Flower production and phenology in Dactylis glomerata

The species Dactylis glomerata is one of the most important sources of airborne grass pollen in the atmosphere of temperate countries. The aim of this study was to determine the relationship between flowers, weather and the contribution of their pollen in the air. The plants were cultivated in an experimental garden in south-western Spain, which lies next to a spore trap and a meteorological station. The flower phenology and variation in the number of inflorescences were studied for 6 years (2009–2014); flower and pollen production were analysed in the first and third years of the study. The flowering process occurs within 20 (11–28) days, commencing at the end of April and extending to the end of May. The average number of days with open flowers per inflorescence was 10.1 (3–17), and rain lengthened this period. There was a statistically significant negative correlation between the number of days in flowering and the flowering onset. The first inflorescences were larger and flowered longer than the final ones. The spikelets and flowers along the inflorescence were not distributed evenly and were more abundant in the middle. The approximation of total pollen production per plant was, on average, approximately 50 million, with differences depending upon the number of inflorescences per plant, which averaged 23.7 (3–108). In Mediterranean areas, D. glomerata flowering occurs within a short period of time, in the middle of spring, but rainy spells lengthen this period. The airborne grass pollen season was influenced by the pollen production of this species during the first half of this pollen season.