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Biological control of plant-parasitic nematodes by neem products in agricultural soil
Applied Soil Ecology 7 Ž1998. 219–223
Biological control of plant-parasitic nematodes by neem products in agricultural soil Mohammad Akhtar
)
Plant Protection DiÕision, Institute of Agriculture, Aligarh Muslim UniÕersity, Aligarh-202 002, India Received 27 November 1996; accepted 23 June 1997
Abstract Various products prepared from neem Ž Azadirachta indica. such as leaf powder, sawdust and oilseed cake, and urea were tested for their activities against plant-parasitic nematodes Ž Hoplolaimus indicus, Helicotylenchus indicus, Rotylenchulus reniformis and Meloidogyne incognita juveniles., a predatory nematode Ž Dorylaimus elongatus ., free-living nematodes and the growth of chickpea Ž Cicer arietinum. in the field. Soil-amendments with these materials resulted in a significant decrease of plant-parasitic nematodes relative to control plots. In contrast, populations of predatory and free-living nematodes increased. Oilcake was most effective, though all the neem products and urea markedly suppressed plant-parasitic nematodes. However, leaf powder increased populations of predatory and free-living nematodes. All treatments resulted in increased fresh and dry weights and the height and number of pods on chickpea plants. q 1998 Elsevier Science B.V. Keywords: Azadirachta indica; Cicer arietinum; Dorylaimus elongatus; Plant-parasitic nematodes; Nematode control urea
1. Introduction Chickpea Ž Cicer arietinum L.., an important pulse crop, is grown in most parts of India, due to its high seed-protein content. Plant-parasitic nematodes are one of the major factors limiting its productivity. Chemical nematicides, though effective in providing rapid kills of nematodes are now being reappraised concerning their environmental hazardousness, high cost and limited availability in many developing countries. Attention of nematologists is now focused on alternative control strategies, including cultural and biological methods. Numerous cultural practices
)
Corresponding author.
can be beneficial by reducing population densities of plant-parasitic nematodes. Organic soil amendments are now widely recognized as ‘non-conventional’ nematode management options ŽMuller and Gooch, 1982.. Plant products are receiving greater attention as an effective means of control for nematode pests mainly because of their presumed safety to non-target organisms. Neem Ž Azadirachta indica. products including leaf powder, seed powder, sawdust, oil and oilcake, and a number of commercially available products have been effective in managing several species of plant-parasitic nematodes in commercial crops ŽAkhtar and Alam, 1993b; Akhtar and Mahmood, 1994a.. Plant-parasitic nematodes generally occur with other soil nematode communities, including predacious and free-living nematodes. Following the addi-
0929-1393r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 9 - 1 3 9 3 Ž 9 7 . 0 0 0 3 1 - 0
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223
220
tion of organic and inorganic fertilizers to soil, populations of free-living Žmicrobivorous. nematodes can increase rapidly and densities of plant-parasitic nematodes may decline ŽMankau and Minteer, 1962; Heald and Burton, 1968; Tomerlin and Smart, 1969.. Abrams and Mitchell Ž1980. and Griffiths Ž1986. suggested that free-living nematodes accelerate the decomposition of organic soil amendments and increase the mineralization of nitrogen and phosphorus. Interest in using predatory nematodes, e.g. Dorylaimus sp. for suppressing plant-parasitic nematodes in the soil is receiving attention. Recently, a few studies have investigated predatory nematodes as control agents in the soil ŽLal et al., 1983; Sayre and Walter, 1991.. The objective of this research was to determine the effects of different amounts of oilcake, leaf powder and sawdust of neem Ž A. indica A. Juss.. and urea on populations of predatory, free-living and plant-parasitic nematodes and the growth of chickpea in a field soil.
