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Volume 7, Pages 222-230
Short Communication

Pre-Exposure to Ozone Predisposes Oak Leaves to Attacks by Diplodia corticola and Biscogniauxia mediterranea

1IPP-CNR, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Firenze, Italy
2Dip. Protezione Piante, Univ. Tuscia, Via de Lellis, I-01100, Viterbo, Italy
3Dip. Protezione Piante, Univ. Sassari, Via de Nicola, I-07100, Sassari, Italy

Received 27 September 2006; Revised 15 December 2006; Accepted 18 December 2006

Academic Editor: Andrzej Bytnerowicz

Copyright © 2007 Elena Paoletti et al.


One-year-old cork oak (Quercus suber) and turkey oak (Q. cerris) seedlings were exposed to ozone (110 ppb, 5 h day˗1, for 30 days) and were inoculated with Diplodia corticola and Biscogniauxia mediterranea, respectively, by spraying a suspension of spores on the leaves. Both fungi are endophytic and may act as weak parasites, contributing to oak decline. Ozone exposure stimulated leaf attacks after inoculation, although the physiological, visible, and structural responses of both oaks to O3 exposure were weak. In fact, steady-state gas exchange, leaf waxes, and wettability were not significantly affected by O3. In Q. cerris, O3 altered the structure of stomata, as observed by scanning microscopy, and reduced the leaf relative water content. No hyphal entry through stomata or growth towards stomata was, however, observed. Inoculations were performed in a humid chamber at low light; stomata were likely to be closed. When Q. cerris was inoculated in natural conditions, i.e., in a forest infected by B. mediterranea, seedlings pre-exposed to the enhanced O3 regime had a higher number of B. mediterranea isolates than the controls. This suggests that pre-exposure to O3 predisposed Q. cerris leaves to attacks by B. mediterranea independent of stomata. The hyphae of both fungi were able to enter the leaf through the cuticle, either by gradual in-growth into the cuticle or erosion of a hollow in the cuticle at the point of contact. The primary cause of increased leaf injury in O3-exposed seedlings appeared to be higher germination of spores than on control leaves.