EFFECTS OF HOMEOPATHIC DILUTIONS ON PLANTS AND THE POTENCIAL USE OF HOMEOPATHY ON PLANT DISEASES. Lucietta Betti1, Grazia Trebbi1, Lisa Lazzarato1, Maria Grazia Fantino1, Daniele Nani2. 1Department of Agroenvironmental Sciences and Technologies, Bologna University, Italy; 2Società Italiana Medicina Antroposofica, Milano, Italy. E-mail: lucietta.betti@unibo.it

Most criticism about homeopathy concerns the lack of a scientific basis and theoretical model. Plant-based bioassays could provide a suitable tool for basic experimentation in homeopathy because they overcome the main disadvantages of clinical trials, such as placebo effects, ethical difficulties, consumption of time, low number of replications, high costs [1]. Scientific literature on the effects of homeopathy on plants provides a limited number of papers. An extensive and critical review on this topic was written in 1984 by Scofield [2], therefore only subsequent literature will be here considered and divided into “germination/growth models”, “phytopathological models” and “field trials” (table 1). Many of the reported plant-based bioassays have a good methodological structure, are supported by statistical analyses and generally show significant results, at least with some of the treatments tested. Unfortunately some papers, cited in different articles and concerning both germination/growth models [3-5] and phytopathological ones [6-12], are hard to find and for this reason they are not included in table 1.
Germination/growth models
Among the numerous plant model systems studied, the classic test of germination and growth has been quoted as a basic model for research on homeopathy since the pioneering work of Kolisko on wheat [13] and many experiments have been performed with this species [14-20]. Moreover, wheat germination is the theme jointly investigated by the Betti and Baumgartner research groups: reproduction trials were performed resulting in significant but opposite effects [19; 20]. Experiments on other species have been carried out, evaluating growth parameters [21-34] and biochemical responses [22-24; 28]. A stable and reliable test system is represented by in vitro growth of yeast [31-34], which seem to react to certain potentised substances by changing its growth kinetics [34].
Phytopathological models
Most of available papers focussed on fungal infections [35-41]: following homeopathic treatments, a decrease of disease symptoms, post-harvest losses, fungal germination and respiration rate of germinating spores were evidenced.
Table 1. Summary of plant bioassays with homeopathic treatments: references (in brackets), experimental main features and observed effects are reported

Germination/Growth models
Reference Species Treatment Working variable Effect
Betti et al., 1994 [14] wheat dH As203 germination +
Pongratz & Endler, 1994 [15] wheat dH AgNO3, PC germination, shoot growth +
Betti et al., 1997[16] wheat dH As2O3, PC shoot growth +
Pongratz et al., 1998 [17] wheat dH AgNO3 shoot growth +
Brizzi et al., 2000 [18] wheat dH As2O3, PC germination +/-
Brizzi et al., 2005 [19] wheat dH As2O3 shoot growth +
Binder et al., 2005 [20] wheat dH As2O3 shoot growth –
Hamman et al., 2003 [21] barley cH gibberellic acid germination, root and shoot growth +
Carvalho et al., 2003 [22] feverfew dH Arnica montana shoot growth, parthenolide content +, –
Carvalho et al., 2004 [23] feverfew
cH Natrum muriaticum, nosode shoot growth,
chlorophyll and proline content n.s.
Carvalho et al., 2005 [24] feverfew cH Arnica montana shoot growth, parthenolide content n.s., –
Projetti et al., 1985 [25] lentil cH CuSO4 root growth +
Bornoroni, 1991[26] oat IAA, cH CaCO3, PC shoot growth +/ n.s.
Endler & Pongratz, 1991 [27] African violet dH IBA, PC root and leaf growth +
Andrade, 2001[28] chambà • homeopathic treatments coumarins content +
Bonato & da Silva, 2003 [29] radish cH, McH Sulfur shoot and root growth +
Baumgartner et al., 2004 [30] dwarf pea dK, dH plant hormones, PC shoot growth +
Steffen 1984 [31] yeast dH Ag NO3, CuSO4, HgCl2, NaCl in vitro growth n.s.
Steffen 1985 [32] yeast cH pulsatilla in vitro growth n.s.
Hagelberg 1987 [33] yeast homeopathic treatments * in vitro growth n.s.
Scherr et al., 2006 [34] yeast 14 substances in dH potencies, PC growth kinetics +/-, n.s.
Phytopathological models
Reference Species/pathogen Treatment Working variable Effect
Saxena et al., 1987 [35] reed okra/ seed-borne fungi cH Thuja, nitric acid, Sulphur, Calcarea carb., Teucrium Q fungal spore germination –
Khanna & Chandra, 1989 [36] mango, guava, tomato/ Pestalotia spp., Fusarium roseum homeopathic treatments and adjuvants post-harvest losses –
Khanna & Chandra, 1992 [37] different fungi•• dH treatments spore respiration rate,
organic acid pool in spores –
Aggarval et al., 1993 [38] wild taro/
Phytophthora colocasiae homeopathic treatments** disease symptoms, fungal growth and spore germination

