Molecular Breeding for Striga Resistance in Sorghum - Translational Genomics for Crop Breeding: Biotic Stress - page 90

combination of variety and herbicide, that both
are needed to control the Striga , and that farmers
should wash their hands after handling imazapyr-
treatedmaize seed before planting other seed.
Information should also be provided on comple-
mentary control technologies to increase aware-
ness of ISC options and value for Striga control
and for wider yield improvement (e.g., fertiliza-
tion). Research support is thus needed to guide
safe and efficient use and to develop alterna-
tive options for diverse dryland cereal production
environments.
Integrated Striga management packages have
been designed that include: Striga resistant vari-
eties; judicious and appropriate timing and appli-
cation of phosphate, nitrogen, and composite
fertilizers in combination with organic fertil-
izers; and water conservation measures using
tied ridges (or local alternatives). When demon-
strating ISC technologies to farmers, including
at least one method in all packages that gives
rapid Striga control would facilitate sustained
interest in ISC, allowing the sustained adop-
tion of longer-impact technologies such as tools
to improve soil fertility to continue (Douthwite
et al. 2007). Of these approaches, development
of resistant crop cultivars has been recognized as
the most effective and feasible method. To date,
Striga -resistant sorghum cultivars - such as N13,
SRN39, Framida, 555, ICSVs, SRN39 deriva-
tives (P401 to P409), Soumalemba (IS15401),
Seguetana CZ, and CMDT45 - have been iden-
tified and, as has been observed by Tabo et al.
(2006) and ICRISAT (2009), these can be inte-
grated with available crop management options
to enhance productivity. However, understanding
the molecular nature of the plant-plant interac-
tions is a major barrier. High genetic variabil-
ity of parasite populations coupled with large,
long-lived Striga seed banks makes it unlikely
that single-gene resistance will be useful in the
field. The development of durable polygenic
resistance requires pyramiding of appropriate
resistance genes and will depend on knowledge
of the relationship between host resistance and
parasite race structure. QTL studies and MAS

certainly have the potential to aid the develop-
ment of resistant cultivars in the short-to-medium
term. Looking forward, a major challenge is to
exploit genomic technologies to further advance
our understanding of the biology of susceptible
and resistant interactions allowing the develop-
ment of novel control strategies that are appropri-
ate for the agricultural and socioeconomic envi-
ronment where this parasite is such a devastating
problem.

Conclusion

Integrated Striga control remains the most
effective way to manage Striga infestations in
sorghum as a long-term approach. Increased
understanding of the host-parasite interactions
and possibility of identification of newer resis-
tance factors by employing recent technologies
such as NGS tools, RNA sequencing applica-
tions, RNAi technology, and precise phenotyp-
ing platforms will pave the way for developing
cultivars with improved resistance. With molec-
ular biology tools being practiced successfully in
Africa and improved access to recent technolo-
gies such as GbS spreading to remote sorghum
breeding programs, development of resistant cul-
tivars with different resistance factors stacked
together will form best short- and medium-term
approaches toward Striga control.

Acknowledgment

The authors are thankful to a grant from
ASARECA Competitive Grant System for 2006
for fine-mapping striga resistance QTLs and
completing MABC in farmer-preferred varieties.

References

Amusan IO, Rich PJ, Housely T, Ejeta G. 2011. An in vitro
method for identifying postattachment Striga resistnace
in maize and sorghum. Agronomy Journal 103(5): 1472-
1478.
Amusan IO, Rich PJ, Menkir A, Housley T, Ejeta G. 2008.
Resistance to Striga hermonthica in a maize inbred