They said the findings could avoid thousands of tons of fungi-affected crops being discarded every year or being consumed with unacceptable levels of the mycotoxin.
Scientists from The Donald Danforth Plant Science Center, International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Hyderabad, India, US Department of Agriculture (USDA) and Louisiana State University are behind the work.
They are planning future field trials in India for further development of aflatoxin resistant groundnut.
Dual combat approaches
By producing small proteins called defensins, groundnuts can stop the fungus from propagating and infecting it.
Defensins are produced as immune responses to pathogens by some plants (not usually groundnut), animals and humans.
The second approach, Host-Induced Gene Silencing (HIGS), uses a naturally occurring biological mechanism where plants and pathogens often exchange small nucleic acid molecules (RNAi) during the infection process.
Groundnut seeds emit gene-silencing RNA molecules to help shut down the synthesis of aflatoxin by the fungus.
The moulds, Aspergillus flavus and Aspergillus parasiticus, which infect groundnut, maize, cottonseed and chilly produce toxins that suppress the immune system, hinder growth in children and have been linked to liver cancer.
Groundut seeds where exposed to aflatoxin-producing moulds A. flavus and A. parasiticus.
Using High-Performance Liquid Chromatography (HPLC) researchers detected below 1 ppb of aflatoxin after three days of fungus inoculation compared to control seeds that accumulated over 3,000 ppb.
The approach could apply to other crops like maize, cotton seed, chilli, almond and pistachio.
Dr Kiran Sharma, principal scientist and co-author, said: “Recent advances in biotechnologies like RNAi technology and genetic transformation offer great potential in developing crops that can resist the infection and growth of the aflatoxin-producing fungus in the field and stop the production of aflatoxin itself.”
The fungus which produces the toxins can stay dormant in soil for years and infects maize and groundnut during drought and heat stress.
Contamination also happens when grain is stored in hot, humid and poorly-ventilated conditions.
The US does not allow the sale and export of food with aflatoxin levels exceeding 20 parts per billion (ppb) and European Union standards are more stringent at 2 ppb.
Dilip Shah, principal investigator at the Danforth Plant Science Center, said the technology has potential to contribute to food safety in developing countries where mycotoxin contamination poses a major threat to human and animal health.
“Plant defensins exhibit potent antifungal activity against several economically important fungal pathogens and it is exciting to see successful application of this technology for reducing the pre-harvest infection by Aspergillus and alleviating the burden of mycotoxins in genetically modified groundnut.”
Shah and his team transferred small proteins called defensins from alfalfa and the Mediterranean clover to the DNA of an Aspergillus-susceptible peanut variety widely grown in Africa and India, which allowed the groundnut to stop the fungus from infecting the plant.
Scientists at ICRISAT, the USDA and Louisiana State University worked on the other part.
They transferred small RNA molecules from the Aspergillus fungus that are involved in the aflatoxin synthetic pathway. The nuts produced these RNA molecules during fungal attacks and inactivated target genes responsible for aflatoxin synthesis
Dr Pooja Bhatnagar-Mathur, lead author and ICRISAT senior scientist, said it analysed the way the fungus propagates through the pods in groundnut.
“By looking at what exists in nature, we then devised biotechnology tools to develop groundnuts that are immune to pre-harvest Aspergillus infection, and are also able to block aflatoxin production in the field as well as under post-harvest storage.”
Source: Plant Biotechnology Journal
“Peanuts that keep aflatoxin at bay: a threshold that matters”
Authors: Kiran K. Sharma, Arunima Pothana, Kalyani Prasad, Dilip Shah, Jagdeep Kaur, Deepak Bhatnagar, Zhi-Yuan Chen, Yenjit Raruang, Jeffrey W. Cary, Kanniah Rajasekaran, Hari Kishan Sudini, Pooja Bhatnagar-Mathur