Nematode Population Densities Research Articles

Experimental modelling for phenotyping soybean host reaction to Aphelenchoides besseyi

Summary The nematode causing the green stem and foliar retention syndrome of soybean, Aphelenchoides besseyi, is a concern to Brazilian growers, especially in warm and humid climates, where losses can reach 60% of the yields. Management options have not yet been studied properly, but apparently genetic variability is found in soybean genotypes in the resistance to this nematode. However, the correct phenotyping of soybean genotypes is compromised by the scarcity of studies of this pathosystem. Therefore, the objective of this study was to evaluate the inoculum densities of A. besseyi and the plant ages at inoculation to obtain the correct phenotyping of soybean genotypes. Experiments were conducted under glasshouse conditions with the soybean ‘Elite’, using a completely randomised design and a factorial scheme (five nematode population densities: 150, 300, 600, 1200 and 2400 nematodes plant−1, and three plant ages at inoculation: 7, 12 and 17 days after planting). Evaluations were performed 35 days after inoculation, extracting nematodes from soil, roots and shoot parts of plants to obtain the final population of the nematodes of each replicate. The inoculum of 150-300 A. besseyi specimens per plant is the most suitable to assess the reaction of soybean genotypes to this nematode as it resulted in the greatest reproduction factors. Population densities higher than 1500 nematodes per plant could lead to misclassification of the host reaction because of the inconsistent reproduction factors obtained.

Soybean development under different Aphelenchoides besseyi and Meloidogyne incognita populations

The green stem Aphelenchoides besseyi and gall Meloidogyne incognita phytonematodes cause soybean yield losses. Thus, the objective of this study was to evaluate the effects of different populations of A. besseyi and M. incognita on soybeans. The experiment had 10 treatment groups [T1: control, T2: A. besseyi (500), T3: M. incognita (2,000), T4: A. besseyi (250) + M. incognita (2,000), T5: A. besseyi (500) + M. incognita (2,000), T6: A. besseyi (250) + M. incognita (4000), T7: A. besseyi (500) + M. incognita (4,000) individuals, T8: A. besseyi (250) + M. incognita (8,000), T9: A. besseyi (500) + M. incognita (5,000), and T10: A. besseyi (1,000) + M. incognita (8,000) individuals] with six replicates. Inoculations were done on day 10 after soybean germination, and evaluations were conducted after 60 d. Plant height, shoot fresh weight, root fresh weight, number of pods (NP), pod fresh weight, number of grains (NG), grain yield (GY), amount of A. besseyi in the shoot, and M. incognita in the roots were analyzed. The 500 A. besseyi + 8,000 M. incognita treatment reduced all variables and led to considerable damage to soybean development. In addition, GY, NG, and NP were reduced in the different nematode population density groups, influencing soybean agronomic characteristics.

Kök Lezyon Nematodlarının (Pratylenchus thornei (Sher et Allen) Pratylenchus neglectus (Rensch) Filipjev & Schuurmans Stekhoven (Tylenchida: Pratylenchidae) ve Soğan-sak Nematodu Ditylenchus dipsaci (Kühn, 1857) (Tyleneida) 'nın Nohut Yetiştirme Alanlarında Dikey Dağılımı

Investigation of the vertical distribution of three plant-parasitic nematodes was conducted in two southeastern (Şanlıurfa) and central Anatolia (Ankara) Turkey chickpea fields during 2015/2016 and 2016/2017 growing season. Twelve accessions of wild Cicer species representing three Cicer species (Cicer reticulatum L. and C. echinospermum L.) were used in the experiments for it. Soil samples were collected around the plant roots at a 10-20 cm and 20-30 cm depth by using an auger at each site. Maximum population densities of the root-lesion nematodes (Pratylenchus thornei (Sher et Allen) and (Pratylenchus neglectus (Rensch) Filipjev & Schuurmans) were observed at the depth of 20-30 cm, pod filling stage, and harvest time on most sampling. Also, the population density of root-lesion nematodes at the depths of 20-30 cm was observed as higher than Ditylenchus dipsaci (Kühn, 1857) (Tylenchida: Anguinidae) in the chickpea field. Population density of root-lesion nematodes was positively correlated with the contents of depth, site, time sampling, species chickpea, and there was determined significant difference between soil depth and population density of nematodes in both sites statistically.

Suppressive Effect of Soil Microbiomes Associated with Tropical Fruit Trees on Meloidogyne enterolobii.

