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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 arable 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
 
 
During the first quarter of 2015, the project team continued to gather and analyze data via RNA-sequencing. Project PI Runo is conducting bioinformatic analyses to determine which genes are candidates for Striga resistance as well as which genes Striga uses to overcome host resistance. The team was also able to leverage support from US partner Mike Timko to carry out genetic transformation of maize using the RSG3 gene for Striga resistance in maize. The new seeds of transgenic maize will be available for analysis in the last quarter of the PEER project.

A new MSc student, Dorothy Annah Mbuvi, was also recruited this quarter. Her thesis project focuses on the bioinformatics identification and analysis of Striga effectors and the macroscopic and microscopic analysis of Striga resistance in wild accessions of sorghum.

In the coming months, Dr. Runo and the project team will continue their molecular and bioinformatic analyses of Striga resistance/ virulence genes and macroscopic and microscopic analyses of Striga resistant sorghum. The team also plans to organize a workshop for farmers in June and, in July, Dr. Runo will travel to China to present at the World Congress on Parasitic Plants.
 
 
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