Indutores de resistência e demais associações no manejo da ferrugem e cercosporiose do cafeeiro (Coffea arabica): análises bioquímicas e fisiológicas

Abstract

Coffee leaf rust (CLR) and Brown eye spot are the main fungal diseases of coffee plants in Brazil, caused by Hemileia vastatrix and Cercospora coffeicola, respectively. The use of resistance inducers (RIs) in the management of plant diseases is a promising measure, since these products activate the mechanisms of defense against a broad spectrum of pathogens. Thus, this study aims at evaluating the effect of resistance inducers in the management of those diseases in different plant growth conditions: field, growth chamber (Fitotron) and greenhouse. Under field conditions, sources of phosphonates and copper - basic formulation and formulation based on products of the coffee crop industry, were applied alone or in association with fungicide. It was observed that all the associations and the fungicide applied alone showed a better behavior than the other treatments. Among all the alternative products tested alone, K phosphonate (2) stood out from the others for rust control, which was similar to the fungicide. Of the treatments applied in isolation, the Greenforce CuCa (by-product formulation of the coffee industry added copper and calcium) and cuprous oxide provided less percentage of defoliation. For productivity, among the treatments without association with fungicide, Greenforce CuCa and K phosphonate (2) were significantly better than the others. Regarding the chemical composition of the grains, the treatment with Mn phosphonate presented the highest values for trigonelline, caffeine, and chlorogenic acid. For plants kept in Fitotron, Greenforce CuCa was selected to study its biochemical and physiological effects on the interaction of coffee plants with H. vastatrix compared to the standard resistance inducer acibenzolar-S-methyl (ASM). The activity of peroxidase (POX), ascorbate peroxidase (APX), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) enzymes was evaluated, as well as quantification of hydrogen peroxide, lipid peroxidation, phenol and lignin. In addition, parameters related to leaf gas-exchange were evaluated: liquid photosynthesis rate, stomatal conductance, transpiratory rate, intercellular CO2 concentration in the mesophyll (Ci), intercellular CO2 concentration in the mesophyll/current external CO2 concentration (Ci/Ca), water use efficiency, andinstantaneous carboxylation efficiency. It was observed that the foliar application of Greenforce CuCa in coffee seedlings induced resistance in plants, providing better preservation of the photosynthetic apparatus. The anti-oxidant system (SOD, POX and APX)was efficient in eliminating excess reactive oxygen species in order to prevent the cellular damages caused by H. vastatrix. In plants treated with ASM, biochemical modifications were more evident at the level of PAL and PPO enzymes, which suggests alterations related to the metabolism of phenolic compounds. Finally, greenhouse plants were used to evaluate the efficacy of Greenforce CuCa compared to ASM in rust control. Greenforce CuCa showed greater disease control than ASM. On the other hand, there was a decrease in the physiological parameters (leaf gas - exchange and determination of chlorophyll) after the inoculation with H. vastatrix. However, in the IRs (Greenforce CuCa and ASM) treated plants, this decrease was not as drastic as in the control plants. The content in secondary metabolites, chlorogenic acid, trigonelline and caffeine was also analyzed throughout the infection process. The application of resistance inducers and the inoculation with H. vastatrix altered the analyzed variables, indicating the influence of the treatments on both the physiological parameters and the content of the secondary metabolic compounds. The application of IRs contributed in a favorable way to plant integrity.