em>Nacobus </em>spp., <em>Tylenchus </em>spp., <em>Meloidogyne </em>spp.,<em>Criconemella </em>spp.) y nematodos de Vida Libre.</p> <p class="p1">A nivel de raíces, los géneros de nematodos identificados fueron cinco: <em>Helicotylenchus </em>spp., <em>Meloidogyne </em>spp.<em>, Pratylenchus </em>spp., <em>Rotylenchus </em>spp. y nematodos de vida libre. La mayor población de nematodos fitoparásitos observada a nivel de raíz corresponde a los géneros Helicotylenchus spp. con y <em>Pratylenchus </em>spp.</p> <p class="p1">Con manejo convencional se presentaron siete géneros de nematodos fitoparásitos (<em>Pratylenchus </em>spp., <em>Helicotylenchus </em>spp., <em>Tylenchus </em>spp., <em>Meloidogyne </em>spp., <em>Criconemella </em>spp., <em>Haplolaimus </em>spp. y <em>Tylenchorhynchus </em>spp. y nematodos de vida libre, mientras que en suelo de plantas cultivado con manejo orgánico se presentaron seis géneros fitoparásitos <em>Pratylenchus </em>spp., <em>Helicotylenchus </em>spp., <em>Tylenchus </em>spp., <em>Meloidogyne </em>spp., <em>Criconemella </em>spp. y <em>Rotylenchus </em>spp. y nematodos de Vida libre.</p>

Influence of Mulch Materials on Population of Plant Parasitic Nematode, Growth and Yield of Okra (Abelmoschus esculentus L. Moench)

A field experiment was conducted at National Horticultural Research Institute Idi-ishin, Ibadan to investigate the influence of mulching materials on population of plant parasitic nematodes, weed density, soil moisture, temperature content, growth and yields of okra (Abelmoschus esculentus L. Moench). The mulch materials were dried leaves of Azadirachta indica , Terminalia catappa , Eugenia uniflora, Pannicum maximum (grass straw) and plastic mulch with hoeing and no weeding as control. The experiment was conducted between June to September 2010. The experimental design was randomized complete block design in three replications. Data were collected on Vegetative Growth (VG), Gall Indices (GI), nematode reproduction. All data were analysed using ANOVA (p=0.05). GI was reduced by 76.91% in black plastic mulch, 69.28% in Azadirachta indica, 61.43% in no weeding control, 46% in Eugenia uniflora, 23.09% in Terminalia catappa and 15.24% in Pannicum maximum as compared to Hoeing weeding control. The root-knot nematode in the soil were also reduced by 96.63%, 89.28%, 76.81%, 53.63%, 50.72% and 24.63% in black plastic, no weeding control, Eugenia uniflora, Terminalia catappa, Azadirachta indica and Pannicum maximum mulching materials respectively as compared to hoe weeding control. The mulching materials significantly affected the growth and yield of okra (P≤0.05) with black plastic mulch resulting in the highest number of pods (30.0), fresh weight (378.0g) and dry weight (58.3g) per plant. Highest soil moisture retention was observed from hoe weeding plot (6%) while the highest soil temperature was recorded from black plastic mulch (25 o C) and the least weed density (6.0 plant/m 2 ) weed fresh weight (100.0g) and weed dry weight (34.0g) was also recorded on plastic mulch plot. These were significantly lower P≤0.05 compared with other mulched materials and no weeding control. Therefore mulch materials reduced the root-knot nematodes in the soil, weed interference in okra production while, enhancing moisture retention promotes faster plant growth and yield of okra. Keywords: Gall indices, Mulch materials, Nematode population, soil moisture and weed density

Nematode Damage to Plantain (Musa spp. AAB-Group) at Flowering as Affected by Paring and Organic Mulch in Southwestern Nigeria

The experiment investigated the effects of paring, oil palm bunch refuse and sawdust mulches on the flowering of mother plant, development of suckers, and the establishment, population and damage dynamics of plant parasitic nematodes on plantain cultivar Agbagba in Southwestern Nigeria. A multifactorial experiment was laid out in a randomized complete block design. Above-ground plant growth parameters were measured at flowering of mother plants. Twenty-two months after planting (MAP), mats were sampled to assess nematode population densities, root and rhizome damages. Results of this study showed that paring and mulching gave complementarily effect on early flowering of plants, improved root production and the extent of benefit was dependent on the type of mulch material used. Pared plants produced fewer suckers at flowering than the non- pared plants, had healthier roots and lower root infections associated with plant parasitic nematode damage. Oil palm bunch refuse was superior to the sawdust mulch in enhancing plant growth, root health and suppressing nematode population densities. In an integrated pest management context therefore, paring coupled with mulching is recommended to boost plantain production.

