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

Resumo

A major problem in cauliflower cultivation is the fungus Alternaria brassicicola, which causes dark leaf spot in 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 phytotoxicity phenomena. This work investigated the effects of treatments in ultra high diluted form, 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 show 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 but, 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.