Abstract:
Spike morphology characteristics and the free-threshing habit of wheat have
been extensively investigated because of their evolutionary significance and practical
importance. Several genetic systems that govern these traits have been reported. Some
studies suggest polygenic inheritance while others have identified major genes. This
study was conducted to identify and locate quantitative trait loci (QTL) affecting the
free-threshing habit and spike morphology characteristics in the International Triticeae
Mapping Initiative (ITMI) recombinant inbred line (RIL) mapping population. The
ITMI population was planted in three environments in 1999 and 2000. The ITMI RILs
were evaluated for threshability and spike morphology characters. QTL analyses were
performed using simple and composite interval mapping procedures. Two QTLs, one
on chromosome lB and one on 4A, affecting spike length were identified. The QTL
on chromosome 1B has not been described previously. One QTL controlling spikelet
number was also detected on chromosome 4A. This QTL coincided in location with
the QTL on chromosome 4A that affected spike length. One QTL controlling rachis
internode length, a measure of spike compactness, was detected on chromosome 6A.
The location of QTLs that affected spike length, spikelet number, and spike
compactness did not coincide with the location of major genes (Q, C, S1, Ppd1, and
Ppd2) known to affect these traits. Two QTLs, one on chromosome 2D and one on
4D, affecting threshability were identified. The QTL on chromosome 4D has not been
described previously. A QTL that affected glume tenacity was also detected on
chromosome 2D. Coincident QTLs on chromosome 2D that affected both threshability
and glume tenacity are believed to correspond to Tg, a gene for tenacious glumes. In
addition, an amplified fragment length polymorphism (AFLP) marker
(XorstP3747207) that was putatively associated with Tg was identified using bulked
segregant analysis. A QTL on chromosome 5A affecting glume tenacity was also
identified. The QTL on chromosome 5A is believed to represent Q, a gene known to
affect rachis fragility and glume tenacity. Information on the number, position, and
effect of QTLs determining these traits and their associated molecular markers may
facilitate their manipulation for wheat improvement purposes.
