Number Of Nematodes In Soil Research Articles

The Efficiency of Using Some Natural Compounds for Management of Citrus Nematode Tylenchulus semipenetrans

Saadoon, S.M., M.I. Sergany, H.E.M. Mona, A.M.M. Reham and S.B. Gad. 2022. The Efficiency of Using Some Natural Compounds for Management of Citrus Nematode Tylenchulus semipenetrans. Arab Journal of Plant Protection, 40(4): 346-350. https://doi.org/10.22268/AJPP-40.4.346350 The efficacy of chitosan and propolis as well as alcohol and aqueous extracts of cabbage, garlic and ziziphus as bio agents was conducted against Tylenchulus semipenetrans infecting sour orange (Citrus aurantium L.) under greenhouse conditions. All the tested bio-agents significantly reduced in the numbers of nematodes in soil, galls formation and egg masses than those in the untreated (control) and improved plant growth. Results indicated a highly significant increase in total plant shoot fresh and dry weight, plant length was performed for cabbage alcohol extracts (82.1, 104.73 and 119.7%), followed by garlic alcohol extracts (79.5, 103.38 and 100.0%), respectively. Alcohol extracts achieved the highest reduction rate in nematode population with values of 95.92% for cabbage alcohol extract, followed by 94.92% for garlic alcohol extract and 88.73% for garlic aqueous extract, whereas Oxamyl as a systemic nematicide gave the least reduction rate of 60.49%. Results obtained support using bio-nematicides as biological control agents of T. semipenetrans nematode. Keywords: Biological control, extracts, Tylenchulus semipenetrans, citrus

Fitness cost but no selection for virulence in Meloidogyne incognita after two consecutive crops of eggplant grafted onto Solanum torvum

The eggplant Solanum melongena cv. Cristal, either ungrafted or grafted onto the Solanum torvum rootstock cv. Brutus, was cultivated for two consecutive years in the same plots in a plastic greenhouse to assess the level of resistance to Meloidogyne incognita and crop yield. At the end of the second crop, the putative selection for virulence of the nematode subpopulations coming from infected ungrafted and grafted eggplant was assessed in the eggplant and in S. torvum in a pot experiment. Nematode population densities at transplantation in 2017 ranged from 2 to 378 per 100 cm3 of soil and did not differ between ungrafted and grafted eggplant. At the end of each crop, a higher galling index and number of nematodes in soil and in roots was registered in ungrafted compared to grafted eggplant. The grafted eggplant was categorized as resistant in 2017 and as highly resistant in 2018. Eggplant yield did not differ irrespective of grafting in 2017 after being cultivated for 135 days, but it differed after 251 days of cultivation in 2018. In the pot experiment, S. torvum was categorized as resistant to both M. incognita subpopulations. However, the M. incognita subpopulation obtained from roots of S. torvum produced 49.4% fewer egg masses and 56% fewer eggs per plant in the eggplant than the nematode subpopulation obtained from roots of the eggplant cv. Cristal. The results of this study revealed that the infective and reproductive fitness of the nematode decreased without having been selected for virulence.

Evaluation of Selected Nonfumigant Nematicides on Increasing Inoculation Densities of Meloidogyne incognita on Cucumber

The southern root-knot nematode (RKN), Meloidogyne incognita, is particularly difficult to manage because of high susceptibility of all commercial cucumber (Cucumis sativus) cultivars to this nematode. Growers have conventionally relied on nematicide applications to control RKN. Two microplot experiments were conducted in which four nonfumigant nematicides, oxamyl, fluopyram, fluensulfone, and fluazaindolizine, were examined for their efficacy in reducing gall severity and postharvest soil nematode numbers in microplots inoculated with increasing inoculation densities (1,000, 5,000, 10,000, and 20,000 nematodes/microplot), and improving growth and yield of cucumber. Nematicides were applied 1 day prior to transplanting cucumber seedlings, except fluensulfone, which was applied 7 days before transplanting. At harvest, root gall indices differed significantly (P < 0.0001) among nematode inoculation densities and nematicides. All four nematicides were effective in reducing the root gall index when compared with the untreated control on a consistent basis at all M. incognita inoculation densities. At the lowest inoculation density, no significant difference in gall index or final population density was observed among nematicides; however, gall index increased with increasing nematode inoculation densities in nematicide-treated microplots. Correlations between gall index and inoculation density clearly showed that soil treatment with fluensulfone, fluazaindolizine, or fluopyram was more effective in reducing gall severity than treatment with oxamyl. Regression analysis also indicated no significant effect of nematode inoculation densities on yield of cucumber treated with these nematicides. Results of this study will provide guidance for improving nematicide efficiencies in soil with varying inoculation densities of RKN.

