The following points highlight he two main strategies for prevention of mycotoxin in maize. The strategies are: 1. Pre-Harvest Management 2. Post-Harvest Management.
Strategy # 1. Pre-Harvest Management:
Prevention the growth of moulds on storage grains through pre-harvest management is the first step in minimizing the microbial spoilage of stored grains. Association between microbial decay and inadequate storage facilities cannot be ignored. Studies have revealed that some seeds are contaminated with moulds in the field itself.
It is impossible to control, when these infected seeds are exposed to environmental factors as well as stored in poor storage conditions. Once the crop becomes infected under field conditions, the fungal growth will continue during post-harvest stages and storage. Therefore, the pre-harvest management is focused on controlling the main factors that are responsible to enhance the mycotoxin production in maize.
Some Common Management Strategies Insect Infestation:
It has been reported that the incidence of Aspergillus flauus is usually higher in insect damaged kernels and these damaged kernels are the routes for infection for mycotoxins producing fungi. Control of the growth of these fungi will subsequently minimize the fungal contamination.
Discarding the damaged grains before storage helps in reducing the microbial colonization and subsequent formation of mycotoxins during storage.
i. Crop Rotation:
It is an important factor in the spread of inoculum of grain molds. Adequate rotation of crops will provide minimum chance of spread of inoculum of these molds. Therefore, crop rotation will prove an aid to the prevention of mycotoxin contamination; such as maize-soybean rotation yielded a less extensive outbreak of fusarium than maize-maize planting operations.
ii. Management of Crop Residues:
Inoculum potential is a prerequisite for grain molds infection. Soil type and conditions, as well as availability of viable spores are important factors in mycotoxin production. At the time of crop harvesting, some residues remain on the field. This residue provides the source of inoculum for the next crop. Proper management of these crop residues would help to avoid this problem.
iii. Avoidance of Environmental Condition that Favour Infection in the Field:
To minimize the inoculum load, the adequate efforts should be made to avoid extreme conditions of either drought or excessive moisture. It has been observed by many workers that the drought stress followed high moisture condition is ideal for the development Fusarium moniliforme and subsequently production of fumonisin.
Whenever such weather prevails it can be assumed that some degree of mycotoxin contamination will occur and accordingly the management strategies should be explored.
iv. Development of Resistant/Tolerant Plant Varieties:
The search for naturally resistant maize genotypes had not been successful till today. However, the extensive research on development of plant varieties and identifying the sources of resistance against mycotoxin producing molds is being corrected out.
Based on screening of maize genotype mycotoxin producing fungi and level of mycotoxin conducted at DMR Priya sweet corn and Nayjot showed some degree of tolerance up to 6 months stored period, whereas Shaktiman-1, found to be most promising by showing negative reaction for Aflatoxin in absence of A. flavus in cob samples even in 9 months storage period.
In case of healthy maize seed samples, Shaktiman-1, Shaktiman-4 and KMH- 1701 were found most promising by showing negative reaction for Aflatoxins even after 9 months stored period.
In one year stored healthy grain samples, the most promising genotypes identified were Shaktiman-4 with a level of toxin (AFBX) is 0.03 ppb followed by KMH-1701 (0.04 ppb); HQPM-1 (0.05 ppb); and QPM-2-136 (0.06 ppb) whereas the highly toxic samples was RP-4 (50.44) at moisture % ranged from 12 to 11.1% in samples collected from Delhi.
The maximum level of toxin observed in sample Mon-4 with a level of toxin is 62.42 ppb at moisture 12.6% obtained from Hyderabad. Shaktiman 1 also showed minimum (0.46%) disease index of A. flavus in field conditions which again proving that this genotype is promising one.
During harvesting, three factors are very important to control such as:
i. Timeliness harvesting.
ii. Clean up of harvested crop.
iii. Drying of harvested crops.
These practices are essential for preventing microbial decay during storage. Timing of harvesting is greatly influences the microbial growth. Harvesting should be done as soon as the crop is fully grown. It has been observed that the crops left on the field for longer periods of time many present have higher level of toxin contamination. Adequate drying is also essential to prevent fungal proliferation during storage.
Strategy # 2. Post-Harvest Management:
We should ensure the proper grain storage conditions to minimize the potential for mold growth and microbial decay. The grain storage facilities should be monitored regularly to detect grain mold development. Keep moisture in stored grain below 12-13%.
Screening of grains before storage should be done to remove trash cracks and shriveled kernels to minimize the growth of molds. Mould development during storage causes loss of germination in seed grain, discolouration and change in fatty acid profile and other quality parameters. Mould development may also encourage mite and insect infestation.
Precautionary measurements must be done on newly harvested grains so that losses in quality and quantity could be avoided. A recommended and proven method is to reduce the moisture content as early as possible.
This can be accomplished by drying and subsequently controlling the relative humidity and temperature during storage. In addition, chemical application prior to storage and during storage will be administered.
Field drying of most grain has been an accepted practice since commercial farming began; sun and wind are the primary drying agents for the most of farmers’ community worldwide and developing countries in particular. After harvest, the moisture content of the produce must be dried to 12-14% for safe storage with minimal deterioration.
ii. Sun Drying:
Sun drying is probably the oldest and most common way of reducing the moisture content of grains. It utilizes solar energy from the sun directly. In sunny days, the drying process will take 2 to 3 days. Mechanical drying is done by hot air blown by mechanical driers it consumes high power.
Solar energy is tapped by the use of a collector and converted to a more convenient form of energy and either direct use or store it for later delivery to the point of use. In solar driers solar energy heats the air.
Corn at harvesting stage has high moisture content and should be mechanically dried to reduce its moisture content as early as possible to prevent grain quality deterioration by fungal invasion. The field shelled high moisture yellow corns could be dried in 5.5 m (18 ft.) diameter low temperature drying bins.
One bin had two solar collector units, the second bin is used for ambient air only. Microflora activity can be minimized by shorter drying time and by the mixing of lower and higher moisture corn during the transfer to other storage bins.