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(American Journal of Botany. 2004;91:1002-1004.)
© 2004 Botanical Society of America, Inc.

Brief Communication

Suppression of branches in Eucalyptus trees1

P. Senthalir2,4, S. Sharanya2 and M. Paramathma3

2Avila convent Matriculation Higher Secondary School, Coimbatore 641 025, India; 3Forest College & Research Institute, TamilNadu Agricultural University, Mettupalayam 641301, India

Received for publication August 21, 2003. Accepted for publication February 10, 2004.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 LITERATURE CITED
 
The effect of neem oil, which acts as a suckericide in tobacco, on branch suppression in Eucalyptus tereticornis was assessed to help maximize stem biomass. Lateral branches of selected trees were pruned, and neem oil solutions at concentrations of either 80%, 40%, 20%, 10%, or 0% (untreated control) were applied to leaf axils of the pruned branches. Regeneration of branches was suppressed, and the magnitude of suppression was proportional to the concentration of neem oil. Compared to the control, the percentage reduction in branching at 80% neem oil was 41.6%. When regenerated branches were repruned and neem oil applied at either 100%, 80%, or 0% (control), the regenerating ability of these branches was severely repressed by 78% at 100% neem oil relative to the control. Apical shoots were also topped and treated at either 100% or 0% (control) neem oil to identify the principal suppressive component in neem oil. The principal component azadirachtin was tested at 375, 750, 1500, 3125, 6250, 12 500, 25 000, 50 000, and 100 000 ppm and 0 ppm as the control. Reduction in the coppicing shoot was as high as 85%. Azadirachtin was responsible for the suppression. By pruning the lateral branches with neem oil, wasteful consumption of photosynthates can be precluded and the stem biomass maximized.

Key Words: Azadirachta indica • azadirachtin • Eucalyptus • neem oil • suppression of branches


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 LITERATURE CITED
 
Eucalyptus tereticornis is a short rotation species planted over more than 100 000 ha in India alone (Midgley and Boland, 1998 ). Each species of trees has its own branching pattern that is under genetic control. Although the hereditary pattern of branching is unique for each species, it can also be influenced to a certain extent by environment (Zobel and Talbert, 1984 ). If branching behavior could be suppressed, it could be useful in many ways. Wide, spreading branching is useful for shade in avenue plantations (Chundawat and Goutham, 1999 ), while narrow and vertical branching is highly useful in agroforestry systems for higher sunlight absorption by the annual crops and thereby higher productivity of both trees and crops (Nair, 1989 ). There is a wide indigenous awareness that neem oil suppresses the development of lateral branches in teak (Tectona grandis) and other species.

Azadirachtin, a terpene found in the neem kernel, inhibits feeding and disrupts growth in various insect orders (Butterworth and Morgan, 1968 ; Ruscoe, 1972 ; Meisner and Ascher, 1986 ; Rembold et al., 1986 ; Mariappan, 1995 ). When the terminal bud of the tobacco plant is removed to improve the area of the leaf, auxiliary shoots (suckers) develop. Neem oil emulsion is an effective suckericide for tobacco (Bangarayya et al., 1982 ). Eucalyptus, an exotic, is a tree with a wide range of uses, mainly as pulp, but the current productivity of the species under Indian conditions is only 28 000 kg/ha against its potential of 60 000 kg/ha. To maximize its productivity inexpensively, removing lower branches may be advantageous, particularly in increased stem biomass. The present experiments were conducted with the objective of suppressing the regeneration of lateral branches and coppicing in Eucalyptus tereticornis.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 LITERATURE CITED
 
In the first phase of the experiment, 75 1-yr-old Eucalyptus tereticornis trees, which were growing around an apartment at Coimbatore (11°19' N; 76°56' E; 400 m above sea level, annual precipitation 750 mm; pH 7.1; temperature ranging from 20°C to 35°C, winter season) from 28 September 2002 to 20 April 2003 under irrigation with sewage water, were selected. Lateral branches of the trees were pruned. Cotton balls soaked with concentrations of 80%, 40%, 20%, or 10% neemol (neem oil emulsion) were placed on the leaf axils of the cut portion of the branches. Controls were untreated. Five trees were assessed to each treatment (all branches pruned in each tree) and the treatments were replicated three times. Regeneration/bud initiation on the cut branches was observed at weekly intervals, and the data on new branch regeneration (branching) and branch length were recorded 30 and 60 d after treatment.

In the second phase, two experiments were initiated on 12 December 2002. In the first of these, the regenerated lateral branches were selected from the first pruned 24 trees and repruned. Three treatments were imposed: 100% concentration of neem oil (Bero Enterprises, Coimbatore, India) 80%, and control (0%). Each treatment was applied on eight trees that served as replications. Weekly observations were made, and the total number of lateral branches re-regenerated per repruned branch was recorded 30 and 60 d after treatment.

