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Waldir Cintra de Jesus Junior

Professor of Phytopathology and Forest Pathology at UFSCar - Federal University of São Carlos


Climate change and forest diseases

Global warming is one of the greatest scientific paradigms today. The evidence that climate change is occurring, due to the increase in the concentration of greenhouse gases, has become increasingly consistent and accepted by the scientific community. The Intergovernmental Panel on Climate Change predicts that the global temperature will increase between 1.4 to 5.8 degrees centigrade over the next 100 years.

The concern with the subject is such that, periodically, conferences are held to discuss the subject and try to minimize the problem, such as the 27th United Nations Climate Conference, held in Egypt, in November 2022. With regard to all economic activities, agriculture is the one that is most dependent on climatic conditions. Thus, it is estimated that any change in climate could affect agricultural zoning, crop productivity and management techniques, changing the current scenario of the sector in each region, with serious economic, social and environmental consequences.

Plant disease is a dynamic process, in which host and pathogen, in close relationship with the environment, mutually influence each other, resulting in morphological and physiological changes. For disease to occur, the interaction of three factors (disease triangle) is essential: susceptible plant, aggressive virulent pathogen and favorable environment. Thus, the environment is a relevant component, being able to prevent the occurrence of the disease even in the presence of a susceptible host and aggressive virulent pathogen.

Climate change may alter the current phytosanitary scenario. Certainly, in the near future, changes will occur in the relative importance of each disease, as well as there may be greater potential for the establishment of quarantine pathogens that, if reported in the country, would represent a potential threat to the entire production chain. In addition, opportunistic pathogens will be more likely to cause damage, mainly due to plant stress.

In this article, we will briefly address some of the work carried out by our team on the impacts of climate change on diseases in forest species. It is worth mentioning that we have been working with the subject for 20 years, guiding several undergraduate and graduate students (masters and doctorates) on the subject. We also actively participated in the implementation of the “Nucleus of Excellence in Climate Change”, in which research in the forest area is carried out.

With regard to space-time distribution, our team analyzed the potential impact of climate change on the distribution of risk areas for the occurrence of eucalyptus rust in Brazil, concluding that there will be a reduction in the favorable area for the disease to occur. Despite the results, extensive areas will continue to be favorable to the development of the disease, especially in the coldest months of the year (June and July), so that the zoning of areas and the periods of greatest risk of occurrence, considering climate change, become important knowledge for the development of forecasting and alert models for the management of the disease.

With regard to rubber trees, we analyzed the potential impact of climate change on the development of leaf blight, concluding that it will be highly favorable for the reduction of areas and favorable for the disease, as well as some areas of the country will become more suitable for rubber cultivation . rubber tree, which may favor the emergence and/or greater development of some new planting areas.

The analyzes presented provide a future vision of which regions or states will be more or less favorable to the diseases. Considering the impact of climate change on eucalyptus diseases, it appears that the Ralstonia species solanacea rum, Xanthomonas and Quambalaria eucalypti may be favored by high temperatures, remaining as the main diseases in nurseries.

In the field, Autropuccinia psidii may have its importance reduced, but the Ceratocystis species fimbriata, Oidium eucalypti, Cylindrocladium, Ralstonia solanacearum, Rhizoctonia solani and Xanthomonas will deserve more attention, since they are favored by high temperatures. With regard to chemical control, there is the following question: Will the efficiency of chemical products be the same under conditions of increased temperature and reduced relative humidity?

Despite the lack of studies on the subject, we infer that chemical control will probably also be influenced by climate change, with the following effects expected: changes in the absorption of certain products; changes in translocation and metabolism of systemic fungicides; changes in waste dynamics and product degradation; reduction in the redistribution of protective fungicides; new application calendar, among others.

Biological control will certainly be affected. In the literature, there are works on the effect of temperature on the longevity of parasitoids of certain pests. As an example, we mention that the longevity of the eucalyptus tan bug parasitoid is reduced with increasing temperature.

With regard to changes in resistance effectiveness, we evaluated the effect of varying temperature and carbon dioxide concentration on the behavior of two eucalyptus clones with different levels of resistance to Ceratocystis fimbriata, in two climate scenarios, concluding that the increase in the concentration of carbon dioxide associated with high temperatures, representing the future climate, increased the severity of the disease and reduced the growth of clones. The clones developed better in the current scenario, demonstrating a reduced ability to adapt to Climate Change, which tends to alter the effectiveness of resistance. Another important aspect is that, with Climate Change, the occurrence of physiological disturbances may be intensified. The problem is already serious, like the physiological disturbance in eucalyptus.

In the analysis of Climate Change on diseases, one cannot forget that both the pathogen and the host plant can evolve, given that the process is slow, that is, adaptations will have to happen and need to be considered before hasty and wrong conclusions are pointed out as right. The analysis of the potential impacts of Climate Change is essential for the adoption of mitigating measures, such as the development of resistant cultivars and new management techniques, in order to avoid and/or minimize significant losses.

As a final message, we would like to emphasize the following points: 1) It is of fundamental importance to forecast, even with a certain degree of uncertainty, the impact of Climate Change and how it will affect productivity; 2) It is necessary to foresee the problems, in order to minimize the losses (need for adaptation); 3) Only multidisciplinary work will bring advances in understanding the impact of Climate Change on the forestry sector and its solutions; 4) The changes caused by Climate Change will bring a new dimension to the forest area; 5) More technology and industry unity will be needed to face the problem.

It will not be the end of the forest sector, but the beginning of new times. We must be prepared. We make ourselves available for the development of research in partnerships, in order to contribute to the minimization of such an important problem, which will substantially affect the forestry sector.