SOME ENZIMATIC ALTERATIONS IN POTATO CAUSED BY FUNGICIDES

Abstract

Chemical pest management in potatoes (Solanum tuberosum L.) is the most practical approach. Some fungicides have direct action over the plant, usually in the presence of the pathogen, with no clarification on the host reaction either to the pathogen, to the product or to both. The objective of this study was to evaluate some plant defense enzymatic alterations stimulated by the application of systemic fungicides in the absence of pathogens, and to identify a possible specificity of an enzymatic reaction to a given product. Under greenhouse conditions, potato plants cv. Ágata were weekly sprayed at half and complete dosages of fungicides, sampling foliage with the same frequency followed by analyzing presence-action of several enzymes related to non-specific defense reactions. Total amount of phenols (FEN) was pretty close among treatments, except for the complete dosage of fluoxastrobin, which stimulated phenol synthesis over the other fungicides at the end of the growing cycle. Superoxide dismutase (SOD) activity, on the other hand, was more stimulated along the first half of the growing cycle, especially in the controls. Its action was more uniform among treatments later on, except again for the half dosage of fluoxastrobin, which kept SOD activity higher than the rest of the fungicides. All treatments uniformly stimulated peroxidase (POX) activity over the control (water) at the end of the cycle. Catalase (CAT) activity continuously decreased along the growing cycle in the control plants, while the fungicide treatments stimulated its activity mainly at midseason, with no specific outstanding stimuli by any particular fungicide over this enzyme. Significant interactions were detected between POX and CAT, POX and SOD, and FEN with SOD and POX, as an indication of similar responses or mutual dependency among them to more than one product on non-specific reactions due to the external chemical stimuli. Early specificity was identified for fosetyl-Al as POX stimulant, and for fluoxastrobin for SOD.