Evaluation of Preplant Seed Protectants for the Management of Root-Knot Nematode of Okra in Ghana

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Introduction
Te production of quality okra seeds and maximum yield largely depend on the healthy root system and growth parameters of the okra plant.Damage caused by plant-parasitic nematodes (PPNs) is one of the greatest factors that reduce the optimum yield and quality of seeds in Ghana.Plantparasitic nematodes normally produce symptoms on aboveground plant parts which are presumed to be a nutrient or water defciency or a disease.Nematode infestations on plants therefore go unnoticed by farmers, which results in crop losses with negative impacts on the economy.Nematode parasitism on plants results in stunted growth and chlorosis and this is heightened in instances of increased moisture stress and temperature [1].However, these symptoms can be confused with symptoms from abiotic infections.Most farmers involved in okra cultivation are into the monocropping system [2], which enhances the rapid buildup of root-knot nematode population densities in these soils.
Efective management of plant-parasitic nematodes will involve the use of integrated management approaches.Methods currently utilized in nematode management include cultural, nematicide application, and physical methods; however, there are some limitations to these approaches [3].
Te need for the use of environmentally sustainable control methods such as seed treatments will enhance efective nematode management.Tese seed treatment methods can easily be used by farmers.Te active ingredients (AI) in these seed protectants limit the buildup of plant-parasitic nematode populations.Tese protectants provide room for multiple treatment applications (i.e., fungicides, nematicides, and insecticides) to the same seed [4].Kesba et al. [5] compared the efects of aqueous and ethanolic extracts from solidago and periwinkle on Meloidogyne incognita J2.Te aqueous extracts caused a higher mortality rate, and the periwinkle extracts showed a greater inhibition of egg hatching relative to solidago extracts.In another study involving plant seed oils (canola, cotton, fax, olive, soybean, and sesame), against root-knot nematode in tomatoes, sesame oil had the least efcacy potential in reducing nematode populations in tomatoes and tomato shoot lengths were also reduced [6].Other studies conducted have revealed some variations in relation to the efectiveness of the seed treatments on nematode population reduction, as a consequence of prevailing soil and environmental conditions, as well as chemical concentrations [7][8][9].Further studies are needed to understand the relationships between nematode population densities and the efectiveness of nematode-protectant seed treatments [10].Terefore, there is an urgent need to investigate the efcacy of new biological and plant extracts for root-knot nematode management in okra.Tis study assessed the efcacy of biological seed protectants on the growth and establishment of okra plants and root-knot nematode population reduction in soils planted to okra.

Study Sites.
Te study was conducted between January 2020 and August 2021.Laboratory experiments took place at the Ghana Seed Inspection Division's (GSID) Seed Testing Laboratory (latitude 5 °42′ 0″ north and longitude 0 °18′ 7.2″) and the Plant Pathology Laboratory at the University of Ghana, located in Accra (latitude 5 °39′ 1.79″ north and longitude 0 °11′ 7.80″ east).Fieldwork was carried out at the University of Ghana farm and the Ghana Atomic Energy vegetable growers' farm, both situated in the Greater Accra Region.
Te materials used in this study were obtained from various sources: the okra variety (Legon Finger) was acquired from the Crop Physiology Laboratory at the University of Ghana, the nematicide Velum (fuopyram SC 400 G) was obtained from Bayer West and Central Africa Limited, and the sesame seed extract, neem seed extract, and orange peel oil were acquired from Brimkata Enterprise (B.K Naturals) (Table 1).Petri dishes for the seed germination test were obtained from GSID.

Methodology.
Te study involved two experimental setups.Experiment one was conducted in a laboratory to evaluate the efect of biological seed protectants on the germination and vigor of okra seeds.Experiment two (feldwork at two separate locations) was conducted from August to November 2020 at the University of Ghana farm and from March to June 2021 at the Ghana Atomic Energy vegetable growers' farm.

