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

Natural enemies of plant pathogens might play an important role in controlling plant disease levels in natural and agricultural systems. Yet, plant pathogen-natural enemy interactions might be sensitive to climatic changes. Understanding the relationship between climate, plant pathogens, and their natural enemies is thus important for developing climate-resilient, sustainable agriculture.

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. 

Coffee leaf rust severity was positively related to the maximum temperature. Hyperparasite severity was higher when the minimum temperature was low (i.e. in places with cold night temperatures). 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 the hyperparasite severity during one surveying period. 

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 lead to the worrying prediction that levels of coffee leaf rust will increase, and its hyperparasite will decrease, with climate change. On the other 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.

Methods
Usage Notes

These datasets were collected in Gomma and Gera districts in southwestern Ethiopia at 58 sites during the dry and rainy seasons (2018–2020). 

Details for each dataset are provided in the README file.

Datasets included:

1) Microclimate variables

Average daily minimum temperature (°C):  for each year was calculated by averaging the minimum temperature for both the dry (November to February) and rainy (April to July) seasons. 
Average daily maximum temperature (°C): for each year was calculated by averaging the maximum temperature for both the dry (November to February) and rainy (April to July) seasons.
Monthly average of the daily mean relative humidity (%): for each year was calculated by averaging the relative humidity for both the dry (November to February) and rainy (April to July) seasons. 

2) Coffee leaf rust and its hyperparasite

Coffee leaf rust severity (%): the percentage of rust on a per-leaf basis of all leaves for both the dry and rainy seasons.
Hyperparasite-to-rust ratio (%): the average percentage of rust covered by the hyperparasite for both the dry and rainy seasons.
Hyperparasite severity (%): the percentage of hyperparasite on a per-leaf basis of all leaves, irrespective of whether they had rust or not, both for the dry and rainy seasons.

3) Canopy cover (%): was assessed based on five canopy pictures taken above coffee height and analysed using ImageJ software as the percentage of black pixels. The average of the five canopy cover percentages was used as a canopy cover (%) per site. 

4) Elevation (m.a.s.l): was measured using Garmin GPS at the center of each plot.