Modelling climate change impacts on common bean (Phaseolus vulgaris) and maize (Zea mays) and their pests
Dry bean (Phaseolus vulgaris) and maize (Zea mays) are two of the most important staple grain crops for many developing countries. These crops are the main sources of proteins and carbohydrates in the diet of millions of people in these countries. The highest cultivation percentage of these crops is carried out under rain-fed conditions, therefore weather conditions have a stronger influence on its development and production. Currently, there are no studies of how climate change will affect these crops, neither how will be the new dynamic of pathogenic organisms (pests and diseases) for these crops, or which new pests or diseases might attack dry bean or maize. By having the scenarios of these changes we can reduce and change cropping patterns to mitigate the effects of climate change on these staple crops, placing high priority on food security. In this study we describe the changes on climate suitability for two staples crops and some of their pests and diseases (described below) at a global level using CLIMEX, using two Global Circulation Models (GCMs) (CSIRO-Mk3.0 and MIROC-H), assuming an A2 emissions scenario for 2050 and 2100. At the moment, the climate change effects on these diseases and plagues are unknown, as well as the consequences that these effects could have on maize and common bean production and the subsequent supply of these staple crops.
In the first part of this study, the crop modelled is maize. At the global level, maize is the third most important crop on the basis of harvested area. Given its importance, an assessment of the variation in regional climatic suitability under climate change is critical. CliMond 10'data were used to model the potential current and future climate distribution of maize at the global scale. The change in area under future climate was analysed at continental level and for major maize producing countries of the world. Regions between the tropics of Cancer and Capricorn indicate the highest loss of climatic suitability, contrary to poleward regions that exhibit an increase of suitability. South America shows the highest loss of climatic suitability, followed by Africa and Oceania. Asia, Europe and North America exhibit an increase in climatic suitability. This chapter indicates that globally, large areas that are currently suitable for maize cultivation will suffer from heat and dry stresses that may constrain production. For the first time, a model was applied worldwide, allowing for a better understanding of areas that are currently suitable and that may remain suitable for maize.
In the second part of the study, the fall armyworm (FAW, Spodoptera frugiperda), a maize insect pest, was modelled. FAW (Lepidoptera: Noctuidae), is an endemic and important agricultural pest in America. Several outbreaks have occurred with losses estimated at millions of dollars. Insects are affected by climate factors, and climate change may affect geographical range, growth rate, abundance, survival, mortality, number of generations per year and other characteristics. These effects are difficult to project due to the complex interactions among insects, hosts and predators. The aim of the current research is to project the impact of climate change on future suitability for the expansion and final range of FAW as well as highlight the risk of damage due to the pest under current and future conditions. The possible number of generations was estimated to exceed five in the south-eastern USA by 2100. A unique modelling approach linking environmental suitability and number of generations was developed to project the risks of FAW damage. The results show changes in suitability and risk across America, with an increase in the northern hemisphere and decreases or extinction in the southern hemisphere, except for southern Brazil, Uruguay, Paraguay and northern Argentina, which indicate high future levels of risk. The current study highlights the possible extinction of a tropical pest in areas near the Equator. The two GCMs both projected increases in the low-risk category of 40% by 2050 and 23% by 2100, with the medium- and high-risk categories decreasing by >50% by 2050 and >39% by 2100, compared with the current risk. In general, agricultural pest management may become more challenging under future climate change and variation, and thus, understanding and quantifying the possible impacts of FAW under future climate conditions is essential for the future economic production of crops.
