Spring Influences on Olive Flowering and Threshold Temperatures Related to Reproductive Structure Formation

Several bioclimatic studies have been developed over recent years considering temperature trends and their influence on vegetative and reproductive phenomena during plant growth. In the applied aerobiology laboratory of Perugia University, various studies of olive (Olea europaea L.) flowering and its relationship with climatic variables have been conducted. Since 1999, a flowering monitoring network in central southern Italy has been working to track the biological phenomena over the years, the possible differences between the monitoring stations, and the relationships with climate. Olive flowering was monitored in 15 monitoring stations located in four Italian regions (Campania, Calabria, Puglia, and Sicily) representing 90% of national olive territories. The flowering phenophase was studied through pollen emission monitoring, making use of scientific instruments that capture defined volumes of atmosphere and allow us to ascertain the pollen emission trends, thereby determining daily average pollen concentrations (pollen grains/m(3)). The combined analysis of pollen monitoring and meteorological data permitted identifying various groups of stations characterized by the fact that better relationships between reproductive structure development and growing degree-days are obtained with different spring threshold temperatures (low 7 to 10 C or high 11 to 14 degrees C). Moreover, the study permitted demonstrating particular meteorological and biological behaviors, providing useful information about plant climate relationships in a species of economic interest affected by interincompatibility.