In the second experiment of phase two, the main stem and sucker shoots of all 24 trees from experiment 1 were topped and treated with 100% neem oil. Untreated cut shoots served as controls. The total numbers of coppices regenerated per tree, coppices per shoot, and percentage coppices were recorded 30 and 60 d after treatment.

Neem oil contains the triterpenes limonoides, azadirachtin, salannin, meliantriol, nimbin, and nimbidin. These are the best known and seem to be the major and more significant limonoid constituents. The effect of azadirachtin, easily available commercially, in suppressing lateral branching was studied in the final experiment. One-year-old tissue-cultured clonal plantation of Eucalyptus camaldulensis trees, planted at Forest College and Research Institute, Mettupalayam, India (11°19' N; 76°56' E; 300 m above sea level, 750 mm; pH 7.1, temperature ranging from 22°C to 35°C, pre-summer season) under rain-fed condition, were selected to eliminate genotypic variation arising from seed origin. Lateral branches of the selected Eucalyptus camaldulensis trees were pruned on 14 February 2003.

The content of azadirachtin ranged from 2000 to 9000 ppm in neem oil (National Research Council, 1992 ). Cotton was soaked in either 0, 375, 750, 1500, 3125, 6250, 12 500, 50 000 or 100 000 ppm azadirachtin and placed on the leaf axils of the cut portion of the branches. Three trees were selected for each treatment and treatments were replicated six times. Regeneration/bud initiation on the cut branches was observed at weekly intervals, and the data on branch regeneration were recorded 45 and 60 d after treatment. All data were statistically analyzed as in Panse and Sukhatme (1967) .


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 LITERATURE CITED
 
Towards realizing the stated objectives for the first phase of the studies the differences in branch regeneration between treatments with neem oil were significant at different concentrations at the 1% level on 30 and 60 d after treatment (Table 1). Compared to the control, branching was reduced by 41.6% at 80% neem oil 60 d after treatment. The level of reduction decreased with decreasing level of treatment. However, branch length was not influenced by the treatments (Table 1).


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  		Table 1. Mean values for branching and branch length in Eucalyptus tereticornis trees after neem oil treatment

 
In the second experiment of phase 1, pruned and regenerated lateral branches from experiment 1 were used to study the effect of high concentrations of neem oil on further regeneration. The analysis of variance indicated that differences in total number of branches regenerated per tree, regeneration of branches per pruned branch, and percentage branching after neem oil treatment were significant at the 1% level (Table 2).


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  		Table 2. Mean values for suppression of first pruned vigorous branch es in experiment 2 of phase 1

 
Treatment with 100% neem oil reduced regenerating ability by 81.8% at 30 d and 78.19% after 60 d (Table 2). At this concentration, neem oil also caused scorching of leaves and petioles that contribute to the suppression of branches. At 80% neem oil, the reduction was 57.58%. Hence, application of neem oil greatly inhibits branching. Again the magnitude of inhibition paralleled the concentration of the neem oil.

Relative to the control, there was still only approximately 60% reduction with 80% neem oil (Table 2). This degree of suppression may not be sufficient with irrigation. The analysis of variance for experiment three was highly significant at the 1% level in respect to total number of coppices regenerated per tree, coppices per shoot, and percent coppices (Table 3). Furthermore, 100% neem oil inhibited coppicing for as long as 20 d after topping. Normally, if any tree is topped, branches will proliferate as a result of the release of apical dominance. In the present experiment, coppices for the control averaged 176% per shoot. The comparative figure for the 100% neem oil treatment was only 0.15 per shoot, resulting in suppression of apical dominant growth of 98.3% and 85.1% at 30 and 60 d, respectively, after treatment (Table 3). A similar repressive action by neem oil emulsion was reported to be an effective suckericide in tobacco (Bangarayya et al., 1982 ) and to increase surface area of tobacco leaves (Joshi, 1986 ).


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  		Table 3. Mean suppression of coppicing of main stem by top cutting in phase 2

 
In the third phase of the study, the analysis of variance indicated that differences in total number of branches regenerated per tree and percentage branching after the neem oil component azadirachtin were significant at the 1% level (Table 4). Higher concentrations of azadirachtin, especially 50 000 ppm, were accompanied by a 63.3% reduction in regenerating ability (Table 4). At a concentration as low as 3125 ppm, azadirachtin caused scorching of young growing buds, which also may contribute to the suppression of branching. Even at 3125 ppm of azadirachtin, reduction in branching was as high as 50.4%. Normally, neem oil contains azadirachtin ranging from 2000 to 9000 ppm (National Research Council, 1992 ). Hence, inhibition of branching ability following neem oil application is consistent with a primary role for azadirachtin.


