Gibberella stalk rot and Fusarium stalk rots are distributed worldwide. However, Gibberella stalk rot is more prevalent in cool maize growing regions, while Fusarium stalk rot is most common in dry, warm regions. Gibberella and Fusarium stalk rots can cause extensive crop damage by premature plant death, interference with translocation of water and nutrients during grain filling, and crop lodging. Yield loss depends on a number of factors including host germplasm, prevailing climatic conditions, fertilization rates, crop density, and cultural practices. Estimating precise yield loss due to maize stalk rots is often complicated by the numerous factors involved. Nonetheless, in seasons favorable to stalk rots, extensive crop damage is known to occur.
Gibberella stalk rot is caused by Gibberella zeae (Anamorph: Fusarium graminearum).
Fusarium stalk rot is caused by Fusarium verticilioides syn. Fusarium moniliforme (Teleopmorph: Gibberella fujikuroi).
Symptoms caused by both G. zeae and F. moniliforme are similar. Often the only means to distinguish causal agents is microscopic inspection of spores and fruiting structures from disease lesions. Infected plants typically wilt, leaves turn dull grayish-green and the lower stalk turns from dark green to straw-colored. The internal pith of the lower stem disintegrates and goes soft. When split open, the stalks exhibit a reddish discoloration. Often black perithecia or mycelium growth can be observed at lower stalk nodes where the plant is infected.
Confirmation of the causal agent of stalk rots is best achieved through microscopic examination of spores and fruiting structures in diseased lesions.
Gibberella zeae. Conidia of the asexual stage of Gibberella zeae (Fusarium graminearum) are hyaline, slightly curved, tapering at both ends and 3 to 5 septate. Conidia measure 4-6 × 10-30µm. The perfect stage is produced within infected lesions, usually late in the season. Pertithecia of G. zeae are blackish and contain 8 ascospores. Ascospores are hyaline, up to 3 septate, slightly curved, tapered at both ends, and measure 3-5 × 10-30µm. The fungus frequently overwinters as perithecia and ascospores only mature at the onset of the subsequent season when they are the primary source of disease inoculum. Occasionally chlamydospores are formed in lesions.
Fusarium verticillioides. The perfect stage of F. verticillioides is rarely seen in contrast to that of G. zeae. During the imperfect (asexual) stage, both macroconidia and microconidia are produced. Macroconidia are hyaline, slightly curved, and tapered at both ends. They are 3 to 5 septate and measure 2-5 × 15-60µm. Microconidia are produced prolifically and are borne in chains. They are single-celled and measure 2-3 × 5-12µm.
Why and where it occurs
Both Gibberella and Fusarium stalk rots are documented from most maize growing regions worldwide. Gibberella stalk rot is more prevalent in cooler climates while Fusarium stalk rot is more common in drier, warmer climates.
Figure 1. Countries where Gibberella zeae has been documented
Figure 2. Countries where Fusarium vertilicillioides (teleomorph: Gibberella fujikuroi) has been documented.
F. verticillioides is also known to be seed borne and hence is more prevalent where infected grain is used as seed. Increased crop density and nitrogen fertilization rates favor disease severity. Crops under stress (e.g. due to foliar diseases) are more prone to stalk rots - stalks are already weakened as stalk sugars are diverted for grain filling.
Gibberella zeae infects a range of other cereals, including wheat, barley, oat, and rye. It is also known to infect species of Lycopersicon, Pisum, Trifolium and Solanum, in addition to carnations and other ornamentals.
Fusarium verticillioides infects a range of cultivated crops, including sorghum, sugarcane, wheat, cotton, banana, pineapple, and tomato.
Gibberella zeae. Ascospores produced in perithecia are wind and rain splash disseminated to freshly planted maize. Plants can be infected at the stem, leaf sheaths, and also through the roots. Secondary cycles of disease are initiated by conidia, which are produced within disease lesions on the stem and wind and rain splash disseminated.
Fusarium verticillioides. Mycelium in infected crop debris on the soil surface produces macroconidia and microconidia, which are wind and rain splash disseminated to freshly planted maize. F. verticillioides is also seed borne, in which case the pathogen may be present during the entire life cycle of the plant. Insects such as the European corn borer have also been reported to act as a vector, transferring F. verticillioides spores between plants or causing plant injury that enables the fungi to infect the plant.
Mechanism of damage: Damage is caused by premature plant death, lodging, and interference with translocation of water and nutrients during grain filling, leading to poor yields.
When damage is important: Damage is most severe if infection occurs early in the season. In these cases yield loss is directly affected by premature plant death or reduced kernel filling due to interference with translocation of water and nutrients in the stem. When crops are infected later in the season and lodging occurs, losses can be incurred particularly where maize is machine harvested. F. verticillioides is also seed borne, in which case the majority of plants may suffer from stalk rot leading to severe crop loss.
Economic importance: Precise yield loss data for most stalk rots is difficult to ascertain. However, extensive losses are possible under severe disease infestation.
Cultivation of resistant and tolerant varieties is the most cost effective and practical means of disease management.
Avoid planting above recommended crop densities.
Rotate with non-hosts, such as soybeans.
Where possible, harvest early to avoid yield loss due to lodging.
Manage infected stems and roots during the offseason to prevent perennation of inoculum.
Control insects, such as corn borers, that may serve as vectors or cause injury to plants and make them susceptible to infection.
Ensure seed is fungicide treated.
Application of fungicide on maize crops during the growing season may not be a viable or economic option as disease may be localized to certain parts of the field and spray penetration of the crop canopy may be limited.
Agrios, G.N. 1988. Plant Pathology. Third Edition. San Diego: Academic Press, Inc.
CAB International. 1998. Gibberella zeae. Distribution Maps of Plant Diseases. Edition 1 (October), Map 763. Wallingford, UK: CAB International.
CAB International. 1977. Gibberella fujikuroi. Distribution Maps of Plant Diseases. Edition 5 (October), Map 102. Wallingford, UK: CAB International.
CIMMYT. 2004. Maize Diseases: A guide for Field Identification. 4th Edition. Mexico, D.F.: CIMMYT.
Dodd, J.LO. 1980. The role of plant stresses in development of corn stalk rots. Plant Disease 64: 533-7.
Lipps, P.E., A.E. Dorrance and D.R. Mills. Gibberella stalk rot of corn. Factsheet Extension. Ohio State University Extension. http://ohioline.osu.edu/ac-fact/0033.html (24 August 2007).
Michaelson, M.E. 1957. Factors affecting development of stalk rot of corn caused by Diplodia zeae and Gibberella zeae. Phytopathology 47:499-503.
White, D.G. 1999. Pythium Stalk Rot. In Donald G. White (ed), Compendium of Corn Diseases. St. Paul, Minnesota: The American Phytopathology Society. Pp. 39-42. .
Contributor: Biswanath Das