A maize plantation. Scientists have discovered new maize varieties capable of defend themselves against stemborers by summoning natural enemies of the pest. [Photo/File]

Scientists have discovered that certain “smart” maize varieties have the ability to defend themselves against stemborers by summoning natural enemies of the pest.

The researchers have also determined the genetic markers in such plants that are associated with this “call for help”, presenting strong possibilities for developing maize varieties that are resistant to the pests.

These findings of a study by the International Centre of Insect Physiology and Ecology (ICIPE), Keele University, UK, and International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), have been published recently in Scientific Reports.

Stemborers are devastating pests of cereal crops like maize, rice, sorghum, sugarcane and pearl millet, in Africa.

The pests are most damaging in their larval stage, when they are concealed inside the stem making their control extremely difficult, with yields losses between 10 – 100%. They severely damage plant stems, particularly by destroying the central leaves.

At a later stage of growth, stemborers make extensive tunnels inside the plant stems disrupting the flow of nutrients to the grain.

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The tunnelling also weakens the stem leading to breakage and collapse. Moreover, the stemborers drill into maize cobs, ruin grains and increase vulnerability to aflatoxins.

Genetically superior

The research by icipe and partners analysed the genetic makeup of 146 different types of maize plants, comprising farmer-selected varieties, known as landraces, as well as plants from formal breeding programmes – inbred lines and commercial hybrids.

“We observed that when stemborers lay eggs on some maize cultivars, a defence reaction is triggered in the plants, which then release odours that attract wasps that are capable of parasitizing stemborers, or in other words natural enemies of the pests,” explains Dr Amanuel Tamiru, Scientist, icipe.

He adds: “An interesting finding is that the plants recruit both egg and larval parasitic wasps. As such, the natural enemies parasitize and kill the stemborer eggs before they hatch into larvae, as well as any larvae that may emerge, thus pre-empting damage on the crop.”

The scientists found the defence trait to be more common in landraces than in improved inbred lines and hybrids.

“The fact that we were able to pinpoint the regions in the maize genomes associated with this safeguarding response is important. It means that our findings could be used by maize breeders to promote stemborer resistance in maize cultivars preferred by farmers because of other desirable traits,” notes Prof. Toby Bruce, Keele University.”Moreover, the knowledge is a valuable resource for future research on the interactions between plants, pests and beneficial insects.”

This breakthrough is in line with icipe’s vision of advancing integrated pest management to improve cereal productivity in Africa, by combining the most effective and sustainable options. In fact, the “smart maize” could be incorporated into the phenomenally successful push-pull technology developed by icipe, Rothamsted Research, UK, and partners from East Africa.

The push-pull technology involves intercropping cereal crops with insect repellent legumes in the Desmodium genus and planting an attractive forage plant such as Napier or Brachiaria grasses as a border around this intercrop.

The intercrop emits a blend of compounds that repel (‘push’) away stemborers, while the border plants emit semiochemicals that are attractive (‘pull’) to the pests. In addition, Push-Pull also controls maize ear rots and mycotoxins, while improving soil health and providing high quality fodder, since the companion crops are superior forages. Therefore, the technology facilitates crop-livestock integration thus expanding farmers’ income streams.

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