sweet potato – Cabot Institute for the Environment blog

Last week I helped to harvest and score cassava tubers a breeding trial at the National Crops Resources Research Institute (NaCRRI). The trial is part of the NEXTGEN Cassava project which applies genetic techniques to conventional breeding and aims to produce new varieties with Cassava brown streak disease (CBSD) and Cassava mosaic disease (CMD) resistance.

Why cassava and what’s the CBSD problem?

Approximately 300 million people rely on cassava as a staple food crop in Africa. It is resilient to seasonal drought, can be grown on poor soils and harvested when needed. However cassava production is seriously threatened by CBSD, which can reduce the quality of tubers by 100% and is currently threatening the food security of millions of people.

Cassava brown streak symptoms on tubers

Crossing cassava from around the world

Cassava varieties show a huge variation in traits including disease resistance. The NEXTGEN Cassava project has crossed 100 parent plants from Latin America with high quality African plants to produce new improved varieties, with higher levels of CBSD and CMD resistance. Crossing involves rubbing the pollen from one parent variety on to the female flower part (pistil) of the second parent variety to produce seeds.

Cassava flowers used to cross different varieties

Cutting back on time

The process is not easy. The complex heritability of traits in cassava means that many plants have to be screened to identify plants with the best traits. To cut down on this time, researchers from Cornell University sequenced the DNA from 2,100 seedlings and selected plants containing sequences linked to desirable traits.

Screening for resistance

These plants were transferred to field site in Namulonge, where there is a high level of CBSD, making it easier to spot resistant plants. After 12 months the tubers were dug up and cut into sections. Each root was scored for the severity of CBSD. Plants which show no disease symptoms have now been selected for the next stage of breeding. Eventually varieties will be tested for their performance at sites across Uganda and given to farmers for their feedback.

We harvested and scored tubers for Cassava brown streak symptoms. I then tagged disease free plants for selection!

Time to harvest!

Alfred Ozimati is managing the breeding programme

I helped to score and tag plants, it was hard work! I was impressed by the stamina of the workers who harvested from 8 am until 3 pm without a rest. I was struck by the mammoth task of breeding cassava for so many traits and by the programme manager Alfred Ozimati’s determination to get the work done as quickly as possible. Alfred is currently a PhD student at Cornell University; he kindly offered to answer these questions:

What are the challenges of conventional breeding and how does sequencing help to address these?

Typical conventional breeding cycle of cassava is 8-10 years before parents are selected for crossing. The sequencing information allows a breeder to select parents early at the seedling stage, allowing more crossing cycles over time than conventional cassava breeding. With sequencing, the process of releasing varieties with improved CBSD and CMD resistance should take about 5 years.

What are your long term hopes for the project and the future of cassava breeding?

We hope to use genomic selection routinely, to address any other challenges cassava as a crop of second importance to Uganda will face. And also to take the technology to other East African, cassava breeding programs to faster address their major breeding constraints.

———————————–

This blog has been written by University of Bristol Cabot Institute member Katie Tomlinson from the School of Biological Sciences. Katie’s area of research is to generate and exploit an improved understanding of cassava brown streak disease (CBSD) to ensure sustainable cassava production in Africa. This blog has been reposted with kind permission from Katie’s blog Cassava Virus.

Katie Tomlinson

More from this blog series:

Blog 1: Getting ready to go… cassava virus hunting!

Blog 2: Week one: Settling in to Ugandan life
Blog 3: Learning the ropes
Blog 4: Clean cassava to solve brown streak problem?
Blog 5: Taking a trip to the cassava field!
Blog 6: Using GM to fight cassava brown streak disease

Blog 7: Talking sweet potatoes at the Source of the Nile
Blog 8: Breeding cassava for the next generation

Blog 9: Paying a visit to the plant doctor in Uganda
Blog 10: Saying goodbye and lessons from the field

Last month I was invited to the Source of the Nile agricultural trade show in Jinja, Uganda. The show brings together all aspects of agriculture: from crops to chickens, cows and tractors. The event attracts over 120,000 visitors each year and runs for seven days.

I was needed on a National Crops Resources Research Institute (NaCRRI) stand where Agnes Alajo (a PhD student and breeder) was selling improved sweet potato varieties, which are resistant to pests and diseases with higher levels of pro-vitamin A.

It is estimated that around 35% of children and 55% of child-bearing mothers in rural Uganda suffer from vitamin A deficiency, which is associated with preventable child blindness and mortality. The orange-fleshed NAROSPOT varieties developed by NaCRRI are enriched with pro-vitamin A and it’s hoped their adoption will help improve the deficiency problem.

The stand also had an impressive array of biscuits, cakes and even juice made from processing sweet potato. Agriculture is very important in Uganda; it accounts for around 24% of GDP and 43% of the working population are subsistence farmers (2013). Processing sweet potatoes to produce flour can be economically viable and provides farmers with an opportunity to add value to their crop, boost income and reduce poverty.

The range of products made through processing sweet potato

I had to hurriedly absorb information about sweet potato, as very soon hoards of excited school children arrived. The main challenge was that not everyone can speak English and my UK accent was quite difficult for them to understand. I had to speak clearly and slowly to get my message across. Often teachers had to repeat what I had said in their local language. There are over 40 local languages in Uganda, so even Ugandans can find it difficult to communicate!

Agnes explains the importance of pro-vitamin A rich sweet potatoes to school students

Agnes explains the importance of pro-vitamin A rich sweet potatoes to school students
There was a lot of interest from young people who want to pursue agricultural careers and are attracted to opportunities for commercialization. Most people were very intrigued about the cakes, and couldn’t believe that they were made using sweet potato flour. Unfortunately, we couldn’t give out samples to taste until the end of the week, which caused a lot of pleading and disappointment!

Walking around the show I discovered giant cassava tubers, a “speaking head” and impressive looking cabbages. I later saw the source of the Nile itself!

I had a great time walking around. There was plenty of entertainment and I also got to see where the Nile flows from Lake Victoria!