Impact of climate change on Disease management

HOST RESISTANCE

          Cultivar resistance to pathogens may become more effective because of increased static and dynamic defences from changes in physiology, nutritional status, and water availability.

          Durability of resistance may be threatened, however, if the number of infection cycles within a growing season increases because of one or more of the following factors: increased fecundity, more pathogen generations per season, or a more suitable microclimate for disease development. This may lead to more rapid evolution of aggressive pathogen races.

CHEMICAL CONTROL

          Climate change could affect the efficacy of crop protection chemicals in one of two ways.

          First, changes in temperature and precipitation may alter the dynamics of fungicide residues on the crop foliage.  Globally, climate change models project an increase in the frequency of intense rainfall events, which could result in increased fungicide wash-off and reduced control. The interactions of precipitation frequency, intensity, and fungicide dynamics are complex, and for certain fungicides precipitation following application may result in enhanced disease control because of a redistribution of the active ingredient on the foliage.

          Second, morphological or physiological changes in crop plants resulting from growth under elevated CO2 could affect uptake, translocation, and metabolism of systemic fungicides. For example, increased thickness of the epicuticular wax layer on leaves could result in slower and/or reduced uptake by the host, whereas increased canopy size could negatively affect spray coverage and lead to a dilution of the active ingredient in the host tissue. Both factors would suggest lowered control efficacy at higher concentrations of CO₂. Conversely, increased metabolic rates because of higher temperatures could result in faster uptake by and greater toxicity to the target organism.

MICROBIAL INTERACTION

          Climate change may alter the composition and dynamics of microbial communities in aerial and soil environments sufficiently to influence the health of plant organs Changed microbial population in the phyllosphere and rhizosphere may influence plant disease through natural and augmented biological control agents.  A direct effect of elevated CO2 is unlikely in the soil environment as the microflora there is regularly exposed to levels 10 to 15 times higher than atmospheric CO₂.

QUARANTINE AND EXCLUSION

          Management of climate change will put additional pressure on agencies responsible for exclusion as a plant disease control strategy. In some regions, certain diseases of economic concern do not currently occur because the climate has precluded the causal agents from becoming established. Use of Geographical Information Systems and climate matching tools may assist quarantine agencies in determining the threat posed by a given pathogen under current and future climates.

MITIGATIONS ON CLIMATE CHANGE EFFECTS

          With significant and relatively rapid changes in climate, there will be acceleration in the number of new crops and cultivars introduced to the province. The adaptation of agronomic and horticultural cultivars to regional soil and climatic conditions is a well-established practice that involves comparing agronomic performance in multiple locations over multiple years.

Only cultivars that perform well, on average, across these locations and environments are selected for commercial use.

          This process of agronomic adaptation of plant genotypes appropriate has been highly successful for many years and will be instrumental in continuing to select adapted cultivars under expected climate changes.

          Increased emphasis should be placed on breeding plants for environmental stress tolerance, such as drought stress. Tolerance or resistance of crops to environmental stresses will result in healthier crops that are better able to resist disease and produce improved yields.

          New techniques that enhance the identification and development of host tolerance or resistance to biotic and abiotic diseases will be important in facilitating this adaptation.

          An increase in the number of new introduced plant diseases is also expected to accompany climate change. It will be important to have diagnostic tools and adequate personnel to detect new pathogens that might be harboured in these introductions.

ROLE OF PLANT PATHOLOGIST IN CLIMATE CHANGE RESEARCH

          An opportunity for plant disease research within programs dealing with global climate change was a major topic of discussion. The plant pathologists who take a broad view of their science will be among those to make significant contributions. For example, will the distribution of various races of wheat rusts necessarily coincide with a more northern wheat belt? Will the weeds that are often hosts for important plant parasites, as well as insects that are pathogen vectors, be more or less important than they are now? If parasites and their hosts are affected differently by the changes in the environment, what new problems might arise? How will pathogens modify plant responses to the environmental changes, and vice versa? What will be the impact on pesticide usage? Answers to such and many more questions will provide an opportunity for research in climate change scenario. Plant pathologists are uniquely trained to study plant parasite-environment relationships as integrated systems and must be prepared to guide research related to climate change.

Conclusions: 

• Plant disease has a major impact on agricultural and natural systems

• Current strategies for management need to be maintained and improved, even if the climate did not change

• Climate change will increase some disease risks and decrease others

• The effects of climate change will be most important when thresholds and interactions occur to produce unanticipated large responses

Article compiled by Mr. Amol Vijay Shitole (Ph.D. Scholar)

Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola (M.S.)