The basics of Fusarium graminearum species complex (red rot) in maize

October 2014

ANEEN SCHOEMAN and SONIA-MARI GREYLING, ARC-Grain Crops Institute

Maize is the staple food commodity in South Africa and it is plagued by many ear and stem rot diseases.

The fungi infecting maize can also produce mycotoxins, which are toxic substances. Mycotoxicoses can cause various diseases in humans and animals. In this article the focus will be on the Fusarium graminearum species complex and their resultant mycotoxins.

Gibberella ear, crown, root and stalk rots are widespread throughout the South African maize production area. Globally these diseases are caused by 16 fungal species belonging to the Fusarium graminearum species complex. However, only three species have been found on South African maize thus far.

Gibberella ear rot usually occurs where maize is produced under wet, warm conditions. The disease has been common in the moderate eastern production areas and has recently been noticed to be on the increase in the western production areas. The pathogen can also infect wheat, oats and barley.

Maize grown in monoculture or rotation with other graminaceous crops can increase disease levels depending on the amount of inoculum that is carried over from one crop to the next. The disease can also increase in reduced tillage fields because of an increase in inoculum levels due to stubble retention. Gibberella ear rot can cause yield losses and affect grain quality, while root, crown and stalk rots can also have financial implications.

Ear infections initially appear as white fungal growth on the ear tips which grow toward the base of the ears (Photo 1). The mycelium will later turn red-pink in infected kernels. If the disease starts early during the growth stage of the development of the ear, the mycelia may cover the whole ear and tightly adhere the husks together.

Symptoms of root, crown and stalk rots become evident by the appearance of brown or discoloured patches in a field, by uneven growth, plants that become chlorotic or show symptoms of dwarfing. In severe cases the plants will lodge.

When infected roots, crowns or stems are cut open, a characteristic pink to red tinge of the tissue (Photo 2) is visible. It is important to send diseased material to an institution that can help correctly identify the fungal species causing the disease.

The fungi in this complex are known to produce mycotoxins such as deoxynivalenol (DON), nivalenol (NIV) and the estrogenic metabolite zearalenone (ZEA), which are harmful to humans and livestock.

NIV and DON are known protein synthesis inhibitors and the consumption of grain contaminated with these mycotoxins can cause anaemia, skin lesions, vomiting, diarrhoea, and damage to haematopoietic (liver) tissues in humans and animals. Zearalenone-contaminated feed can lead to animals developing reproductive problems.

Control measures

• Host-resistant or -tolerant varieties are the most cost-effective and practical means of combating the disease.
• Avoid planting maize at unacceptably high population densities as this increases stress and crop susceptibility.
• Rotate with non-hosts of the Fusarium graminearum species complex such aslegumes, cotton or sunflower.
• Harvest early to avoid losses due to lodging.
• Control insects such as stalk borers which may serve as possible vectors, observing the threshold value of 10% of infested plants for chemical control.
• In order to prevent ear rot after harvest, store grain under low moisture and temperatures.

At the ARC-GCI we are performing research on the Graminearum complex and we focus on Gibberella root, crown and stalk rot, as well as Gibberella ear rot on maize plants.

For any questions, please contact Aneen Schoeman at BelgroveA@arc.agric.zaor 018 299 6254/6100.

Publication: October 2014

Section: On farm level