Olive inflorescence and flower development as affected by irradiance received in different positions of an east-west hedgerow

Olive tree productivity is highly responsive to radiation conditions, so understanding the responses of the developmental processes that determine yield, including inflorescence and flower differentiation, is essential for orchard design and management. This is particularly true in the new intensive hedgerow orchards, where radiation reception highly depends on canopy height and row orientation and spacing. In an east-west-oriented olive 'Arbequina' hedgerow located in Toledo (Spain), inflorescences were sampled from both sides (south and north) of the hedgerow canopy, at heights of 0-0.4, 0.8-1.2 and 1.6-2.0 m above the soil. Floral quality was determined at different levels of morphogenetic organization: inflorescence, flower, and ovary. Daily irradiance intercepted during 1 month before flowering by each canopy position was estimated using a model. The more highly illuminated south side received 31% more irradiance overall than the north side. Upper-layer irradiance was greater than the bottom layer, 4.0 and 1.5 times for the north and south sides, respectively. Inflorescence flower number and perfect flower proportion were similar at different heights on the south side. In contrast, north-side upper-layer inflorescences had more total flowers and perfect flowers than at lower hedgerow heights. At each height, perfect flower proportion was higher on the south than north side, while the remaining traits were similar between sides. Ovary tissue size, observed in histological preparations, did not vary among heights on each side, but was higher on the south than north side due to endocarp size. Simulated irradiance at flowering explained 90% of the observed variation of perfect flower number per inflorescence. Overall, the results emphasize the importance of irradiance at different hedgerow sides and heights on olive floral structures.