Identification and Mapping of QTL for Number of Spikelets per Spike in Wheat (Triticum aestivum L.)

Wheat production will need to increase substantially to satisfy the projected rise in global food demands. To accelerate gains in wheat yield, we need a better understanding of the gene networks regulating individual yield components and their interactions. In this study, we characterized a locus regulating the number of spikelets per spike (SPS), which determines the maximum number of grains that can be formed in a wheat spike. We performed two genome-wide association studies (one including a global collection of 875 spring wheat lines and the other one including 300 photoperiod insensitive spring wheat lines), and identified a QTL for SPS on the long arm of chromosome 7AL. This QTL was validated in the biparental population Berkut x RAC875. SPS showed high heritability (h² = 0.88), which facilitated its precise genetic mapping to a 2 Mb region of chromosome 7AL (LOD score = 3.3). The 7AL QTL explained 20% of the observed phenotype variation for SPS. On average, lines carrying the Berkut allele for SPS had 2.4 more spikes per spike compared to lines carrying RAC875 allele for the peak region of the 7AL QTL. We developed a large high density population from two heterozygous inbred families (HIFs) to precisely map and eventually clone the gene underlying this QTL.