Resumen de Phytopathological aspects in the cork oak forest management
Antonio Franceschini, Piero Corda, Francesco Marras
In Sardinian cork oak woods a progressive worsening of the phytosanitary conditions has been observed over the last decades. This appears closely related to the climatic changes which have occurred in the Mediterranean environment, leading essentially to a progressive reduction of annual rainfalls and to their irregular distribution over the seasons. As a result, both defoliating insects and pathogenic fungi of cork oak have frequently encountered favourable conditions for giving rise to epidemic outbreaks; meanwhile, the plants suffered heavy water stress, making them more susceptible to adversities and, chiefly, to decline phenomena.
In the aethiology of these phenomena, several adverse factors: abiotic, biotic and/or anthropic are involved. They may vary for type and incidence in the different forest situations in which the cork oak grows, so that the prevention measures and, therefore, the management strategies of the cork oak stands would be diversified for each situation. However, the strategies must always include means suitable for preventing infections of the endophytic fungi widespread in the cork oak forests. Some of these have a crucial role in decline pathogenesis, since they can act as opportunistic pathogens during periods of stress in the host, causing its progressive decay up to death. Therefore, in order to hinder further onset and spread of the decline, the endophytic mycocoenoses in the various cork oak areas and the epidemiology of opportunistic pathogens must be carefully investigated.
In Sardinia, Biscogniauxia mediterranea and Discula quercina are the most widespread opportunistic pathogens involved in cork oak decline. In a previous work the epidemiological features of B. mediterranea were outlined. In this paper, the results of a research carried out in a declining cork oak stand in order to detect the climatic conditions and the time for endophytic infections of D. quercina are reported. Its attacks occurred throughout the year except in August, with higher incidence during rainy months (January and February) and drier ones (June and July). It may affect all the aerial organs but mainly leaves. In vitro tests D. quercina shows a mesophilic behaviour, with a temperature range for growth between 5 and 35°C and optimum of 25°C.
Finally, in light of these results and those regarding B. mediterranea, the implications for the sustainable management of cork oak forests are discussed. It is necessary to integrate the productive requirements with the protective ones, mainly regarding the attacks of opportunistic pathogens. Their inoculum potential must be reduced by: a) the removal and burning of infected trees; b) the prevention of attacks, both directly through suitable treatments following debarking, and indirectly by avoiding stress to the plants.
