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African Centre for Crop Improvement

“Training African Breeders on African Crops, in Africa”

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Breeding drought-tolerant wheat without losing quality

A PhD student at the ACCI has tackled a burning issue affecting global wheat production — breeding for drought-tolerance without loss of quality — with promising results.

Bread wheat (Triticum aestivum) is the second-most popular cereal crop in the world, with an estimated 700 million tonnes produced each year, but yield and grain quality are being severely affected by drought and heat stress caused by climate change.

Although plant breeders are successfully breeding for increased yield, this is usually at the expense of grain quality, due to a generic inverse association between the two traits. Zamalotshwa Thungo, who hails from Ladysmith, South Africa, has been working on solving this problem.

She started off studying Dietetics but quickly switched to agriculture. “After the first year I wasn’t enjoying it and realized I was more interested in agriculture and plants, so I changed to a BSc Agribusiness,” she said. After completing honours and masters in crop science, a chance encounter with Professor Hussein Shimelis, the ACCI’s deputy-director, led to her registering to do a PhD with the ACCI in 2016.

Thungo’s research is part of a larger project Shimelis has been supervising looking at breeding heat and drought-tolerant wheat. This project has so far involved five other ACCI students, starting with Dr Learnmore Mwadzingeni in 2014. He conducted a genetic analysis of 100 wheat genotypes for grain yield and yield-influencing traits. These genotypes were obtained mainly from CIMMYT’s drought- and heat-tolerance nurseries.

Zamalotshwa Thungo

Explaining Thungo’s contribution, Shimelis said her work was to “select wheat genotypes with drought tolerance and grain quality and to integrate these traits into one genetic background to develop and release cultivars”.

Thungo started working in 2017 with about 50 of the CYMMIT bread wheat genotypes selected by Mwadzingeni for drought tolerance. She evaluated 28 lines for drought tolerance, assessing their agronomic and physiological traits in two contrasting environments, controlled and uncontrolled. She also evaluated the genotypes for grain yield stability under drought-stressed and non-stressed conditions. In both studies she selected the most stable genotypes.

The next step involved assessing for grain protein quality and technological capability. Using mature seeds from the previous experiment, Thungo analysed the total protein content and fractions including gliadin, glutenin, gluten and gliadin: glutenin ratio. Parents were chosen that were tolerant of heat and drought and had improved grain quality attributes.

 The 28 genotypes were also evaluated for grain quality stability and the best candidates were chosen.

In addition, Thungo looked for genetic diversity in these genotypes using DNA fingerprinting and SSR analysis. “I wanted to select genetically different and complementary genotypes,” she said. The last experiment was to test the genotypes’ combining ability (i.e. ability to combine and transmit desirable genes to their progenies) and gene action.

“I had to select 10 genotypes showing good attributes for grain yield and grain quality. We are trying to develop new crosses that combine high yield and high protein quality because these qualities are inversely related, i.e. when grain yield is improved it occurs at the expense of grain quality,” she said.

The ten parents selected from the previous experiment were crossed to produce 45 progenies and the 15 best were chosen, all with high yield potential and acceptable levels of grain quality attributes. With her PhD complete, Thungo said the next project will be to advance these crosses to the sixth generation using Single Seed Descent Selection in conjunction with Speed Breeding technique, which she is hoping to do should she get an opportunity for post-doctorate work.

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