Resistance to powdery mildew is an important trait of interest in many wheat breeding programs.  The information on genes conferring resistance to powdery mildew in wheat cultivars is useful in parental selection.  Winter wheat breeding line DH51302 derived from Liangxing 99 and cultivar Shimai 26 derived from Jimai 22 showed identical infection patterns against 13 isolates of Blumeria graminis f. sp. tritici (Bgt) that causes wheat powdery mildew.  DH51302 and Shimai 26 were crossed to a powdery mildew susceptible cultivar Zhongzuo 9504 and the F_2:3 families were used in molecular localization of the resistance genes.  Fourteen polymorphic markers, which were linked to Pm52 from Liangxing 99, were used to establish the genetic linkage maps for the resistance genes PmDH51302 and PmSM26 in DH51302 and Shimai 26, respectively.  These genes were placed in the same genetic interval where Pm52 resides.  Analysis of gene-linked molecular markers indicated that PmDH51302 and PmSM26 differed from other powdery mildew resistance genes on chromosome arm 2BL, such as Pm6, Pm33, Pm51, MlZec1, MlAB10, and Pm64.  Based on the results of reaction patterns to different Bgt isolates and molecular marker localization, together with the pedigree information, DH51302 and Shimai 26 carried the same gene, Pm52, which confers their resistance to powdery mildew.

 

Analysis of genetic progress for lodging-related traits provides important information for further improvement of lodging resistance.  Forty winter wheat cultivars widely grown in the Yellow-Huai River Valleys Winter Wheat Zone (YHWZ) of China during the period of 1964–2015 were evaluated for several lodging-related traits in three cropping seasons.  Plant height, height at center of gravity, length of the basal second internode, and lodging index decreased significantly in this period, and the average annual genetic gains for these traits were –0.50 cm or –0.62%, –0.27 cm or –0.60%, –0.06 cm or –0.63%, and –0.01 or –0.94%, respectively.  Different from other traits, stem strength showed a significant increasing trend with the breeding period, and the annual genetic gains were 0.03 N or 0.05%.  Correlation analysis showed that lodging index was positively correlated with plant height, height at center of gravity, and length of the basal second internode, but negatively correlated with stem strength.  Meanwhile, significantly positive correlations were observed between plant height, height at center of gravity, and length of the basal first and second internodes.  By comparison with the wild types, dwarfing genes had significant effects on all lodging-related traits studied except for length of the basal first internode and stem strength.  Principle component analysis demonstrated that plant height and stem strength were the most important factors influencing lodging resistance.  Clustering analysis based on the first two principle components further indicated the targets of wheat lodging-resistant breeding have changed from reducing plant height to strengthening stem strength over the breeding periods.  This study indicates that the increase of stem strength is vital to improve lodging resistance in this region under the high-yielding condition when plant height is in an optimal range.