Laboratory Experiment.
Okra seeds were coated with 40% sesame oil, 50% neem oil, 100% citrus oil, velum at 3.8 ml/7L of water, and a control (seeds were soaked in sterile distilled water) at diferent time intervals of 30 min, 60 min, 90 min, and 120 min to determine the germination percentage and vigor.Te coating was done by immersing the seeds in the various oils and nematicide for the defned time intervals, and then, the seeds were removed and dried before sowing.Te experimental setup was laid out in a completely randomized design (CRD) with three replications using a Jacobson table for the germination test.In a laboratory experiment, the following data were collected.Te percentage of germination was calculated by dividing the number of seeds that sprouted by the total number of seeds planted and then multiplying the result by 100: where NSG is the number of seeds germinated and TNSP is the total number of seeds planted [11,12].
where MRL is the mean root length, MSL is the mean shoot length, and PSG is the percentage of seed germination [13].
Root and shoot lengths were measured using a meter rule.

Field Experiment.
Te farms were ploughed to loosen the soil, and the feld layouts were performed with pegs and lines as well as a tape measure.Te total feld size was 34.1 m × 51.5 m.Each plot size was 3.2 m × 2.5 m with a 1 m alley left between plots.
Tere were nine treatments in total (4 treatments for seed coating prior to sowing for 30 min and 4 treatments for drenching 2 weeks after sowing and one control).Te drenching was performed by making a hole (drench) around the base of the plant and pouring the chemical in and covering it.Treatments were laid out in a randomized complete blocked design (RCBD) with four replications.Te various treatments used are as follows: T1 � sesame oil at 40% as seed coating for 30 min prior to sowing T2 � sesame oil at 40% as drenching two weeks after germination T3 � neem oil at 50% as seed coating for 30 min prior to sowing T4 � neem oil at 50% as drenching two weeks after germination T5 � citrus oil at 100% as seed coating for 30 min prior to sowing T6 � citrus oil at 100% as drenching two weeks after germination 2 International Journal of Agronomy T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination.T9 � control (no application)

Sowing and Treatment Application for Both Farms.
Okra seeds for T1, T3, T5, and T7 were coated with 40% sesame oil, 50% neem oil, 100% citrus oil, and velum at 3.8 ml/1L for 30 minutes and then dried for 5 minutes.Seeds for T2, T4, T6, T8, and T9 were sown without coating.Seeds were picked and sown with a pair of forceps after drying.Drenching was performed two weeks after sowing seeds for T2, T4, T6, and T8 at 100 ml/plant each of 40% sesame oil, 50% neem oil, 100% citrus oil, and velum at 9.8 ml/15L.Te planting distance was 80 cm × 50 cm within and between rows, with each plot containing 20 plants and a total population of 720 plants.

Cultural Practices for Both Farms.
Handpicking and occasional use of a hoe were the main methods for controlling less dense weeds, with no weedicides applied.Daily watering was performed using watering cans.At 4 weeks after planting, the entire feld received 0.5 t/ha of fertilizer N : P : K 15 : 15 : 15.Insects on the feld were managed by spraying Orizon.

Nematode Extraction and Counting for Both Farms.
Nematode extraction and count were performed in the Plant Pathology Laboratory of the Department of Crop Science, University of Ghana, Legon.Nematode populations were determined before sowing and after harvesting at 13 weeks.Nematode extraction was undertaken using the sieving and sucrose-centrifugation method [15].
Sucrose solution was prepared by adding deionized water to 454 g of sugar to bring the volume to 1 liter and stirred until completely dissolved.
200 cc soil sample after rocks and roots were removed was packed lightly into a beaker for uniformity.Soil samples were placed in a bucket and covered with water twice its volume, vigorously mixed for complete dispersion, and allowed to settle for 5 minutes.Clayey soil samples were left to settle for 7 minutes.Tree laboratory test sieves with diferent apertures were used: 90 μm, 71 μm, and 36 μm.Te sieves were nested onto each other in the order listed and the supernatant was carefully poured through the sieves.Te 90 and 71 μm sieves trapped the soil particles while the 36 μm trapped both nematodes and nematode eggs.Using the fne spray wash bottle, samples trapped on the 36 μm mesh sieve were washed into centrifuge tubes at equal volumes (where necessary, water was added to equalize volumes in centrifuge tubes).Tubes were placed in balanced pairs in the centrifuge and spun at 1700 rpm for 5 minutes and then allowed to settle for 5 minutes.Supernatants were aspirated to about 1 cm above the pellets.Te tubes were flled with sucrose solution to cover the pellets after which a spatula was used to stir to break the pellets until complete dispersion.Samples were spun at 1000 rpm for 1 minute.Nematodes and clay were suspended in the sucrose supernatant.Te supernatant was then sieved out through the 36 μm sieve to trap the nematodes and then transferred into the labeled vials using a fne spray water bottle.A Hand tally counter was used to keep track of each nematode counted within the liquid under the compound microscope.