The third study was about maize fungal diseases. Common rust (Puccinia sorghi) and southern rust (Puccinia polysora) are two of the most important foliar maize diseases worldwide. These fungi have caused severe economic loss to maize yields worldwide. The current and future potential distribution of these diseases was modelled with CLIMEX using the known current geographic locations of the rusts, growth and stress indices. The current projection shows areas with marginal to optimal suitability in all the continents. The models for future projections display a general reduction in the Southern Hemisphere and increase in the Northern Hemisphere, especially for the southern rust. The overlay of the General Circulation Models produce an estimation of the common areas under risk for future climate conditions for the simultaneous occurrence for both corn rusts, with a reduction of the medium-and high-risk categories by 2100. This study highlights the possible effects of climate change at a global level for common and southern rust, as well as the risk of occurrence of both diseases in common areas for future climate that could be particularly harmful for crops.
In the fourth study, the model of common bean was performed. Crops experience different climate stresses during development. The magnitude of damage will depend on the phenological stage of the crop and the stress duration. Climate change could intensify some or all of these stresses, thus negatively impacting agriculture. An assessment of staple crop productivity, quality and climatically suitable areas under climate change conditions is necessary to undertake any global initiatives to tackle food security issues. The common bean (Phaseolus vulgaris L.) is a staple crop and the main source of proteins and nutrients in Africa and Latin America. The purpose of this study is to develop a process-oriented niche model (CLIMEX) to assess the impacts of climate change on the current and future potential distribution of common bean and to use this model to investigate the changes in heat, cold, dry and wet stresses under climate change. In this study, we used A2 and A1B emission scenarios and two different global climate models, CSIRO-Mk3.0 and MIROC-H, for the years 2050 and 2100. Our results indicate future climate conditions are more favourable for common bean cultivation in the Northern Hemisphere, but are less favourable in the Southern Hemisphere. Heat and dry stresses are the main factors limiting and reducing common bean distribution under current and future projected conditions. Africa and Latin America are projected to decrease with respect to suitability for common bean cultivation. The model projections indicate that a shift in the common bean productive areas is highly likely with a loss of suitability of the current common bean cultivation areas and an increase in cold regions such as Canada, the Nordic countries and Russia. The results indicate the likelihood of changes in climatic suitability and the distribution of common bean at a global scale under a future climate, which will affect regions where this legume is a staple crop and an important source of household income. Regions in the Northern Hemisphere could take advantage of the increase in suitability by increasing the production and exportation of this grain.
In the fifth study, we used the overlays of the distributions of beet armyworm (Spodoptera exigua), a secondary common bean insect pest, soybean rust (Phakopsora pachyrhizi), a secondary fungal diseases of common bean and P. vulgaris as potential host to demonstrate and assess their interactions. Worldwide, crop pests (pathogens and insects, CPs) affect agricultural crops detrimentally. These negative effects, coupled with the impact of climate change, are a cause of major nutritional and economic losses. Secondary pathogens may increase in importance under global warming conditions. The use of species distribution models, such as CLIMEX, is invaluable for projecting current and future suitability of CP localities. The soybean rust and beet armyworm model projections show consistent agreement with the known global distribution. In the current scenario, suitable climate conditions for both CPs are predicted in all continents. A general reduction in suitability between the Tropic of Cancer and the Tropic of Capricorn is likely under future scenarios. Regarding the risk of these CPs occurring in common bean, a reduction is likely for the middle and the end of the century. The most relevant findings of this study were the reduction of the suitable areas for the CPs, the reduction of the risk under future scenarios and the similarity of trends for the CPs and host. The current results highlight the relation between and the coevolution of host and pathogens. Thus, the study overlays the distributions of two CPs and a potential host to demonstrate and assess their interactions, which has rarely been performed previously in climate change studies.
In the last study, we focus our study on Mexico to analyse in depth the global models previously performed. A general reduction in suitability for maize and common bean as well as for the plagues and diseases under study is shown through for territory by the middle and end of the century. The reduction of suitability may be caused by the increase of heat and dry stresses. We also propose a methodology of downscaling and other techniques to improve the model in CLIMEX of the current and future suitability of the species under study. Later we will be able to continue doing the same investigations in other countries to discover their particular strengths and weaknesses for the future productions of these two staple crops under climate change.