Aflatoxin grim problems in maize

Aflatoxin (AF) is a term generally used to refer to a group of extremely toxic chemicals produced by Aspergillus flavus and Aspergillus parasiticus. These toxins may be produced when the moulds attack certain plants and plant products.

The most important subgroups of Aflatoxins include Aflatoxin B1, Aflatoxin B2, Aflatoxin G1 and Aflatoxin G2. The most potent hepatocarcinogenic and hepatotoxic among these is Aflatoxin B1.

The international agency for Research on cancer Categorized Aflatoxin B1 as a group 1 carcinogen for humans. AF are regulated at least in 100 countries and the average range of these regulatory limits varies from 1-20 and 0-35µg/Kg for AFB1 and total AF, respectively.

In the EU rules the maximum limit is 2 and 4 µg/kg for AFB1 and total Aflatoxin, respectively. Maize is one of the most important cereal in all over the world. More than 200 million people of world are gaining food from morning till noon.

Maize is ranked third and is most grown cereal crop. In Pakistan, maize stands at fourth position after wheat, cotton and rice. Maize contributed 2.7% in the value addition in agriculture and 0.5% to GDP of Pakistan.

Maximum acceptable levels of Aflatoxins in maize used for feed and food, as established by the Food and Drug Administration (µg/kg)

• Distribution of Fungi associated with Aflatoxins

Mycotoxigenic Genera of Fungi associated with maize have often been broadly classified as either field or related to storage. The field infection of maize by A. flavus can result in Aflatoxin production in the maize before harvest.

Extreme heat, Drought and corn ear injury from insect feeding induce stress in maize and create an environment favorable to these fungi and Aflatoxin production.

• In the Field

Initially it was believed that Aspergillus flavus and Aspergillus parasiticus occurs on maize only in storage. But field studies shown that Aspergillus flavus can also attack maize in the field. In maize field Aspergillus flavus is evident as a Yellowish brown to Greenish Yellow. A. flavus can appear as a powdery mold growth on or between corn kernels.

• Favourable temperature for Aspergillus flavus

Temperature ranging from 80 to 100 degrees F and relative humidity of 85% are optimum for A. flavus growth and Aflatoxin production. Heat stress during the growing season, especially during pollination and as kernels mature, favour infection.

Aspergillus flavus grows best at high temperatures.

• During storage

Aspergillus flavus can also develop or continue to develop on corn during storage. The extent and severity of attack by A. flavus and production of Aflatoxin in stored maize are influenced by various grain and storage conditions such as temperature and moisture content of the stored grain, length of storage and physical condition of the grain going into storage.

• Favourable MC for Aspergillus flavus

 Aspergillus flavus grow best on corn at 18.0 to 18.5% MC. Moisture content below 13% prevents growth of A.flavus. As the fungus grows respiration occurs releasing heat and moisture into the surrounding environment in the grain mass.

This results in an increase in the MC and Temperature of the surrounding maize, causing a hot spot. If MC and temperature continues to increase, the environment for A. flavus becomes more favorable. Maize contaminated by fungus going into storage will deteriorate at lower MC and at a shorter time than maize that is undamaged and free of this fungi.

Management practices to reduce Aflatoxin in maize: In field

• Plant hybrids with resistance to earworm
• Use of balanced fertilizers
• Sowing of crop at optimum time
• Follow recommended management practices
• Use irrigation practices to deliver optimum water from silking stage to late dough stage
• Begin harvest when grain MC is about 24%
• Alfa-Guard can be applied at beginning tassel stage of growth to minimize the development of Flavus on maize kernels

   During storage

• clean bins, areas around bins and all grain handling equipment
• maize should be dried to 13% MC after harvest
• for long term storage 10-12% MC is safe
• aerate grain to safe and equalized temperatures throughout the grain mass
• protect grain from insects
• maintain low moisture and proper temperature
• routinely, checking of grains

Contamination of maize grains with Aflatoxin cannot be ignored and needs thorough inspection before end use. Strategies should be developed to control the contamination of this crop as well as to reduce the risk of exposure to such hazardous contaminants.

Authors: Akhtar Abbas*¹, Arslan Ali¹, Rashid Rafique¹, Ehsan khalid¹, Noman Iftikhar²

¹Seed Physiology Lab, Department of Agronomy, University of Agriculture, Faisalabad-38040, Pakistan.²Institute of Microbiology, University of Agriculture, Faisalabad-38040, Pakistan.

 * Corresponding Author Email: itz.akhtar@gmail.com