Securing East Africa’s Cassava

Conserving Cassava Diversity

“Smallholder farmers in East Africa generally use cassava landraces that have been selected because they are well liked,” Morag says. “But we may lose those landraces as very few of them have been properly conserved and are vulnerable to extinction.”

Cassava genetic diversity has been lost in the past. Most landraces in Madagascar were lost during a severe attack of cassava mosaic disease between 1934 and 1936. Farmers lost most of their landraces in Uganda after a similar epidemic struck in the 1990s.

Some of these varieties could provide the genetic material useful in developing disease-resistant cassava. “A number of Tanzanian landraces such as Nachinyaya and Kiroba do seem to display some resistance to CBSD,” Morag says. “And there could be many others which we haven’t had a chance to evaluate yet.”

“It is vital that these vulnerable landraces that are largely underrepresented in genebanks are collected, conserved and made available to breeders, farmers and those that value germplasm diversity,” says Morag. “They’ve been selected by farmers, so they should be a useful guide to breeders on consumer preferences, as well as providing useful genetic variability and adaptation to the local environment.”

In 2016, the Genebank CGIAR Research Program led by the Crop Trust funded a small project to support IITA’s collaboration with the Tanzanian Agriculture Research Institute (TARI) to collect cassava landraces in Tanzania for conservation and use, under the SMTA (Standard Material Transfer Agreement) of the International Treaty. Other germplasm collecting missions have taken place in Rwanda and Burundi, and to some extent in Uganda. So far, these collected materials have been kept in the field, where they remain vulnerable to diseases and expensive to maintain. Ideally, they should be put in long-term conservation at IITA’s genebank in Nigeria and made available worldwide. But the majority of the collected landraces are infected with at least one virus.

“We can’t move infected germplasm from East Africa to West Africa. CBSD does not occur in West Africa. The last thing anyone wants is material that could bring the disease to other parts of Africa and cause huge devastation. So we are temporarily conserving it in Tanzania,” says Lava Kumar, Head of IITA’s Germplasm Health Unit in Ibadan. “But we can eliminate the viruses and generate virus-free stocks so that this material can eventually be transported to Nigeria. Morag has been quite successful in achieving that goal.”

Eliminating the Virus

“Ultimately our goal is to make virus-free and well-characterized cassava landraces from East Africa readily available to anyone anywhere,” says Morag. “None of that can happen until we eliminate the viruses.”

To conduct the virus elimination work, Morag has partnered with the Kenya Plant Health Inspectorate Service (KEPHIS). KEPHIS is the national quarantine agency of Kenya and the regional quarantine station for East Africa. They have the facilities and expertise in virus elimination and also provide necessary phytosanitary certificates required for further transfer/distribution of germplasm to other countries.

IITA has a protocol for the establishment of virus-free cassava. “It all starts in a conviron, or rather a growth chamber,” says Morag. “We place cassava stakes in the chambers under very high heat, around 38°C for four to six weeks and wait till they sprout.” The sustained high heat slows the virus spread in the cassava tissue.

“We can then excise from the stake what we hope will be a clean part of the tissue at the growing point or meristem. That takes a lot of skill and experience but our partners at KEPHIS have mastered the techniques,” says Morag. The excised meristem tip is then established in tissue culture.

Once Morag’s team does establish the cuttings in culture, they multiply and harden them, which can take up to five months.

“Finally, we run virus diagnostics to determine if the plantlet is virus free,” Morag confirms. “If the virus is still there, we run the whole cycle over again.” With an estimated total time of one cycle at six months, that’s a whole lot of time.

Conserving East Africa’s Cassava Forever

But it will be worth it in the long run. Morag and her IITA colleagues are hoping that they will plug this gap in the cassava collection at IITA and that these unique landraces will have a long-term home in Nigeria, from where they can be distributed in a clean and healthy state to anyone who needs them. It represents one of the many contributions that the CGIAR Genebank Platform, which succeeded from the Genebanks CRP, is making towards meeting Sustainable Development Goal Target 2.5 on maintaining genetic diversity.

“We’ve still got many challenges ahead,” Morag says. “Once we secure what we have already collected we want to explore further potential gaps that may exist. Democratic Republic of Congo, Kenya, Malawi, Mozambique, Angola and Madagascar are likely to have unique cassava diversity with interesting traits that is still uncollected.”

It’s the crop that feeds much of sub-Saharan Africa and Morag and her colleagues at IITA and KEPHIS are working to ensure that farmers have the best opportunities to grow strong and resilient cassava that has those familiar characteristics that cassava consumers in the region know and love.

This article was originally published by the CGIAR Genebank Platform, a project which ran from 2017 to the end of 2021. It enabled CGIAR Research Centers to fulfill their legal obligation to conserve and make available 750,000 seed samples of crops and trees on behalf of the global community under the International Treaty on Plant Genetic Resources for Food and Agriculture. The Platform supported day-to-day genebank operations, and activities to improve efficiency, enhance use and ensure compliance with international policy. This work was supported jointly by donor contributions to the CGIAR Fund and the Crop Trust Endowment Fund.