Nematode Reproductive Factors.
Te reproductive factor (an indicator of the suitability of a host plant for nematodes) of the nematodes was determined using Oostenbrink's reproduction factor (RF) [16], which was calculated as follows: RF � (Pf )/(Pi), where Pf is the fnal nematode population and Pi is the initial nematode population.
2.9.Nematode Identifcation.Nematodes were identifed only at the genera level.Tey were identifed based on their morphological features (length of stylet, head region, stylet knob, intestine thickness, and tail shape of adult nematodes) as described by Luc et al. [17] and Siddiqi and Alam [18] and the website of the University of Nebraska-Lincoln for nematode identifcation (https://nematode.uml.edu/konzlistbutt.htm).Nematode contents in plastic vials were separately emptied gently into 50 mm round plastic counting Petri dishes internally calibrated with 2 mm × 2 mm blue grid lines.Tese lines served as a guide for systematic analysis of nematodes across the liquid.Nematodes were sucked using a small syringe and transferred to another counting dish where selected nematodes for identifcation were mounted on a drop of water on a microscopic slide and placed on a 60 °C hot plate briskly to allow nematode to straighten for identifcation [19].Te compound light microscope with a magnifcation of 400x, manufactured by Optec Optical Technology, was used for nematode identifcation.

Data Collected on Plant Parameters for Both Farms.
Data were collected on six record plants on each plot and the mean number of each plot was determined for each treatment (Table 2).International Journal of Agronomy 2.11.Data Analysis.Data collected were subjected to analysis of variance (ANOVA) using GenStat Statistical Package Edition 12, and means were separated using LSD at 5% where signifcant diferences existed.

Efect of Duration of Coating of Biological Seed Protectants on Seed Germination and
Vigor.Okra seeds were treated with diferent biological seed protectant's (citrus oil, sesame oil, neem oil, velum, and control), and their germination percentages and vigor indices were evaluated at 30 min, 60 min, 90 min, and 120 min intervals.Tere were signifcant diferences (P < 0.05) across all four diferent time intervals that were assessed for each of the fve treatments (Figures 1 and 2).Tere was a general decrease in germination percentages for all treatments as the time for seed treatment increased from 30 min to 60 min, with the exception of the control (Figure 1).Sesame oil had the least germination rates for the four time points and showed a sharp decrease (64% to 3%), as the soaking time increased from 30 min to 120 min.Te germination percentage of the control however increased gradually over the time points (64% to 80%).At 30 min, velum and citrus oil had the highest germination percentage (90% and 80%), respectively.Tere was a general decrease in seedling vigor for neem (994 to 343) and sesame (610 to 7) oils, for the time points 30 min and 120 min, respectively (Figure 2).Sesame oil therefore had the least seedling vigor among the four treatments.Te control had a gradual increase in seedling vigor (899 to 1036) for the time points 30 min and 120 min, respectively.

Biological Seed Protectants on Okra Growth and
Establishment (University of Ghana Farm)

Efect of Treatments on the Height of Okra Plants.
Plant height increased as the plants aged over 5-11 weeks.Treatment 9 (control) had the tallest plants of 19 cm, 69 cm, and 71.4 cm for weeks 5, 8, and 11, respectively (Figure 3).Treatment 8 (velum at 9.8 ml/15L of water as drenching two weeks after germination) had the shortest plants.Te treatments did not show any signifcant diferences in plant height for the specifc weeks.

