Quantitative trait loci (QTL) of stem strength and related traits in a doubled-haploid population of wheat (Triticum aestivum L.)

Scoring for lodging resistance is difficult under natural field conditions. The stem strength of wheat has been used as an index of lodging resistance. However, this is a complex trait comprised of two characters, i.e. stem mechanical elasticity and rigidity. Therefore it is closely associated with stem morphological and anatomical features. A study of the genetics of stem strength and related traits of basal stem internodes is very important for genetic improvement of lodging resistance in wheat. In this study, a doubled-haploid (DH) population derived from anther culture of the cross CA9613/1-11488 was used. Stem strength and related basal internode traits were measured at the milk stage. A molecular map of the DH population was constructed using 189 SSR markers, and quantitative trait loci (QTL) for each trait were analyzed based on this molecular linkage map. A total of six QTL for stem strength, culm wall thickness, pith diameter and stem diameter were identified: 1) Two QTL (QSs-3 A and QSs-3 B) for stem strength were detected on chromosomes 3A and 3B, exhibiting 10.6 and 16.6% phenotypic variance, respectively. 2) Two QTL (QPd-1A and QPd-2D) associated with pith diameter were detected on chromosomes 1A and 2D, respectively, jointly explaining about 30% of phenotypic variance. 3) As far as stem diameter and culm wall thickness were concerned, one QTL was detected on chromosomes 3B and 2D, respectively; QSd-3B explained 8.7% of the phenotypic variance of stem diameter, whereas QCwt-2D explained 9.6% of the phenotypic variance of culm wall thickness. In addition, among the QTLs detected, two with pleiotropic effects were observed. Correlated traits are usually associated with the pleiotropic effects of the same QTL(s) or linkage of different QTLs. But this was not true in some cases. The results of QTL mapping showed that stem strength can be improved by breeding for wider stems with a higher stem diameter/pith diameter ratio. This can be facilitated by using the markers linked to QSd-3B and QCwt-2D. Combining stem strength, stem diameter and culm wall thickness may be used as a selection index for lodging resistance with marker-assisted selection (MAS) to improve lodging resistance in this population.