IITA Researchers Uncover New Cassava Genetics

An IITA farm officer, Anetor Omonuwa, holds cassava variety undergoing field testing
Along with partners from the NextGen Cassava Breeding Project, researchers at International Institute of Tropical Agriculture (IITA) have uncovered new details about the genetic architecture of cassava, which is one of Africa’s most vital crops.

The findings will make it easier for breeders to identify traits for crop breeding.

The Next Generation Cassava Breeding project aims to modernise cassava breeding in Africa and use cutting-edge tools for efficient delivery of improved varieties of cassava.

The ultimate beneficiaries of this project are the cassava farmers of sub-Saharan Africa, who will receive improved varieties that increase fresh root yields, are more resilient to devastating virus diseases, and exhibit other traits preferred by smallholder farmers.

The scientists carried out a genome-wide association study (GWAS) and outlined their findings in a research article recently published in Plant Molecular Biology. They analysed large breeding populations composed of 5130 clones developed in Nigeria at the IITA Cassava Breeding Programme.

The four-year study involved extensive multi-locational testing at four IITA field trials in Nigeria. The genome-wide association analysis explored genomic regions most responsible for desirable traits in cassava, which is a food crop that provides the primary source of calories for more than 500 million people worldwide.

The scientists found more than 40 quantitative trait loci (QTL) associated with 14 traits, responsible for characteristics such as disease responses, nutritional quality, and yield. These traits were classified broadly into four categories: biotic stress, root quality, plant agronomy, and agro-morphology.

“Our findings provide critical new entries into the catalog of major loci available to cassava breeders”, said Ismail Rabbi, a molecular geneticist and plant breeder at IITA and a member of the NextGen project. “These markers should greatly improve cassava research and provide another powerful tool for the breeders’ toolbox.”

Ismail Yusuf Rabbi is a geneticist based in IITA Ibadan, Nigeria. His main research involves the development and application of genomic resources for crop improvement.

During his postdoctoral work at IITA, he helped develop the first SNP-based genetic map of cassava and participated in uncovering the genomic regions underlying resistance to cassava brown streak disease.

Currently, Ismail is applying the latest high-throughput genotyping technology and statistical methods to find genes in cassava that are associated with several critical traits, including disease resistance, high pro-vitamin A content, dry matter, and plant architecture.

Breeders can then select these genes to develop superior cultivars much faster than by using phenotypes alone. He is also part of a new cassava improvement initiative, dubbed, “Next Generation Cassava Breeding” that involves Cornell University, IITA, and Nigerian and Ugandan National Breeding Programs. Dr Ismail is a Kenyan, and did his B.Sc. and M.Sc. in Biochemistry and Biotechnology at Kenyatta University. A DAAD scholar, Ismail graduated (magna cum laude) from the University of Hohenheim, Stuttgart, Germany with a doctorate in Agricultural Sciences. He had a short stay at Cornell University where he attended a course in Statistical Genetics.

Chidozie Egesi, a co-author and NextGen Programme Director, noted the importance of cassava as both a food and industrial crop, which will be even more so in the future, “as climate change reshapes agriculture everywhere.”

Egesi has just been engaged as Senior Extension Associate (Project Manager) of NEXTGEN Cassava Breeding project based in Umudike. He provides programmatic coordination of the Project with partners in Cornell University.

Prior to this time, Chiedozie was an assistant director and coordinated biotechnology research at the National Root Crops Research Institute (NRCRI), Umudike, Nigeria. He also served as the lead cassava breeder at NRCRI and with partners at IITA led efforts at developing and releasing to Nigerian cassava farmers several improved varieties of cassava including pro-vitamin A cassava.

His research activities involve the use of cross-cutting breeding and biotechnology tools in increasing the rate of genetic improvement of cassava. Chiedozie supports several African NARS cassava breeding programs in developing adaptive breeding schemes.

He studied at the University of Ibadan where he obtained a PhD in Plant Genetics and spent his time as a visiting research scholar at IITA during that period in the Genetic Resources and Yam breeding units.

As a result, he said it is foundational to have a better understanding of cassava’s complex genome.

“A complete understanding of cassava’s genetic architecture is the critical step needed to accelerate genetic improvement and bring lasting benefits to farmers and consumers who depend on this crop for food and income throughout the world”, he says.