2. Materials and methods The experiment was established at Aligarh Muslim University Agricultural Research Farm, Aligarh,
India. The soil was ploughed by chisel thoroughly to a depth of 10–15 cm and divided into small plots measuring 2 = 3 m separated from each other by 0.5-m strips. The plots were established on an alluvial soil Žsand 60%, silt 17%, clay 23%. of pH 8.3 and 1.0% organic matter. Nine treatments and a control were established. Oilcake, sawdust or leaf powder of neem and urea were each applied at two rates equivalent to 110 and 220 kg Nrha. Control plots received no soil amendments or fertilizers. All treatments were applied 15 days prior to sowing chickpea Ž C. arietinum L... The experimental design was a randomized complete block with five replications of each treatment including control plots. Crops were irrigated as needed, but no pesticides or additional fertilizers were applied. Ninety days after sowing, chickpea plants were harvested and fresh and dry weights, heights and number of pods of the plants were recorded. Dry weights were determined by placing the plants in an oven for 24 h at 608C. Soil samples consisting of 32–40 cores Ž2.5 cm diameter, 20–25 cm deep. were collected from the centre of each plot three days before treatment Žinitial population. and one day after harvest. Cores were bulked, mixed and sieved before subsampling and a 100-g sub-sample was used for nematode extraction. Populations of nematodes were extracted from the soil by Cobb’s sieving and decanting method
Table 1 Effect of neem Ž A. indica. treatment of final populations of plant-parasitic nematodes on chickpeaa Neem treatment
Initial population Oil cake Leaf powder Sawdust Urea Control LSD Ž P F 0.05. a b
Rate Žkg Nrha.
110 220 110 220 110 220 110 220 y
Data are means of five replicates. J2 , second stage juveniles.
Plant-parasitic nematodesr100 g soil Meloidogyne Ž J2 . b
Hoplolaimus
Helicotylenchus
Rotylenchulus
1566 116 72 199 121 244 172 274 195 7593 42
365 96 38 116 78 142 84 157 101 1448 17
373 89 37 128 88 138 78 127 99 1599 21
716 106 89 162 105 192 114 184 89 3251 23
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223 Table 2 Effect of neem Ž A. indica. treatment on final populations of predatory and free-living nematodes on chickpeaa Neem treatment
Initial population Oil cake Leaf powder Sawdust Urea Control LSD Ž P F 0.05. a
Rate Žkg Nrha.
110 220 110 220 110 220 110 220 y
Nematodesr100 g soil Dorylaimus
Rhabditis
44 54 75 172 210 148 178 131 172 49 13
145 205 245 545 749 395 465 281 315 172 22
Data are means of five replicates.
followed by the Baermann funnel extraction ŽHooper, 1986. and preserved in 5% formalin. The nematodes in each extract were counted and identified separately as free-living, predatory Ž Dorylaimus elongatus de Man. or plant-parasitic nematodes Ž Hoplolaimus indicus Sher, Helicotylenchus indicus Siddiqui, Rotylenchulus reniformis Linford and Oliveira, and Meloidogyne incognita Kofoid and White Chitwood. Data were analysed statistically using analysis of variance and Fisher’s least significant differences ŽFLSD. were calculated for separation of means. Unless otherwise stated, all differences referred to in the text were significant at P F 0.05.
221
3. Results 3.1. Effect on nematode populations Populations of plant-parasitic nematodes increased in control plots because chickpea is a highly nematode-susceptible crop. The addition of oilcake, sawdust and leaf powder of neem significantly Ž P F 0.05. reduced the population densities of plant-parasitic nematodes ŽTable 1.. In general, greatest reduction in plant-parasitic nematode populations was observed with oilcake followed by leaf powder, sawdust and urea. This difference between treatments applied most specifically to Meloidogyne and Hoplolaimus. In the case of Helicotylenchus and Rotylenchulus, the differences between leaf powder, sawdust and urea were respectively small and generally insignificant. Increased doses of the amendments were found effective in further reducing the populations of plant-parasitic nematodes. In the case of neem oilcake, doubling the dose resulted in a significant reduction of the number of these nematodes. There was no significant change in the population of predatory and free-living nematodes between sowing and harvesting the crop. In all the treated plots, however, the nematode population significantly increased especially with neem leaf powder applied at the largest dose ŽTable 2.. Populations of free-living nematodes were most strongly increased by the incorporation of leaf powder followed by sawdust, urea and oilcake ŽTable 2.. There was a significant
Table 3 Effect of neem Ž A. indica. treatment on growth parameters of chickpea plantsa Neem treatment
Oil cake Leaf powder Sawdust Urea Control LSD Ž P F 0.05. a
Rate Žkg Nrha.
110 220 110 220 110 220 110 220 y
Data are means of five replicates.
