Production of perithecia by isolates of Gnomonia fructicola

More isolates of Gnomonia fructicola formed perithecia on Leonian's agar than on potato-dextrose or cornmeal agar. Fortifying these media with a strawberry petiole extract stimulated perithecium formation on potato-dextrose agar but not on Leonian's or cornmeal agar. All eight isolates studied produced perithecia on strawberry petioles and one produced them only on petioles. The eight isolates segregated into four cultural races according to their ability to form perithecia on the agar media and petioles. This explains why different media have been reported to be best for perithecium production in this fungus.