Economic Impact, Epidemiology and Environmental Drivers of Charcoal Rot of Soybean

Charcoal rot, caused by Macrophomina phaseolina, is a major constraint to soybean (Glycine max) production worldwide, particularly in warm and drought-prone environments. This review synthesizes current knowledge on the biology, epidemiology, diversity, and economic impact of M. phaseolina in soybean, and identifies key knowledge gaps relevant to disease management. Our functional data analysis of long-term field data in Australia identified significant impact of charcoal rot on soybean yield, with both high maximum air temperatures and low rainfalls significantly associated with high levels of charcoal rot in soybean fields. Misconceptions about host range and microsclerotia longevity, combined with contradictory findings from earlier studies, have contributed to a perception that agronomic practices such as crop rotation and cover cropping are ineffective for managing charcoal rot, thus, eroding confidence in these approaches. However, inconsistencies in previous research may stem from pathogen misidentification as well as context-dependent interactions between local Macrophomina populations, crop genotypes, and environmental conditions. It is now recognized that management outcomes are influenced by the genetic variability of both the local pathogen populations and locally adapted host genotypes, as well as site-specific factors. Macrophomina phaseolina is likely composed of both 'generalist' and 'specialist' sub-populations with differing levels of aggressiveness and host specialization. Considering these findings, traditional agronomic practices should not be dismissed but re-evaluated under local conditions, using locally adapted pathogen populations and host genotypes.