Foliar anthracnose is one of the main diseases of onion (Allium cepa L.) under tropical and subtropical conditions. Thus far, only Colletotrichum gloeosporioides has been reported as the causal agent of this disease in Brazil. However, there are no extensive studies characterizing Colletotrichum isolates associated with onion anthracnose in the country. Here, 38 Colletotrichum isolates obtained from onion plants displaying foliar anthracnose across major Brazilian onion-producing regions were characterized using morphometric and molecular information. The Bayesian and Maximum Liklihood methods were used for an initial analysis of the β-tubulin gene (tub2) sequences of all isolates, resulting in the discrimination of nine haplotypes. Three haplotypes grouped with the reference species of the C. acutatum complex and six with the C. gloeosporioides complex. Sequences of either the glyceraldehyde-3-phosphate dehydrogenase (gapdh), actin (act), and calmodulin genes or the intergenic spacer (IGS) region between DNA lyase (apn2) gene and the mating-type mat1–2-1 locus were used to characterize a subset of isolates representing these nine distinct tub2 gene haplotypes. These analyses revealed five anthracnose-inducing Colletotrichum species, including three members of the C. acutatum species complex (C. nymphaeae, C. scovillei, and C. tamarilloi) and two of the C. gloeosporioides species complex (C. fructicola and C. theobromicola). Bioassays confirmed that all these Colletotrichum species are pathogenic to onion, inducing typical anthracnose symptoms on bulbs and leaves. Twenty-six out of 38 isolates were identified as C. theobromicola, indicating this fungus as the prevalent anthracnose pathogen under Brazilian conditions. This Colletotrichum species diversity will affect anthracnose management strategies, including chemical and cultural control as well as the identification and deployment of onion cultivars with species-specific and/or wide-spectrum tolerance/resistance.

叶面炭疽病是洋葱（的主要疾病之一洋葱L.）热带和亚热带的条件下。迄今为止，在巴西仅报道了炭疽菌（Colletotrichum gloeosporioides）作为该病的病原体。但是，在该国没有广泛的研究来鉴定与洋葱炭疽病有关的炭疽菌分离株。在这里，使用形态计量学和分子信息对38种从巴西主要洋葱产区展现出叶炭疽病的洋葱植物中分离出的炭疽菌分离株进行了表征。使用贝叶斯和最大似然法对β-微管蛋白基因（tub2）所有分离物的序列，导致区分9个单倍型。与所述的参考物种分组三个单元型C. acutatum复杂和六个与炭疽菌复杂。甘油醛-3-磷酸脱氢酶（gapdh），肌动蛋白（act）和钙调蛋白基因或DNA裂解酶（apn 2）基因与交配型垫1-2-1位点之间的基因间隔区（IGS）区域的序列用来表征代表这九种不同的tub 2基因单倍型的分离株的子集。这些分析揭示了5种炭疽病诱导炭疽菌物种，其中包括3种C. acutatum物种络合物（C. nymphaeae，C. scovillei，和Ç。tamarilloi）和两个所述的Ç。glossporioides物种复杂（C. fructicola和C. theobromicola）。生物测定法证实，所有这些炭疽菌物种均对洋葱具有致病性，在鳞茎和叶片上诱发典型的炭疽病症状。在38株分离物中，有26株被鉴定为可氏梭状芽胞杆菌，表明该真菌是巴西条件下普遍存在的炭疽病菌。这种炭疽菌 物种多样性将影响炭疽病的管理策略，包括化学和文化控制以及具有特定物种和/或广谱耐受性/抗性的洋葱品种的鉴定和部署。