Resumo:
Environmental stress refers to any change in environmental resources needed for optimal plant development, preventing them from reaching their maximum production capacity. The coffee crop is overly sensitive to stress, with low temperatures and drought being the main constraints on its global production. There has been an increase in extreme natural events in Brazilian coffee-growing areas over the past few decades, which raises concerns about coffee production in Brazil. The use of plant nutrition has been proven effective in mitigating the negative effects of these adversities, with selenium (Se) being highlighted as a valuable tool in combating such adverse conditions. Previous studies have demonstrated that Se supply leads to a more effective antioxidant system, improved water relations, and modulated carbohydrate production and breakdown in plants. However, the impact of Se application on the coffee crop has not been thoroughly addressed in the literature. The objective of this thesis was to explore whether foliar application of Se to coffee plants under low temperatures and drought stress can alleviate the negative effects and contribute to more efficient plant nutrition strategies under such challenging conditions. The first trial evaluated the plant responses of two coffee species (Coffea arabica cv. Arara and Coffea canephora clone 31) to low temperatures (10°C day/4°C night) and during the rewarming period temperatures (25°C day/20°C night). Notable variations in plant responses were observed among species, with Coffea canephora being more sensitive to low temperatures. Plant responses were more pronounced during the rewarming period. Selenium application increased carbohydrate and proline contents in the leaves after stress, enhancing the plant’s ability to overcome the stress. In the second trial, the optimal timing for Se application in Coffea arabica cv. Catuai plants under osmotic stress induced by PEG-6000 was assessed. The results showed that pre-application of foliar Se promoted higher activities of antioxidant enzymes and improved water relations in the leaves compared to the control. However, Se application after the osmotic stress appeared to induce additional stress in the plants, resulting in a reduction of leaf water potential. Overall, Se application stimulated metabolic responses to tackle abiotic stress in coffee plants, and the findings of this thesis may provide support for nutritional management techniques to mitigate the negative effects of stresses on coffee trees.
