4d.Progress report.
This report serves to document research and activities carried out under a grant to the Donald Danforth Plant Science Center. The work falls under the auspices of and is funded by a reimbursable agreement between ARS and USAID (0210-22310-002-84R). Two major activities were proposed and undertaken. 1. Development of genetic transformation systems for Kenyan cassava germplasm – training of Kenyan scientist • All five Kenyan cassava landraces imported from the Kenyan Agricultural Research Institute (KARI) were screened for their embryogenic potential and capacity for genetic transformation o All five landraces generated organized embryogenic structures but the efficiency of this process varied between them. Four performed in a manner equal to cv. 60444, the model type employed in cassava transformation, while one, Kibandameno, performed at levels significantly below 60444 and was therefore eliminated from further study. o Friable embryogenic callus (FEC), the target tissue used for transformation of cassava, was generated from four of the Kenyan landraces o Transformation of Kenyan FECs was carried out with the cvs LBA 4404, Cry5 and EHA105. LBA and Cry5 were found to be more effective than EHA105 for production of GUS expression cells four days after transformation o Killing curves for Kenyan cvs against the selectable marker paramoycin were generated, showing varying genotypic response to presence of this antibiotic in the medium. o Replicated transformation experiments were successful in generating high frequencies of transient marker gene expression but to date no transgenic callus lines were recoverable from these experiments.

2. Screening of new transgenic 60444 plants for resistance to cassava mosaic disease. In 2005, approximately 500 transgenic cassava plants were recovered in our laboratory expressing the AC1 (replicase) gene from African cassava mosaic virus (ACMV) • A total of 1700 plants from 227 independent transformation events were inoculated with infectious clones of ACMV. Infectious DNA was “shot” into young leaves of the transgenic cassava plants using the Helios micorparticle delivery device. Of the 227 lines challenged to date, 25 were found to exhibit increased resistance compared to the non-transgenic controls. • Further rounds of viral challenging are on-going with increased levels of inoculum and with different species of geminiviruses causing cassava mosaic disease.