Mean Efect of the Treatments on the Number of Leaves on Okra.
Over the course of weeks 5 to 11, there was a noticeable increase in the number of leaves as the plants matured.Specifcally, treatments 6, 5, and 2 exhibited the most robust leaf growth at weeks 5 (47 leaves), 8 (110 leaves), and 11 (127 leaves), respectively.Conversely, treatment 8 displayed the lowest leaf count at week 8, while treatment 1 consistently had the least number of leaves at both weeks 5 and 11.Te diference between the treatments with a higher number of leaves and those with a lower number of leaves was only signifcant (P < 0.05) at week 11.Tere were no signifcant diferences (P > 0.05) between any of the treatments either at week 5 or week 8.

Mean Efect of Treatments on the Number of Fruits and
Weight of Fruits at Two Weekly Intervals.Treatment 9 had the highest fruit count (20) during week 1, which is signifcantly diferent from treatments 6 and 7 with the lowest counts (12) (P < 0.05) (Table 3).However, within week 2, treatment 6 had the most fruits (35), followed by treatment 1 (34), and treatment 8 had the least (27); however, there were no signifcant diferences among the treatments (P > 0.05).
Regarding fruit weight, treatment 9 had the highest weight (0.7 kg/ha) during the harvest in week 1, which is signifcantly diferent from treatment 6 with the lowest Figure 1: Germination percentage (%) of treatments at four time intervals.T1 � sesame at 40% as seed coating for 30 min prior to sowing, T2 � sesame at 40% as drenching two weeks after germination, T3 � neem at 50% as seed coating for 30 min prior to sowing, T4 � neem at 50% as drenching two weeks after germination, T5 � citrus at 100% as seed coating for 30 min prior to sowing, T6 � citrus at 100% as drenching two weeks after germination, T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing, T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination, and T9 � control (no application).Figure 2: Seedling vigor index for treatments at four time intervals.T1 � sesame at 40% as seed coating for 30 min prior to sowing, T2 � sesame at 40% as drenching two weeks after germination, T3 � neem at 50% as seed coating for 30 min prior to sowing, T4 � neem at 50% as drenching two weeks after germination, T5 � citrus at 100% as seed coating for 30 min prior to sowing, T6 � citrus at 100% as drenching two weeks after germination, T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing, T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination, and T9 � control (no application).
International Journal of Agronomy weight (0.4 kg/ha) (P < 0.07) (Table 3).Treatments 1 and 9 had the highest fruit weights (1.2 kg/ha), while treatment 8 had the lowest fruit weight (0.9 kg/ha) in week 2 of the harvest.However, there were no signifcant diferences observed among the treatments (P > 0.05).

Mean Efect of Treatments on Fresh and Dry Shoot
Weights and Fresh and Dry Root Weights.Tere were no signifcant diferences (P > 0.05) among the treatments for fresh and dry shoots and root weights (Table 4).

Mean Efect of Biological Seed Protectants on Nematode
Populations.Signifcant diferences (P < 0.05) existed among the treatments in relation to nematode population reduction percentages (Table 5).Te treatment with the least nematode reduction percentage was T9.Tis is also refected in the high RF value of 0.9.However, there were no signifcant diferences (P < 0.05) among the other treatments.Nematode RF values ranged from 0.1 to 0.4 for treatments (T1 and T3), respectively.T1 � sesame at 40% as seed coating for 30 min prior to sowing, T2 � sesame at 40% as drenching two weeks after germination, T3 � neem at 50% as seed coating for 30 min prior to sowing, T4 � neem at 50% as drenching two weeks after germination, T5 � citrus at 100% as seed coating for 30 min prior to sowing, T6 � citrus at 100% as drenching two weeks after germination, T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing, T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination, and T9 � control (no application).Means followed by the same letters in a column are not signifcantly diferent at LSD (P < 0.05).T1 � sesame at 40% as seed coating for 30 min prior to sowing; T2 � sesame at 40% as drenching two weeks after germination; T3 � neem at 50% as seed coating for 30 min prior to sowing; T4 � neem at 50% as drenching two weeks after germination; T5 � citrus at 100% as seed coating for 30 min prior to sowing; T6 � citrus at 100% as drenching two weeks after germination; T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing; T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination; T9 � control (no application).