Plant-parasitic nematodes are one of the main biotic factors limiting agricultural production worldwide, with root-knot nematodes (Meloidogyne spp.) being the most damaging group. This study was conducted to evaluate the efficacy of soil microbiomes, associated with various subtropical fruit trees, on the management of a Meloidogyne enterolobii population. Of 14 soil microbiomes tested for nematode suppression, 9 samples in the first experiment and 10 samples in the repeat experiment had significantly (p ≤ 0.05) lower numbers of eggs and J2 compared to the untreated control. The highest nematode suppression was recorded for SA12 extracted from a papaya orchard with a 38% reduction in the nematode population density. In addition, the presence of some bacteria (Bacillus aryabhattai, B. funiculus and B. simplex) and fungi (Metarhizium marquandii, Acremonium sp. and Mortierella sp.) was correlated to a higher suppression potential in some samples. Substantial variations were observed for the diversity of bacterial and fungal isolates among the samples collected from various crop hosts and regions. This suggests that the nematode suppression potential of different soil microbiomes highly depends on the abundance and diversity of fungal and bacterial strains present in the soil. The study confirmed that among all variables, soil dryness, pH, Fe, Zn, organic matter, altitude, and crop cultivar strongly influenced the soil microbial composition.

Evaluation of root-knot nematodes (Meloidogyne spp.) population density for disease resistance screening of tomato germplasm carrying the gene Mi-1

The root-knot nematode Meloidogyne spp. causes yield losses of up to 68% on tomato (Solanum lycopersicum L.) crops. Genetic resistance in the host plant makes the crop sustainable and it can breakdown when there is a high population density of the pathogen. The objective of this study was to determine the nematode population density that allow determining the resistance potential of tomato germplasm associated with the Mi-1 resistance gen. The Mi-1 gene was evaluated with the molecular marker SCAR Mi-23 and specific primers in the genotypes COLY007, IAC1687, LA0445, IAC1622 and two commercial controls (susceptible and resistant). The damage scale and the number of individuals recovered (eggs and juveniles) were assessed, with different population densities of the pathogen inoculated (0, 1000, 2000, 3000, 4000 and 5000 individuals plant-1), in a split plot design, with six replicates and a plant as the experimental unit. The genotype IAC1687 and the resistant commercial control presented the resistance allele of the Mi-1 gene and were classified as moderately resistant to a density of 1000 individuals plant-1. Despite having the Mi-1 gene, the COLY007 genotype was classified as moderately susceptible and with densities greater than 1000 individuals plant-1 can break resistance in all genotypes evaluated. Additionally, it is necessary to correlate the genotypic and phenotypic responses to guarantee the success of the selection supported by molecular markers such as SCAR Mi-23 and identify promising genotypes that could be included in a long-term breeding and also used as rootstocks in an integrated management of root-knot nematode.

Additional fertilizer and nematicide combinations on upland cotton to manage Rotylenchulus reniformis and Meloidogyne incognita in Alabama.

Plant parasitic nematodes are major pests on upland cotton worldwide and in the United States. The reniform nematode, Rotylenchulus reniformis and the southern root-knot nematode Meloidogyne incognita are some of the most damaging nematodes on cotton in the United States. Current management strategies focus on reducing nematode populations with nematicides. The objective of this research was to integrate additional fertilizer and nematicide combinations into current practices to establish economical nematode management strategies while promoting cotton yield and profit. Microplot and field trials were run to evaluate fertilizer and nematicide combinations applied at the pinhead square (PHS) and first bloom (FB) plant growth stages to reduce nematode population density and promote plant growth and yield. Cost efficiency was evaluated based on profit from lint yields and chemical input costs. Data combined from 2019 and 2020 suggested a nematicide seed treatment (ST) ST + (NH4)2SO4 + Vydate® C-LV + Max-In® Sulfur was the most effective in increasing seed cotton yields in the R. reniformis microplot trials. In R. reniformis field trials, a nematicide ST + (NH4)2SO4 + Vydate® C-LV at PHS supported the largest lint yield and profit per hectare at $1176. In M. incognita field trials, a nematicide ST + 28-0-0-5 + Vydate® C-LV + Max-In® Sulfur at PHS and FB supported the largest lint yields and profit per hectare at $784. These results suggest that combinations utilizing fertilizers and nematicides applied together across the season in addition to current fertility management show potential to promote yield and profit in R. reniformis and M. incognita infested cotton fields.

Interactive Effects of Filamentous Fungi and Cucurbitacin Phytonematicide on Growth of Cowpea and Suppression of Meloidogyne enterolobii.

