Biology, pathogenicity, and haplotype analyses of Colletotrichum cliviae: a novel soybean anthracnose agent in warm tropical areas

Abstract

Soybean anthracnose is a complex disease, comprising isolates of Colletotrichum truncatum and at least six other species. In Brazil, C. cliviae was recently reported as a novel causal agent of soybean anthracnose but very little information is available about the C. cliviae-soybean pathosystem. Here we report the occurrence of C. cliviae in commercial soybean fields in the Tocantins State, TO (Northern Brazil). We also describe its most distinctive morphological, biological, cultural, and pathogenic aspects, particularly in contrast with C. truncatum (the prevalent anthracnose-causing species in Brazil), including symptoms, production of sexual structures, host range, seed infection and aggressiveness to soybean cultivars. The results indicated that the involvement of C. cliviae as an anthracnose-inducing species might impact current control strategies, including crop rotation systems and the replacement of susceptible cultivars. Studies were also carried out to clarify if the Brazilian soybean-infecting C. cliviae isolates were introduced into the country via contaminated seeds or if populations are endemic. The haplotype diversity of Brazilian as well as of a worldwide collection of C. cliviae isolates (available at the GenBank) was investigated based upon polymorphisms in three genomic regions (β-tubulin 2, glyceraldehyde-3-phosphate dehydrogenase, and actin). Nine haplotypes were identified among worldwide C. cliviae isolates from six different hosts. The Brazilian soybean isolates were placed into the closely related haplotypes 5 (composed by isolates from Mato Grosso State) and 6 (which included the isolate from TO), which were discriminated from each other by one single nucleotide polymorphism. Haplotype 6 group was also composed by a Chinese isolate from Camelia sinensis. The results suggest that this cosmopolitan fungal species is more likely endemic to Brazil where it has been reported in association with plant species across distinct botanical families. Therefore, the recent outbreaks of C. cliviae isolates on soybeans can be explained by either previous misdiagnosis or they may represent a recent shift/adaptation of this fungus to this legume crop. Thus far, the geographic occurrence of C. cliviae on soybeans is restricted to northern (warm) tropical regions of Brazil. The present report adds novel and relevant information with potential for the control of anthracnose caused by C. cliviae isolates in Brazil, and possibly in warm regions elsewhere.