Results from the Ghana Atomic Energy Vegetable
6 International Journal of Agronomy weeks 5, 8, and 11, respectively, which was also the case at the University of Ghana farm.A signifcant diference was observed between treatments 9 and 8 as okra plants aged from weeks 8 to 11.

Efect of Treatments on the Number of Leaves on Okra
Plants.At week 5, treatment 7 had the highest number of leaves (47), followed by treatments 5 (46) and 6 (46), while treatment 1 had the least number of leaves (41).At week 8, treatments 2 and 8 obtained the highest (107) and lowest (81) number of leaves, respectively, and the diference between these two treatments was signifcant (P < 0.05).Treatment 5 had a signifcantly (P < 0.05) higher number of leaves (128) than treatment 1, which had the lowest number of leaves (106) at week 11.consistently had the largest girths in both farms and at weeks 5 and 8, respectively.Both at week 5 and week 8, treatments with the highest and lowest plant girths were signifcantly diferent (P < 0.05).

Mean Efect of Treatments on Chlorophyll Content at
Weeks 5 and 8. Tere were signifcant diferences (P < 0.05) among the treatments for chlorophyll content for weeks 5 and 8 (Table 6).Treatment 1 (sesame at 40% as seed coating for 30 minutes prior to sowing) had the highest chlorophyll content of 51.83 CCI at week 5, with treatment 2 having the highest chlorophyll content at week 8 (60.0 CCI).Treatment 9 had the lowest chlorophyll content, measuring 36.2CCI and 37.2 CCI at weeks 5 and 8, respectively.

Mean Efect of Treatments on the Number of Fruits and
Weight of Fruits at Two Weekly Intervals.Tere were no signifcant diferences (P > 0.05) among the diferent treatments for the number of fruits and fruits harvested.Treatment 2 (sesame at 40%, applied as a drench two weeks after germination) had the most fruits ( 17) during the Means followed by the same letters in a column are not signifcantly diferent at LSD (P < 0.05).T1 � sesame at 40% as seed coating for 30 min prior to sowing; T2 � sesame at 40% as drenching two weeks after germination; T3 � neem at 50% as seed coating for 30 min prior to sowing; T4 � neem at 50% as drenching two weeks after germination; T5 � citrus at 100% as seed coating for 30 min prior to sowing; T6 � citrus at 100% as drenching two weeks after germination; T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing; T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination; T9 � control (no application).T1 � sesame at 40% as seed coating for 30 min prior to sowing; T2 � sesame at 40% as drenching two weeks after germination; T3 � neem at 50% as seed coating for 30 min prior to sowing; T4 � neem at 50% as drenching two weeks after germination; T5 � citrus at 100% as seed coating for 30 min prior to sowing; T6 � citrus at 100% as drenching two weeks after germination; T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing; T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination; T9 � control (no application).
International Journal of Agronomy harvest in week 1 (Table 7).On the other hand, treatments 6, 7, and 9 had the least number of fruits (12 each).Te harvest in week 2 showed treatment 6 (citrus at 100%, applied as a drench two weeks after germination) with the most fruits (35), while treatment 9 had the least fruits (28).

Mean Efect of Treatments on Fresh and Dry Shoot
Weights and Fresh and Dry Root Weights.Tere were no signifcant diferences (P > 0.05) among the treatments for fresh and dry shoots and root weights (Table 8).