Growth parameters per plant Height Žcm.
Fresh shoot weight Žg.
Dry shoot weight Žg.
No. of pods
56.2 48.5 51.4 54.4 40.4 45.2 36.7 40.1 10.5 2.96
41.5 52.2 37.4 42.5 34.9 39.6 28.4 31.5 14.4 3.73
6.6 7.5 5.1 6.9 4.8 5.9 2.9 3.5 2.3 0.56
114 172 105 168 99 107 87 78 27 10.7
222
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223
difference in the effect of dose rate on the numbers of nematodes in soil. 3.2. Effect of plant growth A significant improvement in the growth Žplant fresh weight, dry weight and height. and yield Žnumber of pods. of chickpea was observed in all the treatments as compared with the control ŽTable 3.. In general, the improvements were more pronounced for plants grown in plots treated with highest amendments. In the control plots, plant growth parameters were much reduced, presumably due to the increase in population of plant-parasitic nematodes, a lack of fertilizer or both. Neem oilcake resulted in the greatest improvement of plant growth and yield while urea was found to be the least effective ŽTable 3..
4. Discussion Application of the amendments to soil caused a significant reduction in population of plant-parasitic nematodes and resulted in enhanced chickpea plant growth and yield. Presumably, this resulted from a release of toxic compounds which either were not present or were present at sublethal concentrations in the rhizosphere of chickpea. Rodriguez-Kabana et al. Ž1987. suggested that the plant-parasitic nematode control effects of organic additives depend on their chemical compositions and the composition and activity of the decomposer community that develops during degradation. Some of the products of decomposition can be toxic to plant-parasitic nematodes ŽAkhtar and Alam, 1993b.. Neem is known to contain several chemicals Že.g. azadirachtin, rimbocinol, nimbin, etc.., that have been reported to have nematicidal properties ŽAkhtar and Alam, 1993a; Akhtar and Mahmood, 1994b.. Nitrogen may also be a factor involved in controlling plant-parasitic nematodes, as a result of the application of oilcake and leaf powder of neem. Rodriguez-Kabana Ž1986. reported that nitrogenous amendments to soil released ammoniacal nitrogen and this form of nitrogen can suppress plant-parasitic nematode populations. Equal amounts were added in all treatments, but the availability of nitrogen was different, because different substrates have different
mineralization rates, so that equal amounts of N in organic form will not lead to equal amounts of inorganic N. Other nutrients were present in different quantities in the different substrates, which may have affected the plant growth response. The present findings also indicate that the addition of neem products encourages the development of populations of predatory and free-living nematodes. Opperman et al. Ž1993. pointed out that ammonia nitrogen concentrations were enhanced immediately after the addition of cattle manure and resulted in simultaneous increase in the population of free-living nematodes. Release of nitrogen resulted in microbial activity in amended soil known to bring about increased conversion of N to nitrate Žnitrification.. Triterpenes compounds in neem cake inhibit the nitrification process and provide more nitrogen in the form of ammonium to the plants for the same amount of nitrogen applied by the amendments ŽAkhtar and Alam, 1993a.. Predatory nematodes are comparatively large and therefore favour coarse soil with high organic matter. Neem sawdust and leaf powder increase the organic matter in soil. Akhtar and Mahmood Ž1993. and Akhtar Ž1995. observed that the symptoms caused by the root-knot nematode M. incognita were suppressed by the predatory nematode Mononchus aquaticus. There was further suppression of root-knot development when neem and castor leaves were incorporated into soil. The contributions of nutrients other than nitrogen from the organic amendments to the plant response, the contribution of predatory nematodes to the suppression of plant-parasitic nematodes, and the nematode control effects on plant growth need further study to assess the feasibility of using the tested neem products in integrated pest management. References Abrams, B.I., Mitchell, M.J., 1980. Role of nematode–bacterial interactions in heterotrophic systems with emphasis on sewage-sludge decomposition. Oikos 35, 404–410. Akhtar, M., 1995. Biological control of the root-knot nematode Meloidogyne incognita in tomato by the predatory nematode Mononchus aquaticus. Int. Pest Control 37, 18–19. Akhtar, M., Alam, M.M., 1993a. Control of plant-parasitic nematodes by ‘Nimin’—an urea coating agent and some plant oils. Plant Disease and Protection 100, 169–171.