Long-term biological effectiveness of Pochonia chlamydosporia var. catenulata against Meloidogyne incognita infection in a crop rotation systemi

ABSTRACTThe aim of this study was to determine the effectiveness of Pochonia chlamydosporia var. catenulata and the bacteria Tsukamurella paurometabola strain C-924 (HeberNem™), to control Meloidogyne incognita infection in a crop rotation system (cucumber, tomato and pepper) under greenhouse production during six crop cycles. We determined gall index, prevalence, intensity of disease, and number of juvenile nematodes in soil. At the end of the sixth cycle, plants protected with P. chlamydosporia showed a reduction in gall index (≤2), prevalence, and median (42%) intensity of disease similar or more pronounced than those observed in plants protected with T. paurometabola (80%). Both treatments were more efficient at reducing galling than at reducing prevalence and therefore reduction of intensity of disease was mainly due to the reduction in galling. The hydrolytic activity of P. chlamydosporia and its resistant spores make this fungus one of the best options for the long-term control of RKNs by decreasing egg masses or galls. Pochonia chlamydosporia var. catenulata is an important part of a potential biological control strategy in rotation systems of vegetable crop and can be used for long-time IPM strategies in Cuba and the Caribbean.

Influence of Some Bionematicide and Entomopathogenic Nematodes Against Meloidogyne incognita and Rotylenchulus reniformis Infecting Papaya Plant

The efficacy of Agrein, Bioarc, Bionema, Biozeid, Micronema and two entomopathogenic nematodes (EPNs), Steinernema carpocapsae (All), Heterorhabditis bacteriophora (B20) as biological control agents of Meloidogyne incognita and Rotylenchulus reniformis nematodes infecting papaya, Carica papaya L. were evaluated under greenhouse conditions. All the tested bionematicide and (EPNs) significantly reduced in the numbers of nematodes in soil, galls formation, eggmasses and eggs per eggmass than those in the untreated (check) and improved plant growthparameters. The highly significant increase in weights of both shoot and root of plant grown in soil treated with Agrein and Steinernema carpocapsae. This research may contribute in the novel direction of using bionematicide and entomopathogenic nematodes (EPNs) a biological agent against plant parasitic nematode.

Evaluation of Desmodium uncinatum, Fagopyrum esculentum and Brachiaria humidicola as potential green manure crops for nematode management in sugarcane

Plant-parasitic nematodes remain a challenge to sugarcane growers in South Africa, and alternatives to chemical control are desirable. This project aimed to determine the impact of green manure crops Desmodium uncinatum, Fagopyrum esculentum and Brachiaria humidicola on nematodes and subsequent sugarcane yield. A pot trial examined the growth of these crops and their effect on plant-parasitic nematodes and subsequent sugarcane growth. Brachiaria produced the greatest biomass (to the detriment of the succeeding sugarcane crop) and significantly reduced the numbers of Pratylenchus nematodes in soil and roots. In a subsequent field trial, plots were planted to these same three green manure crops, with control plots either planted to sugarcane or left as a bare fallow. Four months later, sugarcane was replanted over the whole area. There were no significant differences between treatments in sugarcane growth or yield after growing these crops, and changes in selected nematode genera at different stages during the crop cycle were inconsistent across nematode genera and treatment. Further work is needed to investigate the nematode control potential of these crops before the system can be adopted at the field scale.

