Crop health management systems can be designed according to practices that help to reduce crop losses by restricting pathogen development and promoting host plant growth. A good understanding of pathogen and host dynamics, which are interdependent, is therefore needed. In this article, we used a holistic approach to explain the behavior of coffee leaf rust (CLR), a major coffee disease. We monitored coffee plant and CLR dynamics simultaneously in plots under different disease management and agroforestry systems. Diseased leaves were also collected to characterize inoculum stock and rust life stages (latent rust area, area with uredospores, necrosis due to rust) through picture analysis. We used structural equation modeling to obtain an overview of CLR pathosystem functioning on a plant scale. This overview integrates processes such as disease dilution by host leaf renewal, direct and indirect effects of fruit load on CLR development, antagonistic effects of shading depending on rust life stages, the tonic effect of copper-based fungicides on leaf retention, and effects on rust life stages depending on fungicide types. From our results, we also deduced that the inoculum stock could be calculated in unsprayed plots from the rust area with uredospores, with uredospores at 58 × 103 cm−2, on average.
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.
Knowledge of the host range of a biocontrol agent (BCA) is fundamental. Host range determines the BCA’s economic potential, as well as the possible risk for non-target organisms. Entomopathogenic fungal strains belonging to the genus Beauveria are widely used as BCA, but our knowledge of their physiological host range is only partial. The aim of this study was to improve our understanding of the physiological host range of three Beauveria strains belonging to two species, B. hoplocheli and B. bassiana. We performed laboratory mortality bioassays to assess their pathogenicity and virulence against nine insect pests, belonging to three orders: Lepidoptera, Coleoptera and Diptera. Mortality rate, mean survival time and mycosis rate were used to estimate virulence. Pathogenicity was assessed as the capacity to cause a disease and induce mortality. Virulence was assessed as the severity of the disease based on mortality rate, mean survival time and mycosis rate. The results of this study revealed significant differences in the physiological host range of the three Beauveria strains tested. The three strains were pathogenic to all Diptera and Lepidoptera species tested. In the case of the Coleoptera, only the B. hoplocheli strain was pathogenic to the white grub Hoplochelus marginalis and only the B. bassiana strains were pathogenic to Alphitobius diaperinus. The B. hoplocheli strain was less virulent on Lepidoptera and Diptera than the two B. bassiana strains. The latter both exhibited very similar virulence patterns. The fact that B. hoplocheli and B. bassiana strains have different host ranges means that they can be used as BCA to target different pests. Impacts on non-target insects across multiple orders cannot be ruled out in the absence of ecological host range studies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.