Highly diluted arsenic affects plant resistance to pathogens and nutraceutical properties

In recent decades intensive agriculture posed severe environmental problems with detrimental consequences on human health. For this reason, in recent years there has been a spread of environmentally and economically sound agricultural methods. Among these, organic production systems are now under widespread development. In this context homeopathic preparations, due to their extreme dilutions, could be suitable for use in organic agriculture. The present work is aimed at evaluating the effects of highly diluted arsenic trioxide (As2O3) on three plant models: 1) Tobacco plants carrying the TMV resistance gene N inoculated by tobacco mosaic virus (TMV); 2) Cauliflower inoculated by the fungus Alternaria brassicicola; 3) In vitro bean germination 1) In this model , As2O3 treatment was chosen on the basis of the hypersensitive-like reaction (necrotic spots) induced by As2O3 in phytotoxic concentration on healthy tobacco leaves .The experimental set-up consisted in a blind, randomized scheme using tobacco leaf disks. TMV inoculated leaf disks were floated for 3 days in the homeopathic treatments and in control (distilled water). The working variable was the area and the number of hypersensitive lesions per disk evaluated 3 days after virus inoculation. Results showed that 5 and 45 decimal potencies of arsenic induced significant reductions of area and number of necrotic lesions vs. control. 2) In cauliflower/Alternaria brassicicola model, growth chamber (i) and field (ii) experiments were performed: (i) As2O3 35 dH (As) , As diluted 1:5000 and a bentonite treatment (10 g/l) were compared with copper oxicloride (Cu) at 0.3, 1, and 3 g/l, and ß-aminobutyric acid (BABA, 5 mM), the control being water; (ii) the field was divided in plots (6 plants/treatment), each treatment being replicated four times in a randomized complete block design. Treatments were sprayed weekly on the leaves before and after artificial fungal inoculation. Results of (i) confirmed the significant effect in disease control of As (infection level reduction vs. control of about 40%); Cu and BABA significantly reduced disease severity. In (ii), disease assessments on cauliflower heads showed a similar and significant reduction of disease symptoms for As, bentonite and Cu 3 g/l, with a relative efficacy vs. control of 46%, 42%, 45%, respectively. Moreover, As treatments induced an increase of total glucosinolate content in healthy cauliflower heads. 3) In vitro bean germination experiments are still in progress: the aim is to verify the effects of highly diluted treatments on germination percentage and rate; moreover, an evaluation of nutraceutical properties (phytoestrogens and melatonin content) will be performed.