Pleiotropic Effect of the <i>compactum</i> Gene and Its Combined Effects with Other Loci for Spike and Grain-Related Traits in Wheat

Club wheat (<i>Triticum aestivum</i> ssp. <i>compactum</i>) with a distinctly compact spike morphology was conditioned by the dominant <i>compactum</i> (<i>C</i>) locus on chromosome 2D and resulted in a redistribution of spike yield components. The disclosure of the genetic basis of club wheat was a prerequisite for the development of widely adapted, agronomically competitive club wheat cultivars. In this study, we used a recombinant inbred line population derived from a cross between club wheat Hiller and modern cultivar Yangmai 158 to construct a genetic linkage map and identify quantitative trait loci associated with 15 morphological traits. The club allele acted in a semi-dominant manner and the <i>C</i> gene was mapped to 370.12–406.29 Mb physical region on the long arm of 2D. Apart from compact spikes, <i>C</i> exhibited a pleiotropic effect on ten other agronomic traits, including plant height, three spike-related traits and six grain-related traits. The compact spike phenotype was correlated with decreased grain size and weight, but with an increase in floret fertility and grain number. These pleiotropic effects make club wheat have compatible spike weight with a normal spike from common wheat. The genetic effects of various gene combinations of <i>C</i> with four yield-related genes, including <i>Ppd-D1</i>, <i>Vrn-D3</i>, <i>Rht-B1b</i> and <i>Rht8</i>, were evaluated. <i>C</i> had no epistatic interaction with any of these genes, indicating that their combinations would have an additive effect on other agronomically important traits. Our research provided a theoretical foundation for the potentially effective deployment of <i>C</i> gene into modern breeding varieties in combination with other favorable alleles.