Gibberella zeae

Scientific Name Gibberella zeae (Schwein.) Petch [teleom.], Fusarium graminearum [anam.] Schwabe, Fusarium graminearum [anam.] Schwabe Group 2
Synonyms Fusarium roseum var. graminearum, Fusarium roseum Link, Fusarium roseum f.sp. cerealis, Gibbera saubinettii Mont., Gibberella saubinetii (Mont.) Sacc., Sphaeria zeae Schwein. G. zeae is the cause of of ear and stalk rot of maize; the anamorph is F. graminearum. The cause of root and crown rot of cereals formerly known as F. graminearum Group 1 is now recognised as a separate species, F. pseudograminearum (teleomorph G. coronicola).
Common Names English: Cobweb disease, ear rot of maize, fusarium root and stalk rot, gibberella ear rot, gibberella stalk rot, headblight of maize, malformation disease, pink ear rot, red ear rot, root rot of maize, scab of maize, stalk rot of maize.
Description 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.

Biology

Damage

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.

Lifecycle

Mature perithecia may be present throughout the year. The anamorph survives as hyphae in crop debris colonized parasitically or saprophytically during crop senescence. The pathogen may be seed-borne and can be also transmitted by birds and insects which favor infections also by physical injury of the plants.

Ascospores are released preferably at night and germinate at 4 - 35 °C (optimum 25 - 28 °C) within 4 to 8 h. Kernel infection by G. zeae is influenced by temperature and moisture, but does not require exogenous nutrients. Germination is inhibited by <81 % relative humidity.

Cause

The primary inoculum source of G. zeae is infested crop debris from which the fungus releases ascospores and conidia.

Occurrence

Additional Crop Information

In addition to corn, many plant species are affected by G. zeae; crops of major importance include small grains, particularly wheat, barley, rye and triticale. Other plants may show no disease symptoms, but may serve as a source of inoculum.

Agricultural Importance

Losses are not restricted to yield quantity, but ear rot also affects yield quality. Mycotoxins - in particular deoxynivalenol (DON), T2-toxin, zearalenone - produced in infected kernels contaminate food and feed. Infected kernels contaminated with mycotoxins are not suitable for animal or human consumption if the mycotoxin content exceeds specified limits.

Control

Integrated Crop Management

In corn, variability in the genetic resistance to stalk-rot, ear rotting and deoxynivalenol production has been described. The level of resistance, however, seems to be often insufficient.
Ploughing-disking in spring significantly reduces maize stalk rot; however, the effects on cob colonization and ear rot are less pronounced.

Chemical Control

Whereas in wheat an effective control of Fusarium ear diseases can be achieved with DMI fungicides such as tebuconazole and prothioconazole, in corn no chemical control by spray applications is available in the field.

Due to the fact that seedborne inoculum is contributing to the overall infection pressure, seed treatment may be suggested as a hygiene measure, especially when the seed is significantly infested by G. zeae.

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