Impact of organic soil amendments, including poultry-litter biochar, on nematodes in a Riverina, New South Wales, vineyard

This field trial investigated the effect on vineyard nematodes of organic soil amendments: poultry-litter (PL) biochar, composted cow manure, composted green waste and un-composted rice hulls. To investigate their effects on disease suppression, we chose a vineyard containing healthy grapevines proximal to grapevines with fungal root disease (caused by Ilyonectria spp.). Spring and winter surveys showed that nematodes did not interact with Ilyonectria root disease. Plant-parasitic citrus and ring nematodes predominated in deep soil (10–20 cm), whereas Rhabditis spp. (bacterial-feeder) and omnivorous Dorylaimidae (excluding plant-parasitic and predators) predominated in shallow soil (0–10 cm). After 2 years, the amendments generally decreased the total plant-parasitic nematode (TPPN) populations while increasing the total (non-plant-parasitic) free-living nematodes (TFLN), thus increasing the TFLN : TPPN ratios. PL biochar caused the greatest TPPN decreases (8.5- and 12.9-fold for diseased and asymptomatic grapevines, respectively). The changes caused by the organic amendments were less favourable in a drier season and for diseased grapevines, indicating the importance of seasonal conditions and initial disease status for interpretation of soil organic amendment trial results. This is the first vineyard investigation comparing the impact of PL biochar and other organic soil amendments on parasitic and non-parasitic nematodes.

Sugarcane straw and the populations of pests and nematodes

The green cane harvesting represented a significant change in sugarcane ecosystem due to the presence of straw left on the soil and to the absence of fire. These two factors may affect the populations of pests and their natural enemies. Among the pests benefit from the green cane harvesting stand out the spittlebug, Mahanarva fimbriolata, the curculionid Sphenophorus levis and sugarcane borer, Diatraea saccharalis. In areas of green cane harvesting, the population of these species grew faster than in areas of burnt cane. On the other hand, there are virtually no records of attacks by lesser cornstalk borers in areas of green cane harvesting. Populations of plant parasitic nematodes and the beetles Migdolus fryanus, very important pests of sugarcane, were apparently not affected by the green cane harvesting. Despite the absence of more consistent information, it appears that populations of ants and the giant borer Telchin licus can increase in green cane areas, due primarily to the difficulty of pest control. The partial or total removal of straw from the field represents an additional change to the ecosystem that could alter the status of pests and nematodes. It is likely that spittlebug, the curculionid S. levis and sugarcane borer populations decrease if a portion of the straw is removed from the field. However, the pest populations in areas where the straw is collected will not return to their original conditions at the time of burnt cane harvesting because the absence of fire will be maintained.

In vitro investigations on the biological control of Xiphinema index with Trichoderma species

Abstract The application of Trichoderma spp. for the suppression of plant-parasitic nematode populations is a promising tool in biological control. Sixteen strains of six Trichoderma species (T. atroviride, T. harzianum, T. rossicum, T. tomentosum, T. virens and T. asperellum) were tested in vitro in order to identify the most appropriate strains to control the dagger nematode Xiphinema index. Mortality assays revealed that the strains of the widely investigated T. harzianum species have caused significant reduction of X. index populations, although T. harzianum strains were not the most efficient among all the tested fungi. Certain T. virens and T. atroviride strains and T. rossicum have triggered faster and higher mortality. Generally, our data indicate that Trichoderma species have innate ability to decrease X. index population. Furthermore, as we had difficulties with maintaining X. index in vitro, we successfully used a newly developed method to keep X. index specimens viable during the experiments.

Influence of different fertilization regimes on plant-parasitic nematodes in the black soil region of Northeast China

