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Generating
striga resistant maize:
Identification of sources of resistance in wild relatives
A.L.
Gurney, D. Grimanelli, S.J. Hearne, F. Kanampiu,
D. Hoisington, J.D. Scholes & M.C. Press
Parasitic weeds of the genus
Striga can devastate grain
production in small-holder farms in Africa. Complete resistance to Striga
infection has not been identified for cereals, moreover, genetic
variation in maize for Striga resistance/tolerance is extremely limited. There is an urgent
need to understand the physiological and molecular basis of the cereal-Striga
association to help provide strategies for the long-term control of Striga.
One approach to generate Striga-resistant
material is to identify sources of resistance from wild relatives of
maize. The genetic potential of a number of diploid and tetraploid Tripsacum
accessions was assessed to determine their value as a source of alleles
for maize breeding. Novel sources of resistance were observed in
tetraploid Tripsacum dactyloides.
Tripsacum did not support Striga
growth as development of the parasite was arrested soon after attachment
and initial development of the haustorium. The haustorium is a unique
organ that provides a physiological bridge between host and parasite,
acting as a conduit for host derived water and solutes. Vascular
continuity was established between parasite and host but histological
analysis demonstrated inferior haustorial development on Tripsacum
compared with maize. The hyaline body, a metabolically active region of
cells within the haustorium, was either absent or poorly developed.
These results strongly suggest that Striga
fails to develop on Tripsacum
due to nutrient starvation. Recent results indicate that Tripsacum
may produce a negative signal that impairs normal haustorial development
and function. Evaluation of
a number of maize-Tripsacum
hybrids in the laboratory indicated that resistance to Striga
decreased as the proportion of maize present in the genome increased.
The use of maize-Tripsacum addition lines may allow putative locations for resistance
gene(s) to be identified. This approach will help to assess the
feasibility of introducing Tripsacum-based
resistance into maize using conventional wide cross techniques.
Attention is also focused on identifying the resistant trait in Tripsacum.
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