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223 Akhtar, M., Alam, M.M., 1993b. Utilization of waste materials in nematode control: A review. Biores. Technol. 45, 1–7. Akhtar, M., Mahmood, I., 1993. Effect of Mononchus aquaticus and organic amendments on Meloidogyne incognita development on chilli. Nematol. Medit. 21, 251–252. Akhtar, M., Mahmood, I., 1994a. Potentiality of phytochemicals in nematode control: A review. Biores. Technol. 47, 189–201. Akhtar, M., Mahmood, I., 1994b. Nematode populations and short term tomato growth in response to neem-based products and other soil amendments. Nematropica 24, 169–173. Griffiths, B.S., 1986. Mineralization of nitrogen and phosphorus by mix culture of the ciliate protozoa Colpoda steinii, the nematode Rhabditis sp. and the bacterium Pseudomonas fluorescens. Soil Biol. Biochem. 18, 637–642. Heald, C.M., Burton, G.W., 1968. Effect of organic and inorganic nitrogen nematodes on turf. Plant Disease Reporter 52, 46–48. Hooper, D.J., 1986. Extraction of free-living stages from soil. In: Southey, J.F. ŽEd.., Laboratory Methods for Work with Plant and Soil Nematodes. Min. Agr. Fish and Food, HMSO, London, UK, pp. 5–22. Lal, A., Sanwal, K.C., Mathur, V.K., 1983. Changes in the nematode population undisturbed land in the introduction of
223
land development practices and cropping sequences. Indian J. Nematol. 13, 133–140. Mankau, R., Minteer, R.J., 1962. Reduction of soil populations of citrus nematode by addition of organic materials. Plant Dis. Reptr. 46, 375–378. Muller, P.S., Gooch, P.S., 1982. Organic amendments in nematode control: An examination of the literature. Nematropica 12, 319–326. Opperman, M.H., Wood, M., Harris, P.J., Cherrett, C.P., 1993. Nematode and nitrate dynamics in soils treated with cattle slurry. Soil Biol. Biochem. 25, 19–24. Rodriguez-Kabana, R., 1986. Organic and inorganic amendments to soil as nematode suppressants. J. Nematol. 18, 129–135. Rodriguez-Kabana, R., Morgan-Jones, G., Chet, I., 1987. Biological control of nematodes: Soil amendments and microbial antagonists. Plant and Soil 106, 237–247. Sayre, R.M., Walter, D.E., 1991. Factors affecting the efficacy of natural enemies of nematodes. Annu. Rev. Phytopathol. 29, 149–166. Tomerlin, H.A., Smart, G.C., 1969. The influence of organic soil amendments on nematodes and other soil organisms. J. Nematol. 1, 29–30.
Biological control of plant-parasitic nematodes by neem products in agricultural soil Mohammad Akhtar
)
Plant Protection DiÕision, Institute of Agriculture, Aligarh Muslim UniÕersity, Aligarh-202 002, India Received 27 November 1996; accepted 23 June 1997
Abstract Various products prepared from neem Ž Azadirachta indica. such as leaf powder, sawdust and oilseed cake, and urea were tested for their activities against plant-parasitic nematodes Ž Hoplolaimus indicus, Helicotylenchus indicus, Rotylenchulus reniformis and Meloidogyne incognita juveniles., a predatory nematode Ž Dorylaimus elongatus ., free-living nematodes and the growth of chickpea Ž Cicer arietinum. in the field. Soil-amendments with these materials resulted in a significant decrease of plant-parasitic nematodes relative to control plots. In contrast, populations of predatory and free-living nematodes increased. Oilcake was most effective, though all the neem products and urea markedly suppressed plant-parasitic nematodes. However, leaf powder increased populations of predatory and free-living nematodes. All treatments resulted in increased fresh and dry weights and the height and number of pods on chickpea plants. q 1998 Elsevier Science B.V. Keywords: Azadirachta indica; Cicer arietinum; Dorylaimus elongatus; Plant-parasitic nematodes; Nematode control urea
1. Introduction Chickpea Ž Cicer arietinum L.., an important pulse crop, is grown in most parts of India, due to its high seed-protein content. Plant-parasitic nematodes are one of the major factors limiting its productivity. Chemical nematicides, though effective in providing rapid kills of nematodes are now being reappraised concerning their environmental hazardousness, high cost and limited availability in many developing countries. Attention of nematologists is now focused on alternative control strategies, including cultural and biological methods. Numerous cultural practices
)
Corresponding author.
