The development and differentiation of Gibberella zeae (anamorph: Fusarium graminearum) during colonization of wheat

Worldwide, one of the most devastating pathogens of small grains is the head blight fungus, Gibberella zeae. Ascospore-laden perithecia of this fungus develop on mature cereal crops and crop debris and provide the primary inoculum of the disease. We characterize the process of colonization of wheat tissue that leads to perithecium production. Stems were colonized systemically and extensively following inoculation of the wheat head. Haploid mycelia moved down the vascular system and pith and then colonized the stem tissue radially. Dikaryotic hyphae developed at two distinct stages: in the xylem, in support of radial hyphal growth and in the chloremchyma, in support of perithecium development. Perithecium formation was initiated in association with stomates and silica cells. Vascular occlusions prevented mycelia from colonizing the stem in 25% of inoculated plants. Implications of these findings are discussed for developing resistant cultivars and improving chemical control of the disease.