Influência da temperatura nos aspectos reprodutivos da oliveira (Olea europaea L.) na região sul do Rio Grande do Sul

Abstract

The main objective of this work was to investigate the phenological aspects and thermal requirements of olive cultivars in the Southern Region of Brazil, as well as to evaluate the effects of temperature on stigma receptivity, pollen germination, and pollen tube growth. Additionally, it aimed to verify whether the application of boron at different concentrations could mitigate the effects of temperature on the latter two processes. The first article refers to the phenological characterization of the main olive cultivars in the southern region of Rio Grande do Sul between 2015 and 2024, relating the phenological stages to local thermal conditions. The base temperature (Tb) and accumulated thermal sum (STa) were determined for each stage. The cultivars Arbequina and Koroneiki showed lower Tb values and longer phenological cycles, while Picual required a higher Tb, accumulated more STa, and completed its cycle in less time. The second article evaluated the thermal requirements of four olive cultivars (Arbequina, Koroneiki, Picual, and Arbosana) between 2015 and 2024, focusing on the bud break and flowering stages. Chill hours (CH), chill units (CU), and accumulated thermal sum (STa) were determined. Results showed that chill accumulation ranged from 136 to 419 CH, while STa for bud break and flowering ranged from 61.50 to 242.80°C·day⁻¹. Arbequina and Koroneiki required less chilling and presented higher STa, whereas Picual demanded more chilling and lower STa. Mild winters anticipated phenological events, and insufficient chilling compromised floral synchrony. The study reinforces the importance of proper cultivar choice and thermal management to maintain productivity in subtropical regions. The third article assessed the effects of temperature (18 °C and 28 °C) and stigma exposure time (24, 48, 72, and 96 hours) on stigma receptivity in olive cultivars (Arbequina, Koroneiki, and Picual), analyzing pollen adhesion, germination, and pollen tube penetration. Conducted under controlled conditions in Southern Brazil (2023–2024), results indicated that ‘Picual’ showed greater stability and reproductive performance. At 28 °C, stigma receptivity was prolonged, and pollen germination increased. ‘Koroneiki’ and ‘Arbequina’ showed greater thermal sensitivity. These data highlight the importance of thermal control to optimize olive fruit set. For the fourth article, in vitro effects of different temperatures (12°C, 22°C, 25°C, and 12–22°C alternation) and boron concentrations (0, 100, 150, 200, 250, and 300 mg·L⁻¹) on pollen germination and pollen tube growth of the olive cultivars Arbequina and Manzanilla were evaluated. Pollen germination and pollen tube growth in olive trees vary according to temperature and boron concentrations. ‘Manzanilla’ tolerates low temperatures and requires higher boron levels, while ‘Arbequina’ performs better at higher temperatures and moderate boron concentrations. Doses above 200 mg·L⁻¹ are toxic, requiring cultivar-specific management.