温度和[CO2]升高下转Bt水稻种植对土壤活性碳氮和线虫群落的短期影响

Interactions of global change and transgenic Bt rice( Huahui-1,HH1) cropping on soil ecosystem remain largely unexplored. Here we conducted an OTC( Open Top Chamber) experiment to evaluate the effects of transgenic Bt rice cropping on soil labile organic carbon and nitrogen,and nematode communities under elevation of temperature and [CO2] with two rice varieties including non-Bt rice( MH63) and its transgenic Bt line( HH1). Results showed that( 1) Under the condition of elevated [CO2]and warming,transgenic Bt rice cropping significantly affected the content of soil dissolved organic carbon,dissolved organic nitrogen and NO-3-N. Significantly interactions of transgenic Bt rice,warming and elevated [CO2]were observed for the content of soil dissolved organic carbon and dissolved organic nitrogen. Further,the transgenic Bt rice reduced microbial biomass carbon and nitrogen significantly under ambient temperature and [CO2]; whereaswarming and [CO2]elevation reversed that trend.( 2) At ambient temperatures and[CO2],the total number of nematodes in soil grown with transgenic Bt rice cropping were significantly more than those in soil grown with the parental line. Herbivorous nematodes tended to increase under the condition of warming and elevated [CO2],though not reaching to a significant level. Transgenic Bt rice and warming significantly increased the Nematode Channel Ratio,demonstrating the shift from bacteria-dominated to fungi-dominated energy channel. But [CO2]elevation and transgenic Bt rice significantly increased the nematode Enrichment Index. In conclusion,climate change modified the responses of soil labile organic matter and nematode community to transgenic Bt rice cropping,though it does not lead to negative effects on soil based on the results of short-term experimental duration.

Nematode communities in continuous tomato-cropping field soil infested by root-knot nematodes

Soil nematode communities in greenhouses with different duration of continuous cropping were investigated from October 2007 to June 2008. Total nematode populations and trophic groups were observed. Fourteen families and 24 genera were identified; the genera Protorhabditis, Diploscapter, Meloidogyne and Helicotylenchus comprised 74.4% of the total population (from all tested samples). Plant-parasitic and bacterivorous nematodes were most abundant among the trophic groups. Populations of both trophic groups increased with increasing times of continuous cropping. The numbers of soil nematodes at different soil depths were significantly different (p <0.05). Shannon–Wiener index (H′) and Simpson index of diversity (D) were highest in 0-yr soil of all soils. Plant parasite index (PPI) and PPI/MI (maturity index) of soil nematodes increased with the increasing times of continuous cropping suggesting that continuous cropping resulted in gradual shift of plant-parasitic nematodes from k-strategists to r-strategists.

Effects of Azadirachtin and Neem-based Formulations for the Control of Sweetpotato Whitefly and Root-knot Nematode

Toxicity of the plant-derived natural pesticide azadirachtin and two types of commercial neem (Azadirachta indica A. Juss)-based formulations, Neema (liquid type) and Neema-plus (pellet type), were evaluated based on the mortality rate and developmental inhibition of the sweetpotato whitefly (Bemisia tabaci) and root-knot nematode (Meloidogyne incognita). In a laboratory assay, when B. tabaci adults were fed leaves containing 5 or 10 ppm of azadirachtin solutions, the rates of female oviposition, subsequent egg hatch, and adult eclosion were significantly reduced to 23.1, 53.2, and 26.6% of the control, respectively. At a tomato greenhouse, the rates of adult colonization, oviposition and egg hatch were reduced to 78.2, 47.0, and 71.2% by Neema foliar spray and 31.3, 34.1, and 66.8% by soil treatment with Neema-plus relative to the control, respectively. When isolated soil nematodes were exposed to various concentrations of azadirachtin, Neema, and Neema-plus, the immobility of juvenile nematodes showed no change at 2 h after treatment, whereas a reduction of 36.3% was observed at day 1 with 10 ppm of azadirachtin. Nevertheless, the effects of neem formulations were faster and much higher than those of azadirachtin. At a cucumber greenhouse, soil treatments with neem formulations significantly reduced the numbers of soil nematodes and plant root-knots; the reduction with Neema was 12.1 and 9.0%, and with Neema-plus 26.4 and 24.6% of the control, respectively. Furthermore, soil treatment with Neemaplus greatly improved the growth of cucumber plants in nematode-infested pots. These results showed that azadirachtin and neem-based formulations were highly effective on the developmental inhibition of both whiteflies and root-knot nematodes. Thus, soil application of the neem-based formulations would be applicable for the control of both leaf-sucking and soil pests.

