Maize defends banana against nematodes

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Scientists at the International Institute of Tropical Agriculture (IITA) and the University of Leeds have finally succeeded in developing a maize-based defense mechanism against a devastating microscopic worm that attacks banana roots.

The worm, commonly known as nematode, is one of the most economically damaging pests affecting the fourth most important staple crop in sub-Saharan Africa. Once attacked, the roots cannot hold and the plant easily falls.

Researchers were able to reinforce the crop against the pest by infusing a cystatin gene from maize and a synthetic nematode-repelling protein.

The cystatin found in maize kernel prevents nematodes from digesting proteins,  “starving” them and greatly reducing their population. On the other hand, the nematode-repelling protein makes the plantain’s roots secrete a synthetic peptide that prevents the nematodes from detecting the host.  Scientists infused the plantain, cv. Gonja manjaya, with either one or both  of the genes to confer to it a single or dual defense against the pest.

Feeding on the roots, nematodes restrict the flow of nutrients into the plants which leads to stunted growth. Farmers easily lose about 40 per cent  or more of their produce because of nematode infestation, especially in areas prone to tropical storms and high winds. This is because nematodes damage the roots, weakening the plant’s anchorage and causing them to completely topple over during strong winds.

The results of the study have been published in the latest edition of the journal Molecular Plant Pathology.

During the study, 245 independent transgenic lines (plantlets) were developed and assessed for their resistance to nematodes in screen house trials. Out of these, 11 showed strong resistance to nematodes. They will be further evaluated in a confined field trial in Uganda after approval from the National Biosafety Authority.

“This is indeed a breakthrough against one of the most important pests of plantain, which many farmers are usually not aware of due to its microscopic nature,” said  Dr Leena Tripathi, IITA’s biotechnologist and one of the researchers in the study.

“This research has given us highly promising resistant lines as part of our efforts to enhance food security for the millions of people who depend on the crop for their food and income,” she added. ‘And while the safety of the two constructs has been proven in many researches, we will still carry out more safety studies alongside field trials to ensure they pose no risks to humans or the environment,” she emphasized.

Pest management in banana is mainly based on crop rotation and chemical control. However, crop rotation is not often practiced due to unavailability of land and nematicides are not affordable to most subsistence farmers. There are also limited sources of nematode resistance and tolerance among banana and plantain varieties for conventional breeding purposes.

Banana and plantain are mostly sterile and do not produce seeds, thereby making conventional breeding of the crops difficult and slow. However, these same qualities make them safer for biotechnology-based transformation as there is minimal risk of contaminating local varieties.

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