Cowpea [(Vigna unguiculata (L.) Walp)] is highly susceptible to the emerging guava root-knot nematode, Meloidogyne enterolobii, with available management options being limited due to the withdrawal of effective fumigant nematicides from the agrochemical markets. Filamentous fungi, available as Biocult (a.i. Glomus species + Trichoderma asperellum Lieckf and Nirenberg) and Nemafric-BL phytonematicide (a.i. cucurbitacin B) each improves plant growth and suppresses nematode population densities. However, when filamentous fungi like Biocult are combined with other biocontrol agents, the combined effects either have synergestic or antagonistic effects on the test variables. The combined effects of Biocult and cucurbitacin phytonematicides on plant growth and nematode suppression remain undocumented. The objective of this study was therefore to determine the combined effects of Biocult and Nemafric-BL phytonematicide on growth of cowpea var. Eureka and suppression of M. enterolobii population densities. Eureka was subjected to the effects of the two products in a 2 × 2 factorial experiment on a field infested with M. enterolobii. At harvest, the interaction of Biocult and Nemafric-BL phytonematicide was highly significant (P ≤ 0.01) on plant and nematode variables, with a two-way table used to assess the findings. Relative to untreated control, Biocult alone increased plant growth variables from 15 to 74%. Similarly, NemafricBL phytonematicide increased plant variables from 14 to 61%, whereas the combined effects significantly increased dry shoot mass (19%) and dry harvestable leaf mass (21%), but did not have significant effects on plant height and stem diameter. Relative to untreated control, Biocult alone reduced nematode eggs in root (80%), J2 in root (84%) and J2 in soil (53%), whereas the combined relative effects of the two products did not have significant effects on nematode population densities. In conclusion, Biocult and Nemafric-BL phytonematicide had antagonistic effects on growth of cowpea and suppression of M. enterolobii population densities and therefore, should be used separately in cowpea production.

Biofertilizers in the control of Pratylenchus brachyurus in soybean crop

Nematodes are of great importance in soybean cultivation, especially the Pratylenchus brachyurus known as root lesion nematode. Its attack on plant roots causes less efficiency in the absorption of water and nutrients, in addition to damaging the plant's development. There is still no fully efficient method to control this phytopathogen, however, some products are available on the market, including biological control. Thus, the aim of this study was to evaluate commercial biological products in the efficiency of reducing the nematode population in soybean crop in Goiás, Brazil. The design was completely randomized in a 2x4 factorial scheme, the first factor being two soybean genotypes (Brasmax Bônus and Nidera NS 8383) and the second factor the treatments consisting of different dosages in an association of three commercial products: No-Estio®, Bio-fertility® and Radic®. The treatments used were: T1 control - without application of the products; T2 half the recommended dose; T3 the recommended dose and T4 a dose and a half that recommended by the manufacturer. Plant evaluation was carried out after 75 days of nematode inoculation. The results obtained showed that both cultivars hosted P. brachyurus, however, the treatments using the products had a lower population density of this nematode. It was concluded that the two soybean cultivars are hosts of Pratylenchus brachyurus. The agronomic character plant height was more affected when there was no application by the biological method. The association of No-Estio®, Bio-fertility® and Radic® products reduced the population density of nematodes in infected plants.

The Effects of Conservation Agriculture Practices on the Population Density of Fungivorous and Free-Living Nematodes in Different Crop Rotation Patterns

The Effects of Conservation Agriculture Practices on the Population Density of Fungivorous and Free-Living Nematodes in Different Crop Rotation Patterns

Plant-Parasitic and Free-Living Nematodes from Organically Farmed Fields in Illinois and Wisconsin

Plant-parasitic nematodes feed on soybean roots resulting in potential yield losses. Surveys of nematodes in certified organic soybean fields have been infrequent compared with surveys in nonorganic soybean fields. We conducted a nematode survey from certified organic soybean fields in northern and central Illinois and southern Wisconsin to determine the frequency and population densities of plant-parasitic and free-living nematodes. Fields surveyed included both long-term (with soybean planted every fifth year or longer in the rotation) and short-term (with soybean planted every third year in the rotation). A total of 27 composite soil samples, each consisting of multiple cores to a depth of 20 cm, were collected from 14 fields in 2019. Common plant-parasitic nematode taxa included spiral (Helicotylenchus spp.), lesion (Pratylenchus spp.), cyst (Heteroderidae), stunt (Tylenchorhynchus spp.), dagger (Xiphinema spp.), and pin nematodes (Paratylenchus spp.). Among the taxa, spiral, lesion, and dagger nematodes were above previously reported damage threshold levels in some fields. From the summer season–sampled soils, cyst nematode population densities and nematode abundance were significantly higher and lower, respectively, from fields under short-term versus long-term rotation with soybean. From the fall season–sampled soils, the structure index but not the other diversity and community indices of free-living nematodes were significantly higher from fields under long-term versus short-term rotation with soybean. Overall, these results provide evidence for the occurrence of plant-parasitic and free-living nematodes from organically farmed soybean fields in Illinois and Wisconsin that varied in rotation length.

