November 14, 2022, by Lexi Earl

Improving the drought tolerance of pearl millet

Today at COP27 the focus of discussions is on water. Ensuring agricultural crops are resilient to drought, especially in the face of climate change is a huge undertaking but extremely important. Our researchers are investigating ways to make pearl millet more drought tolerant and ensure nutrient uptake. 

Pearl millet is a key crop that contributes significantly to food security across the Sahel region in Africa (places bordering the southern edge of the Sahara). It is well adapted to arid and semi-arid conditions, and is generally cultivated in low input agricultural systems. Yields of pearl millet are limited by the soil conditions and rainfall, as the crop is not irrigated. As climate change increasingly plays havoc with seasons and rainfall in the Sahel region, sometimes resulting in drought, yield losses are becoming more common. This is problematic as pearl millet is a dietary staple crop for over 90 million people in the region, 90% of which is grown by smallholder farmers. Coupled with climate change is a rapidly growing population. We therefore need to develop more productive, drought tolerant varieties that farmers can grow.

In order to help farmers adapt to these changing conditions, our researchers have been working in central Senegal, alongside partners from ISRA/CERAS and IRD Montpellier, to investigate what happens after pearl millet is exposed to drought. The team examined how 150 different varieties of pearl millet coped after watering was stopped. Data for important traits like yield, root architecture and anatomy were collected using a range of phenotyping approaches. For example, the 2022 trial collected over 3800 samples for root anatomical and leaf ionomic analysis, while approximately 7500 root crown images were taken to understand how root architectural traits like angle is altered by drought. This is in addition to the 3800 root and leaf samples and 5500 root crown images taken in 2021. To prepare root samples, plants first had to be harvested from the field, roots were washed and then prepared for imaging and sampling. This was a labour-intensive job that our researchers and partners undertook under very challenging conditions with temperatures often reaching over 45C!

Harvested leaf and root samples are shipped back to Nottingham for ionomic and anatomical analysis. Preparing anatomical sections using conventional approaches is slow, labour intensive, and requires a high level of skill. Using Laser Ablation Technology (LAT) at our Hounsfield Facility, researchers are able to examine the cellular anatomy of roots at a much faster and more accurate rate. Identifying the genes that control key root anatomical traits, like the size of xylem water transporting cells, will allow breeders to select new crops with improved drought tolerance and nutrient uptake.

Analysing anatomical traits like the size and numbers of cells in a single root image is very time consuming, even for experienced researchers. When LAT generates 20 images for each of the 3800 root samples collected in Senegal, this becomes an impossible task to perform manually.  The solution is to exploit advances in AI-based image analysis by colleagues in the Computer Vision Lab at Nottingham. Once root images are analysed, anatomical information for each of the 150 pearl millet varieties can be compared to their DNA differences. This approach (termed genome-wide association studies; GWAS) can identify genes that control traits like the size of xylem water transporting cells. Once identified, these genes can be converted to DNA markers for breeders to select new varieties of pearl millet better adapted to a rapidly changing climate.

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