Inhibition of germination of <i>Mycosphaerella brassicicola</i> ascospores on young cabbage and cauliflower leaves

Abstract

SUMMARY Symptoms of ringspot of brassicas, caused by Mycosphaerella brassicicola , rarely appeared on rapidly expanding leaves of cabbages and cauliflowers but were common on fully expanded leaves. M. brassicicola ascospores did not germinate, or germinated poorly, on expanding leaves or on recrystallised wax deposits taken from these young leaves. A high proportion germinated on expanded leaves, on waxes taken from expanded leaves and on various other surfaces in the absence of nutrients. A volatile metabolite, present in the younger leaves, appears to inhibit ascospore germination.