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Partnerships for enhanced engagement in research (PEER) SCIENCE
Cycle 1 (2011 Deadline)

Characterization of cassava mosaic gemini viruses and their satellites in cassava at the cellular level 

PI: Joseph Ndunguru, Mikocheni Agricultural Research Institute
US Partner:  Linda Hanley-Bowdoin, North Carolina State University
Project Dates: May 2012 - April 2014

Project Overview 

Cassava is an important staple crop in Africa and Asia, where it is eaten by more than 700 million people every day. It is grown by subsistence farmers in the poorest villages and is often the only food source when other crops fail or are destroyed by conflict. Cassava can grow under drought, high temperature, and poor soil conditions, but its production is severely limited by viral diseases. Cassava mosaic disease (CMD) is caused by a DNA virus complex consisting of seven geminivirus species that act synergistically to enhance disease severity. Recently, two satellite DNAs associated with the complex have been shown to break resistance and enhance symptoms.

1-232 Tanzania 3

Tanzania Partnership Picture D

Cassava plants maintained in a tissue culture lab ready for sub-culturing at MARI. (Photo courtesy Joseph Ndunguru). A research student getting prepared for sub-culturing of cassava plants at MARI(Photo courtesy Joseph Ndunguru).

Cassava mosaic geminiviruses (CMGs) induce diverse symptoms in cassava depending on the host genotype, age of infection, amount of virus inoculum, virus strain, vector activity, and environmental and other host factors. Research on CMGs has generated extensive information about viral diversity, genome sequence, replication, transmission, disease epidemiology and disease control. In contrast, there are no reports that describe the changes that occur in cassava leaves at a cellular level in response to CMG infection. The goal of this proposal is to establish cell biology infrastructure and expertise at Mikocheni Agricultural Research Institute (MARI) in Tanzania and to use these resources to characterize CMG infection in cassava. A combination of light and fluorescent microcopy will be used to examine CMD processes at a cellular level in cassava leaves. Using in situ hybridization to detect CMG and satellite DNAs in cassava leaves, these researchers will seek to determine if different CMGs infect different leaf cell types and if the nature and number of the target cells change in mixed infections and/or in the presence of the satellites. The research team will also examine the cellular architecture of infected leaves as a first step toward understanding the physiological basis of the extreme leaf deformation phenotypes correlated with the presence of CMD-associated satellites. The application of cell biology to CMD represents a unique opportunity to study the interactions of different viruses with a common host and with each other and satellite DNAs. The increased knowledge to be gained through the project should contribute to understanding of this important plant virus and to the development of sustainable strategies to control it and thereby limit its economic and nutritional impact.
Summary of Recent Activities
With the newly acquired microscope, camera, and microtome with a vibrating blade in full operation and the training in cell biology techniques completed, the team has been conducting simultaneous comparison of infection pattern of CMGs in single or dual infections and comparison of CMG infection pattern in the presence and absence of satellite DNAs. The research team designated DIG-labeled probes for detection of Africa Cassava Mosaic Viruses (ACMV) and East Africa Cassava Mosaic Viruses (EACMV). Optimization of the protocols to perfect the system is still in progress. Young cassava plants are grown in a tissue culture lab followed by acclimatization in the screen house for further in situ virus localization study. Going forward, the team is planning to test more probes to be used for in situ hybridization after bombarding plants with infectious clones. The plants will be bombarded with either the virus alone or in combination with satellite DNA II and III, and negative control plants will not be inoculated. Training efforts will continue as well - project research assistant Mr Linus Paul is planning to attend two week training at St. John University of Tanzania March 10-21, 2014.

Tanzania Partnership Picture A

Tanzania Partnership Picture B

Scientists from Mikocheni Agricultural Research Institute (MARI) are being trained on to use the vibratome and fluorescent microscope (Photo courtesy Joseph Ndunguru). Linus Paul, who is in charge of microscopy at MARI, is working with a vibratome (Photo courtesy Joseph Ndunguru).

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