Physiological effects of Phytophthora Cinnamomi infestations on Quercus Suber seedlings

Resumen

Oak decline is among the more serious environmental problems in the Mediterranean Basin. Phytophthora cinnamomi Rands has been identified as the main pathogen involved in the decay and death of holm and cork oaks in the southwest of the Iberian Peninsula. In this work, we examined the variation of physiological parameters in two-year-old plants of cork oak infested by P. cinnamomi fungi. Seedlings from 10 different families were grown in 300 cm3 forest pots containing a commercially substrate (peat + perlite) or a natural one (forest soil + perlite). During their second year of life, half of the plants were inoculated with P. cinnamomi mycelia. Survival, gas-exchange parameters (photosynthesis, transpiration), water relations (water potential of leaves, relative water content, stomatal aperture) and status of the photosynthetic system were monitored on a periodic basis. Four months after inoculation, stem hydraulic conductance was measured in a plant sample. The results revealed considerable susceptibility of cork oak to the fungus. Thirty-eight days after inoculation, the plants exhibited significant differences in water status between treatments, but not between substrates or families. The water potential of inoculated plants exceeded that of non-inoculated plants by 43%. These differences in plant water status were not echoed by any significant differences in photosynthesis or transpiration rate, however. Hydraulic conductance was higher in plants grown in natural soilthan in those grown in the commercial substrate (peat + perlite). There were significant differences in maximum specific conductance referred to leaf area between inoculation treatments; thus, non-inoculated plants exceeded inoculated plants by 21% in this respect.