Differential susceptibility responses of Greek olive cultivars to Fomitiporia mediterranea

Wood decay caused primarily by Fomitiporia mediterranea is considered to be an emerging disease for citrus and olive trees in Mediterranean countries. The pathogen cannot be currently controlled by chemicals whereas there is no available information about the source and level of resistance even for the most important cultivars where the global citrus and olive industries are based on. In the present study, five of the most significant Greek olive cultivars (Amfissis, Chalkidikis, Kalamon, Koroneiki and Mastoidis) were evaluated for their resistance to F. mediterranea by conducting artificial inoculation experiments. Disease reactions were evaluated by measuring the length of bark and wood lesions, 33 months post inoculation. Trunk sections scanning and image pixel analysis were employed to estimate the total discoloration and decay area of infected wood, whereas positive re-isolation ratio of F. mediterranea was also taken into account in resistance evaluation. Data on symptom development along with wood tissue colonization by the pathogen indicated that the resistance of olive cultivars to F. mediterranea varied significantly. Based on the cumulative stress response index (CSRI), ‘Kalamon’ and ‘Koroneiki’ were classified as resistant, ‘Chalkidikis’ and ‘Mastoidis’ as intermediately resistant, whereas ‘Amfissis’ was susceptible. Determination of lignin in trunk wood showed that the resistance of olive cultivars to F. mediterranea could be associated with their lignin content. This is the first experimental evidence of differential susceptibility responses of olive cultivars against F. mediterranea, and reveals for the first time the potential exploitation of host resistance as a promising approach in the effort to control wood decay disease of olive in practice.