can be beneficial by reducing population densities of plant-parasitic nematodes. Organic soil amendments are now widely recognized as ‘non-conventional’ nematode management options ŽMuller and Gooch, 1982.. Plant products are receiving greater attention as an effective means of control for nematode pests mainly because of their presumed safety to non-target organisms. Neem Ž Azadirachta indica. products including leaf powder, seed powder, sawdust, oil and oilcake, and a number of commercially available products have been effective in managing several species of plant-parasitic nematodes in commercial crops ŽAkhtar and Alam, 1993b; Akhtar and Mahmood, 1994a.. Plant-parasitic nematodes generally occur with other soil nematode communities, including predacious and free-living nematodes. Following the addi-
0929-1393r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 9 - 1 3 9 3 Ž 9 7 . 0 0 0 3 1 - 0
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223
220
tion of organic and inorganic fertilizers to soil, populations of free-living Žmicrobivorous. nematodes can increase rapidly and densities of plant-parasitic nematodes may decline ŽMankau and Minteer, 1962; Heald and Burton, 1968; Tomerlin and Smart, 1969.. Abrams and Mitchell Ž1980. and Griffiths Ž1986. suggested that free-living nematodes accelerate the decomposition of organic soil amendments and increase the mineralization of nitrogen and phosphorus. Interest in using predatory nematodes, e.g. Dorylaimus sp. for suppressing plant-parasitic nematodes in the soil is receiving attention. Recently, a few studies have investigated predatory nematodes as control agents in the soil ŽLal et al., 1983; Sayre and Walter, 1991.. The objective of this research was to determine the effects of different amounts of oilcake, leaf powder and sawdust of neem Ž A. indica A. Juss.. and urea on populations of predatory, free-living and plant-parasitic nematodes and the growth of chickpea in a field soil.
2. Materials and methods The experiment was established at Aligarh Muslim University Agricultural Research Farm, Aligarh,
India. The soil was ploughed by chisel thoroughly to a depth of 10–15 cm and divided into small plots measuring 2 = 3 m separated from each other by 0.5-m strips. The plots were established on an alluvial soil Žsand 60%, silt 17%, clay 23%. of pH 8.3 and 1.0% organic matter. Nine treatments and a control were established. Oilcake, sawdust or leaf powder of neem and urea were each applied at two rates equivalent to 110 and 220 kg Nrha. Control plots received no soil amendments or fertilizers. All treatments were applied 15 days prior to sowing chickpea Ž C. arietinum L... The experimental design was a randomized complete block with five replications of each treatment including control plots. Crops were irrigated as needed, but no pesticides or additional fertilizers were applied. Ninety days after sowing, chickpea plants were harvested and fresh and dry weights, heights and number of pods of the plants were recorded. Dry weights were determined by placing the plants in an oven for 24 h at 608C. Soil samples consisting of 32–40 cores Ž2.5 cm diameter, 20–25 cm deep. were collected from the centre of each plot three days before treatment Žinitial population. and one day after harvest. Cores were bulked, mixed and sieved before subsampling and a 100-g sub-sample was used for nematode extraction. Populations of nematodes were extracted from the soil by Cobb’s sieving and decanting method
Table 1 Effect of neem Ž A. indica. treatment of final populations of plant-parasitic nematodes on chickpeaa Neem treatment
Initial population Oil cake Leaf powder Sawdust Urea Control LSD Ž P F 0.05. a b
Rate Žkg Nrha.
110 220 110 220 110 220 110 220 y
Data are means of five replicates. J2 , second stage juveniles.
Plant-parasitic nematodesr100 g soil Meloidogyne Ž J2 . b
Hoplolaimus
Helicotylenchus
Rotylenchulus
1566 116 72 199 121 244 172 274 195 7593 42
365 96 38 116 78 142 84 157 101 1448 17
373 89 37 128 88 138 78 127 99 1599 21
716 106 89 162 105 192 114 184 89 3251 23
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223 Table 2 Effect of neem Ž A. indica. treatment on final populations of predatory and free-living nematodes on chickpeaa Neem treatment
Initial population Oil cake Leaf powder Sawdust Urea Control LSD Ž P F 0.05. a
Rate Žkg Nrha.
