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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
The end of 2014 saw Dr. Runo and the project team obtain equipment necessary for microscopic observations of Striga/host interactions. This equipment will be used under a newly optimized set of protocols that Dr. Runo has introduced at the University of Kenyatta. The PI studied the protocols, which apply to Striga genetic transformation, and the assaying of Striga infection at the microscopic level by sectioning, at the University of Virginia. The University of Virginia also assisted on transcriptomic work on dual RNAsequencing and the team has made substantial progress in creating libraries for ILLUMINA sequencing and sequencing will be underway soon.

As part of the program objectives, Dr. Runo recruited a Master of Science student for the project to develop capacity for Striga research at Kenyatta University. Her thesis project will be on the histological observation of Striga resistance at a microscopic level using the new sectioning equipment.

In the coming months, Dr. Runo and the project team will continue to analyze and their data. The team also plans to organize a workshop for farmers and, in July, Dr. Runo will travel to China to present at the World Congress on Parasitic Plants.
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