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1. Introduction

Forests are an indispensable resource for human existence in different regions of the world. Forests are often concentrated in a few parts and vary in sizes. The most important and extensive green reserve on earth is the Amazon rainforest. In the Amazon, as in other tropical forests, just one or two tree species spread across tens of millions of hectares. In many cases, the dominant species produce fruits, seeds, or oils of economic importance. The species Euterpe oleracea, Grias peruviana, Jessenia bataua, Mauritia flexuosa, Myrciaria dubia, and Orbignya phalerata have been studied in Brazil and Peru.

The Amazon rainforest is the world's most biodiverse region, home to a rich variety of plant and animal species and a crucial source of goods and services. Large-scale deforestation causes a decline in biodiversity and the availability of forest products, but these values ​​have been largely neglected. In the Amazon, land use goes far beyond the clearing of vast areas of forest, and selective logging and other canopy damage are much more widespread. Deforestation damages surrounding forests through increased drying of the forest floor, increased frequency of fires, and reduced productivity. The loss of healthy forests causes serious losses, including carbon storage in biomass and soil, regulation of water balance and river flow, modulation of regional climate patterns, and mitigation of infectious diseases.

Unfortunately, this fundamental resource, like others on other continents, is continually suffering massive losses due to various factors. Almost all European forests have been altered by human activity, weather events, and by several biotic stressors and therefore original forests are very rare. Some rare patches of original forests can be found in remote mountainous areas of Central and Eastern Europe, in the far north of Europe, and in the boreal zone of European Russia. The different uses of forests over the centuries have influenced land use, landscapes and their fragmentation, forest stand structures, historical sites and monuments, settlements in forest areas, and rural development.

Extreme climate events will increase the frequency and intensity of stress on forests, significantly impacting their health. Various fungal tree diseases could become more devastating due to various factors. Drought and flooding make trees more susceptible to pathogen attack, rising temperatures and humidity influence the sporulation and dispersal of pathogens, and changes in climate could favor some of them. Furthermore, pathogen migration triggered by climate change may increase the incidence or geographic spread of diseases when pathogens encounter new hosts and/or potential vectors, and new threats may emerge due to changes in tree species composition or invasive species.

In addition to abiotic stresses and deforestation to obtain other arable lands, microbial diseases, particularly those caused by pathogenic fungi, significant damage the forestry heritage which spread of undergrowth species, particularly in reforestation practices. Severe economic losses are also suffered by timber producing countries and associated industries including paper mills. Fungi that cause oak decline include atrophied leaves and necrotic areas, dead branches, dead root tips, dead suckers, localized necrotic areas in the bark and phloem, locally dead and discolored sapwood in debarked areas, localized discolorations within the sapwood, large necrotic areas on the trunks, and dead trees. 80 Species of fungi, mainly belonging to the Ascomycetes and Deuteromycetes, have been found among oak pathogens. Different fungal species have been more frequently associated with the same type of symptom than others. A recent review report Phytophthora species and latent pathogens, including some species of Botryosphaeriaceae among the most significant biotic stressor for European oaks. Among them Biscogniauxia mediterranea, the causative agent of black canker, and the oak anthracnose fungus Apiognomonia quercina have been underlined. Other biotic stressors include powdery mildew fungi of the genus Erysipe, which have been reported more sporadically and with limited effects, wood-rotting fungi such as Armillaria spp. and other basidiomycetes. The authors also suggested that “to reduce oak decline, could be important to create more resilient forests, better adapted to global environmental changes and current disturbance regimes, through integrated management that includes proactive silviculture, innovative disease and pest control methods, and ecological restoration efforts”.

This review reports briefly the classification of quercus plants and extensively the isolation, chemical, and biological properties of phytoxins produced by their pathogenic fungi, discussing their role in pathogenesis. Microbial competition, the structure-biological activity relationship, and the potential applications of some these phytotoxins in agriculture and medicine are also discussed. Furthermore, for the Diplodia species the comparison between their secondary metabolite profile and taxonomy with those of fungal pathogens of other close forest plants is reported.

This manuscript reports on fungal diseases of numerous oak trees and the serious damage they cause to the forest heritage, which is important for the survival of all living species on earth. The severe damages on wood industry and nurserie was also evaluated. The phytotoxins produced by these fungi, which play a fundamental role in disease in-duction, are described in detail, with their chemical and biological properties. For some phytotoxins the enatioselective synthesis, the structure-biological activity relationships, and the potential applications in agriculture and medicine are also discussed. In addition, for the Diplodia species the comparison between their secondary metabolite profile and taxonomy with those of pathogens of other close forest plants was discussed. Finally, the potential applications in medicine and agriculture of some phytotoxins is also described.