Plant-parasitic nematodes in Nova Scotia vineyards

Plant-parasitic nematode populations were analyzed from composite soil samples collected from 62 vineyard blocks throughout Nova Scotia in 2018 and 2019. Nematode groups of potential concern that were found included ring nematodes (family Criconematidae), dagger nematodes (Xiphinema spp.), and root-knot nematodes (Meloidogyne spp.). Ring nematodes were overall the most widespread and abundant group of plant-parasitic nematodes, recovered from 79% of blocks with an overall average population density of 114 nematodes per 100 cm3 soil. Ring nematodes tended to be more abundant in older blocks. DNA sequence analyses of a subset of the ring nematode populations confirmed the presence of Mesocriconema xenoplax, which is the species known to be damaging to and most widely associated with grapevine globally. The analyses indicated that Criconema permistum was also present, notably in samples with the greatest ring nematode population densities. The results indicate that ring nematodes could be affecting the health of Nova Scotia vineyards, particularly in the future as populations continue to develop in relatively young vineyards and as older blocks are replanted. Additional research is needed to delineate the distribution of M. xenoplax vis-à-vis other species and to experimentally assess the host-parasite relationship between C. permistum and grapevine.

The main stages of development of agricultural nematology

Goal. Analyze the biological patterns underlying the principles of creating methods for monitoring and control of nematodes of field crops and woody plants, as well as the possibility of creating biological products based on EPN from local strains identified by the laboratory of nematology.
 Methods. Analysis of the results of laboratory developments for 30 years of research.
 Results. The high level of the number of parasitic species of nematodes (200—800 individuals in 100 cm3 of soil) has a significant impact on the growth, development and yield of the main field and flower ornamental crops. Losses can reach 35—55% of biomass (or ornamental) crops and 20—30% of the crop. Agrocenoses are more sensitive than natural coenoses to changes in the environment. Due to this, such agrotechnical measures as crop rotation, species and varietal composition of crops in crop rotation, fertilization system, tillage methods, etc. significantly affect the population density of parasitic nematodes, so they can be used to regulate their numbers. According to the results of laboratory tests in Ukraine, the pine wood nematode B. mucronatus was found, which is the cause of suppression and drying of Scots pine plantations. Methods for monitoring this new species of phytoparasitic nematodes have been developed. Long-term studies of the spread of entomopathogenic nematodes in Ukraine have made it possible to identify three species that quite densely (21.2% of the analyzed samples) inhabit the habitats of Ukraine, show high effectiveness against soil and other pests, so are promising for biopreparations based on entomopathogenic nematodes.
 Conclusions. The use of methods developed in the laboratory for monitoring and controlling the number of populations of phytopathogenic nematodes will keep the damage from this group of pathogens at a low level, preserving up to 20—30% of the crop, and prevent drying of coniferous forests from bursaphelenchosis.

Integrated management of Meloidogyne graminicola under basmati rice (Oryza sativa)-wheat (Triticum aestivum) cropping system

Survey conducted in and around village Bambawad, Gautam Budh Nagar, UP, for nematode population density infested basmati rice and wheat during 2015 indicated low population of rice root-knot nematode, Meloidogyne graminicola in IPM adopted fields compared with farmer's practices (FP). With this view, the study was carried out to manage M. graminicola under basmati rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system taking advantage of IPM technology developed and validated by ICAR-NCIPM for basmati rice during 2016-19 with some modifications such as soil solarisation, bio-agents etc. Soil solarisation of nursery beds reduced population density of test nematode up to 93.4%, whereas an increase of up to 46% in FP compared to initial population. Analysis of root and soil samples of both rice and wheat crop from IPM fields showed either no visible galling or only 1-3% root galling severity (RGS) and significantly (P>0.05) low population density compared to FP. In addition, the population of beneficial soil nematodes (BSN) remained high and significantly (P>0.05) higher in IPM as compared to FP with student's t-test. Role of BSN in increasing the nutrient availability through organic matter decomposition has already been established. It is evident from the study that IPM technology might have played important role in antagonising the M. graminicola and increased the density of BSN. This technologycould be a safe and eco-friendly alternative to manage M. graminicola below ETL. Also, it has helped in sustaining IPM by the way of saving on the cost of application of pesticides and enhancing the benefit-cost ratio.