Plant-parasitic nematodes can cause serious plant diseases and adversely affect crop production. We investigated the temporal and vertical dynamics of plant-parasitic nematodes in northeast China to determine if long-term fertilizer application suppresses the population of plant-parasitic nematodes and influences their vertical distribution in the black soil region. The long-term fertilizer application lasted for 14 years, and included three treatments: pig manure combined with chemical fertilizer (MCF), chemical fertilizer (urea and ammonium phosphate, CF), and no fertilizer (NF). A 3-year corn-wheat-soybean rotation was grown on the field site, soil samples were obtained in the corn phase and nematodes were extracted, identified and counted. Six plant-parasitic nematode genera with relative abundance over 0.1% were found in this study. Heterodera was the dominant genus in all three fertilizer treatments, and its relative abundance was highest in NF (45.4%) and lowest in MCF (32.8%). Fertilizer application had a significant effect on abundance of total soil nematodes but not on either plant-parasitic nematodes or Heterodera. Significant differences in the abundance of total soil nematodes, plant-parasitic nematodes and Heterodera were observed among soil depths and interaction of fertilizer × soil depth. Total soil nematodes were mainly distributed in the 0–20 cm soil layer, and plant-parasitic nematodes and Heterodera were mostly distributed in the 10–30 cm soil layer. Fertilizer application did not show a significant effect on plant-parasitic nematodes or Heterodera at any of the sampling depths from 0 to 80 cm. The results indicated that fertilizer has no effective control on plant-parasitic nematodes when dominant genera and their respective plant hosts exist in relatively high abundance.

Application of stabilized biosolids and fly ash mixtures as soil amendments and their impact on free living nematodes and carrot (Daucus carota) yield

Background: In light of existing regulations regarding the use of nematicides coupled with the global loss of agricultural outputs due to nematodes, new strategies are needed to ensure soil ecosystem health while promoting crop production without the use of potentially dangerous chemicals. Proof of concept methodologies can be used by soil/agricultural scientists interested in identifying potential shortcomings of a given strategy and to identify additional parameters for future work. Using this limited approach allows for the dissemination of information in a stepwise fashion so that changes in research strategies can be initiated prior to final ‘definitive’ results. This work tests the viability of using coal fly ash, stabilized biosolids, or a mixture of the two to manage plant-parasitic nematode populations and increase carrot yield. Results: The fly ash and biosolids chosen for this work did not alter soil pH or metal content enough to impact significantly on nematode populations. Data on all parameters were combined to see overall trends. The soil and amendments are basic in nature with pH values close to 8 and only fluctuating between 0.2 (season 1) and 0.4 (season 2) pH units from baseline to harvest. Fly ash played a minor role in B and Fe increases, and biosolids contained slightly more Ca, Cu, K, Mg, P, and Zn than the soils, but none of these elements were present in concentrations that affected nematode ontogeny. Fly ash was more important in altering electrical conductivity than biosolids and had the greatest impact on nematode population changes. Biosolids were most important for increasing carrot yields either alone or in mixtures. Conclusions: Not all fly ash or biosolids are equal. The choice of these materials as soil amendments, or natural nematicides, should be based on pre-examination of the soils and the raw materials. Subsequently, ratios and application rates should be chosen so that the physicochemical and microbiological conditions favor nematode management. Biosolids and biosolids mixed with fly ash are capable of enhancing carrot yield significantly at the ratios and application rates tested in this study but had little effect on nematode populations.

Influência de adubações e manejo de adubo verde nos atributos biológicos de solo cultivado com alface (Lactuca sativa L.) em sistema de cultivo orgânico

Devido à carência de informações sobre adubação orgânica para alface e uma avaliação quanto à sua influência nos atributos biológicos do ambiente, este trabalho objetivou estudar o efeito de diferentes sistemas de manejo da mucuna preta e o uso de adubação orgânica sólida sobre a diversidade e biomassa microbiana do solo. Os tratamentos consistiram do manejo da mucuna preta, incorporada ou não ao solo, e aplicação de esterco bovino, composto, adubo orgânico comercial e testemunha sem adubação. Os atributos foram avaliados nas seguintes épocas: momento do manejo da mucuna e aos 15, 55 e 105 dias após esse manejo. O manejo e os tratamentos com adubo orgânico sólido não influenciaram de forma significativa na biomassa microbiana e na população bacteriana do solo. Houve aumento na população de fungo coma incorporação da mucuna preta. A incorporação da mucuna preta e o tratamento com composto foram favoráveis para o incremento de fungos micorrízicos. O tratamento com composto, seguido da incorporação da mucuna preta, e o tratamento testemunha proporcionaram população superior de nematoides saprófitas, enquanto a incorporação da mucuna ao solo aumentou as populações de fitonematoides.

