Loss of CMD2-mediated resistance to cassava mosaic disease in plants regenerated through somatic embryogenesis
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Date
2016
Journal Title
Journal ISSN
Volume Title
Publisher
Molecular plant pathology
Abstract
Cassava mosaic disease (CMD) and cassava brown streak disease
(CBSD) are the two most important viral diseases affecting
cassava production in Africa. Three sources of resistance are
employed to combat CMD: polygenic recessive resistance, termed
CMD1, the dominant monogenic type, named CMD2, and the
recently characterized CMD3. The farmer-preferred cultivar TME
204 carries inherent resistance to CMD mediated by CMD2, but
is highly susceptible to CBSD. Selected plants of TME 204 produced
for RNA interference (RNAi)-mediated resistance to CBSD
were regenerated via somatic embryogenesis and tested in confined
field trials in East Africa. Although micropropagated, wildtype
TME 204 plants exhibited the expected levels of resistance,
all plants regenerated via somatic embryogenesis were found to
be highly susceptible to CMD. Glasshouse studies using infectious
clones of East African cassava mosaic virus conclusively
demonstrated that the process of somatic embryogenesis used to
regenerate cassava caused the resulting plants to become susceptible
to CMD. This phenomenon could be replicated in the
two additional CMD2-type varieties TME 3 and TME 7, but the
CMD1-type cultivar TMS 30572 and the CMD3-type cultivar TMS
98/0505 maintained resistance to CMD after passage through
somatic embryogenesis. Data are presented to define the specific
tissue culture step at which the loss of CMD resistance occurs
and to show that the loss of CMD2-mediated resistance is maintained
across vegetative generations. These findings reveal new
aspects of the widely used technique of somatic embryogenesis,
and the stability of field-level resistance in CMD2-type cultivars
presently grown by farmers in East Africa, where CMD pressure
is high.
Description
Keywords
Cassava, Cassava mosaic disease, CMD2, Geminivirus resistance, Somaclonal variation, Somatic embryogenesis, Susceptible
Citation
Beyene, G., Chauhan, R. D., Wagaba, H., Moll, T., Alicai, T., Miano, D., ... & Taylor, N. J. (2016). Loss of CMD2‐mediated resistance to cassava mosaic disease in plants regenerated through somatic embryogenesis. Molecular plant pathology, 17(7), 1095-1110. DOI: 10.1111/mpp.12353