Tree Effects on Coffee Leaf Rust at Field and Landscape Scales

Abstract

While integrating trees into agricultural systems (i.e., agroforestry systems) provides many valuable ecosystem services, they can also interact with plant diseases. We demonstrate that a detailed understanding of how plant diseases interact with trees in agroforestry systems is necessary to identify key tree canopy characteristics, leaf traits, spatial arrangements, and management options that can help control plant diseases at different spatial scales. We focus our analysis on how trees affect coffee leaf rust, a major disease impacting one of the world’s most significant crop commodities. We show that trees can both promote and discourage the development of coffee leaf rust at the plot scale via microclimate modifications in the understory. Based on our understanding of the role of tree characteristics in shaping the microclimate, we identify several canopy characteristics and leaf traits that can help manage coffee leaf rust at the plot scale: namely, thin canopies with high openness, short base height, horizontal branching, and small, dentate leaves. In contrast, at the edge of coffee farms, having large trees with high canopy volume and small, thick, waxy leaves is more useful to reduce throughflow wind speeds and intercept the airborne dispersal of urediniospores, an important consideration to control disease at the landscape scale. Seasonal pruning can help shape trees into the desired form, and trees can be spatially arranged to optimize desired effects. This case study demonstrates the added value of combining process-based epidemiology studies with functional trait ecology to improve disease management in agroforestry systems.

Impact of climate on a host–hyperparasite interaction on Arabica coffee in its native range

“…For example, when high maximum temperatures are favouring the coffee leaf rust, farmers can plant additional shade trees, or less intensively prune the existing shade trees. Notably, the absence of a direct effect of canopy cover on rust severity might indicate that canopy cover does not affect rust severity through reduced splash dispersal, even though shade tree composition (and accompanying differences in leaf traits) might play an important role (Avelino et al., 2022; Gagliardi et al., 2021). We found no significant negative relationship between the hyperparasite‐to‐rust ratio and coffee leaf rust severity.…”

“…(Berkeley & Broome, 1869), is one of the world's most devastating crop diseases, with a major historical and ongoing impact on Arabica coffee cultivation (McCook, 2019). Coffee leaf rust causes defoliation, as well as reductions in berry numbers and berry size, which can result in heavy crop loss (Avelino et al., 2015, 2022). The rust uredospores penetrate the coffee leaf through stomata and form orange lesions on the underside of the leaves (Avelino et al., 2015).…”

“…Uredospores are primarily dispersed by wind, but may also be dispersed by rain splash (Avelino et al., 2004; Gagliardi et al., 2020). Coffee leaf rust also causes secondary losses in years following an epidemic, due to the death or weakening of heavily defoliated branches that no longer produce berries (Avelino et al., 2022). Breeding for coffee leaf rust resistance is considered a major solution for the control of the coffee leaf rust (McCook & Vandermeer, 2015; Silva et al., 2018).…”

Leaf functional traits and pathogens: Linking coffee leaf rust with intraspecific trait variation in diversified agroecosystems

“…The lifecycle H. vastatrix has been extensively described and reviewed [26][27][28][29]. Similar to coffee leaf ITV, microclimate conditions, which are shaped by agroecosystem design [30][31][32], largely constrain different lifecycle stages of H. vastatrix [32,33]. Generally, H. vastatrix uredospores, the only important infectious unit of H. vastatrix of coffee, germinate on the underside of coffee leaves and penetrate the leaf via stomata given appropriate temperatures, solar radiation, and moisture levels.…”

“…vastatrix has been extensively described and reviewed [ 26 – 29 ]. Similar to coffee leaf ITV, microclimate conditions, which are shaped by agroecosystem design [ 30 – 32 ], largely constrain different lifecycle stages of H . vastatrix [ 32 , 33 ].…”