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Can wild relatives of maize provide new sources of
resistance to the root hemi-parasite Striga
hermonthica?
J.D. Scholes, A.L. Gurney, D.
Grimanelli, D. Hoisington & M.C. Press
The
haustorium is an organ that forms a physiological bridge between host
and parasite acting as a conduit for host derived solutes. The root
hemiparasite Striga is
dependent on its host for water, nitrogen and some carbon, however, the
role of the haustorium in solute acquisition and metabolism is
relatively unknown. Studies of other parasitic plants such as mistletoes
suggest that the haustorium may play an important role in the metabolism
of host-derived nutrients. To date, complete resistance to Striga infection has not been identified in maize, however, a near
relative of maize, Tripsacum
dactyloides, did not support Striga
growth. Histological analysis demonstrated inferior haustorial
development on Tripsacum
compared with haustorial development on maize, in particular poor tissue
differentiation. The hyaline body, a
metabolically active region of cells within the haustorium, was either
absent or poorly developed. A lack of internal strucure is likely
to affect haustorial function which may have serious consequences for
parasite nutrition and subsequent development.
Non-functional haustoria on Tripsacum
may be a result of the absence of a positive signal from the host or the
presence of a negative signal. Secondary haustoria produced by Striga
were manipulated so that one individual Striga
plant could be attached to two hosts; a susceptible maize host and a
resistant Tripsacum host. Our
aim was to determine whether i) a positive signal(s) produced by maize
could influence haustorial development on Tripsacum
or ii) whether a negative signal produced by Tripsacum
could influence haustorial development on maize. Early results strongly
suggest that Tripsacum may
produce a negative signal influencing haustorial development and
preventing successful parasite infestation.
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