The presence of dark spots on oat (Avena sativa) kernels has been a limiting factor toward their commercialization in Brazil since they make affected kernels less acceptable to the industry. The mycelium localization of Pyrenophora avenae on the kernels and its enzymatic activity may be involved in the cause of the spots. The objectives of this work were to determine the localization of P. avenae mycelium on the caryopsis tissues, its enzymatic activity and its effects on lipids and protein contents. The localization of the mycelium in tissues was determinated by analysis of kernel slices under microscope and stereomicroscope after hydration. The evaluation of the enzymes lipase, protease, and amilase was performed on 18 isolates, selected from the most cultivated areas of southern Brazil, by growing the isolates on enzyme-specific media. Proteins and lipids were analyzed by Kjeldahl and Bligh & Dyer methods, respectively. The P. avenae mycelium is the main cause of kernel spots in oats and its growth is restricted to the cells of the pericarp. Pyrenophora avenae has good lipase and protease enzymatic activity but poor amylase activity. Spotted oat kernels did not differ in protein and lipid content when compared to healthy ones. In particular, their content was higher in the external tissues of the pericarp than in the rest of the grain, regardless of the presence of the spots. These results may explain the superficial growth of P. avenae mycelium in oat cariopsis and its association with the kernel spot.