Nematodes as indicators of soil recovery in tailings of a lead/zinc mine

Trophic groups and functional guilds of soil nematodes were measured under four mine tailing subsystems in the Baoshan lead/zinc mine, Hunan Province, southern China to test the indicator value of nematodes for heavy metal pollution. No obvious correlation was found between heavy metal concentration and the total number of nematodes. However, the densities of c–p3, c–p4 and c–p5 nematodes were negatively correlated with Pb and Zn concentrations, suggesting that the abundance of nematode groups of high c–p values is useful indicators of heavy metal contamination. The “weighted faunal analysis” provided a better assessment of soil health condition than Maturity Index (MI) in situations where there were extremely low numbers of soil nematodes. Results showed that the effect of heavy metal contamination on soil nematodes might be strongly influenced by plants. Although the abundance of plant-feeding nematodes did not reflect the heavy metal conditions in the soil, it might be used as an index for assessing the soil remediation potential of pioneering plants. Patrinia villosa seems superior to Viola baoshanensis as a pioneer plant species for soil remediation based on analysis of rhizosphere nematode community.

Furfural Approaches as Control Measures against Root Rot and Root-Knot Incidence of Tomato under Greenhouse and Field Conditions

The fungicidal and nematicidal activity of an emulsifiable formulation of furfural (2-furan- carboxaldehyde) against root rot and root-knot pathogens was studied in laboratory, greenhouse and field experiments. The linear growth of tested soilborne pathogenic fungi was dramatically reduced with the increasing of furfural concentrations added to the growth medium up to 4 000 ppm where no growth was observed, while the bacterial and fungal bioagents showed more tolerance to these concentrations and failed to grow at 6 000 and 7 000 ppm, respectively. Pot and field experiments indicated that furfural at 6 000 ppm combined with bioagent treatments proved to have superior suppressive effect against tomato root rot incidence, caused by Fusarium solani and Rhizoctonia so- lani, comparing with each individual treatment. Numbers of nematodes in soil declined sharply in direct response to furfural application with the sharpest reductions in its population. No symptoms of root-knot incidence, caused by Meloidogyne incognita as well as no detected galls and eggmasess were observed in the root system of tomato plants grown in either artificially or naturally infested soil with the parasite at the same concentration under greenhouse and field conditions. Results from these experiments indicate that a variety of effective broad-spectrum formulations of furfural can be developed for control of economically important soilborne pests.

Orchard floor management practices that maintain vegetative or biomass groundcover stimulate soil microbial activity and alter soil microbial community composition

Groundcover management systems (GMS) are important in managing fruit-tree orchards because of their effects on soil conditions, nutrient availability, tree growth and yields. We employed a polyphasic approach, incorporating measures of soil microbial abundance, activity and community composition, to study the long-term effects of different GMS on biotic and abiotic factors in an orchard soil. Four GMS treatments – Pre-emergence residual herbicides (Pre-H), post-emergence herbicide (Post-H), mowed-sod (Grass), and hardwood bark mulch (Mulch) – were established in 2-m-wide strips within tree rows in an apple orchard in 1992, and have been maintained and monitored annually until the present. We have measured soil water and nutrient availability, tree growth, and yields annually from 1993 to 2003. Soil nematode numbers and trophic groups were evaluated in July and Oct. 2001, and Sept. 2003. Numbers of culturable bacteria and fungi, soil respiratory activity, eubacterial and fungal community composition were determined in May and Sept. 2003. The Pre-H treatment soil had the fewest culturable bacteria, while the Grass treatment had the largest population of culturable fungi. Soil nematode population size and diversity were also affected by GMS treatments; the Pre-H treatment had the lowest ratio of (bacteriovores + fungivores) to plant parasitic nematodes. Soil respiration rates were higher in the Mulch than in other treatments during a 40-day incubation period. Hierarchical cluster dendrograms of denaturing gradient gel electrophoresis (DGGE) fingerprints for eubacterial community 16S rRNA genes indicated that Post-H and Grass treatments clustered together and separately from the Pre-H and Mulch treatments, which were also grouped together. The influence of GMSs on the fungal community, as assessed by PCR-DGGE of the internal transcribed spacer (ITS) region, was not as pronounced as that observed for bacteria. Soil fungal community composition under the Mulch differed from that under other treatments. The effects of GMS on soil microbial community abundance, activity, and composition were associated with observed differences in soil organic matter inputs and turnover, nutrient availability, and apple tree growth and yields under the different GMS treatments.