Rivas et al., 1996 [39] wheat,tomato/ Alternaria solani cH treatments*** seed and spore germination +/-
Rolim et al., 2001 [40] apple/Podosphaera leucotricha cH treatments**** powdery mildew symptoms –
Diniz et al., 2006 [41] tomato/ Phytophthora infestans cH isopathic treatment late blight symptoms n.s.
Cheema et al., 1986 [42] papaya/Papaya mosaic virus homeopathic treatments disease symptoms –
Cheema et al., 1993 [43] tomato/Tobacco mosaic virus Clerodendrum aculeatum, cH Thuja disease symptoms –
Betti et al., 2003 [44] tobacco/Tobacco mosaic virus dH As2O3, PC virus-induced hypersensitive lesions –
Sukul & Sukul, 1999 [45] cowpea/Meloidogyne incognita cH Cina plant growth,
nematode infection +

Datta, 2006 [46] mulberry/ M. incognita cH Cina plant growth, nematode infection +, –
Sukul et al., 2006 [47] lady’s finger/ M. incognita cH Cina, Santonin, Ethanol nematode infection
root-protein and -water content –

Field trials
Reference Species/pathogen Treatment Working variable Effect
Kaine, 1991 [50] rye grass cH Sulphur, Silicea, Carbo vegetalis plant growth n.s.
Trebbi et al., in preparation [51] cabbage/Alternaria brassicicola dH As2O3 disease severity –
dH, cH, McH = decimal, centesimal, hundred thousand hannemanian potency; dK = decimal korsakovian potency; PC = potentized control (as additional control); IAA = indole acetic acid; IBA = indole butric acid
• = Justitia pectoralis; •• = Alternaria alternata, Colletotrichum gloeosporioides, Fusarium roseum, Gloeosporium psidii, Pestalotia mangiferae, Pestalotia psidii;
*= Sulphur, Arnica montana, Chamomilla, Bryonia alba, Euphrasia officinalis, Pulsatilla; ** =Kali iodatum, Arsenicum album, Blatta orientalis, Thuja occidentalis; ***= Arsenicum album, Calcarea, Cuprum, Ferrum metallicum, Lycopodium, Natrum, Phosphorus, Selenium, Silicea, Sulphur; **** = Kali iodatum, Lachesis trigonocephalus, Staphysagria, Sulphur, Oidium lycopersici
+ = stimulating or increasing effect; – = inhibiting or decreasing effect; +/- = different effects according to the potency used or plant physiological conditions

