Effects of acidity on in vitro germination and tube growth of pollen from declining Fagus sylvatica

1. Pollen from beech trees (Fagus sylvatica) belonging to different damage classes was put to germinate in substrates of varying degrees of acidity, 2. As the damage classes increased in severity, the viability and germination of pollen grains was significantly decreased, whereas the length of the pollen tube did not appear to be influenced by the damage class. 3. Cultures in increasingly acid media showed a progressive inhibition both of germination and of tube growth. 4. No significant interaction between damage class and pH was detected for pollen germination, while the average growth of pollen tubes from more severely damaged trees appeared to be less inhibited by acidity than material derived from less damaged trees. 5. In summary, even in the most severely affected trees, as long as the culture medium pH did not fall below 4.2, some pollen grains were still able to germinate and to produce tubes long enough to guarantee fertilization.