Temperature and CO₂ Interactions Reshape Hemileia vastatrix Urediniospore Germination In Vitro

Area of Science:

• Plant Pathology
• Climate Change Biology
• Agricultural Science

Background:

• Coffee leaf rust (CLR), caused by *Hemileia vastatrix*, poses a significant threat to coffee production.
• Climate change, particularly rising temperatures and atmospheric carbon dioxide (CO2), is expected to influence CLR epidemics.
• Limited research exists on the combined effects of temperature and CO2 on CLR, with conflicting findings on disease incidence and severity.

Purpose of the Study:

• To investigate the impact of varying temperature and CO2 concentrations on *H. vastatrix* urediniospore germination.
• To understand how combined climate factors influence a key epidemiological process of CLR.
• To provide data for improved CLR risk modeling under future climate change.

Main Methods:

• Conducted controlled experiments using phytotrons to test thirty combinations of temperatures (16°C–32°C) and atmospheric CO2 concentrations (181–707 ppm).
• Assessed *H. vastatrix* urediniospore germination as an indicator of pathogen response.
• Applied a generalized linear model with a binomial distribution to analyze germination probability data.

Main Results:

• Urediniospore germination probability showed a quadratic response to atmospheric CO2, with optima dependent on both CO2 and temperature.
• Optimal germination occurred below current CO2 levels at 24°C and 28°C, and above current CO2 levels at 16°C and 32°C.
• Elevated CO2 partially compensated for suboptimal temperatures but reduced germination within the current optimal temperature range.

Conclusions:

• Rising CO2 reshapes, rather than uniformly increases, coffee leaf rust infection opportunities.
• Climate change presents a complex trade-off for CLR epidemiology.
• Findings offer crucial data for refining predictive models of CLR outbreaks under evolving climate conditions.