A few studies took into account viral infections [42-44] and in this case, too, a weaker symptomathology was observed. In particular, in blind, randomized experiments using tobacco plants, carrying tobacco mosaic virus (TMV) resistant gene N, inoculated with TMV, a significant enhancement of plant resistance was obtained following As2O3 dH 5 and 45 potencies [44]. As far as nematode infection is concerned, a few papers are available as well [45-47]: plants treated with homeopathic preparations showed improved growth (in terms of shoot and root length) and reduced nematode infection (in terms of root gall number and nematode population in root and soil). Root- and leaf-protein content and root-water content are also affected by homeopathic treatments.
Field trials
Scientific literature provides very few and outdated descriptions of field trials. Aside from two studies on trees affected by virus [48] or fungus [49], the only paper easily available is that of Kayne [50], who reported the results of a field trial on rye grass. The application of homeopathic sprays (cH Sulphur and mixture of cH Sulphur, Silicea and Carbo vegetalis) did not give significant effects on plant growth, however some methodological hints for testing homeopathic treatments emerged: the choice of remedy, potency and frequency of application is crucial and should be made with great care to ensure the best chance of success. As there are no guidelines for plants like those of Materia Medica for humans much more experimentation is needed.
The reduction of copper salts in organic agriculture following European directives (Commission Regulation EC no. 473/2002) provided the context for a 3 year project (2003-2006), financed by the Marche region (Italy), on biological control of Alternaria leaf spot caused by Alternaria brassicicola in cauliflower. The disease appears on the leaves and cauliflower heads as dark brown spots. In order to evaluate the effects of homeopathic treatments on fungus infection, experiments in phytotron and a field trial were carried out. Plants were artificially inoculated by spraying a fungal suspension (1×107 conidia ml-1) on the leaves. The effect of homeopathic treatments was compared with those of copper oxiclorure at different concentrations (0.3, 1, and 3 g/l), the control being water treatment. All these treatments were sprayed weekly on the leaves 3 times before and 4 times after fungal inoculation. In phytotron, treatments with As2O3 dH 35 and 45, AgNO3 dH 35, 36, 45 and 46, Sulfur dH6, cH5 and 201, Cuprum dH5, isopathic cH4 were tested. Statistical analysis (ANOVA) did not show any significant result; nevertheless, the more marked reduction of leaf symptoms vs. control was observed in both measurements (13 and 18%, respectively) in plants treated with As2O3 dH 35 (Figure 1A). Copper oxiclorure treatments induced a significant reduction (p<0.05 or p<0.01, ANOVA followed by Dunnett’s post-test) of disease severity at all concentrations. In field trial [51], each treatment (As2O3 dH 35, copper oxiclorure 0.3, 1 and 3 g/l and water as a control) was replicated four times in a randomized complete block design. Disease assessments on cauliflower heads, performed in 3 successive times (Figure 1B), showed in the last measurement a significant reduction (46%, p<0.05) of disease symptoms for both As2O3 dH 35 and copper oxiclorure 3 g/l. Since fungal inoculation was performed on the leaves before flowering, we can hypothesize that homeopathic treatment As2O3 dH 35 induced a plant resistance increase to fungal infection. The similar symptom reduction due to copper oxiclorure 3 g/l could be explained as a inhibiting effect of the treatment on fungal spore germination. These results need further investigations but they seem to support the possibility of an agricultural application of homeopathy. The privileged target of agrohomeopathy could be small farms (and in particular, those of nutraceutical and herbalist sectors) practicing organic and sustainable agriculture that strive to be environmentally responsible, economically viable, and socially just.Conclusions and perspectives The literature on homeopathy and plants is limited in comparison with medical studies and not as easily available. Nevertheless, interest in this field appears to be growing in recent years and several projects are in progress, mainly in Central and South America. In general, the potential prospects for homeopathic treatments in agriculture can be considered promising, but much more work is needed especially at a field level, since the influence of environmental and agronomical factors (temperature, drought, humidity, plant cultivars and so on). might significantly change the quality of yields and thus the results of successive experimentations. Finally, we must stress that results of all research and projects, whether successful or not, should be made widely available so that others can learn from these, thus avoiding duplication and inefficiency. Moreover, replication of results and multicentre trials should be performed, to be published in international journals with an impact factor or wide circulation, to gain credibility and facilitate funding.References 1) Betti L, Borghini F, Nani D. 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