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The relationship between climate, disease and coffee yield: optimizing management for smallholder farmers
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.ORCID-id: 0000-0002-4658-7850
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Climate change and diseases are threatening global crop production. Agroforestry systems, which are characterized by complex multispecies interactions, are considered to provide nature-based solutions for climate change mitigation and pest and disease regulation. Understanding the role of the abiotic environment and species interactions in shaping diseases and yield in agroforestry systems would enable us to develop effective ecologically-informed pest and disease management under a changing climate, support sustainable agricultural practices, and maximize the benefits gained from agroforestry systems. To gain such a comprehensive understanding of what shapes pest and disease levels and yield in agroforestry systems, we need to investigate how the interactions between agroforestry system components, such as trees, crops and their associated organisms, vary in space and time, and how they are influenced by abiotic factors in terms of pests and diseases and yield. 

In this thesis, my overarching goal was to understand how microclimate and management impact major coffee pests and diseases, their natural enemies, and coffee yield, as well as farmers’ perceptions of climate change and climate-mediated changes in disease dynamics and yield, with the aim of using these insights to optimize management decisions for smallholder farmers in southwestern Ethiopia. With this aim, I selected 58 sites along a gradient of management intensity, ranging from minimal management in the natural forest to moderate management in smallholder farms and intensive management in commercial plantations. As an approach, I combined observational and interview studies to examine i) the impact of shade tree species identity and canopy cover on coffee pests and diseases, ii) the effect of climate and management on coffee berry disease and yield, iii) the impact of climate on a host-hyperparasite interaction, and iv) farmers’ perceptions of climate change and climate-mediated changes in disease dynamics and yield. 

I found that tree identity affected the incidence and severity of coffee diseases, whereas insect pests were strongly affected by canopy cover, but in a species-specific way (I).  Both climate and management affected coffee berry disease and yield. Importantly, the effect of climatic variables on disease and yield differed strongly between the developmental stages from flowering to ripening (II). In chapter (III), I found that the climatic niches of coffee leaf rust and its hyperparasite differed, with coffee leaf rust severity preferring high maximum temperatures, whereas the hyperparasite preferred cold nights. The interviews revealed that the majority of farmers perceived long-term changes in one or more aspects of the climate, and the majority of farmers perceived an increase in coffee leaf rust and a decrease in coffee berry disease. Climate data also supported farmers’ knowledge on climate-disease-yield relationships (IV). 

Taken together, my thesis advances our understanding of the relationship between climate and management of coffee pests, diseases and yield, and this may contribute to the development of ecologically-informed pest and disease management strategies for coffee production and other agroforestry crops.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2023. , s. 48
Nyckelord [en]
Agroforestry, Arabica coffee, climate change, fungal disease, host-hyperparasite interaction, insect pest, minimum temperature and maximum temperature, shade cover, shade tree species, smallholder farmers, yield
Nationell ämneskategori
Jordbruksvetenskap
Forskningsämne
ekologi och evolution
Identifikatorer
URN: urn:nbn:se:su:diva-216221ISBN: 978-91-8014-278-6 (tryckt)ISBN: 978-91-8014-279-3 (digital)OAI: oai:DiVA.org:su-216221DiVA, id: diva2:1749585
Disputation
2023-05-31, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-05-08 Skapad: 2023-04-10 Senast uppdaterad: 2023-04-24Bibliografiskt granskad
Delarbeten
1. The impact of shade tree species identity on coffee pests and diseases
Öppna denna publikation i ny flik eller fönster >>The impact of shade tree species identity on coffee pests and diseases
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2022 (Engelska)Ingår i: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 340, artikel-id 108152Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The multifunctional role of shade trees for conservation of biodiversity and ecosystem services in natural forests and agroforests is well documented, yet we lack insights into the impact of shade tree species identity on pest and disease dynamics on agroforestry crops such as coffee and cacao, and its implications for management. We conducted two surveys on the impact of shade tree species identity and canopy cover on pests, diseases and a fungal hyperparasite on Arabica coffee in southwestern Ethiopia, which is one of the areas of origin of Arabica coffee. One survey was in a commercial plantation, and the other along a management gradient from only little managed coffee growing in the natural forest to intensively managed commercial plantations. To link these findings to current shade tree selection criteria, we complemented these surveys by interviews with farmers and managers. Shade tree species identity left a weak imprint on insect pest levels, and insect pests levels differed strongly in the strength and direction of their response to canopy cover. In contrast to the insect pests, the incidence of coffee leaf rust and its hyperparasite, as well as coffee berry disease, differed among shade tree species, with particularly high levels of coffee leaf rust and the hyperparasite underneath the canopy of the shade trees Acacia abyssinica and Croton macrostachyus, and coffee berry disease underneath the canopy of Acacia abyssinica and Polyscias fulva. Smallholder farmers used many criteria for selecting shade trees, such as leaf traits and competition for soil moisture, but low priority is given to the effect of shade tree species identity on pests and diseases. Our findings help to understand spatial variation in pest and disease dynamics in natural forests and agroforests, and may inform the selection of shade tree species by coffee producers and thereby contribute to ecologically-informed pest and disease management. Importantly, our finding highlight the potential for using tree identity for the sustainable management of pests and diseases, with relevance for global agroforestry systems.

