Aerobiologia 16: 347–352, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 347 Experimental results about Platanus pollen deposition Emma Bricchi, Giuseppe Frenguelli * & Gianfranco Mincigrucci Department of Plant Biology, University of Perugia, Italy ( * Author for correspondence, e-mail: freng@unipg.it; fax: +39 075 5856425) Received 16 June 1999; accepted in final form 14 September 2000 Key words: Platanus, pollen production, pollen deposition Abstract A comparison between the aerobiological and floristic data carried out for Platanus are reported. The source was constituted by 60 Platanus trees. When they were pollinating we calculated the total pollen prodution of the source, controlling the number of male inflorescences for each plant, the number of anthers for each inflorescence and the number of pollen for each anther. Aerobiological data were obtained with 16 Durham gravimetric samplers positioned over an area of approximately 25 km 2 at variable distances and in different directions to capture pollen transported by winds coming from any direction. In the first year of analysis, we carried out two kind of aerobiological monitoring positioning a Hirst volumetric trap near the closest gravimetric sampler. The two methods showed a similar trend in Platanus pollen profiles. In the following years, only Durham gravimetric samplers were used to study pollen dispersion. The data showed that there were high concentrations of pollen on the soil near the source while at distances higher than 800 m pollen concentration decreased dramatically. About 1/4 of all the pollen produced fell in an area within 400 m from the source and at a distance of 2750 m only 9 pollen grains/cm 2 fell throughout the entire season. Introduction Numerous studies have been carried out on pollen and spore deposition distances and/or gradients with different approaches. Many of the papers concern aerobiology (Gérard Peeters and Zoller, 1988; Tampieri et al., 1977), agronomy (Lambert et al., 1980; McCartney, 1994) or were studies for allergo- logical purposes (Hjelmroos, 1992). Recently a new field of research about the risk of dispersion of pollen from transgenic crops was developed (Mikkelsen et al., 1996; Raybould and Gray, 1993). In this study we report a comparison between the aerobiological and floristic data carried out for Platanus. We chose Platanus for the following reas- ons: it is a genus which can only be found in public areas and in limited numbers, therefore easily identi- fiable and quantifiable; its pollen cannot be confused with other taxa; moreover the period of pollination is restricted in time and well defined. Lastly its pollina- tion is principally anemophilous. The aims of this work were to quantify the pollen grains produced by Platanus trees, the area and the gradient of their deposition. Materials and methods The study lasted for 3 years: it started in 1994 and for three consecutive years it was carried out in a large area to control global deposition. We examined the deposition of Platanus pollen in an area where the number of plants was easily determined and there were no other Platanus plants in a range of at least 5 km from the examined area. This area (Figure 1) is near the city of Perugia in the valley of the river Tiber. In this zone of relatively recent urbanization, there are 60 Platanus plants (the dotted zone in the centre of the map) which were planted about 50 years ago.