The mycotoxin research programme at the ARC-GCI under the spotlight

ANEEN SCHOEMAN, ARC-GRAIN CROPS INSTITUTE

At the ARC-Grain Crops Institute (ARC-GCI) in Potchefstroom, the mycotoxin research programme has been running for almost ten years. Mycotoxins are toxic substances that are produced by fungi. The researchers that are involved in the mycotoxin research are: Prof Bradley Flett (programme coordinator), Dr Belinda Janse van Rensburg, Mr Edson Ncube and Ms Aneen Schoeman.

In the mycotoxin programme, the primary focus is on Fusarium and Gibberella ear rot of maize. Most producers will recognise Fusarium ear rot as the white, pale pink or pale purple fungal growth that occurs late in the season on infected maize ears (Photo 1).

This specific ear rot is caused by the fungus Fusarium verticillioides and the toxins produced are known as fumonisin. Gibberella ear rot is caused by Fusarium boothii and the producer will recognise it as pink-red to red fungal growth on the maize ears (Photo 2).

This fungus is part of the Fusarium graminearum species complex and the fungi in thiscomplex can also cause stem and root rot ofmaize. Mycotoxins that can be produced areDeoxynivalenol (DON), Nivalenol (NIV) andZearalenone (ZEA).

Fusarium/Gibberella ear rot can directly contribute to yield losses and affect grain quality. Stem and root rot can lead to lodging of plants in the field and thus lead to yield losses. The mycotoxins can contribute to mycotoxicoses of animals, which means they are being poisoned. Fumonisin can affect the brain of horses, lungs and pancreas of pigs. Fumonisin is of international importance and the World Health Organisation and the International Agency for Research on Cancer classified fumonisin as a Group 2B carcinogen. This means that there is enough evidence found in animals that shows that the toxin can cause cancer, but not enough evidence in humans or vice versa.

Research performed in China, Italy and South Africa found that oesophageal cancer is statistically linked to people consuming maize contaminated with high levels of fumonisin. This is particularly a great concern for resource-poor producers and they are encouraged to pick out the infected kernels and only eat symptomless kernels in order to reduce levels of fumonisin consumption.

NIV and DON produced by the Fusarium graminearum species complex fungi areknown protein synthesis inhibitors and theconsumption of grain contaminated withthese mycotoxins can cause anaemia, skinlesions, vomiting, diarrhoea, and damage to liver tissues. ZEA-contaminated feed can lead to animals developing reproductiveproblems.

The aims of the research at the ARC-CGI are to understand how these fungi function in order to produce mycotoxins and also what control measures can be applied in order to reduce mycotoxin levels in maize.

Research carried out by Schoeman focuses on the fungus F. verticillioides. Each fungal isolate can differ in their ability to produce fumonisin and ear rot symptoms. The aim isto investigate this variation that occurs at DNA/gene level and to try and understand why certain isolates produce little and others, high amounts of fumonisin. This will help create a picture of which isolates occur where in South Africa and also what their potential are to produce Fusarium ear rot symptoms and fumonisin.

Dr Janse van Rensburg studied the role of environmental conditions on the production of mycotoxins and together with collaborators they have developed an epidemiological model for fumonisin and F. verticllioides. Present studies include effects of stress in plants and how they can influence mycotoxin levels.

Ncube is investigating the interaction between the fungus and the maize stem borer, Busseola fusca, and how this influences fumonisin production in the maize plant. The role that Bt maize plays in the accumulation of fumonisin is also explored. He is also involved in a national collaboration to determine mycotoxin levels in subsistence farmers’ maize in South Africa. These include aflatoxins, fumonisin, ZEA, DON, NIV and other lesser known mycotoxins.

A PhD study is presently being carried out to better understand Gibberella ear-, stem- and root rot of maize. Maize samples are being collected from maize producing areas in South Africa affected by these diseases. The fungi from the Fusarium graminearum species complex, as well as the mycotoxinsproduced, will be recorded and the potentialrisk of mycotoxin exposure will be established.The PhD student, Ms Sonia-Mari Greyling, will discuss this fungal complex ingreater detail in this issue of SA Graan/Grain.

If there are any enquiries regarding mycotoxins, we can be contacted at 018 299 6100 or BelgroveA@arc.agric.za.