A survey of Australian temperate pastures in summer and winter rainfall zones: soil nematodes, chemical, and biochemical properties

Data for soil nematode numbers, total microbial activity, microbial biomass carbon (C), and various soil chemical properties were collected from permanent and semi-permanent pastures at 108 locations in 2 contrasting environments: a summer rainfall zone in northern New South Wales (n = 60) and a winter rainfall zone in south-east South Australia and western Victoria (n = 48). Nematodes were also categorised according to their feeding habits and reproductive rates, and the abundance of various nematode groups was used to compute 3 indices that indicate the condition of the soil food web [enrichment index (EI), structure index (SI), and channel index (CI)]. At each location, pasture species herbage mass (kg DM/ha) was estimated and locations were grouped according to dominant species (lucerne, subterranean clover and phalaris in both rainfall zones; perennial ryegrass, winter rainfall zone only) as well as total soil microbial activity. The objective of the survey was to obtain a general indication of the biological status of soils used for pasture production in temperate regions of Australia, compare the soil biology in the 2 study areas, and determine whether it was influenced by pasture species composition. The most common plant-parasitic nematode was lesion nematode (Pratylenchus spp.), which was found at 67% of locations in the summer rainfall zone and 29% of those in the winter rainfall zone. Generally, there were more free-living nematodes in the soil than plant-parasitic nematodes. Numbers of free-living nematodes were highest in the winter rainfall zone, while in the summer rainfall zone there were more free-living nematodes in subterranean clover and phalaris pastures than lucerne pastures. Graphical representations of data for EI and SI indicated that the soil food webs at all sites in the summer rainfall zone were either structured or degraded. Food webs in the winter rainfall zone were more variable, with relatively high EI values indicating that more resources were available to support the soil biology. Climate had a major effect on CI values, with the mean in the winter rainfall zone being 28 (indicating a bacterial-dominant detritus food web) compared with 72 (indicating fungal dominance) in the summer rainfall zone. Mean total microbial activity was twice as high (2.6 v. 1.3 µg fluorescein diacetate/g.min) in soils from the winter than the summer rainfall zone. Mean levels of total organic C, total nitrogen, and labile C were also higher for the winter rainfall zone than the summer zone. For both rainfall zones, mean microbial biomass C was 0.09 mg/g soil, labile C was 9.05% of total organic C, and microbial biomass C was 3.5% of labile C. In the summer rainfall zone, values for all measured biochemical properties were lower in lucerne pastures than in other pasture types. We concluded that the biological status of soils in the winter rainfall zone was better than soils in the summer rainfall zone, and that the biology under lucerne pastures in the summer rainfall zone differed from pastures dominated by phalaris and subterranean clover. Soils in both study areas were generally healthy, as they had relatively high levels of total organic C and labile C, high numbers of free-living nematodes, high microbial activities, and a general lack of problems associated with plant-parasitic nematodes. However, there were exceptions, as there was considerable within-site variability for some biological and biochemical parameters at some sites.

Nitrogen availability and nematode populations in soil and litter after gap formation in a semi-natural beech-dominated forest

Small-scale spatial variation in N availability, substrate induced respiration (SIR) and population dynamics of nematodes in mineral soil and beech ( Fagus sylvatica L.) litter were studied along two transects through a newly formed gap and surrounding forest in a semi-natural mixed deciduous forest in Denmark for three years after gap formation. In the litter, C/N ratio dropped, while decomposition rates and numbers of nematodes were stimulated in the gap as compared to under closed canopy. In contrast, the number of nematodes in soil were inhibited in the gap for two years after gap formation, but gradually recovered in the third year. Recovery was most marked in the northern part of the gap centre where dense regeneration of ash ( Fraxinus excelsior L.) occurred. Omnivorous and predatory nematodes became more prevalent one year after gap formation. Effects on trophic groups of nematodes had disappeared by the end of the study period. The maturity index for nematodes was low one year after gap formation and was still lower in the gap than in the surrounding forest at the end of the study period. SIR in soil was lowest in the gap. Results thus indicate a stimulation of decomposers in the litter layer due to formation of the gap and a contrasting inhibition followed by recovery of decomposers in the soil, possibly governed by changes in C input from living roots. Soil C/N ratio, content of soil organic matter (SOM) and monthly nitrification and net N mineralization rates were not affected by a change in forest development phases caused by gap formation. However, seasonal trends and large spatial variation in net N mineralization and nitrification rates were apparent. Soil NH 4–N concentrations dropped markedly at the onset of the growing season in the second year and remained lower in the gap than in the closed forest throughout the growing season, possibly reflecting an increased N demand of the ash regeneration.

