A challenging job: Plant pathology in the urban environment

According to Agrios (2005), “Plant pathology is a science that studies plant diseases and attempts to improve the chances for survival of plants when they are faced with unfavorable environmental conditions and parasitic microorganisms that cause disease”. So, it is a discipline that has a practical and noble goal of protecting the food (quantity and quality) available for humans and animals. Nowadays to this crucial task at least another mission must be added: “to ensure the presence of well performing and safe plants (especially trees) in our cities”. This is because plant diseases, by their presence, menace the survival of the plants, shorten their life expectancy and make them dangerous in the urban environment representing a limiting factor for citizen’s security. At world level, far more than 50% of human beings currently live in an urban area and at least 70% will live there in the year 2050. Cities are similar to an organism in that they consume resources from their surroundings and excrete wastes. Urbanization concentrates people, materials and energy into relatively small geographical areas (cities and towns are estimated to be less than a mere 3% of the total land of our planet), whose environmental conditions are often critical. Quality of life in cities relies on a range of components, such as social equity, income and welfare, housing, social relations and education and a healthy environment. The environmental elements for an adequate quality of life include good air quality, low noise levels, clean and sufficient water, fair urban design with sufficient and high-quality public and green spaces, and a good local climate or opportunities to adapt to climate change. Urban trees provide a number of important (but not easily quantified) aesthetic, economic, and psychological benefits (“ecosystem services”) for humans. They increase property values, promote tourism, provide educational opportunities, encourage healthy life styles and outdoor activities, improve the visual appeal of urban areas, mitigate stress and encourage biological diversity. But trees, just as all other plants, may be sick and attacked by biotic and abiotic stress factors, and a diseased tree may represent an intolerable risk factor for human welfare. Plants in the city guarantee multiple benefits and satisfactions, but they are exposed to a variety of site conditions, environmental factors, and physical disturbances which influence their survival. Climate change has the potential to influence almost all components of the urban environment and to raise new, complex challenges for the quality of urban life, health and urban biodiversity. Due to human activity, the temperature in an urban microclimate is higher than that of the surrounding areas.