Despite the importance of onion (Allium cepa) leaf anthracnose caused by Colletotrichum gloeosporioides in Latin America, Africa, and Asia, few studies have focused on host resistance to the pathogen. Therefore, in this study, resistance components of two cultivars and eight accessions of onion to four isolates of C. gloeosporioides were evaluated under greenhouse conditions. Inoculations were performed either by spraying inoculum suspension or by placing a mycelial disc on the leaf. The cultivars and accessions differed significantly regarding initial infection frequency and monocyclic progress rate (r g) with the spray-inoculation, and regarding incubation period and lesion area with the mycelial-disc inoculation. Correlation coefficient (r) values were estimated between the components with the mycelial disk inoculations. Values of r were 0.98 between disease severity visually assessed nine days after inoculation (SEV9) and area under the disease progress curve (AUDPC), 0.80 between SEV9 and disease severity assessed with the leaf area meter (SEV), 0.72 between SEV9 and r g, 0.64 between SEV9 and infection frequency nine days after inoculation, 0.81 between SEV and AUDPC, and 0.64 between SEV and r g. Considering both the significant r values associated with SEV9 and that to estimate SEV9 there is no need of rating diagrams, this component is potentially useful to evaluate onion germplasm against C. gloeosporiodes. The spray inoculation procedure was faster, simpler, and provided higher infection efficiency and lower variability than the mycelial disk inoculation technique. Therefore, this should be the preferred inoculation procedure when assessing onion germplasm.
