engleski

The role of site in Austrian pine predisposition to Sphaeropsis sapinea - a case study

During the last century, Austrian pine (Pinus nigra) was commonly planted in Croatia on various sites to prevent land from erosion and/or to restore forest vegetation, mainly in the karst area. In the 1990-ties, Sphaeropsis sapinea caused several outbreaks in pine plantations with good health status, and in plantations with various dieback symptoms, causing tree dieback in some sites. Analyses of meteorological data for the area revealed drought periods since 1990-ties. Drought was presumed as the most influencing pine predisposing factor to Sphaeropsis sapinea. Investigations on the pathogen presence revealed the evidence that pine's health status was not related only to drought stress but also to site conditions. Study in the period 2001- 2015 was preformed in healthy looking and variously affected plantations on 11 sites. S.sapinea was confirmed in all studied plantations by its presence either on cones, needles, shoots and/or branches. Other pathogens, insect pests and/or abiotic factors were excluded as the cause of revealed dieback. Site characteristics, which we found relevant as predisposition factors, mainly in combination, were: soil sub-types (flysch, limestone-dolomite), soil types and depth, site rockiness, site exposition and inclination. Analyses of nutrition status in needles revealed significant differences among nitrogen (N) and potassium (K) values. In pines on flysch, with lower N/K ratio, the disease symptoms were not observed, but in pines on limestone-dolomite , with increased N/K ratio, various dieback symptoms were revealed, following nitrogen and potassium relation in general. Inoculation experiment confirmed S.sapinea pathogenicity and confirmed that isolates obtained from healthy pines and ones with symptoms can cause bark necrosis. Previous fertilization with ammonium sulphate influenced increased seedlings growth (according to treatments 0-80 g/m2) and increased length of bark necrosis as well. According to obtained results it can be concluded that S.sapinea in drought periods turned to serious pathogen and caused dieback in predisposed trees on some pine sites in Istria. Under the drought stress, studied site conditions, including nutrition status, were revealed important in pines' susceptibility to the disease.

Pinus nigra, pathogen, dieback, drought, site conditions, nutrition status

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