Fusarium head blight, fusarium ear blight
Fusarium culmorum, Gibberella zeae, Fusarium graminearum
G. zeae is an ascomycetous fungus belonging to the order Hypocreales, family Nectriaceae forming perithecia. Ovoid ascomata (diameter 140 - 250 µm) are superficial on a thin stroma forming in clusters around the lower nodes or base of infected stems. Asci are 60 - 85 x 8 - 11 µm, claviform, with a short stipe and 8 normally distichous hyaline to light-brown ascospores (0 - 3 septate, 19 - 24 x 3 - 4 µm).
The macroconidia (sickle-shaped or markedly dorsiventral, 3 - 7 septate, 25 - 50 x 3 - 4 µm, with an often pedicellate foot cell) of the anamorph F. graminearum are produced from conidiogenous cells (10 - 14 x 3.5 - 4.5 µm), formed laterally or on short multi-branched solitary conidiophores; microconidia are absent. The formation of globose chlamydospores (intercalar, single, in chains or clumps, diameter 10 - 12 µm) is rare. Studies on the genetic diversity of this pathogen indicate that more than 6 phylogenetically distinct species may exist distributed in different regions.
Stalk rot: Early infections result in dull greyish-green leaves and tan to dark-brown lower internodes which become soft. Colonized tissue within the stalks is often pink to reddish. The pathogen causes shredding of the pith and sometimes forms tiny black perithecia on the stalks. Brownish-red lesions with sunken centres or discoloration may develop concentric rings. Gibberella ear rot:
The disease is characterized by a reddish mold, often at the tip of corn ears. Early infections may cause completely rotting of ears within the husks. Fungal mycelium may be visible as a pinkish to reddish mold between the husks and ear.
The primary inoculum source of G. zeae is infested crop debris from which the fungus releases ascospores and conidia.