Cropping system impact on soil quality determinants

Worldwide interest in soil quality evaluation has increased rapidly throughout the past decade, prompting us to evaluate the long-term impact of four cropping systems on several biological, chemical and physical determinants of soil quality. We hypothesized that after 17 years several of the determinants would show significant differences between conventional cereal and low input/organic rotations. Four crop rotations were imposed on a silt soil from 1982 through 1999. Rotation A was a conventionally managed cereal rotation that received 100% of the recommended mineral fertilizer each year. Rotation B was also managed conventionally from 1982 until 1993, although it received only 50% of the recommended mineral fertilizer. From 1994 through 1999, rotation B was managed as an organic rotation. Rotations C and D were low-input rotations with plant residues returned either untreated (C)or composted (D)from 1982 until 1994.From 1994 through 1999,they were also anaged organically. Significant decreases in extractable phosphorus (P)and potassium were observed in rotations C and D compared with rotation A, presumably because their yearly nutrient inputs were somewhat lower. The amount of soil organic carbon (Corg), soil water holding capacity, the numbers and biomass of earthworms and the microbial biomass carbon and nitrogen were or tended to be higher in low input/organic than in conventionally managed plots. These effects may be in connection with the slightly increased levels of Corg in soil of the organic rotations. Activities of twelve enzymes were strongly affected by sampling time (early-versus late-summer), but much less by long-term management. Litter decomposition, numbers of soil nematodes, arbuscular mycorrhizal (AM)fungal diversity,AM spore density and AM functioning were little affected by rotation. However,AM spore density correlated positively with the high amounts of extractable calcium and P which were a result from excessive liming applied to some plots in 1982. The crucial question to be answered in future is whether plant growth and yield will correlate with the changes in soil properties. This question will be dealt with in a further paper using data from the same experiment.;

Growth of the Fungus Duddingtonia flagrans in Soil Surrounding Feces Deposited by Cattle or Sheep Fed the Fungus to Control Nematode Parasites

Abstract The results reported in this paper represent work from two separate experiments, namely a plot trial using cattle feces conducted at Kungsangen in Uppsala, Sweden and a plot trial using sheep feces undertaken at Tastrup in Copenhagen, Denmark. In both trials, a technique was used to monitor the level of Duddingtonia flagrans propagules in soil surrounding feces. The feces were from animals fed or not fed D. flagrans fungal chlamydospores. Also presented are the numbers of soil nematodes in soil surrounding sheep feces. The results indicate that D. flagrans has little growth beyond the fecal environment into surrounding soil when chlamydospores are fed to either sheep or cattle. This is substantiated by the soil nematode data. No statistical differences in the number of nematode taxa identified, Shannon Weiner H′, proportion of various feeding groups, and B/B + F (B and F are the proportions of bacterial and fungal-feeding nematodes) were found when soil surrounding sheep feces containing chlamydospores and parasitic nematode eggs was compared to soil surrounding feces containing parasitic nematode eggs alone. It is unlikely that the application of D. flagrans as a biological control agent against the free-living stages of nematode parasites of these livestock will negatively affect populations of nontarget soil nematodes.

