Assessment of Azadirachta indica and Cleome viscosa liquid-formulations as bio-nematicides in the management of nematode pests of okra

The efficacy of Azadirachta indica and Cleome viscosa liquid-formulations were assessed as bionematicides on the performances of okra planted in nematode infested soil at Teaching and Research Farm of Ladoke Akintola University of Technology, Ogbomoso, Nigeria during 2014 planting season. NHAE-47 okra variety which, is susceptible to root knot nematodes, was the test crop. The experimental design was randomized complete block design, with 11 treatments and 4 replicates. The okra plots that were inoculated but not treated with neither bio-nematicides nor adjuvants served as the controls. The results show that A. indica and C. viscosa liquid-formulations significantly improved the growth and yield of okra planted on nematode infested soil as compared to growth and yield of okra obtained in the control experiments. The least growth rate and yield were obtained where no treatment was applied. The population of the plant parasitic nematodes (Meloidogyne, Trichodorus, Paratrichodorus, Helicotylenchus and Xiphinema) were significantly reduced on the okra plots treated with A. indica and C. viscosa liquid-formulations, when compared with plots where adjuvants and water were applied.


INTRODUCTION
Okra (Abelmoschus esculentus (L.) Moench) is an important vegetable in the world which belongs to the family Malvaceae.Nematodes are simple roundworms, colourless, unsegmented organisms, with bilaterally symmetrical body without appendages, which belong to the phylum Nematoda.Plant parasitic nematodes are important pathogens on most food, vegetable, horticultural and fiber crops and without adequate control will cause loss of yield and quality.Root-knot nematodes (Meloidogyne species) infect almost all plants and cause considerable damage.During surveys, most vegetable crops including okra were found to be infected by Meloidogyne incognita (Khan et al., 2004).Meloidogyne, Longidorus, Pratylenchus, Ditylenchus, Aphelenchoides, Globodera, and Heterodera nematode genera do cause severe loss to okra due to their feeding habit and disease causation.The most prevailing nematode genera that affect okra is root knot nematodes (Meloidogyne species) (Olabiyi, 2005).
Nematode management do cause complicated diseases on okra and at the moment chemical control is employed in okra production in order to maintain nematode population below economic threshold level (Eapen et al., 2005).
Recently, the control of plant parasitic nematodes by using chemicals has declined internationally because of the inherent toxicity of many existing synthetic pesticides to non-target organisms and their persistency in the environment.There is increasing need to find more acceptable alternatives.The potential for nematicidal activity of indigenous plants and their products has been reported by earlier workers (Adekunle and Fawole, 2003).Due to the residual effect of chemicals, botanicals and antagonistic organisms are considered to be the best and safe means of controlling nematodes.
Bio-nematicides are certain types of pesticides, that are used in controlling nematode pest; these pesticides are derived from such natural materials as animals, plants, bacteria, and certain minerals.Bio-nematicides are usually inherently less toxic than conventional pesticides; they generally affect only the target pest and closely related organisms, in contrast to broad spectrum conventional pesticides, that may affect non-target organisms such as birds, insects, livestock, environment and mammals, including human beings.They are effective in and often decompose quickly, thereby resulting in lower exposures and largely avoiding the pollution problems caused by conventional pesticides.Most plant materials have proved to be useful in nematode control (Adekunle and Fawole, 2003;Khan et al., 2004;Olabiyi, 2005).
The objective of this research was to assess the effectiveness of Azadirachta indica and Cleome viscosa liquid-formulations on the performances of okra planted nematode infested and non-infested soil.

MATERIALS AND METHODS
The research was carried out at Ladoke Akintola University of Technology Teaching and Research Farm, Ogbomoso, Nigeria.The experimental site had a total of 44 treatment plots with each bed having a dimension of 2 m by 1 m and alleyways of 0.5 m.Each bed was labelled accordingly.The experimental design was randomized complete block design with 11 treatments and 4 replicates.Soil samples (250 cm 3 per plot) were taken randomly from the experimental site for initial soil nematode population count at 3 weeks after planting, but 3 days after, the application of organic fertilizer.Nematode population (initial and final) counts were done following the method described by Southey (1986).
The okra seeds were sown at the rate of two seeds per hole with spacing of 60 cm by 30 cm.Weeding was carried out twice manually.20 g of organic fertilizer made from wild sunflower were applied to each stand, 3 weeks after planting.Two weeks after planting okra plants were inoculated with 10g root knot nematode infected Celosia argentia.
Leaves of Azadirachta indica and Cleome viscosa were harvested, air dried, ground using attrition mill and soaked in water for 24 hours at the ratio of 1kg to 5 litres water.The content was sieved using muslin cloth and the filtrate gotten was mixed singly with adjuvants (black soap or Tetrapleura tetraptera) at the ratio of 1: 10 (adjuvant: plant extract).The A. indica and C. viscosa which were formulated with the adjuvants were diluted at two rates (3 and 5 L of bio-nematicides into knapsack sprayer) before the application.A. indica and C. viscosa liquid formulations, black soap and Tetrapleura tetraptera served as treatments, while with the untreated but inoculated okra served as control.
Data were collected on plant height, number of leaves per plant, number of pods per plant, pod length, pod weight, dried pod weight, number of seeds per pod, root length, root weight, dried root weight, root gall index and soil nematode populations in 250 cm 3 per plot at final harvest).Data were collected on 10 plants that were at the middle of each treatment plot.The data collected were analysed using analysis of variance (ANOVA) and the differences among the means were partitioned, with Duncan multiple range test (DMRT) at 5% probability level.

