The African Cereal Killer – Striga (witchweed)

A majority of smallholder farmers in sub-Saharan Africa (SSA) depend on cereals such maize, millet, sorghum, and cowpea for subsistence. However, production of these cereals is greatly constrained by members of the genus Striga – Striga hermonthica and S. asiatica and S. gesnerioides – parasitic plants that attach to the roots of their hosts causing severe stunting and loss of yield. It is estimated that Striga invades about 50 million hectares of land in Sub Saharan Africa resulting in devastating production losses of up to US$8 billion among small-scale farmers, contributing to poverty and hunger in the region. In Kenya, it is estimated that over 200,000 hectares of land are infested with Striga causing crop losses amounting to nearly 400,000 tons worth US$ 80 million per year’’

‘Striga seeds can remain viable in the soil for up to 14 years…... each Striga flower spike can produce over 50,000 seeds…… the weed intricately links its lifecyle to that of the host… ’

Smallholder farmers in SSA have battled with different control methods aimed at reducing Striga seed density in the soil, they include reducing the amount of Striga seed contaminating crop seed supplies, hand-weeding, crop rotation, and the use of ‘trap crops’ to encourage parasite germination on incompatible hosts. However, despite the extensive use of these methods crop losses and the host range of these parasites have continued to increase. Managing Striga is hampered by two factors; its ability to produce huge numbers of seeds – as each Striga flower spike can produce over 50,000 seeds, and ability to intricately link its lifecycle to that of the host – as Striga only germinates in response to host cues. In addition, Striga seeds can remain viable in the soil for up to 14 years.


 plant

Face of the ‘cereal’ killer. Striga’s beautify falsifies its wicked true nature.

 

 

 researcher

Master of Science student Duncan Njora holding a bouquet of Striga flowers in one of the field visits.

 

Derailing the Witch Weed

Dr. Steven Runo from the Department of Biochemistry and Biotechnology, Kenyatta University is leading a project to identify mechanisms controlling release of Striga virulence genes as a first step toward developing breeding strategies that can be used to build durable resistance to Striga. Dr. Runo in his project titled ‘Derailing witchweed (Striga) virulence in rice to achieve durable and broad-spectrum resistance’ aims to provide a comprehensive assessment of the mutations or genetic variations in Striga virulence factors as well as their role in host plants. Additionally, the research hopes to identify novel sources of Striga resistance from wild cereal relatives. Expected outcomes from the research include; identification of multiple factors (effectors) that help Striga evade resistance by its host, quantification of how these factors are able to change with time and acquire ability to invade new hosts, identification of corresponding resistance genes and the identification of the specificity of different Striga virulence races (ecotypes) to different host cultivars.

Application of the Research.
Knowledge generated in the project will directly be applied to breeding of new seed varieties that are resistant to Striga, through gene pyramiding. Since the yields of important cereal crops in Africa is on the decline due to the impact of Striga, the results of this project will have significant influence on agricultural productivity in the region and others where the parasitic plant is a problem.

‘‘The most efficient and cost effective way to control Striga infestations would be to develop crops that are resistant to Striga – while reducing evading Striga virulence’’


Research led by:

Dr. Steven M. Runo
Department of Biochemistry and Biotechnology
Kenyatta University

Project title: Derailing witchweed (Striga) virulence in rice to achieve durable and broad-spectrum resistance

Project financed by: Partnership for Enhanced Engagement in Research (PEER) Science Cycle 2

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