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  		Table 4. Mean regeneration of branches by application of azadirach tin at 45 and 60 d in phase 3

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
LITERATURE CITED
 
Neem oil inhibited regeneration of lateral branches in Eucalyptus. The suppression is consistent with the action of pure azadirachtin, which is present in neem oil in concentrations of 2000–9000 ppm. The lower level branches grow actively and are therefore a greater drain on photosynthate. However, their contribution to photosynthesis is minimal (Kramer and Kozlowski, 1960 ). By pruning the lateral branches, the photosynthates that they would have consumed will be diverted to the formation of more stem, which is the harvestable structure.

Suppression of lower branches in Eucalyptus tereticornis trees by application of 100% neem oil will also improve yield by allowing more incident radiation to the ground storey arable crops. The number of trees per unit area can thereby be increased to augment the unit area productivity of trees, benefiting the agroforestry industry. Because neem oil is a proven botanical pesticide against a wide range of pests, its use will also suppress pests in eucalypts stands.


   FOOTNOTES
 
1 The authors acknowledge Dr. Ganesh Kumar, Dr. M. Muthuraman, Professors Entomology, Dr. Md. Yassin, Professor Agroforestry, Dr. K. T. Parthiban, Professor Forestry, for their interaction during these experiments and Dr. R. S. V. Rai, Professor, Forestry Rtd., for his critical comments and constructive suggestions. The authors also thank the Intel for the award of first prize in the National Science Talent Discovery Fair held at Bangalore, India and for sponsoring them as finalists to participate in the Intel International Science and Engineering Fair 2003, Cleveland, Ohio, USA, and judging this for the fourth grand award and second prize under special award. Back

4 Address for reprint requests: D/o. M. Paramathma, C2. IHDL apartment, Amman koil Street, venkittapuram, Coimbatore 641 013, India (e-mail: senthalirp{at}yahoo.co.in ) Back


   LITERATURE CITED
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 LITERATURE CITED
 
Bangarayya M. C. B. Sarma T. Narasimhamurthy D. Prabhakarababu 1982 Suppression of suckers with non-edible oils in f.c.v.tobacco. Tobacco Research 8: 25-29

Butterworth J. H. E. D. Morgan 1968 Isolation of a substance that suppresses feeding in locusts. Chemistry Communication 28: 23-24

Chundawat K. L. Goutham 1999 Text book of agroforestry. IBH, New Delhi, New Delhi, India

Joshi B. G. 1986 Use of neem products of the Tobacco in India. In H. Schumutterer and K. R. S. Ascher [eds.], Natural pesticides from the neem tree and other tropical plants, Proceedings of the Third International Neem Conference, held at Nairobi, 1986, 479–494. GTZ, Eschborn, Germany

Kramer P. J. T. T. Kozlowski 1960 Physiology of trees. McGraw-Hill, New York, New York, USA

Mariappan V. 1995 Neem for the management of crop diseases. Associated Publishing New Delhi, New Delhi, India

Meisner J. K. R. S. Ascher 1986 Insect growth-regulating effects of neem products on Spodoptera littoralis. In H. Schumutterer and K. R. S. Ascher [eds.], Natural pesticides from the neem tree and other tropical plants, Proceedings of the Second International Neem Conference held at Eschborn, Rauischholzhausen, Germany, 1986, 345–352

Midgley S. D. Boland 1998 Influence on the international exchange of forest genetic resources—an Australian perspective. In IUFRO Conference on forest genetics and tree improvement, Contribution of genetics to the sustained management of global forest resources, 1998, Beijing, China, 22–28

Nair P. K. R. 1989 Agroforestry systems in the tropics. Kluwer Academic, London, UK

National Research Council. 1992 Neem tree for solving global problems. National Academy Press, Washington, D.C., USA

Panse V. G. P. V. Sukhatme 1967 Statistical methods for agricultural workers. Indian Council of Agricultural Research, New Delhi, New Dehli, India

Rembold H. H. Forster C. H. Czoppelt P. J. Rao K. P. Sieber 1986 The azadirachtins, a group of insect growth regulators from the neem tree. In H. Schumutterer and K. R. S. Ascher [eds.], Natural pesticides from the neem tree and other tropical plants, Proceedings of the Second International Neem Conference held at Eschborn, Rauischholzhausen, Germany, 1986, 153–162

Ruscoe C. N. E. 1972 Growth disruption effects of an insect antifeedant. Nature, New Biology 236: 159-160[CrossRef][ISI][Medline]

Zobel B. J. Talbert 1984 Applied tree improvement. John Wiley, New York, New York, USA





This Article
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Right arrow Articles by Senthalir, P.
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Right arrow Articles by Senthalir, P.
Right arrow Articles by Paramathma, M.
Agricola
Right arrow Articles by Senthalir, P.
Right arrow Articles by Paramathma, M.

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