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Open AccessArticle

Forest Decline Triggered by Phloem Parasitism-Related Biotic Factors in Aleppo Pine (Pinus halepensis)

1
Mediterranean Center for Environmental Studies (CEAM Foundation), Joint Research Unit University of Alicante-CEAM, Ctra. Sant Vicent del Raspeig s/n, Sant Vicent del Raspeig, 03690 Alicante, Spain
2
Departament of Ecology, University of Alicante, Ctra. Sant Vicent del Raspeig s/n, Sant Vicent del Raspeig, 03690 Alicante, Spain
3
Sanidad Agrícola Econex S.L., Calle Mayor 15Bis, Siscar-Santomera, 30149 Murcia, Spain
4
SILCO S.L, Calle Escalinata 12B, Guadarrama, 28440 Madrid, Spain
*
Authors to whom correspondence should be addressed.
Forests 2019, 10(8), 608; https://doi.org/10.3390/f10080608
Received: 15 June 2019 / Revised: 18 July 2019 / Accepted: 22 July 2019 / Published: 24 July 2019
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
Climate models predict increasing mean temperatures and reduced precipitation for Mediterranean ecosystems already subjected to major hydrological fluctuations. Forest decline phenomena relate extreme droughts or heat waves with other organisms, e.g., insects or microorganisms acting as pests, but their role needs to be elucidated. A biotic factor responsible for forest diseases is Candidatus Phytoplasma pini which is a phloem-parasitism that negatively affects Spanish pine forests in drought-prone areas. In several healthy and declining Aleppo pine stands, we monitored pine infection by PCR (Polimerase Chain Reation), determined the tree phloem tissue terpene composition, carbohydrate content, measured several relevant morpho-physiological variables and examined trees affected by bark beetles. PCR confirmed C. P. pini infection was widespread in all stands, regardless of to the presence of symptomatically affected trees. However, visible symptomatic decline only occurred in trees living under more stressful conditions. The terpene composition of pines in declining stands differed from those in healthy ones, and could be related with bark beetle attacks when pines were previously weakened by the phytoplasma disease. Our results indicate that biotic factors, such as C. P. pini, affecting phloem tissue may be triggering factors for drought-mediated forest decline and suggest that phloem diseases can play a key role in forest declining processes during extreme drought. View Full-Text
Keywords: climate change; drought; forest decline; phloem disease; phytoplasma; tree growth; tree mortality; triggering factors climate change; drought; forest decline; phloem disease; phytoplasma; tree growth; tree mortality; triggering factors
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Morcillo, L.; Gallego, D.; González, E.; Vilagrosa, A. Forest Decline Triggered by Phloem Parasitism-Related Biotic Factors in Aleppo Pine (Pinus halepensis). Forests 2019, 10, 608.

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Forests, EISSN 1999-4907, Published by MDPI AG
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