Discussion
In a previous study by Oyekale et al. [20], natural botanicals such as sesame, neem, and citrus extracts were utilized as short-and medium-term storage treatments for seeds and these gave the highest germination and vigor percentages.Te germination % and vigor index of all treatments varied signifcantly; however, the 30-minute seed treatment was the most efective.Other investigators, such as Hoque et al. [21], Ashraf et al. [22], and Lawan et al. [23], have indicated that there are specifc weeds and plant species which contain secondary plant products with allelopathic potentials, infuencing a decrease in seed germination and growth.
Seed treatment with biocontrol agents ofers an efective approach for introducing benefcial organisms into the soilroot environment.Tis method protects the seed from both seed and soilborne pathogens, such as plant-parasitic nematodes, enabling successful germination and healthy seedling establishment [24].
Te current study demonstrates that the use of biological protectants leads to improved plant growth, e.g., plant height, compared to synthetic protectants used as controls.In a previous study, biological protectants provided superior protection against root-knot nematodes and improvement in plant establishment [20].
Kumar and Khanna [25] have also observed the suppressive efects of neem extract, a natural protectant, on nematode multiplication and root galling severity, leading to enhanced plant growth in tomatoes.Investigations reveal that soil amendments with aqueous and powdered citrus peel extracts not only show the absence of phytotoxicity to cowpea plants but also exhibit nematicidal properties, thus improving the growth and yield of cowpea plants.Other reports have also confrmed growth improvements in plants [26,27].Seed treatment with biocontrol agents, such as neem extract and citrus-based compounds, proves to be a promising approach for enhancing plant growth by reducing nematode populations and providing protection against harmful pathogens [24].Tese natural protectants ofer signifcant advantages over synthetic alternatives and contribute to the establishment of healthy and thriving crops [20,[25][26][27].T1 � sesame at 40% as seed coating for 30 min prior to sowing, T2 � sesame at 40% as drenching two weeks after germination, T3 � neem at 50% as seed coating for 30 min prior to sowing, T4 � neem at 50% as drenching two weeks after germination, T5 � citrus at 100% as seed coating for 30 min prior to sowing, T6 � citrus at 100% as drenching two weeks after germination, T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing, T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination, and T9 � control (no application).8 International Journal of Agronomy Other investigators have indicated the usefulness of neem applied as a biocontrol formulation against plantparasitic nematodes [28,29].In the current study, neem applied at a concentration of 50% as seed coating for 30 min prior to sowing (T3) had a high efcacy of percent nematode reduction.Neem releases phenols, amino acids, aldehydes, and fatty acids that are hostile to root-knot nematodes [30].Metabolites produced by neem's chemical ingredients  Means followed by the same letters in a column are not signifcantly diferent at LSD (P < 0.05).T1 � sesame at 40% as seed coating for 30 min prior to sowing; T2 � sesame at 40% as drenching two weeks after germination; T3 � neem at 50% as seed coating for 30 minutes prior to sowing; T4 � neem at 50% as drenching two weeks after germination; T5 � citrus at 100% as seed coating for 30 min prior to sowing; T6 � citrus at 100% as drenching two weeks after germination; T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing; T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination; T9 � control (no application).Means followed by the same letters in a column are not signifcantly diferent at LSD (P < 0.05) T1 � sesame at 40% as seed coating for 30 min prior to sowing; T2 � sesame at 40% as drenching two weeks after germination; T3 � neem at 50% as seed coating for 30 min prior to sowing; T4 � neem at 50% as drenching two weeks after germination; T5 � citrus at 100% as seed coating for 30 min prior to sowing; T6 � citrus at 100% as drenching two weeks after germination; T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing; T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination; T9 � control (no application).
International Journal of Agronomy (azadirachtin, salannin, limonoids, triterpenoids, phenolic compounds, carotenoids, steroids, and ketones) drive plant cells to produce aberrant metabolites that deter nematodes from infecting plant roots [31].Studies have shown bioactive extracts including saponins, favonoids, sterols, and alkaloids are poisonous to pathogenic nematodes and inhibit their activities [27].In addition, citrus oil contains limonene viz.limonene tetrabromide, carvone, and monoterpenes such as a-terpineol, linalyl acetate, linalool, and limonene [32,33].Tese oils pose the potential to limit fungal growth [31] and nematicidal activity against Meloidogyne incognita [33].In a previous study, maximum root-knot nematode egg hatch inhibition and juvenile mortality were by carvone at 1500 μg ml −1 after 96 hours of treatment application [33].In our study, feld evaluations showed citrus at 100% concentrations as seed coating (T5) with the highest nematode reductions (90.1%) and least reproductive factors (RFs) of 0.05 at the atomic farms.Te potential of this oil in limiting nematode production can be attributed to limonene and its derivatives.
Nematodes, in particular Meloidogyne incognita, which has the ability to alter the normal physiology of plants and cause poor nutrient uptake, lower growth, and consequently low quality and quantity of the yield, are implicated in the improved performance of the treated plants.Sesame oil in the current study had the least efcacy in reducing nematode reproduction in soil and compared to another study which involved plant seed oils such as cotton, fax canola, olive, soybean, and sesame applied against root-knot nematode in tomato; sesame oil was inefcient in reducing nematode populations in tomato [6].

