Current Status of Soybean Anthracnose Associated with <i>Colletotrichum truncatum</i> in Brazil and Argentina

Brazil and Argentina have a combined soybean area of 53.6 million hectares, which accounts for over half of the total global production. The soybean crop in South America extends from latitude 8&#8722;10&#176; S to 32&#8722;36&#176; S. Such a vast, almost contiguous area imposes a serious sanitary risk to the crop. Currently, the prevalence of anthracnose is increasing, with recurring reports of severe epidemics and expressive yield losses. Soybean anthracnose is mainly associated with <i>Colletotrichum truncatum</i>, although other <i>Colletotrichum</i> species have also been reported as causal agents of this disease. Knowledge about the morphological, cultural, and molecular variability of <i>C. truncatum</i> in South America is crucial for disease management. Here, we present data on the molecular, morphological, biological, cultural, and pathogenicity of <i>C. truncatum</i> isolates collected in Brazil and Argentina. Light microscopy and randomly-amplified polymorphic DNA (RAPD) analysis were used for estimating the variability of isolates. <i>Colletotrichum truncatum</i> displayed three types of conidiogenesis, viz. conidial formation from conidiogenous cells on hyphal extremities, in conidiomas in acervuli, and directly from fertile setae (a mechanism yet-unreported for <i>C. truncatum</i>). RAPD profiling was effective in revealing the genetic diversity among <i>C. truncatum</i> isolates. The intra-group similarity was greater among the Argentinian isolates when compared to the Brazilian group. Furthermore, the results indicated a strong correlation between geographical origin and molecular grouping, with the exclusive or semi-exclusive assembling of Brazilian and Argentinian isolates in distinct clades. Finally, a preliminary account of the reaction of soybean accessions to <i>C. truncatum</i> is also included.