Diseases known as 'pine wilt' and 'pitch canker' are those which affect conifer plantations in the Basque Country the most, especially Pinus radiata, the most common tree species in this Autonomous Community. Researchers at the Basque Institute for Agricultural Research and Development, Neiker-Tecnalia, have managed to find genetic material resistant to both pathologies, opening up great possibilities, through genetic enhancement, for achieving trees immune to them. Likewise the researchers consider that correct forestry management could significantly limit the pernicious effect of both diseases, even to the point of eradication in the case of 'pitch canker'.
Pinus radiata occupies 42% of the forest-covered terrain on the slopes of the Cantabrian range of mountains in the Basque Country witch is about 145,000 hectares. This abundance has meant monoculture in many regions and where many health problems are detected, such as those due to climatic factors, nutritional deficiencies, attacks by plagues of insects such as the pine processionary caterpillar and the bark beetle and, above all, diseases of a fungal nature, i.e. those caused by fungi. Amongst these latter, those which have greater impact on the plantations of pinus radiata are the 'pine wilt' and 'pitch canker', caused by the Diplodia pinea and Fusarium circinatum fungi respectively.
The Neiker-Tecnalia research has opened up an important way to tackle the two diseases. The researchers analysed the 15 most common species in the plantations of conifers in Spain. In each one of these species they found examples resistant to both fungi. Once the resistant trees are selected, they can be used to generate clones that will not be affected. Genetic enhancement is, therefore, one of the most suitable ways to combat these diseases.
This research was the basis of the PHD thesis of Ignacio Garca Serna witch has been directed by Dr. Eugenia Iturritxa, in charge of Forestry Health at Neiker-Tecnalia, and Dr. Gustavo Renobales from the University of the Basque Country (UPV/EHU). The fungi Diplodia pinea and Fusarium circinatum were inoculated into the 15 species of conifers analysed. The most resistant were the Sequoia type - Sequoia sempervirens and Sequoiadendron giganteum- and the pine of the Pinus taeda species. The most vulnerable turned out to be Pinus radiata.
958 forest zones analysed
The Diplodia pinea fungus is distributed over most part of pine plantations in Euskadi, according to the research. Out of a total of 958 forest zones studied, the fungus was detected in 817 of them. The disease caused by it 'pine wilt' produces the wilting of buds and the appearance of cankers (breaks in the tree's tissues) and deformations in trunks and branches, besides causing a bluish colouration of the part of the wood exposed to the air.
As regards its geographical distribution, the highest levels of infection by Diplodia pinea have been found in zones affected by hail or strong winds over the last ten years. With this data, Neiker-Tecnalia proposes that plantations of pinus radiata, the most vulnerable species, should not be undertaken in those areas with these climatic conditions, given that strong winds and hail cause damage to the trees and whereby the fungus enters.
`Pine wilt' greatly reduces the capacity for growth of the trees and can even end their lives. To this can be added the fact that timber of the affected individuals lose quality due to the deformations caused in the trunks.
Pitch canker favoured by rainfall
In the case of Fusarium circinatum, this is much less widespread and appears almost exclusively in the forest masses of pinus radiata located in the north-east of Gipuzkoa and in two large areas in the centre of Bizkaia. Of the 958 wooded zones studied, this fungus appears in 131, its appearance is favoured by the abundance of rainfall during hot periods of the year.
To combat and even eradicate this fungus, Neiker-Tecnalia proposes the strict compliance with the Community and State norms. These regulations set out the obligation, on the part of plantation owners, to chop down `pine wilt' diseased trees and burn them in a controlled manner. After cutting them down, the soil should be in quarantine for two years before replanting.
`Pine wilt' disease causes the wilting of leaves and desiccation of the upper part of the pine tree, thus impeding its growth. Moreover, it gives rise to the formation of large cankers in the trunk with abundant expulsion of resin.
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