RESULTS
A. indica and C. viscosa liquid-formulations as bionematicides were assessed on the growth of okra planted on nematode infested soil (Table 1).The growth of okra was significantly enhanced by the application of A. indica and C. viscosa liquid-formulations.This resulted to significantly higher plant height and number of leaf per okra plant.Okra plants that were treated with adjuvants and water have significantly lower growth rate than those that were treated with A. indica and C. viscosa liquidformulations.
Table 2 shows the effect of A. indica and C. viscosa liquid-formulations as bio-nematicides on the yield of okra planted on nematode infested soil.Okra plants treated with A. indica and C. viscosa liquid-formulations significantly have higher yield compared with others.Notably, okra that were treated with black soap, T. tetraptera and water have significantly lower yield than okra that were treated with A. indica and Cleome viscosa liquid-formulations.This follows the same trends for other yield parameters.The effect of Azadirachta indica and Cleome viscosa liquid-formulations as bio-nematicides on okra root planted on nematode infested soil was presented in Table 3. Root development was significantly enhanced in the soils that were treated with different application rates of A. indica and C. viscosa liquidformulations, as bio-nematicides.The two application rates (3 L and 5 L bio-nematicides into 15 L water) were at par with one another in their performances on okra root development.
The result presented on Table 4 shows the effect of A. indica and C. viscosa liquid-formulations as bionematicides on okra root damage and root knot nematode (Meloidogyne species) populations in the soil.The root damage (root gall index) and final root knot nematode population count were significantly reduced in the soil treated with A. indica and C. viscosa liquidformulations as bio-nematicides.However, the initial root knot nematode population in the soil (that is, soil condition before the application of treatment) were         statistically homogenously distributed.The result on Table 5 shows the effect of A. indica and C. viscosa liquid-formulations, prepared as bio-nematicides, on the soil populations of Trichodorus, Paratrichodorus, Helicotylenchus and Xiphinema nematodes on which okra was grown.The result indicates that the population of plant parasitic nematodes were significantly lower in the treatment plots than were treated with A. indica and C. viscosa liquid-formulations than where adjuvants and water were applied.

DISCUSSION
The results of this research show that A. indica and C. viscosa liquid-formulations significantly enhanced the growth and yield of okra; and also suppressed the root damage and plant parasitic nematode population building.These findings corroborate earlier findings of Oluwatoyin et al. (2013) that used aqueous extract of leaves of Calotropis procera to control root knot nematode infection in okra.Ahmad et al. (2010) also used extract from Lantana camara leaf to control M. incognita at different concentrations.Adediran et al. (2005) has used siam weed and other plant material alongside with fallowing to control different species of nematode.The results also corroborate earlier findings of Wani (2006) that reported that neem seed and castor leaves are good bio-nematicides to control root-knot nematode in okra.Adekunle and Fawole (2003) reported that application of water extracts of neem leaves, siam weed leaves and root delayed the development and consequently reduced the population of nematode egg masses and eggs as well as root gall index.
Figures having the same letters along the same column are not significantly different from one another.
Figures having the same letters along same column are not significantly different from one another.

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Figures having the same letters along same column are not significantly different from one another.
Figures having the same letters along same column are not significantly different from one another.

Table 1 .
Effect of A. indica and C. viscosa liquid-formulations as bio-nematicides on the growth of okra planted on nematode infested soil.

Table 2 .
Effect of A. indica and C. viscosa liquid-formulations as bio-nematicides on the yield of okra planted on nematode infested soil.
a 10.8

Table 3 .
Effect of A. indica and C. viscosa liquid-formulations as bio-nematicides on okra root planted on nematode infested soil.

Table 4 .
Effect of A. indica and Cleome viscosa liquid-formulations as bio-nematicides on okra root damage and root knot nematode population in the soil.

Table 5 .
Effect of A. indica and C. viscosa liquid-formulations as bio-nematicides on the soil populations of Trichodorus, Paratrichodorus, Helicotylenchus and Xiphinema nematodes on which okra was grown.Figures having the same letters along same column are not significantly different from one another.Initial populations of Trichodorus, Paratrichodorus, Helicotylenchus and Xiphinema nematodes were in parentheses.