Experiments on dialog models of prognosis of the population density of Globodera rostochiensis in soil at different types of crop rotation

On predictive dialogue models, computer experiments were carried out to obtain data on the dynamics of population density of golden potato nematode in the soil after growing susceptible potato varieties, globoder-resistant potato varieties and unaffected plants in a 10-field crop rotation. When carrying out computer experiments on the model for predicting the population density of golden potato nematode in the soil after growing globoder resistant potato varieties in a 10-field crop rotation, it was found that when growing these varieties, it will take 8-9 years to completely destroy golden potato nematode population in the soil under favorable or average long-term conditions growing potatoes and other crops. Under unfavorable growing conditions for agricultural crops and globoder resistant potato varieties, the larvae of the ZKN remain in the soil for more than 10 years. In addition to predicting the population density of golden potato nematode after growing unaffected crops and potato varieties of varying degrees of resistance to nematode Globodera rostochiensis, computer models make it possible to theoretically substantiate optimal fruit changes and crop rotations, which will make it possible to effectively clear fields from phytoparasite.

Impact of the genetic diversity of three cyst nematodes on the effectiveness of root exudates to induce hatching

Cyst nematodes are sedentary endoparasites of plants which cause important economic losses worldwide. New nematode control measures are needed since the removal of effective chemical nematicides from the market due to their negative impact on environment and human health. Induced hatching of second-stage juveniles in the absence of host plant using root exudates, also named “suicide hatching”, could be a sustainable alternative method to reduce nematode population densities in infested soils. Unfortunately, biocontrol methods are often less effective in agricultural fields than in laboratory or greenhouse and this could be due to, among other reasons, a different susceptibility of nematode populations to root exudate stimulation. Testing this intra-specific variability would help to anticipate any drop in the efficiency of this new biocontrol strategy. A selection of root exudates from different plant species, maximizing the hatching level highlighted in a previous study, was tested on the hatching of representative populations of the genetic diversity for Globodera pallida, Heterodera schachtii and Heterodera carotae. Results showed significant differences between populations for given nematode species but not correlated with the genetic structure. Overall, root exudates tested provide a high level of hatching of these three nematode species. Surprisingly, the root exudate from broccoli induces hatching of European populations of the potato cyst nematode G. pallida.

Nematode pests of some major cereals in Nigeria: Need for integration of morphological/morphometrical, biochemical, and molecular diagnostic approaches for accurate identification

AbstractPlant‐parasitic nematodes pose a major threat to crop production in Nigeria. Comprehensive data on yield losses for most cereal crops are not readily available. Research on maize (Zea mays), rice (Oryza sativa), and sorghum (Sorghum bicolor) has shown an 18%–67% reduction in yield linked to the destructiveness of parasitic nematodes, particularly root‐knot and root‐lesion nematodes. Continuous monoculture and a conservative approach to agriculture increase the incidence and population density of nematodes, leading to higher levels of damage and losses in most cultivated cereal crops. These losses affect the food security of the growing population of Nigeria and many African countries that are heavily dependent on cereals. The accurate identification of nematodes is fundamental for effective management strategies. Nematode taxonomy based on morphology has been difficult due to intraspecific character variations coupled with the limited expertise of indigenous nematologists. Biochemical and molecular marker‐based tools and approaches have allowed efficient diagnosis of most nematode species affecting cereal production globally. These approaches have proved useful due to their practicality, rapidness, accuracy, and cost‐effectiveness. This review describes the important economic effects of these parasitic nematodes on cereal production and highlights the need for integrative approaches to taxonomy for accurate species identification that will improve nematode diagnosis, thereby contributing to the increase of food production in Nigeria.

