Plant Molecular Biology 48: 713–726, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Mapping QTLs associated with drought resistance in sorghum (Sorghum
bicolor L. Moench)
, P.K. Subudhi
and H.T. Nguyen
Molecular Genetics and Plant Genomics Laboratory, Department of Plant and Soil Science, Texas Tech Univer-
sity, Lubbock, TX 79409-2122, USA (
author for correspondence; e-mail firstname.lastname@example.org);
104 MB Sturgis
Hall, Department of Agronomy, Louisiana State University, Baton Rouge, LA 70803, USA;
Texas A&M University
System, Texas Agricultural Experiment Station, Lubbock, TX 79401, USA
Received 27 February 2001; accepted in revised form 20 August 2001
Key words: abiotic stress, genome mapping, QTL, sorghum, stay-green
Drought is a major abiotic stress factor limiting crop production. Identiﬁcation of genetic factors involved in
plant responses to drought stress will provide a solid foundation to improve drought resistance. Sorghum is well
adapted to hot dry environments and regarded as a model for studying drought resistance among the grasses.
Signiﬁcant progress in genome mapping of this crop has also been made. In sorghum, rapid premature leaf death
generally occurs when water is limited during the grain ﬁlling period. Premature leaf senescence, in turn, leads to
charcoal rot, stalk lodging, and signiﬁcant yield loss. More than 80% of commercial sorghum hybrids in the United
States are grown under non-irrigated conditions and although most of them have pre-ﬂowering drought resistance,
many do not have any signiﬁcant post-ﬂowering drought resistance. Stay-green is one form of drought resistance
mechanism, which gives sorghum resistance to premature senescence under soil moisture stress during the post-
ﬂowering period. Quantitative trait locus (QTL) studies with recombinant inbred lines (RILs) and near-isogenic
lines (NILs) identiﬁed several genomic regions associated with resistance to pre-ﬂowering and post-ﬂowering
drought stress. We have identiﬁed four genomic regions associated with the stay-green trait using a RIL population
developed from B35 × Tx7000. These four major stay-green QTLs were consistently identiﬁed in all ﬁeld trials
and accounted for 53.5% of the phenotypic variance. We review the progress in mapping stay-green QTLs as
a component of drought resistance in sorghum. The molecular genetic dissection of the QTLs affecting stay-
green will provide further opportunities to elucidate the underlying physiological mechanisms involved in drought
resistance in sorghum and other grasses.
Drought is a major limiting factor to agriculture and
considered as the most important cause of yield re-
duction in crop plants (Boyer, 1982). Identiﬁcation of
genetic factors involved in plant responses to drought
stress will provide a solid foundation to breed plants
with improved drought resistance. While consider-
able work has been done regarding plant responses to
drought, little progress has been made on the use of
speciﬁc physiological traits to enhance drought resis-
tance, partly because of the poor understanding of the
physiological mechanisms associated with it (Bohnert
et al., 1995).
The excellent drought characteristics of sorghum
make it one of the most important food and feed
crops in the arid and semi-arid regions of the world.
Sorghum ranks ﬁfth in importance among the world’s
crops. It is a staple food in parts of Africa and Asia
and a major feed crop in the USA, Mexico, Aus-
tralia, and South Africa (Mann et al., 1983). More
than 80% of commercial sorghum hybrids in the USA
are grown under non-irrigated conditions. In the USA,
sorghum was planted to ca. 3.5 million hectares in
2000 (National Agricultural Statistics Service, 2000).