110 220 110 220 110 220 110 220 y
Nematodesr100 g soil Dorylaimus
Rhabditis
44 54 75 172 210 148 178 131 172 49 13
145 205 245 545 749 395 465 281 315 172 22
Data are means of five replicates.
followed by the Baermann funnel extraction ŽHooper, 1986. and preserved in 5% formalin. The nematodes in each extract were counted and identified separately as free-living, predatory Ž Dorylaimus elongatus de Man. or plant-parasitic nematodes Ž Hoplolaimus indicus Sher, Helicotylenchus indicus Siddiqui, Rotylenchulus reniformis Linford and Oliveira, and Meloidogyne incognita Kofoid and White Chitwood. Data were analysed statistically using analysis of variance and Fisher’s least significant differences ŽFLSD. were calculated for separation of means. Unless otherwise stated, all differences referred to in the text were significant at P F 0.05.
221
3. Results 3.1. Effect on nematode populations Populations of plant-parasitic nematodes increased in control plots because chickpea is a highly nematode-susceptible crop. The addition of oilcake, sawdust and leaf powder of neem significantly Ž P F 0.05. reduced the population densities of plant-parasitic nematodes ŽTable 1.. In general, greatest reduction in plant-parasitic nematode populations was observed with oilcake followed by leaf powder, sawdust and urea. This difference between treatments applied most specifically to Meloidogyne and Hoplolaimus. In the case of Helicotylenchus and Rotylenchulus, the differences between leaf powder, sawdust and urea were respectively small and generally insignificant. Increased doses of the amendments were found effective in further reducing the populations of plant-parasitic nematodes. In the case of neem oilcake, doubling the dose resulted in a significant reduction of the number of these nematodes. There was no significant change in the population of predatory and free-living nematodes between sowing and harvesting the crop. In all the treated plots, however, the nematode population significantly increased especially with neem leaf powder applied at the largest dose ŽTable 2.. Populations of free-living nematodes were most strongly increased by the incorporation of leaf powder followed by sawdust, urea and oilcake ŽTable 2.. There was a significant
Table 3 Effect of neem Ž A. indica. treatment on growth parameters of chickpea plantsa Neem treatment
Oil cake Leaf powder Sawdust Urea Control LSD Ž P F 0.05. a
Rate Žkg Nrha.
110 220 110 220 110 220 110 220 y
Data are means of five replicates.
Growth parameters per plant Height Žcm.
Fresh shoot weight Žg.
Dry shoot weight Žg.
No. of pods
56.2 48.5 51.4 54.4 40.4 45.2 36.7 40.1 10.5 2.96
41.5 52.2 37.4 42.5 34.9 39.6 28.4 31.5 14.4 3.73
6.6 7.5 5.1 6.9 4.8 5.9 2.9 3.5 2.3 0.56
114 172 105 168 99 107 87 78 27 10.7
222
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223
difference in the effect of dose rate on the numbers of nematodes in soil. 3.2. Effect of plant growth A significant improvement in the growth Žplant fresh weight, dry weight and height. and yield Žnumber of pods. of chickpea was observed in all the treatments as compared with the control ŽTable 3.. In general, the improvements were more pronounced for plants grown in plots treated with highest amendments. In the control plots, plant growth parameters were much reduced, presumably due to the increase in population of plant-parasitic nematodes, a lack of fertilizer or both. Neem oilcake resulted in the greatest improvement of plant growth and yield while urea was found to be the least effective ŽTable 3..