Nyckelord
Canopy cover, Coffee leaf rust, Coffee berry disease, Hyperparasite, Insect pest, Shade tree species
Nationell ämneskategori
Lantbruksvetenskap, skogsbruk och fiske Biologiska vetenskaper
Identifikatorer
urn:nbn:se:su:diva-210268 (URN)10.1016/j.agee.2022.108152 (DOI)000859051400007 ()2-s2.0-85137291406 (Scopus ID)
Tillgänglig från: 2022-10-12 Skapad: 2022-10-12 Senast uppdaterad: 2023-04-12Bibliografiskt granskad
2. Impact of climate and management on coffee berry disease and yield in Arabica coffee’s native range
Öppna denna publikation i ny flik eller fönster >>Impact of climate and management on coffee berry disease and yield in Arabica coffee’s native range
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

Climate change might increase plant diseases, reduce crop yields and threaten the livelihoods of millions of smallholder farmers globally. It is thus important to understand the relationships between climate, disease levels and yield to improve management strategies for sustainable agroforestry in a changing climate. One of the major threats to coffee production in Africa is coffee berry disease, caused by the fungal pathogen Colletotrichum kahawae. To investigate the effects of climatic and management variables on coffee berry disease and yield, we recorded daily minimum and maximum temperature and relative humidity, as well as incidence of coffee berry disease and yield in 58 sites along a broad environmental and management gradient in southwestern Ethiopia in both 2018 and 2019. Coffee berry disease was affected by several climatic and management variables, with relatively high consistency between years. For example, coffee berry disease incidence was higher in sites with high minimum temperatures during the fruit expansion stage from March to April, and was lower in sites with high minimum temperatures during the endosperm filling stage from May to June. Coffee berry disease incidence was negatively affected by the proportion of resistant cultivars, whereas management intensity had no effect on disease incidence. Coffee yield decreased with increasing minimum and maximum temperatures during the flowering period in 2018 and the fruit developmental period in 2019, respectively. Coffee yield was negatively affected by canopy cover, and positively affected by management intensity, in both years. Our findings highlight that coffee berry disease and yield were affected by different climatic and management variables. Yet, managing for low disease-high yield is practically difficult, as the effect of several climatic variables was season-dependent, and at the same time climatic variables were highly correlated between seasons. One way to break the correlation of climatic variables between seasons might be to take advantage of differences among shade trees in the presence or timing of leaf drop. To reduce levels of coffee berry disease, an effective strategy is to use resistant cultivars, but this might threaten the wild coffee genetic reservoir.

