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Aflatoxin problem in groundnut

Aflatoxins are toxic substances produced by certain fungi called Aspergillus flavus and Aspergillus parasiticus.The word "aflatoxin"derived as:A stands for Aspergillus,fla for flavus and toxin for poison.This fungus is present normally in air, soil and water and is associated with living or dead plants and animals throughout the world.

 

Aflatoxins have become the subject of concern in agriculture, as well as in animal and human health on a global scale.A very small amount of aflatoxin in feed (10-20 parts per billion) can produce fatal liver cancer in young animals.Aflatoxin contamination is a serious quality problem in groundnut.

Factors contributing to contamination

  Pre-harvest

• Presence of fungus in soil and air. This infection of groundnut, which occurs at every stage from pre-harvest to storage, causes aflatoxin production in the kernels.
• Use of susceptible cultivars.
• End-of-season moisture stress to the crop for more than 20 days.
• Mean soil temperatures of 28-31^oC in the pod zone.

 

                                                     Growth Cracks on Groundnut Pods.

Drought affected crop is susceptible to the attack of Aspergillus

• Growth cracks and mechanical injury to the pod.
• Insect damage to pods by termites or pod borers.
• Death caused by diseases (stem, root and pod rots) at pod maturity stage.
• Nematode damage to the pod.

Post-harvest

• Harvesting over-mature crop.
• Mechanical damage to the pod at the time of harvest.
• Stacking the harvest when pod moisture is more than 10% or under high humidity conditions.

 

        Pod damage from insects lead to aflatoxin contamination

Pod Damage During Harvesting

• Damage to the pod by insects during storage.
• Storing haulms with immature or small pods (they tend to contain more aflatoxins).
• Wetting of stored pods due to high ground-moisture or roof leakage.

  Effects of aflatoxin contamination  

• Causes marked deterioration in pod and kernel quality because of fungal growth.
• Contaminated kernels are unfit for consumption.
• Reduced price for the produce
• Causes decay in both seeds and non-emerged seedlings.
• Severely affects the export of groundnut and its products.

 

           Deterioration in pod                        kernel quality

Management of aflatoxin contamination

Pre-harvest

• Use of groundnut varieties resistant to A. flavus invasion and/or do not allow A. flavus to produce the aflatoxins.
• The following genotypes have been identified as resistant to A. flavus invasion and colonization: CGC 2, CGC7, 1-4, 1-7, S 230 by NRCG, Junagadh Ah 7223, Var.27, Faizpur, Monir 240-30 by ICRISAT J-11, Karad 4-11, Kopergaon 1, US 26 (PI 246388) by National Institute of Nutrition, Hyderabad.
• Select sound seed and treat them with Diathane M45 (at 3 g/kg) before planting.
• Maintain optimal plant population in the field (33 plants per sq m)
• Availability of adequate mineral nutrients to the crop is helpful to reduce the contamination. So, apply farm yard manure or compost at 5-10 tons/ha.
• Calcium is the only nutrient that has been shown to have an effect on aflatoxin contamination; therefore gypsum may be applied at 400-500 kg/ha at flowering.
• Apply biofertilizer Trichoderma at 1 kg/ha to provide competitive and antagonistic effects to Aspergillus.
• Control soil inhabiting insects like termites, white grubs which damage the pods.
• Avoid end-of-season drought with irrigation, if possible.
• Remove manually damaged pods, loose-shelled kernels and immature groundnut which are the most likely to be contaminated.
• Remove dead plants from the field before harvest.
• Harvest the crop at right maturity.

Post-harvest

• Dry the harvested produce for 3-5 days using the inverted windrow drying method.
• Dry the produce until the pod moisture is below 8%.
• Strip or thresh the pod immediately after drying. Avoid stacking.
• When using mechanical threshers, use appropriate sieves based on pod size so that immature pods are blown off.
• Remove mechanical and insect damaged pods.
• Remove all immature pods attached to the haulms.
• Separate the fully mature large pods (to be used for raw consumption) from the remaining produce (used for oil extraction).
• Do not mix the gleaned pod with the main produce.
• If necessary, dry the stripped/ threshed pod once again to maintain seed moisture below 8%.
• Stack the pod-filled gunny bags on a wooden plank and store them in well aerated, waterproof storage.
• Prevent insect damage to the pods in storage.