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Partnerships for enhanced engagement in research (PEER) SCIENCE
Cycle 2 (2012 Deadline)

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

PI: Steven Runo (Kenyatta University)
U.S. Partner: Michael P. Timko (University of Virginia)
Project Dates: August 2013 to July 2015

 Ethiopia Partnership Picture 1
Striga infests two-thirds of arble African land, and constitutes the biggest single biological cause of crop damage in terms of grain yield loss, worth $US 7 billion annually (Photo courtesy Dr. Runo).

Striga spp. are successful parasitic plants that are notoriously difficult to control mainly because the mechanisms of the biological processes underpinning host-parasite compatibility are poorly understood. Striga affects plant growth very quickly after attaching to the host roots. Within 2-4 days of attachment the crop plants are already visibly stunted. Although the mechanism underlying this early negative effect on crop growth is presently unknown, it has implications for control of the parasite, as control measures need to act before or very shortly after attachment of the parasite to the host. It is now emerging that Striga, like other plant pathogens, produces an array of virulence factors (effectors) that may be allowing the parasite to circumvent and subdue the host defense. The long-term goal of the researchers conducting this project is to identify mechanisms controlling release of these virulence factors as a first step toward developing breeding strategies that can be used to build durable resistance to Striga hosts. The specific aims of the current project are designed to provide a comprehensive assessment of the mutations or polymorphisms in Striga effectors as well as their effect in plant cells. The project should result in the identification of various races of Striga for effector genes and their role in virulence, which is of fundamental importance to understanding the molecular nature of the plant-plant resistance interactions.
 
An output of this project will be identification of multiple factors (effectors) that help Striga evade resistance by its host. An additional output will be quantification of how these factors are able to change with time and acquire ability to invade new hosts. It is hoped that the specificity of different Striga virulence races (ecotypes) to different host cultivars will be identified. This knowledge can then be directly applied to breeding of new cultivars resistant to Striga, through gene pyramiding. Because yields of some of the most important crops in Africa, including rice, corn, millet, and sorghum, are being reduced due to the impact of Striga, the results of this project could have a significant impact on agricultural productivity in this region and others where the parasitic plant is a problem.
 
Summary of Recent Activities
 
The first quarter of the project year focused heavily on lab work. Though the team was able to make the occasional trip to western Kenya to collect Striga seeds, most of the progress was made in identifying effector genes and readying seedlings for DNA analysis. The team worked towards developing an assay for testing these candidate effector genes, which, if they could be triggered or manipulated, could subdue the plant’s virulence in crop-growth areas, thereby increasing yields. In this phase of the project, U.S. collaborator Mike Timko’s laboratory has shown that growth regulatory factors (GRFs) can be regulated up or down in both resistant and susceptible strains of cowpeas and checkpeas. The research team is using this resistance gene to transform rice for Striga resistance.
 
In the first quarter of 2014, the project team will visit Tanzania and Uganda to collect Striga seeds, harvest their DNA, and use that DNA pattern as a template for amplification of candidate effector genes. The PI is also planning an extended visit to the U.S. collaborator at the University of Virginia from May to December 2014 to work on RNA and cDNA molecules.
 
Back to PEER Cycle 2 Grant Recipients