Preliminary Exploration of the Source, Spread, and Distribution of Rht24 Reducing Height in Bread Wheat

Rht24 is a major dwarfing allele that not only reduces plant height but also increases grain weight. The objective of this study was to trace the source, spread, and distribution of Rht24 and determine its frequency in conjunction with other important dwarfing alleles for Rht1 (Rht-B1b), Rht2 (Rht-D1b), and Rht8. Allele-specific cleaved amplified polymorphic sequence (CAPS) markers were developed for accurate and effective genotyping of Rht1 and Rht2, and closely linked flanking markers were used for genotyping of Rht8 and Rht24. Marker analysis showed that Rht24 occurs at a higher frequency (84.2%) than other important dwarfing alleles in elite wheat (Triticum aestivum L.) varieties and usually couples with Rht2 or Rht8. Geno-typing of old varieties and landraces showed that Rht24 was widely used in wheat breeding before the Green Revolution (GR). 'Akakomugi' and 'Norin 10', the donors of Rht8 and GR genes Rht1 and Rht2, respectively, harbored Rht24, so Rht24 likely followed the transfer routes of GR genes and Rht8 to spread worldwide. Pedigree analysis showed that many Chinese elite lines and backbone parents were derived from Akakomugi, contributing to the high frequency of Rht24 in Chinese varieties. Additionally, Norin 10-derived semidwarf varieties from the CIMMYT were widely used in Chinese wheat breeding. Finally, Rht24 was also detected in 30 old Chinese varieties and landraces. Overall, these findings show that the presence of Rht24 in modern Chinese elite varieties originated from Akakomugi, Norin 10, or Chinese landraces. Thus, Rht24 was introgressed early, spread widely, and became genetically fixed in a wide range of modern Chinese wheat germplasm.