Farmers in Africa will soon benefit from new sorghum varieties resistant to Striga — also known as witchweed — one of the most devasting parasitic weeds that impact crop yields on the continent. Improved sorghum lines with resistance to Striga have been developed using gamma ray irradiation, with the support of the IAEA and the Food and Agriculture Organization of the United Nations (FAO). “This important achievement is of great significance, especially as we prepare for the International Year of Plant Health 2020,” said Qu Liang, Director of the FAO/IAEA Division of Nuclear Techniques in Food and Agriculture.
“For African farmers, the availability of Striga-resistant sorghum varieties will be a major breakthrough: it will improve livelihoods for rural communities and contribute to food security,” said Abdelbagi Ghanim, a plant breeder and geneticist at the Joint FAO/IAEA Division. Striga infestation is a scourge that continues to pose a huge challenge for crop productivity, reducing national and regional capacity for food production, he added.
Striga is present in parts of Africa, Asia, and Australia, with the greatest crop losses in Africa’s savannahs. FAO estimates that annual crop loss due to Striga across Africa exceeds US $7 billion, impacting over 300 million people. Up to 50 million hectares of crop land are Striga infested, Ghanim said. “Striga is a major biological constraint to cereal production in most of sub-Saharan Africa and semi-arid tropical regions of Asia.” Crops such as sorghum, millet, maize and upland rice face the biggest threat from this parasitic weed.
Research support to combat Striga
Striga attacks crops from under the ground — its seeds remain viable in soil for over 20 years — sucking nutrients and water from their roots, killing crops in hordes. The two most destructive Striga strains are Striga hermonthica and Striga asiatica, Ghanim said.
To combat Striga, new varieties of sorghum have been developed using irradiation, in a technique known as plant mutation breeding (see What is Plant Mutation Breeding?). “Thanks to Glass-house and field trials, we succeeded in the selection of improved lines, and we expect that new resistant varieties developed from these lines will be released to farmers within the next two years, in some of the participating countries,” Ghanim said.
In plant breeding programmes, the primary challenge is to identify new and improved lines, with desired traits, before they can be developed into varieties that can be cultivated by farmers. The ongoing research and development using irradiation has identified such lines with proven resistance to Striga, and these are being developed into varieties that can be disseminated to farmers in the near term.
“I am so excited to see the power of nuclear technology applications for mutation breeding; I hope the varieties developed from the improved sorghum lines selected in this project will finally restore production of cereals in the heavily Striga infested areas in Africa,” said Phillipe Nikiema, a researcher at Burkina Faso’s Institute for the Environment and Agricultural Research and a participant of an IAEA Striga coordinated research project.
The results of this project focus specifically on understanding and developing solutions for resistance to Striga in cereal crops, involving experts from twelve countries.
“The affected African countries, including my own, Burkina Faso, will benefit from new improved sorghum lines and varieties developed through this project. Results of the project will also help to understand the physiological and molecular bases of host-parasite interaction to enable the development of further solutions to restore cereals production and boost food security in Africa,” he added. “Striga threatens food security in rural areas where it has been expanding and taking over millions of hectares, including those owned by of poor farmers.”
Experts are now analysing the induced resistance in different sorghum varieties to enable combining more than one defense mechanism and produce even more resistant sorghum varieties to restore production and ensure food security and the livelihoods of farmers.
What is Plant Mutation Breeding?
Plant mutation breeding is the process of exposing plant seeds, cuttings or cell cultures to radiation, such as gamma rays, and then planting the seed or cultivating the irradiated in vitro material in a sterile medium that generates a plantlet. The mutated plants, after selection for improved agronomic traits over several generations, are then multiplied, evaluated and released as improved varieties.
Plant mutation breeding does not involve genetic transformation, but rather uses a plant’s own genetic resources and mimics the natural process of spontaneous mutation, the motor of evolution. By using radiation, scientists can significantly shorten the time it takes to breed new and improved plant varieties.
This technique focuses on the use of radiation in combination with biotechnologies to develop favourable crop traits. New varieties of plants are bred to thrive in harsh conditions such as heat and drought), or to improve their nutritional value, to resist diseases or pests, to grow in saline soils, or to use water and nutrients more efficiently.