Skip to main content

Clean cassava to solve brown streak problem?

Since arriving in Uganda, I’ve been learning a lot about the affects of Cassava brown streak disease (CBSD), which is devastating cassava production and threatening food security. The disease is spread by the whitefly insect, which picks up the virus from an infected plant and carries it to neighbouring healthy plants.

Cassava plants are grown by planting stem cuttings in the ground, which go on to become new plants. If farmers use cuttings from infected plants, the new plants will also become infected. This is a big problem, as infected cuttings can be transported to new areas, spreading CBSD across large distances.

What can be done?



Tolerance


Huge efforts are being put into a number of different solutions. These include breeding new cassava varieties, which are tolerant to CBSD. This is a very long and challenging process, as cassava plants also need to be resistant to Cassava mosaic disease (CMD) and have yield/taste properties which farmers and consumers prefer.

The National Crops Resources Research Institute (NaCRRI) has recently developed a new variety: NAROCASS1, which is tolerant to CBSD and resistant to CMD. This is now being used in areas where CBSD is particularly common and severe. Unfortunately, even tolerant cassava varieties can contain CBSD viruses and so it’s vital that farmers have access to clean cuttings.
Cassava variety NAROCASS1 with CBSD tolerance and CMD resistance.


Clean seed system (CSS)


The cassava CSS project in Uganda is run by NaCRRI and involves picking the very youngest tip of the cassava plant to produce embryonic tissue, which develops into a new plant. These plants are then checked to see whether the CBSD virus is present before being taken to nurseries where they are carefully multiplied and eventually used for clean planting material for farmers. As you can imagine, this process takes a long time and is much more expensive than taking cuttings from a mature cassava plant. However it means that farmers can benefit from quality assurance that the cuttings they buy are virus free and stand the best chance of remaining healthy.
A clean cassava plantlet produced through tissue culture.
The cassava CSS project has been running as a pilot for three years. It will be very interesting to hear how this project goes, as it’s likely to be a major solution to the CBSD problem.

Reviewing progress


Last week I had helped take minutes for the annual CSS review at NaCRRI, which involved lots of manic typing and concentration! As part of the review I got to visit a field where an entrepreneur is growing clean cassava plants. The plants certainly looked healthy, with no CBSD and CMD symptoms at all. With so much to think about, we still found time to have a cocktail party to let of some steam!

Clean cassava seed entrepreneur David Mpanga explains how he uses record keeping to track of outgoings and income.
-----------------------------------
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:  

Popular posts from this blog

Converting probabilities between time-intervals

This is the first in an irregular sequence of snippets about some of the slightly more technical aspects of uncertainty and risk assessment.  If you have a slightly more technical question, then please email me and I will try to answer it with a snippet. Suppose that an event has a probability of 0.015 (or 1.5%) of happening at least once in the next five years. Then the probability of the event happening at least once in the next year is 0.015 / 5 = 0.003 (or 0.3%), and the probability of it happening at least once in the next 20 years is 0.015 * 4 = 0.06 (or 6%). Here is the rule for scaling probabilities to different time intervals: if both probabilities (the original one and the new one) are no larger than 0.1 (or 10%), then simply multiply the original probability by the ratio of the new time-interval to the original time-interval, to find the new probability. This rule is an approximation which breaks down if either of the probabilities is greater than 0.1. For example

1-in-200 year events

You often read or hear references to the ‘1-in-200 year event’, or ‘200-year event’, or ‘event with a return period of 200 years’. Other popular horizons are 1-in-30 years and 1-in-10,000 years. This term applies to hazards which can occur over a range of magnitudes, like volcanic eruptions, earthquakes, tsunamis, space weather, and various hydro-meteorological hazards like floods, storms, hot or cold spells, and droughts. ‘1-in-200 years’ refers to a particular magnitude. In floods this might be represented as a contour on a map, showing an area that is inundated. If this contour is labelled as ‘1-in-200 years’ this means that the current rate of floods at least as large as this is 1/200 /yr, or 0.005 /yr. So if your house is inside the contour, there is currently a 0.005 (0.5%) chance of being flooded in the next year, and a 0.025 (2.5%) chance of being flooded in the next five years. The general definition is this: ‘1-in-200 year magnitude is x’ = ‘the current rate for eve

Coconuts and climate change

Before pursuing an MSc in Climate Change Science and Policy at the University of Bristol, I completed my undergraduate studies in Environmental Science at the University of Colombo, Sri Lanka. During my final year I carried out a research project that explored the impact of extreme weather events on coconut productivity across the three climatic zones of Sri Lanka. A few months ago, I managed to get a paper published and I thought it would be a good idea to share my findings on this platform. Climate change and crop productivity  There has been a growing concern about the impact of extreme weather events on crop production across the globe, Sri Lanka being no exception. Coconut is becoming a rare commodity in the country, due to several reasons including the changing climate. The price hike in coconuts over the last few years is a good indication of how climate change is affecting coconut productivity across the country. Most coconut trees are no longer bearing fruits and thos