Aplicação foliar de cobre, cálcio e magnésio na cercosporiose e respostas de defesa em mudas de cafeeiro

Abstract

The growing demand for sustainably produced food is driving the search for alternative measures for managing diseases in agricultural crops, such as in coffee cultivation (Coffea arabica). However, its production can be affected by the occurrence of cercosporiosis, a disease caused by the fungus Cercospora coffeicola. A promising measure is the activation of plant defense mechanisms through the application of micro and macronutrients. This study aimed to evaluate the effect of applying nutrients containing different doses of copper, together with calcium, magnesium, and their combinations, in the management of cercosporiosis in coffee plants. Experiments were conducted under greenhouse conditions using the Catuaí Vermelho IAC 144 cultivar. The applied treatments consisted of a negative control (without nutrient application), a positive control (fungicide: pyraclostrobin and fluxapyroxad), and six combinations of pentahydrated copper sulfate (Cu) associated with magnesium oxide (Mg), calcium oxide (Ca), and calcium oxide and magnesium oxide (CaMg) in the proportions of 4:1 and 2:1 (4Cu1Ca; 4Cu1Mg; 4Cu1CaMg; 2Cu1Ca; 2Cu1Mg; 2Cu1CaMg). The plants were inoculated with C. coffeicola seven days after the application of treatments. Subsequently, the disease progress and the activity of defense enzymes phenylalanine ammonia-lyase (PAL), peroxidase (POX), and superoxide dismutase (SOD) were evaluated at 6, 24, 48, and 72 hours after inoculation (hai). Additionally, the levels of soluble lignin, total phenolic compounds, chlorophyll a and b were analyzed at 15 days after application. The results indicated that the application of nutrients resulted in a reduction in the disease progress, with the treatment 4Cu1Ca standing out. Additionally, there was an increase in the activity of the POX enzyme at the evaluated time points, and an increase in PAL enzyme activity only at 6 hai. The SOD enzyme activity was significantly similar across treatments. Differences were observed in the interaction of calcium and magnesium when evaluating lignin levels, although this difference was not observed in total phenolic compound levels nor in the levels of chlorophyll. These results suggest that the application of nutrients can trigger defense responses in plants, including the accumulation of lignin, which strengthens cell walls and assists in plant resistance to pathogens.