Drought and Pathogen Effects on Survival, Leaf Physiology, Oxidative Damage, and Defense in Two Middle Eastern Oak Species

Ehsan Ghanbary,Ghasem Ali Parad,Shahram Jafarnia,Mehrdad Zarafshar,Masoud Tabari,Omid Fathizadeh,Iman Pazhouhan,Martin Karl-Friedrich Bader

doi:10.3390/f12020247

Abstract

The charcoal disease agents, Biscogniauxia mediterranea and Obolarina persica are two latent, ascomycetous oak pathogens in the Middle Eastern Zagros forests, where they have devastating effects, particularly during drought. Under greenhouse conditions, we investigated the effects of the two charcoal disease agents individually and in combination with drought on survival, growth, foliar gas-exchange, pigment content, oxidative stress and the antioxidant response of Quercus infectoria and Q. libani, two of the dominant tree species in this region. Commonly, the strongest negative effects emerged in the drought–pathogen interaction treatments. Q. infectoria showed less severe lesions, higher survival, more growth, and less leaf loss than Q. libani under combined biotic and abiotic stress. In both oak species, the combination of pathogen infection and drought resulted in more than 50% reduction in foliar gas-exchange parameters with partial recovery over time in Q. infectoria suggesting a superior defense system. Indeed, enhanced foliar anthocyanin, total soluble protein and glutathione concentrations imply an upregulation of the antioxidant defense system in Q. infectoria under stress while none of these parameters showed a significant treatment response in Q. libani. Consequently, Q. infectoria foliage showed no significant increase in superoxide, lower lipoxygenase activity, and less electrolyte leakage compared to the highly elevated levels seen in Q. libani indicating oxidative damage. Our findings indicate greater drought tolerance and pathogen resilience in Q. infectoria compared to Q. libani. Under future climate scenarios, we therefore expect changes in forest community structure driven by a decline in Q. libani and closely associated organisms.

Highlights

The current study examines the charcoal disease and drought issue from a different angle focusing on survival, growth, gas-exchange, relative water content (RWC), pigments, oxidative damage, and non-enzymatic antioxidant levels of Q. infectoria and Q. libani exposed to charcoal agents (B. mediterranea and O. persica), drought, and their interaction
In this study we examined the effects of the two charcoal disease-causing pathogens (Biscogniauxia mediterranea and Obolarina persica) and drought as well as their combination on survival, growth, foliar gas-exchange, pigment content, oxidative stress, and antioxidant response in seedlings of two dominant oak species of the Zagros forests in Iran
Our findings clearly underline the importance of the interaction between abiotic and biotic stress on oak seedling health and performance, suggesting that the devastating effects of the charcoal disease in the Zagros oak forests are likely to become worse in the future given the projected increase in drought frequency and severity [111] together with the expected range expansion of the two fungal disease agents

Summary

Introduction

Plants are often challenged by a combination of two or more stress factors simultaneously or in quick succession [1,2]. In these cases, abiotic stress may exacerbate the impacts of concurrent biotic stress by direct physiological interactive effects or it may even trigger a plant disease [3]. Fungal pathogens represent a major biotic stress factor, especially under prolonged or harsh drought periods that may promote the outbreak of disease [4].

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