Conjoint effect of oil-seed cakes and Pseudomonas fluorescens on the growth of chickpea in relation to the management of plant-parasitic nematodes

Soil application of organics has been explored as an alternative means of organic management of plant-parasitic nematodes. Efficiency of different oil-seed cakes of neem (Azadirachta indica), castor (Ricinus communis), groundnut (Arachis hypogaea), linseed (Linum usitatissimum), sunflower (Helianthus annuus) and soybean (Glycine max) were evaluated in field conditions with association of Pseudomonas fluorescens in relation to growth parameters of chickpea and population of plant-parasitic nematodes. Their efficacious nature was highly effective in reducing the population of these dominant soil nematodes. Significant improvement was observed in plant-growth parameters such as plant weight, percent pollen fertility, pod numbers, root-nodulation and chlorophyll content of chickpea, seemed to be due to reduction in disease incidence and might be due to growth promoting substances secreted by P. fluorescens. The multiplication rate of nematodes was less in the presence of P. fluorescens as compared to its absence. Most effective combination of P. fluorescens was observed with neem cake.

Plant-parasitic Nematodes Associated with Commercial Orchards of Passion Fruit and Adjacent Cerrado Vegetation in the Brazilian Federal District

Empresa Brasileira de Pesquisa Agropecuaria, Embrapa Cerrados, BR 020, Km 18, 73310-970, Planaltina, DF, Brazil(Received on January 18, 2012; Revised on July 6, 2012; Accepted on July 7, 2012)Populations of plant-parasitic nematodes were evaluat-ed in soil and root samples from areas planted withpassion fruit, or covered with adjacent native cerradovegetation, in five different cropping regions of theBrazilian Federal District. From July 2007 to January2008, twenty samples had been collected in five RuralCenters (Nucleo Rural–NR) planted with passion fruit.In five sites, samples were also collected in native cerradovegetation. Specimens of nine genera of plant-parasiticnematodes ( Meloidogyne , Helicotylenchus , Rotylenchulus ,Scutellonema, Pratylenchus, Paratylenchus, Hemicyclio-phora, Xiphinema and Criconemoides ) were found in thepresent survey. Important nematode pathogens, such asRotylenchulus reniformis and Meloidogyne spp. wereobserved in the passion fruit plantations throughoutfive major producing regions of the Brazilian FederalDistrict. Keywords : field survey, Meloyogyne, Passiflora spp, root-knot nematodes, Rotylenchulus reniformisPassiflora edulis Simmonds f. flavicarpa Degener is aplant species of a high economic importance in America,whereas Brazil and Ecuador are important world producersand consumers of passion fruit (Souza et al., 2008). Theeconomic importance of P. edulis and other Passifloraspecies relies on the quality of the fruits for consumptionand on its medicinal properties (Crochemore et al., 2003).Due to favorable climatic and soil conditions, extensiveproduction of sour passion fruit occurs in commercialorchards in the Brazilian Cerrado. Despite the advantages mentioned above, sour passionfruit is susceptible to pests and diseases. Soil pathogens areof main concern among passion fruit growers, especiallyplant-parasitic nematodes. Nematodes belonging to severalgenera have been reported in association with Passifloraroot systems in Brazil (Sharma et al., 1999; Soares et al.,2003; Dias-Arieira et al., 2008), however, for the majorityof them their role as pathogens remains unknown forthis crop. On the other side, the root-knot nematodes(Meloidogyne javanica, M. incognita, and M. arenaria),and the reniform nematode (Rotylenchulus reniformis) areamong the most destructive soil pathogens for passion fruit.These sedentary nematodes lead to root damage, poor plantdevelopment, and consequently to decreased yield andplant longevity.In addition to preventive measures, such as planting insoil free of harmful nematodes, crop rotation is the mostappropriate control measure available to lower populationlevels of nematodes in passion fruit plantations underBrazilian conditions. At the present time there is no nemati-cide registered for this crop. Despite richness of geneticvariability among Passiflora germplasm, and efforts tobreed nematode resistant varieties (Castro et al., 2011; El-Moor et al., 2009; Sharma et al., 2002), commercial vari-eties are not yet available to growers. Thus, knowledge ofthe distribution and population levels of nematodes isrequired for implementation of management practices.Direct field seeding, instead of planting seedlings fromnurseries is a common practice among passion fruit growersin the Brazilian Federal District (DF). This practice contri-butes to avoid dissemination of nematodes and otherpathogens from the nurseries through planting materials.Under these conditions, the sources of soil contamination ofplant-parasitic nematodes in the commercial orchards arepossibly from previous crops, weeds, or accidental intro-duction of infested soil from other locations. Susceptibleplants from the native vegetation may also be the source ofplant-parasitic nematodes when the area is claimed foragricultural purposes. For instance, Souza et al. (1994)reported the association of Meloidogyne spp. with severalnative plants of cerrado vegetation in Brazilian FederalDistrict (DF). The fact that the same plant-parasitic nema-todes appear associated with crops and plants in theassociated native vegetation is an indication that these