2. Phytotoxins Involved in the Quercus Fungal Diseases

Forests are an indispensable resource for human existence in different regions of the world. Forests are often concentrated in a few parts and vary in sizes. The most important and extensive green reserve on earth is the Amazon rainforest. In the Amazon, as in other tropical forests, just one or two tree species spread across tens of millions of hectares. In many cases, the dominant species produce fruits, seeds, or oils of economic importance. The species Euterpe oleracea, Grias peruviana, Jessenia bataua, Mauritia flexuosa, Myrciaria dubia, and Orbignya phalerata have been studied in Brazil and Peru.

The Amazon rainforest is the world's most biodiverse region, home to a rich variety of plant and animal species and a crucial source of goods and services. Large-scale deforestation causes a decline in biodiversity and the availability of forest products, but these values ​​have been largely neglected. In the Amazon, land use goes far beyond the clearing of vast areas of forest, and selective logging and other canopy damage are much more widespread. Deforestation damages surrounding forests through increased drying of the forest floor, increased frequency of fires, and reduced productivity. The loss of healthy forests causes serious losses, including carbon storage in biomass and soil, regulation of water balance and river flow, modulation of regional climate patterns, and mitigation of infectious diseases.

Unfortunately, this fundamental resource, like others on other continents, is continually suffering massive losses due to various factors. Almost all European forests have been altered by human activity, weather events, and by several biotic stressors and therefore original forests are very rare. Some rare patches of original forests can be found in remote mountainous areas of Central and Eastern Europe, in the far north of Europe, and in the boreal zone of European Russia. The different uses of forests over the centuries have influenced land use, landscapes and their fragmentation, forest stand structures, historical sites and monuments, settlements in forest areas, and rural development.

Extreme climate events will increase the frequency and intensity of stress on forests, significantly impacting their health. Various fungal tree diseases could become more devastating due to various factors. Drought and flooding make trees more susceptible to pathogen attack, rising temperatures and humidity influence the sporulation and dispersal of pathogens, and changes in climate could favor some of them. Furthermore, pathogen migration triggered by climate change may increase the incidence or geographic spread of diseases when pathogens encounter new hosts and/or potential vectors, and new threats may emerge due to changes in tree species composition or invasive species.

In addition to abiotic stresses and deforestation to obtain other arable lands, microbial diseases, particularly those caused by pathogenic fungi, significant damage the forestry heritage which spread of undergrowth species, particularly in reforestation practices. Severe economic losses are also suffered by timber producing countries and associated industries including paper mills. Fungi that cause oak decline include atrophied leaves and necrotic areas, dead branches, dead root tips, dead suckers, localized necrotic areas in the bark and phloem, locally dead and discolored sapwood in debarked areas, localized discolorations within the sapwood, large necrotic areas on the trunks, and dead trees. 80 Species of fungi, mainly belonging to the Ascomycetes and Deuteromycetes, have been found among oak pathogens. Different fungal species have been more frequently associated with the same type of symptom than others. A recent review report Phytophthora species and latent pathogens, including some species of Botryosphaeriaceae among the most significant biotic stressor for European oaks. Among them Biscogniauxia mediterranea, the causative agent of black canker, and the oak anthracnose fungus Apiognomonia quercina have been underlined. Other biotic stressors include powdery mildew fungi of the genus Erysipe, which have been reported more sporadically and with limited effects, wood-rotting fungi such as Armillaria spp. and other basidiomycetes. The authors also suggested that “to reduce oak decline, could be important to create more resilient forests, better adapted to global environmental changes and current disturbance regimes, through integrated management that includes proactive silviculture, innovative disease and pest control methods, and ecological restoration efforts".

This review reports briefly the classification of quercus plants and extensively the isolation, chemical, and biological properties of phytoxins produced by their pathogenic fungi, discussing their role in pathogenesis. Microbial competition, the structure-biological activity relationship, and the potential applications of some these phytotoxins in agriculture and medicine are also discussed. Furthermore, for the Diplodia species the comparison between their secondary metabolite profile and taxonomy with those of fungal pathogens of other close forest plants is reported.