Conclusion
Okra seeds treated with 100% citrus oil and 50% neem oil were efcacious in reducing nematode reproduction in soil and also enhanced seed germination and seedling vigor, with an improvement in growth and yield.Sesame oil was the least efective in enhancing seed germination and vigor and is therefore not recommended as a preplant protectant.

Figure 4 :
Figure4: Plant height from weeks 5 to 11 after treatment application (Ghana Atomic Energy vegetable growers' farm).T1 � sesame at 40% as seed coating for 30 min prior to sowing, T2 � sesame at 40% as drenching two weeks after germination, T3 � neem at 50% as seed coating for 30 min prior to sowing, T4 � neem at 50% as drenching two weeks after germination, T5 � citrus at 100% as seed coating for 30 min prior to sowing, T6 � citrus at 100% as drenching two weeks after germination, T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing, T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination, and T9 � control (no application).

Table 1 :
Treatments and their active ingredients, formulation type, and mode of action.

Table 2 :
Data collected on plant growth parameters in feld experiments.After week 13, the plants were uprooted, shoots were separated from the roots, attached soil was washed of, and then, it was allowed to air dry for fve minutes and then weighed on the weighing balance Shoot dry weight (g) Shoot fresh weights taken after week 13 were dried in the oven at 70 °C for 72 hours and weighedRoot fresh weight (g) After 13 weeks, the roots were abscised from the shoots and washed thoroughly then allowed to dry for fve minutes and weighed on a balance Treatment 6 (citrus at 100% as drenching two weeks after germination) had the highest girth of 11.54 cm, with treatment 8 (velum at 9.8 ml/15L of water as drenching two weeks after germination) having the lowest girth of 8.84 cm at week 5.At week 8, treatment 1 (sesame at 40% as seed coating for 30 min prior to sowing) had the highest girth of 4.33 cm, while treatment 3 (neem at 50% as seed coating for 30 min prior to sowing) obtained the lowest girth of 3.96 cm.

Table 3 :
Efect of treatments on the number and weight of fruits, at two-week intervals (University of Ghana farm).

Table 4 :
Efect of treatments on fresh and dry shoot and root weights (University of Ghana farm).

Table 5 :
Percent reduction in nematode populations (University of Ghana farm).

Table 6 :
Efect of treatments on chlorophyll content at week 5 and week 8.

Table 7 :
Efect of treatments on the number and weight of fruits, at two-week intervals (Ghana Atomic farm).Means followed by the same letters in a column are not signifcantly diferent at LSD (P < 0.05).T1 � sesame at 40% as seed coating for 30 min prior to sowing; T2 � sesame at 40% as drenching two weeks after germination; T3 � neem at 50% as seed coating for 30 min prior to sowing; T4 � neem at 50% as drenching two weeks after germination; T5 � citrus at 100% as seed coating for 30 min prior to sowing; T6 � citrus at 100% as drenching two weeks after germination; T7 � velum (check) at 3.8 ml/1L as seed coating for 30 min prior to sowing; T8 � velum (check) at 9.8 ml/15L of water as drenching two weeks after germination; T9 � control (no application).

Table 8 :
Efect of treatments on fresh and dry shoot and root weights (Ghana Atomic farm).

Table 9 :
Percent reduction in nematode populations (Ghana Atomic farm).