IITA is a key partner of the NextGen Cassava Breeding Project, whose goal is to empower smallholder cassava farmers in sub-Saharan Africa by developing, releasing, and distributing improved cassava varieties.

The four-year (2016-2019) ‘Building a Sustainable, Integrated Seed System for Cassava in Nigeria’, or BASICS, project is working to strengthen all components of the cassava seed value chain.

The project is comprised of four components: For the past decades, Africa, has been grappling with the sustainable diffusion of improved cassava varieties due to a weak and uncoordinated dissemination strategy.

Consequently, improved varieties have often failed to reach the hands of farmers, forcing the yields of cassava in Africa to remain low.

However, the project— Building an Economically Sustainable, Integrated Cassava Seed System (BASICS) has demonstrated that the cassava seeds system can be profitable for the players involved across the value chain and can sustainably deploy improved varieties of cassava stems to farmers while creating jobs.

Researchers say in the last 5 years, BASICS has created a viable and sustainable cassava seed system in Nigeria, opening a vista of opportunities for seed entrepreneurs and cassava farmers looking for new and improved varieties for cultivation.

The Project Director, Dr. Hemant Nitturkar, explained that the project was able to link breeders and researchers who developed improved cassava varieties and technologies; with farmers and processors who benefited from high quality planting materials.

According to him, the BASICS project has created over 150 community based seed entrepreneurs who are running viable cassava stem businesses in states like Benue, Cross River, Abia and Imo; and facilitated the establishment of two seed companies (namely IITA GoSeed located on the IITA campus in Ibadan, and Umudike Seed at National Root Crops Research Institute (NRCRI) in Umudike, Abia State) to ensure reliable supply of breeder and foundation seeds of varieties in demand.

Until the coming of BASICS, there was no formal seed sector for cassava stems. Farmers would usually share cassava stems with their fellow farmers. In some cases, government would buy improved stems and share them to farmers free of charge.

However, most of the stems shared by the government are usually not certified and in small quantity due to the bulky nature of cassava. Such distributions happened only occasionally, either to address some exigencies or to introduce new varieties, and that too were targeted at certain segments/locations of farmers. This approach has proved unsustainable as the spread of improved varieties still hovers less than 40 percent.

Nitturkar said, “In Nigeria, 46 varieties were released in the last 20 years, but we have seen that people do not know about or use more than about five of these varieties.”

“We encouraged development of village seed entrepreneurs because cassava stems can be costly to transport over long distances, so we aimed at locating seed production closer to the cassava growing communities. These village seed entrepreneurs multiplied improved stems, and they made certified seeds available to the farmers on a commercial basis”, he explains.

He stated that apart from ensuring that seeds of different varieties are always available to farmers, the seed entrepreneurs formed a vital link between researchers and farmers because “as they are selling these seeds, they also learn from the farmers what new features they require in the varieties. The seed entrepreneurs push up this information to the seed companies who take it back to the breeders.”

Nitturkar stressed that the Nigerian seed market has come to stay with 50 per cent of the informed farmers doubling as seed entrepreneurs and root farmers who made additional profits of up to $1200 from selling stems for two seasons and harvesting the roots in the second season. He said interested seed entrepreneurs can talk with the village seed entrepreneurs or reach out to IITA GoSeed or Umudike Seed for training on how to produce quality stems, how to get certified and how to approach the market.

Dr Peter Kulakow, Cassava Breeder with the International Institute of Tropical Agriculture said one of the greatest achievements of BASICS was its ability to work with young people and women and to empower them in seed production.

Researchers from IITA, Cornell, the National Root Crops Research Institute (NRCRI) in Nigeria, the Boyce Thompson Institute, and the US Department of Agriculture-Agriculture Research Service contributed to the study.

Along with Rabbi and Egesi, the co-authors are Siraj Ismail Kayondo, Guillaume Bauchet, Muyideen Yusuf, Cynthia Idhigu Aghogho, Kayode Ogunpaimo, Ruth Uwugiaren, Ikpan Andrew Smith, Prasad Peteti, Afolabi Agbona, Elizabeth Parkes, Ezenwaka Lydia, Marnin Wolfe, Jean-Luc Jannink, and Peter Kulakow.



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