noun
1. also halo spot : a blight of beans and occasionally other legumes that is caused by a bacterium ( Pseudomonas phaseolicola ) and typically produces on the leaves, stems, and pods round water-soaked lesions surrounded by a yellowish zonation, the lesions finally turning brick red
2. : blight affecting the leaves of oats and other grasses caused by a bacterium ( Pseudomonas coronafaciens ) characterized by oval water-soaked lesions turning gray to brownish and surrounded by a pale zonation