Differential effect of nematicide treatments on tuber yields in early- and late-maturing potato cultivars

A 3-year field study examined the effects of 1,3-dichloropropene or oxamyl on tuber yields in four early- and five late-maturing potato cultivars. The nematicide treatments increased total tuber yield by ≈ 12% for early-maturing cultivars, but by less than 2% for the late-maturing cultivars. The treatments reduced the numbers of root lesion nematodes (primarily Pratylenchus penetrans), which were the dominant plant parasitic nematodes at the site. Covariance analysis indicated that treatment effects on total tuber yield were no longer significant after adjusting for root lesion nematodes in soil at harvest, confirming that these nematodes had a direct effect on the host. As expected, there were significant inverse relationships (P = 0·05) between total tuber yields and numbers of root lesion nematodes in soil and in roots. However, the application of nematicides in late-maturing cultivars was found to be of no practical value. Crop production systems designed to reduce or optimize pesticide applications can form one criterion in the development of more environmentally sensitive management strategies. The merit of utilizing chemicals for root lesion nematode control are considered with regard to cultivar maturity.

Responses of trophic groups of soil nematodes to residue application under conventional tillage and no-till regimes

A laboratory and a field study were conducted to monitor the increase in numbers and 14C uptake of different trophic groups of soil nematodes in response to residue addition and to examine the relative importance of bacterivorous and fungivorous nematodes in conventional (CT) and no-till (NT) agroecosystems. In general, soil nematode numbers increased more rapidly in response to residue addition and became much more abundant (greater than five-fold) under laboratory conditions than in the field. Our results showed that bacterivorous nematodes responded to residue addition earlier than fungivorous nematodes under both CT and NT regimes in the laboratory and field studies. A depth effect was observed in NT, but not in the CT treatment; this reflected the vertical residue distribution in both tillage regimes. Soil nematodes were more abundant under NT than under CT in the field. The same pattern was observed at the beginning of the laboratory study but it reversed later. The ratios of fungivorous-to-bacterivorous nematodes (FN-to-BN) were not significantly different between CT and NT treatments at the beginning of the experiment. They were very low (less than 0.2) in both tillage regimes, indicating that bacterivorous nematodes were relatively more important than fungivorous nematodes in both tillage agroecosystems. However, the FN-to-BN ratios increased with time after residue decomposition started, particularly in the CT treatment. This suggested that the relative importance of fungivorous nematodes increased with the progress of residue decomposition. It was more pronounced in the CT treatment during the short period after residue application. In both the laboratory and field studies, the 14C specific activity of soil nematodes and the ratio of 14C bound in nematode biomass to total 14C decayed in the experiment (reported elsewhere) were significantly higher under CT than under NT, suggesting that soil nematodes use carbon more efficiently under CT than under NT. No significant difference of 14C specific activity of soil nematodes was found between the two depths under CT in both the studies; however, 14C specific activity was significantly higher in the 0–2.5 cm than in the 2.5–5.0 cm layer under NT in the laboratory study.

Suppression of plant parasitic nematodes in pastoral soils amended with chitin

White clover and perennial ryegrass plants were grown in pots containing a sandy soil amended with chitin Soil nematode numbers were examined after 6 weeks of plant growth Amendment with chitin significantly reduced the abundance of Heterodera trifolii in white clover roots and Pratylenchus sp in perennial ryegrass roots Abundance of Paratrichodorus minor was significantly reduced by chitin amendment compared to unamended controls The total nematode fauna responded to chitin amendment with large increases in abundance

Application of the most probable number method to estimations of entomopathogenic nematode populations in soil

SummaryThe calculation of most probable numbers (mpn) was used for the estimation of numbers of infective entomopathogenic nematodes in soil. The mpn concept was first introduced in bacteriology as a means of estimating numbers of organisms in a substrate without a direct count, in cases where direct enumeration could not be applied. In the work reported here, soil samples infested with infective juveniles (IJs) of Heterorhabditis megidis (isolate HF85) were diluted with uninfested soil and the diluted soils were baited with mealworm larvae (Tenebrio molitor). The mpn of infective units of IJs in the undiluted soil was calculated. The mpn calculation was found to be applicable to entomopathogenic nematodes in soil under particular conditions. It could be successfully applied to data for the response of soil units but not to the data based on the response of individual insects, as the latter did not confirm to a Poisson series. The calculated mpn represented between 2.9 and 7.1% of the initial inoculum of IJs. It was suggested that IJs might act as a group in infecting an insect host. Using the data for Tenebrio mortality on parasitisation, the mpn based on quantal response of the mealworms would therefore not give the true density of IJs in the soil sample but the effective density, or the quantity of infective units. Although the biological significance of the infective unit needs further clarification, mpn was found to be a useful parameter for use in comparative experiments.