Ultra high diluted arsenic reduces spore germination of Alternaria brassicicola and dark leaf spot in cauliflower

Grazia Trebbi,Lucietta Betti,Maurizio Brizzi,Giovanni Dinelli,Valeria Bregola,Paola Nipoti

doi:10.1590/s0102-05362016003003

Abstract

ABSTRACT A major problem in cauliflower crop is the fungus Alternaria brassicicola, which causes dark leaf spot on Brassicaceae family. The current use of copper salts in agriculture is questioned. In fact, these products present some disadvantages, connected mainly with their deposits in the soil and toxicity on plants. This work investigated the effects of arsenic treatments, in ultra high diluted form (UHD), prepared by a process of repeated dilution and succussion (shaking), through: 1) in vitro germination experiments, where spores of A. brassicicola were suspended in the treatments; 2) in planta experiments and 3) a field trial, where cauliflower plants infected by the fungus were sprayed with treatments. The results showed that ultra high dilutions of arsenic (where no more molecules of this substance are present) were effective in all the experiments, inhibiting spore germination by 60.0%, controlling fungal disease in in planta experiments (relative efficacy of 42.1%), and, in field trial, decreasing the mean infection level in cauliflower heads by 45.7% and 41.6% in artificially inoculated and naturally infected plants, respectively. This is the first study to demonstrate that ultra high dilutions effectively reduce in vitro spore germination and infection of A. brassicicola in cauliflower plants, both under controlled conditions and in the field. Our research is still very experimental, however, in light of the significant results obtained with ultra-diluted arsenic, and given that its extreme high dilution level precludes any toxicity or accumulation in the environment, the use of UHDs could be considered a potential and reliable approach for sustainable agriculture.

Highlights

Arsenico ultra diluído reduz a germinação de esporos de Alternaria brassicicola e mancha foliar escura em couve-flor
Among the natural compounds admitted in such systems, copper-based products are widely applied for the control of dark leaf spot, as well as of most fungal diseases
The emerging discipline of “agro-homeopathy” the application of homeopathy to agriculture - could offer potential benefits because homeopathic preparations, due to their high dilution, are relatively cheap and may have few or no ecological side-effects. This agricultural approach is currently being developed in Brazil, where it is legally provided by the organic production regulations

Summary

Introduction

Arsenico ultra diluído reduz a germinação de esporos de Alternaria brassicicola e mancha foliar escura em couve-flor. The hypothesis is that, since the dynamization process introduces mechanical energy and turbulence into the system, the preparation procedure (dilution and succussion) can generate long-term alterations in UHDs, as evinced by numerous physical and chemical variables (Yinnon & Elia, 2013) Such alterations might act as an “external frequency”, capable of communicating its oscillations, via a process of resonance, to biological fluids and complex “metastable” structures capable of oscillating (macromolecules, alpha-helixes, membranes, filamentous structures, receptors) (Bellavite et al, 2014).The scientific literature on the effects of UHDs on plants includes several studies, recently reviewed (Majevsky et al, 2009; Jäger et al, 2011a), most of which deal with the classical test of in vitro germination and growth. The aim of the present investigation was to select some UHDs that might be proposed for practical use in a sustainable agriculture context To this end, we conducted an initial screening in the laboratory to investigate whether certain test substances can have direct effects on A. brassicicola spores (in vitro germination experiments) or/and control fungal infections in cauliflower plants under controlled conditions (in planta experiments). After selecting the test substances which yielded the best pathogen control, the step was to verify their efficacy in a field trial

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