4. Discussion Application of the amendments to soil caused a significant reduction in population of plant-parasitic nematodes and resulted in enhanced chickpea plant growth and yield. Presumably, this resulted from a release of toxic compounds which either were not present or were present at sublethal concentrations in the rhizosphere of chickpea. Rodriguez-Kabana et al. Ž1987. suggested that the plant-parasitic nematode control effects of organic additives depend on their chemical compositions and the composition and activity of the decomposer community that develops during degradation. Some of the products of decomposition can be toxic to plant-parasitic nematodes ŽAkhtar and Alam, 1993b.. Neem is known to contain several chemicals Že.g. azadirachtin, rimbocinol, nimbin, etc.., that have been reported to have nematicidal properties ŽAkhtar and Alam, 1993a; Akhtar and Mahmood, 1994b.. Nitrogen may also be a factor involved in controlling plant-parasitic nematodes, as a result of the application of oilcake and leaf powder of neem. Rodriguez-Kabana Ž1986. reported that nitrogenous amendments to soil released ammoniacal nitrogen and this form of nitrogen can suppress plant-parasitic nematode populations. Equal amounts were added in all treatments, but the availability of nitrogen was different, because different substrates have different
mineralization rates, so that equal amounts of N in organic form will not lead to equal amounts of inorganic N. Other nutrients were present in different quantities in the different substrates, which may have affected the plant growth response. The present findings also indicate that the addition of neem products encourages the development of populations of predatory and free-living nematodes. Opperman et al. Ž1993. pointed out that ammonia nitrogen concentrations were enhanced immediately after the addition of cattle manure and resulted in simultaneous increase in the population of free-living nematodes. Release of nitrogen resulted in microbial activity in amended soil known to bring about increased conversion of N to nitrate Žnitrification.. Triterpenes compounds in neem cake inhibit the nitrification process and provide more nitrogen in the form of ammonium to the plants for the same amount of nitrogen applied by the amendments ŽAkhtar and Alam, 1993a.. Predatory nematodes are comparatively large and therefore favour coarse soil with high organic matter. Neem sawdust and leaf powder increase the organic matter in soil. Akhtar and Mahmood Ž1993. and Akhtar Ž1995. observed that the symptoms caused by the root-knot nematode M. incognita were suppressed by the predatory nematode Mononchus aquaticus. There was further suppression of root-knot development when neem and castor leaves were incorporated into soil. The contributions of nutrients other than nitrogen from the organic amendments to the plant response, the contribution of predatory nematodes to the suppression of plant-parasitic nematodes, and the nematode control effects on plant growth need further study to assess the feasibility of using the tested neem products in integrated pest management. References Abrams, B.I., Mitchell, M.J., 1980. Role of nematode–bacterial interactions in heterotrophic systems with emphasis on sewage-sludge decomposition. Oikos 35, 404–410. Akhtar, M., 1995. Biological control of the root-knot nematode Meloidogyne incognita in tomato by the predatory nematode Mononchus aquaticus. Int. Pest Control 37, 18–19. Akhtar, M., Alam, M.M., 1993a. Control of plant-parasitic nematodes by ‘Nimin’—an urea coating agent and some plant oils. Plant Disease and Protection 100, 169–171.
M. Akhtarr Applied Soil Ecology 7 (1998) 219–223 Akhtar, M., Alam, M.M., 1993b. Utilization of waste materials in nematode control: A review. Biores. Technol. 45, 1–7. Akhtar, M., Mahmood, I., 1993. Effect of Mononchus aquaticus and organic amendments on Meloidogyne incognita development on chilli. Nematol. Medit. 21, 251–252. Akhtar, M., Mahmood, I., 1994a. Potentiality of phytochemicals in nematode control: A review. Biores. Technol. 47, 189–201. Akhtar, M., Mahmood, I., 1994b. Nematode populations and short term tomato growth in response to neem-based products and other soil amendments. Nematropica 24, 169–173. Griffiths, B.S., 1986. Mineralization of nitrogen and phosphorus by mix culture of the ciliate protozoa Colpoda steinii, the nematode Rhabditis sp. and the bacterium Pseudomonas fluorescens. Soil Biol. Biochem. 18, 637–642. Heald, C.M., Burton, G.W., 1968. Effect of organic and inorganic nitrogen nematodes on turf. Plant Disease Reporter 52, 46–48. Hooper, D.J., 1986. Extraction of free-living stages from soil. In: Southey, J.F. ŽEd.., Laboratory Methods for Work with Plant and Soil Nematodes. Min. Agr. Fish and Food, HMSO, London, UK, pp. 5–22. Lal, A., Sanwal, K.C., Mathur, V.K., 1983. Changes in the nematode population undisturbed land in the introduction of
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