Abstract
In recent years, North-western Spain has experienced an increase in the cultivated area of olive trees. The main propitious areas for olive groves are the Miño and Sil basins, as a consequence of their Oceanic climate with Mediterranean influence. The objective of this study is to determine the characteristics of reproductive biology, phenological and aerobiological behaviour of olive trees in the most northerly new plantation areas of the Iberian Peninsula. The study was carried out in an olive grove growing Olea europaea L. cv. ‘Arbequina’ located in Quiroga (Lugo) from 2016 to 2018. The phenological observations were based upon the main growth stages following the Biologische Bundesanstalt Bundessortenamt and Chemical industry (BBCH) scale. To predict the onset of flowering, a thermal time model was used in order to quantify the chill requirements, and growing degree-days were applied to determine the heat requirement. The production, viability and germination rates of Olea pollen were evaluated from samples selected in nine individual trees for the phenological survey. The aerobiological study was conducted by means of a Hirst-type pollen trap located in the centre of the olive grove. The vegetative period of the olive tree in the study area lasted an average of 259 days. The important phenological stage 6 (flowering) was the shortest stage. An average of 704 Chilling Hours (CH) with a threshold of 2.5 °C was required to overcome the chilling period, 1139 Growing Degree Days (GDD) for the beginning of flowering, and 4463 GDD for harvest. The pollen production per anther was 82589 grains (± 14084 pollen grains), with a rate of 81% viability and 12% pollen tube germination. The main pollen season started on average on May 20th and ended on June 16th with an average duration of 27 days and an annual pollen integral of 833 pollen grains. The low pollen concentrations could be a consequence of the Northern location of the forest, in a bioclimatic transition zone between the Eurosiberian and the Mediterranean areas, at the limit of olive tree distribution.
Highlights
The olive tree (Olea europea L.) is one of the most widespread tree species in the Mediterranean basin, exerting a great economic and social influence through its fruit and its oil [1]
Stage 5 of inflorescence development occurred an average between mid-March and the second week of May depending on the year of study (Figure 2)
The presence of Olea pollen in the olive grove atmosphere was registered between the end of stage 5 and all of stage 6, in which the highest amounts of pollen were recorded (Figure 5)
Summary
The olive tree (Olea europea L.) is one of the most widespread tree species in the Mediterranean basin, exerting a great economic and social influence through its fruit and its oil [1]. The release of floral bud dormancy occurs when olive trees have been exposed to chilling temperatures for a sufficient time depending on the biogeographic area [8,11] Once this chilling is fulfilled, certain amounts of heat-thermal units are required for the correct development of inflorescence [13]. The transition between endodormancy and eco-dormancy is not distinguishable, physiological and anatomical changes were identified in olive flower buds during dormancy when compared to vegetative buds [13] The relationship between both chill and heat requirements has been reported by different authors who consider that chilling temperatures accelerate growth renewal once dormancy is broken; the more chilling units are accumulated, the fewer forcing units are needed later for budburst [14,15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
