Cassava based bio-fumigation – Innovating the natural way to control pest incited post-harvest loss during storage

Post-harvest loss – The big question?

Small scale farmers are often not able to afford warehousing nor are they able to provide adequate storage conditions for their produce. Poor storage facilities lead to build up of temperature and moisture in the storage pile, thus providing suitable breeding environment for various biological agents. Beetles and weevils are the most common insect pests of stored grains such as pulses and cereals. The infested seeds are rendered unfit for both human and animal consumption. In addition, several pathogenic fungi and moulds such as Fusarium, Aspergillus etc. also grow on stored materials under warm, humid conditions. They produce harmful mycotoxins which enter into the food system, posing even more threat to the food security. In developing countries, the post-harvest losses may fall anywhere between 10-30%, a majority of which is due to pest and disease infestation. The currently followed practice against such biotic agents for long term storage include fumigation using chemicals such as Aluminium phosphide, formaldehyde, methyl bromide etc. and sterilization using gamma irradiation. These chemicals may be very effective and cheap in large scale facilities, but inevitably leads to numerous health hazards and environmental issues.

So, how to mitigate pest incited post-harvest losses during storage in a cost effective, eco-friendly and sustainable manner?

Potential solution

It was after thorough perusal of the relevant literatures and several failed attempts for addressing this issue that I stumbled upon a potential answer-‘Bio-fumigation’, a process where biologically active substances (having fumigant properties) of plant origin are used to control pests and pathogens. This may not be a novel concept as one can find hundreds of studies and published papers online regarding it. This is where the next major question comes in, if not new, then why is it still not put to good use?

 Concept note

Cassava (Manihot esculenta), a woody shrub belonging to the Euphorbiaceae family is known for its edible, fleshy tuberous roots. Cassava contains an anti-nutritional factor called linamarin which is a potent cyanogenic glycoside. Among the plant parts, the leaves are found to have the highest concentration of this compound. This compound in the presence of an enzyme called linamarase (also present in the plant) is hydrolysed into hydrocyanic acid/prussic acid possessing very powerful fumigant properties. Naturally, the substrate and the enzyme are compartmentalized within the plant cells and does not come in contact with each other. The reaction occurs only in the event of cell damage such as during herbivory by animals or insects.

I propose to standardize a protocol for the isolation of the substrate linamarin on a commercial scale from the leaves of cassava. As long as the enzyme linamarase remains deactivated or separated from the substrate the reaction will not be initiated. This principle of compartmentalization could further be put to practical use, where the substrate and dormant enzyme are used to create low-cost linamarin/linamarase impregnated storage vessels or packaging material to be used by small scale farmers (even households) for short to medium term storage purposes. The moisture from air activates the enzyme which further hydrolyses the substrate to release the fumigant gases in a slow and controlled manner. These gases permeate within the vessel providing a sterilant effect to the contents stored inside. Further improvising, this reaction system can be used to prepare low-cost, environment friendly bio-fumigation chambers for fruits, vegetables and tubers to extend their shelf life.

Advantages

Due to the pure biological origin, bio-fumigation could be extensively used under organic farming certification. It is easy to upscale the model to an industrial scale during packaging fruits and vegetables as bio-fumigation reduces the inoculum level of pathogens on the food surface thereby increasing its shelf life. It is also easy to downscale the model to even house hold levels for grain storage against insect pest infestation, which is usually detrimental to health when chemical fumigants are used. They will be of low cost, easily adaptable and eco-friendly with minimal or no residual impact.

Social impact – Stakeholders and beneficiaries

Cassava is an energy dense crop with large biomass suited to tropical as well as semi-arid regions. It is grown in several African and Asian countries, with the largest production occurring in Nigeria followed by Thailand, Indonesia and Brazil. Due to large quantity of stored energy in the form of starch, this crop can tackle malnutrition and acute food shortages in several developing countries and help ensure food security. Hence, an innovation involving cassava will invariably lead to generation of food, employment and boost in the economy of such countries. Studies have shown that harvesting leaves of cassava does not affect the root tuber yield if done in a non-invasive sustainable manner. Thus, awareness can be created among farmers for including such an initiative without fearing for the loss of their produce. Companies and institutes working on biological and sustainable plant protection solutions will be the key stakeholders in refining this idea, development of working prototype and it’s up scaling, while from the initial production aspect farmers will play the major role.

Future prospects

The success from cassava based bio-fumigant production will lead to identifying alternative bio-fumigant sources with similar properties. Plants of Brassicasiae family possess a chemical group called glucosinolates whose breakdown products contain isothiocyanates. Plants from this group are already well established soil bio-fumigant when incorpor,ated as soil mulch. The entire concept can be realized into a working prototype in a period of one year after thorough scrutiny and trials. The summit and competition will be utilized for identification of potential mentors, partners and seed funding to initiate the project and develop the product.

Sharath Chandran, India

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