Comparison of Corynespora cassiicola populations from Amazonas and USA isolates from different hosts, based on SSR markers

Abstract Corynespora cassiicola poses a significant global threat in tropical and subtropical regions, infecting over 400 host plant species and causing substantial agricultural losses in crops such as cotton, papaya, tomatoes, and soybeans. In the Amazonian state of Amazonas, Brazil, and West USA, environmental conditions are highly conducive to C. cassiicola outbreaks, leading to target spot disease and resulting in severe economic and ecological consequences. Current management practices rely predominantly on resistant cultivars and fungicides, however, effective control remains limited. Furthermore, there is limited knowledge of the population structure of C. cassiicola in Amazonas, where the target spot is endemic and affects several economically critical crops. To address this gap, we analyzed 126 C. cassiicola isolates from tomato, papaya, and cucumber in Amazonas-Brazil, as well as isolates from cotton and soybean in Tennessee, using 12 SSR markers. Our results revealed low genetic diversity (Hexp = 0.37) across all plant host populations and identified population structure influenced by host specificity. Notably, 63.77% of the genetic variance was attributed to differences among hosts, indicating that populations infecting different hosts were genetically distinct. The population structure in Amazonas and Southern United States was predominantly clonal, with occasional recombination events and significant host-specific clustering. These findings highlight the need for tailored management strategies that consider host specificity and the existence of potential physiological races. In a biodiverse region like the Amazon, where C. cassiicola affects multiple crops, understanding host–pathogen interactions and genetic diversity is essential for developing effective and sustainable disease control measures.