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

Abstract

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.

Effective Defense of Aleppo Pine Against the Giant Scale Marchalina hellenica Through Ecophysiological and Metabolic Changes

“…Indeed, catechin, epigallocatechin, benzoic acid, and quinic acid were accumulated in infested vs. healthy needles toward the end of the intense nymph feeding activity (June) or even during the recovery phase (July) ( Figure 6 ). These phenolic compounds are involved in plant defense and were augmented in poplar leaves and in the phloem of Aleppo pine in response to pathogens ( Wang et al, 2016 ; Ullah et al, 2017 ; Morcillo et al, 2019 ), while they are also shown to be toxic to herbivores ( Barbehenn and Constabel, 2011 ). Moreover, high catechin abundance in different organs of Aleppo pine has been associated with enhanced antimicrobial and antibacterial defense ( Salim et al, 2019 ).…”

SilvAdapt.Net: A Site-Based Network of Adaptive Forest Management Related to Climate Change in Spain

“…Spain is not an exception; in the case of forest fires, for instance, the change in the risk indices, the longer duration of the fire season [19], their increasing frequency and intensity [20,21] and the increasing area affected are metrics that show how recent changes in the fire regime may affect forest resilience [22]. Additionally, the extreme droughts registered in the last years and their interaction with other agents, such as bark beetles or defoliating insects, have affected some forests very negatively [23][24][25][26][27][28]. The incidence of forest pests and diseases is also affected by climate change [25,29,30], either due to more favorable conditions for the life cycle of pathogens or an increase in magnitude underwater-or heat-stress conditions [31,32].…”

Investigating the prevalence of Bark beetles of Pinus halepensis in the North East semi-arid region of Algeria

“…The Aleppo pine (Pinus haleppensis) is the most common tree in Algeria and it has a very important place in the balance of Mediterranean ecosystems. Global warming and its consequences like repeated heatwaves and drought have a significant impact on trees and their predators, resulting in an increased mortality and forest decline (Morcillo et al 2019). However, trees can withstand the stresses and avoid dieback when favorable conditions return, but biotic factors such as pests can aggravate the stress and lead to their death (Anderegg et al 2015).…”