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An in vitro
technique for studying specific Striga resistance mechanisms
in sorghum
Abdalla H. Mohamed1*, T. L. Housley2
and Gebisa Ejeta2
1Agricultural
Research Corporation,
P. O. Box 126, Wad Medani, Sudan.
2Department
of Agronomy, Purdue University, United States of America.
*Corresponding author. E-mail:
abdalla_moh2002@yahoo.com .
Accepted 26 June, 2010 |
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Witchweed (Striga sp.) is a noxious parasitic weed of
many cereals, that causes considerable crop
damage in the semi-arid tropics. Although, a number of
control measures have been suggested, breeding crops which
are resistant to the attack is the most feasible and
effective way of control. However, breeding efforts have
been hampered by the lack of adequate laboratory techniques
that uncover critical host-parasite interactions, that occur
naturally beneath the soil. Germination stimulant production
is the sole Striga resistance mechanism in sorghum [Sorghum
bicolor (L) Moench] that has been extensively studied
and exploited for breeding purposes. Other Striga
resistance mechanisms have not been effectively
characterized and used. The purpose of this study was to
develop an in vitro screening technique for
evaluation of sorghum germplasm for specific Striga
resistance mechanisms. We hereby report the development of a
reliable screening technique, the Extended Agar Gel Assay (EAGA).
Using the technique, we screened seven sorghum genotypes
with known reactions to Striga parasitsm, SRN39,
Framida, IS9830, 555, N13, Dobbs, Serena , CK60B, Shanqui
Red, IS-4225, and two wild sorghum accessions, P78, and
P47121, and we were able to characterize specific host
defense reactions (mechanisms). These reactions indicate the
potential existence of at least four separate mechanisms of
Striga resistance in sorghum: 1) low production of
Striga seed germination stimulants; 2) evidence of
germination inhibitors; 3) low production of the signal
required for haustoria initiation and 4) a hypersensitive
response (characterized by a distinct necrotic area on the
host root at the attachment site that discourage parasitic
establishment. The development of this laboratory assay
enabled us to identify and characterize distinct resistance
mechanisms. These mechanisms can be exploited through
conventional plant breeding programs. Additionally, the
resistance genes can be pyramided into one background for
more durable Striga resistance.
Key words:
Witchweed, Striga resistance, host parasite interaction,
germination, haustoria.
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