Assessing Biogeography of Coffee Rust Risk in Brazil as Affected by the El Niño Southern Oscillation

Area of Science:

• Agricultural Science
• Climatology
• Mycology

Background:

• The El Niño Southern Oscillation (ENSO) is a major climate driver affecting global weather patterns.
• Brazil is the world's largest coffee producer, with yields sensitive to climate variations and pests.
• Coffee leaf rust (CLR), caused by *Hemileia vastatrix*, significantly reduces coffee yield and quality, necessitating regular fungicide applications.

Purpose of the Study:

• To estimate CLR infection rates using a validated empirical model.
• To assess the influence of ENSO phases on the annual risk of CLR across 45 Brazilian sites.

Main Methods:

• Daily cumulative infection rates (CIR) were calculated from October to June.
• An empirical model incorporating daily minimum air temperature and relative humidity was used.
• The Two-One-Sided-Tests (TOST) method compared CIR between extreme ENSO phases (El Niño vs. La Niña).

Main Results:

• A well-defined ENSO influence on CIR was observed only in Paraná State (Southern Brazil).
• No significant ENSO influence on CIR was detected in 18 sites (G2) and 19 sites (G3).
• Regions with major coffee production showed no clear ENSO impact on CLR risk.

Conclusions:

• ENSO's impact on CLR risk is geographically specific, primarily affecting southern Brazil.
• The majority of Brazilian coffee-producing regions are not significantly influenced by ENSO regarding CLR.
• This study provides the first evidence of ENSO-linked regional impacts on coffee rust risk.