Response of three Greek olive cultivars to heat stress during flowering

Flowering is one of the most critical processes of the olive tree . Air temperature during flowering has been reported to influence oil quantity, quality and yield. Previous studies have shown a detrimental effect of temperatures of around 30-35°C on olive flower bud development. Furthermore, temperatures higher than 25°C have been reported to negatively influence pollen tube growth. In this work, three olive cultivars (‘Lefkolia Serron’, ‘Koroneiki’, and ‘Mastoidis’) were used to assess the effect of an exposition of temperature 30°C for 24 h at inflorescence emergence and first flower opening stage on the number of flowers and fruits. In addition, pollen germination and tube growth were analyzed in vitro. Results showed no differences caused by the temperature treatment, and the only differences found in the number of inflorescences and the number of flowers per inflorescence at flower opening were due to the genotype. The highest number of inflorescences and flowers per inflorescence were observed for ‘Koroneiki’ and ‘Mastoidis’, respectively. The number of fruits as well as the pollen germination rate and the pollen tube growth in vitro showed differences between cultivars. Pollen tube length was influenced by the higher temperature in ‘Mastoidis’. We suggest that studies of climate change effects on crops should employ various approaches and techniques to elucidate complex adaptation processes that may underly. In the present case, increased temperature at 30°C had minimal effects on flowering and fruit set when applied in vivo, in contrast with previous in vitro studies reporting severe damages in pollen germination.