Eur. J. For. Path. 22 (1992) 284-290 © 1992 Verlag Paul Parey, Hamburg und Berlin ISSN 0300-1237 Laboratorio di Botanica Forestale, Firenze, Italy New type of damage to Quercus ilex: pollen germination and hydration ability By LoRENZA M. BELLANI and E. PAOLETTI Abstract Pollen grains collected from trees of Quercus ilex L. belonging to different classes of new type damage were analyzed. Five parameters were taken into account: viability, germinability, tube lengthening, grain volume of^ the dehydrated state and after rehydration. Damage to mother plants clearly influences the above mentioned parameters, causing a reduction in pollen grain viability, germinability, and in the ability of the grains to rehydrate. 1 Introduction Several authors reported that the environment affects sexual reproduction, sex ratio being shifted towards male or female individuals (HESLOP-HARRISON 1972; CHARNOV and BULL 1977; WiLLSON 1979). A tendency towards maleness in plant species is well known under unfavorable conditions, e. g. drought (FREEMAN et al. 1976; LEV-YADUN and LIPHSCHITZ 1987) or elevational gradients (CRANT and MITTON 1979). CLAUSER et al. (1989) observed a high production of male flowers in plants grown in urban and rural areas. This phenome- non observed in plants of several species, such as Pinus sylvestris L., Cedrus atlantica Man- etti, Cupressus sempervirens L. and mainly Quercus ilex L., was attributed to background air pollution due to long range transport. In damaged holm oak trees a change in leaf colour has been detected (CELLINI et al. 1988; CLAUSER et al. 1989). Leaves show a grayish colour of the foliage due to the twisting of the leaf-stalk for which the abaxial green-gray surface instead of the dark green adaxial one is shown. If the damage continues, the leaves of the previous and/or the current year are shedded and secondary branch loss in the higher part of the crown is detected. At the time of flowering damaged holm oak trees just keep newly emerged leaves and show a great number of male flowers. When male flowers drop, the holm oak crown is extremely scanty. On the other hand, changes in reproductive processes caused by air pollution are not as readily observed as are foliar injury symptoms (BENOIT et al. 1983). In the present note we try to correlate viability, germinability and tube length in pollen grains collected from Quercus ilex plants with different levels of new type of damage. Simultaneously, the size of grains at the moment of release and their rehydration ability is taken into account. 2 Materials and methods 2.1 Sample collection Based on the Cerman tree damage classification (EEC 1987), plants are considered healthy, with a loss of leaves inferior to 10 % (class 0), slightly damaged with a loss of U. S. Copyright Clearance Center Code Statement: 0300-1237/92/2205-0284/$ 02.50/0