Nyckelord
Climate change, coffee berry disease, management intensity, minimum and maximum temperature, relative humidity, yield
Nationell ämneskategori
Jordbruksvetenskap
Forskningsämne
ekologi och evolution
Identifikatorer
urn:nbn:se:su:diva-216212 (URN)
Tillgänglig från: 2023-04-11 Skapad: 2023-04-11 Senast uppdaterad: 2023-04-12
3. Impact of climate on a host-hyperparasite interaction on Arabica coffee in its native range
Öppna denna publikation i ny flik eller fönster >>Impact of climate on a host-hyperparasite interaction on Arabica coffee in its native range
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]
  1. Natural enemies of plant pathogens might play an important role in suppressing plant disease levels in natural and agricultural systems. Yet, plant pathogen-natural enemy interactions might be sensitive to changes in the climate. Understanding the relationship between climate, plant pathogens, and their natural enemies is thus important for developing climate-resilient, sustainable agriculture.
  2. To this aim, we recorded shade cover, daily minimum and maximum temperature, relative humidity, coffee leaf rust, and its hyperparasite at 58 sites in southwestern Ethiopia during the dry and wet season for two years
  3. Coffee leaf rust severity was positively related to maximum temperature and hyperparasite severity was higher when the minimum temperature was low (i.e. in places with cold night temperatures) during three of the four surveying periods. While canopy cover did not have a direct effect on rust severity, it reduced rust severity indirectly by lowering the maximum temperature. Canopy cover had a direct positive effect on hyperparasite severity.
  4. Synthesis and applications. Our findings highlight that coffee leaf rust and its hyperparasite are both affected by shade cover and temperature, but in different ways. On the one hand, these niche differences between coffee leaf rust and its hyperparasite provide opportunities to develop strategies to manage the environment (such as shade cover and microclimate) in such a way that the rust is disfavored and the hyperparasite is favored. On the other hand, these niche differences lead to the worrying prediction that levels of coffee leaf rust will increase, and its hyperparasite will decrease, with climate change.
Nyckelord
Canopy cover, climate change, coffee leaf rust, Hemileia vastatrix, Lecanicillium lecanii, minimum and maximum temperature, relative humidity
Nationell ämneskategori
Jordbruksvetenskap
Forskningsämne
ekologi och evolution
Identifikatorer
urn:nbn:se:su:diva-216218 (URN)
Tillgänglig från: 2023-04-11 Skapad: 2023-04-11 Senast uppdaterad: 2023-04-12
4. Using local knowledge to reconstruct climate-mediated changes in disease dynamics and yield – a case study on Arabica coffee in its area of origin
Öppna denna publikation i ny flik eller fönster >>Using local knowledge to reconstruct climate-mediated changes in disease dynamics and yield – a case study on Arabica coffee in its area of origin
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]
  • While some countries have monitored major crop diseases for several decades or centuries, other countries have very limited historical time series. In such areas, we lack data on long-term patterns and drivers of disease dynamics, which is important for developing climate-resilient disease management strategies. 
  • We adopted a novel approach, combining local knowledge, climate data, and spatial field surveys to understand long-term climate-mediated changes in disease dynamics in coffee agroforestry systems. For this, we worked with 58 smallholder farmers in southwestern Ethiopia, the area of origin of Arabica coffee.
  • The majority of farmers perceived an increase in coffee leaf rust and a decrease in coffee berry disease, whereas perceptions of changes in coffee wilt disease and Armillaria root rot were highly variable among farmers. Climate data supported farmers’ understanding on the climatic drivers (increased temperature, less rainy days) of these changes. Temporal disease-climate relationships were matched by spatial disease-climate relationships, as expected with space-for-time substitution.
  • Understanding long-term disease dynamics and yield is crucial to adapt disease management to climate change. Our study demonstrates how to combine local knowledge, climate data and spatial field surveys to reconstruct disease time series and postulate hypotheses for disease-climate relationships in areas where few long-term time-series exist.
Nyckelord
Climate change, Coffee berry disease, Coffee leaf rust, Coffee wilt disease, Disease dynamics, Local knowledge, Perception, Yield.
Nationell ämneskategori
Jordbruksvetenskap
Forskningsämne
ekologi och evolution
Identifikatorer
urn:nbn:se:su:diva-216219 (URN)
Tillgänglig från: 2023-04-11 Skapad: 2023-04-11 Senast uppdaterad: 2023-04-12Bibliografiskt granskad

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Ayalew Nurihun, Biruk

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