Nematode resistance technologies for managing thermophilic Meloidogyne species on potato (Solanum tuberosum): A review

Commercially available potato (Solanum tuberosum) cultivars are highly susceptible to root-knot (Meloidogyne species) nematodes, without known genotype with resistance to the genus. This review shall provide an overview on some reasons where using nematode resistance technologies in crop rotations intended to manage nematode population densities results in inconsistent outcomes. The latter is primarily due to the existence of survival strategies in nematode stages and the existence of pre-and post-infectional nematode resistance mechanisms with different capabilities for reducing nematode population densities. Generally, plants with pre-infectional nematode resistance do not allow nematode juveniles to penetrate the root systems, but exude chemicals into the rhizosphere, which repel nematodes, with many entering cryptobiosis as a survival strategy. In contrast, in post-infectional nematode resistance, juveniles penetrate the root system, thereby triggering nematode resistance chemicals, which trap and kill nematodes. Between the two, post-infectional nematode resistance mechanism is well-suited for reducing nematode population densities from the soil for the successful production of nematode susceptible potato cultivars as successor crops in crop rotation systems.

Non-phytotoxic concentration of cucurbitacin containing phytonematicides on Swiss chard (Beta vulgaris var. Cicla) under greenhouse conditions

The cucurbitacin containing phytonematicides have possibility to be developed as an alternative to withdraw synthetic chemical nematicides, with sensitivities to crops that are plant-species specific. Although, the products have been tested on other Beta species, their sensitivities on Swiss chard (cicla) remain undocumented, necessitating such tests since the plant is highly susceptible to root-knot (Meloidogyne species) nematodes. Therefore, a study was conducted during 208-19 at Green Biotechnologies Research Centre of Excellence (GBRCE), University of Limpopo, South Africa with an objective of the study being to determine the non-phytotoxic concentration of Nemarioc-AL and Nemafric-BL phytonematicides for use on Swiss chard in managing population densities of M. incognita under greenhouse conditions. Seedlings were inoculated with 3000 eggs and second-stage juveniles (J2) of M. incognita and subjected to weekly geometric concentration of the two phytonematicides in separate experiments. At 56 days after inoculation, plant variables against increasing concentration of the products exhibited positive quadratic relations, whereas nematode population densities and the products exhibited negative quadratic relations. In conclusion, Nemarioc-AL and Nemafric-BL phytonematicides can be used in managing population densities of M. incognita on Swiss chard.

Population density of free-living nematodes and their relationships with some soil physicochemical properties in forest and agriculture soils of Gapa Valley Chalt, Gilgit, Pakistan

The present study was conducted in Gapa Valley, Chalt, Gilgit-Baltistan, Pakistan to check the relationship of free-living nematodes in association with soil physicochemical properties. Soil samples from five random sites of pine and potato fields were collected. From each site three composite soil samples were collected, one to determine soil bulk density while two to determine the physicochemical parameters and diversity of free-living nematodes. The nematodes were extracted using modified Baermann’s funnel method and the count showed that the population density of free-living nematodes was generally lower in the pine forest than potato fields. About 156 nematodes belonging to 15 families were recorded in the potato field and 39 nematodes belong to 18 families were recorded in pine forests. Moreover, remarkable differences in physiochemical properties viz., SMC (Soil moisture Content), EC (Electrical conductivity), pH, temperature, soil texture, BD (Bulk density), was found between the pine forest and potato fields. The soil of pine forest was highly acidic with pH 5.90 while the soil of potato fields was near to neutral with pH 6.53. Moreover, temperature, EC and SMC of potato fields were higher than that of pine forests. Additionally, the soil texture of potato fields was silty and sandy loamy soil whereas the soil texture of pine forest was silty but with a high amount of silt content. Finally, Pearson’s correlation showed significant positive and negative correlations between some of the soil physicochemical parameters and nematode population. Keywords: Free-living nematodes; Physiochemical; Population density; Correlation http://dx.doi.org/10.19045/bspab.2021.100050

Occurrence and Seasonal Changes in the Population of Root-knot Nematodes on Honeybush (Cyclopia Sp.).

SummaryRoot-knot nematodes in the genus Meloidogyne are an important group of plant-parasitic nematodes causing severe damage on agricultural crops worldwide. A study was conducted to identify the species of root-knot nematodes causing damage on honeybush monocultures and to assess the seasonal variations in the nematode population. Soil samples were collected from six experimental sites in Genadendal, Western Cape province of South Africa from 2016 to 2017. DNA was extracted from single-second stage juveniles and species identifi cation was done using species-specifi c sequence-characterised amplifi ed regions (SCAR) primers. Meloidogyne hapla and M. javanica were identifi ed from the sites. Mean population density of the nematodes varied significantly (p < 0.05) in the six sites, with the peak population being recorded in summer of 2017. The study suggests that seasonal variation in temperature and moisture could contribute to changes in the population density of root-knot nematodes in the soil.