Variability in the tolerance/resistance of Quercus Suber L. seedlings to Phytophthora Cinnamomi rands. Evaluation of survival

Resumen

Phytophthora cinnamomi Rands is the main pathogen behind for holm and cork oak decline in the southwest of the Iberian Peninsula and poses one of the most severe environmental problems currently threatening the ecological and economic sustainability of Quercus forests in this region. In this work, we examined variability in the tolerance/resistance of cork oak saplings to this pathogen. To this end, seeds from 20 individuals in each of 8 different Spanish and Por-tuguese regions were studied. Following pregermination in sterile substrate in the laboratory, seedlings were grown in a greenhouse, using 300 ml pots that were filled with substrate infested with the pathogen at three different levels, namely: N (naturally infested, natural soil containing vermiculite), P (as N, but subjected to partial pasteurization) and A (artificially infested soil obtained by adding a fixed amount of fungal mycelium). The trial was conducted by using an identical experimental design in two different locations, namely: La Rábida (Huelva, Spain) and Oeiras (Portugal). Ten plants of each family were tested at each substrate inoculation level. Plant survival rate and damage were assessed on a periodic basis, and plant size (height and diameter) measured once during the trial. The results revealed substantial susceptibility of cork oaks to the pathogen. In fact, mortality rates were quite high (40% on average) at the three infestation levels and up to 65% in the artificially infested substrate (A.). Location, substrate infestation level, provenance and family had a statistically significant influence on all measured parameters. Overall, seedling response to infestation by P. cinnamomi was highly variable. Also, some parent plants were found to produce a healthy offspring.