Fruit protection against infection by Phyllosticta citricarpa , the causal agent of citrus black spot (CBS), relies heavily on fungicides. Quinone-outside inhibitors (QoIs), which have a site-specific mode of action, have been in use since the early 2000s in South African citrus orchards. This study investigated the occurrence of the F129L, G137R or G143A mutations in codons 129, 137 and 143, respectively, in cytochrome b ( cy...