Identification and Validation of a QTL for Spikelet Number on Chromosome Arm 6BL of Common Wheat (Triticum Aestivum L.)

Abstract

To provide food security for a growing world population, it will be necessary to increase yields of staple crops such as wheat (Triticum aestivum L.). Yield is a complex, polygenic trait influenced by grain weight and number, which are negatively correlated with one another. Spikelet number is an important determinant of grain number, but allelic variants impacting its expression are often associated with heading date, constraining their use in wheat germplasm that must be adapted for specific environments. Identification and characterization of genetic variants affecting spikelet number will increase selection efficiency through their deployment in breeding programs.In this study, a quantitative trait locus (QTL) on chromosome arm 6BL for spikelet number was identified and validated using an association mapping panel, a recombinant inbred line population, and seven derived heterogeneous inbred families. The superior allele, QSn.csu-6Bb, was associated with an increase of 0.248 to 0.808 spikelets per spike across multiple environments that varied for mean spikelet number. Despite epistatic interactions between QSn.csu-6B and three other loci (WAPO-A1, VRN-D3 and PPD-B1), genotypes with a greater number of superior alleles at these loci consistently exhibit higher spikelet number. The frequency of superior alleles at these loci varies among winter wheat varieties adapted to different latitudes of the United States Great Plains, revealing opportunities for breeders to select for increased spikelet number using simple molecular markers. This work lays the foundation for the positional cloning of the genetic variant underlying the QSn.csu-6B QTL to strengthen our understanding of spikelet number determination in wheat.

Overexpression of the WAPO-A1 gene increases the number of spikelets per spike in bread wheat

“…However, the WAPO-A1b allele has a larger effect on the number of SPS in the winter wheat NIAB MAGIC population (+2.1 SPS) compared to the spring wheat CSIRO MAGIC population (+1.1 SPS) and an epistatic interaction between WAPO-A1, VRN-D3, PPD-B1 and Qsn . csu-6B has been described 45 . These data together support the conclusion that the phenotypic effect of WAPO-A1 alleles on SPS is finetuned by the timing of developmental transitions and the genetic constitution of PPD1 and VRN1 .…”

“…An epistatic interaction between WAPO-A1, VRN-D3, PPD-B1 and Qsn . csu-6B has recently been described 53 . These data together support the conclusion that the phenotypic effect of WAPO-A1 alleles on SPS is finetuned by the timing of developmental transitions and the genetic constitution of PPD1, VRN1 and VRN3 .…”

“…This would explain the low SPS observed for Soissons, carrying the early PPD-D1a allele, despite having the high-SPS WAPO-A1b allele, an observation mirrored for Fielder in comparison to Yitpi. WAPO-A1 native alleles on the other hand have not been reported to cause large changes in flowering time in field trials 25,45 and while transgenic expression delayed flowering, CRISPR and EMS mutants had no significant effects 27 . However, the WAPO-A1b allele has a larger effect on the number of SPS in the winter wheat NIAB MAGIC population (+2.1 SPS) compared to the spring wheat CSIRO MAGIC population (+1.1 SPS) and an epistatic interaction between WAPO-A1, VRN-D3, PPD-B1 and Qsn.csu-6B has been described 45 .…”

“…WAPO-A1 native alleles on the other hand have not been reported to cause large changes in flowering time in field trials 25,45 and while transgenic expression delayed flowering, CRISPR and EMS mutants had no significant effects 27 . However, the WAPO-A1b allele has a larger effect on the number of SPS in the winter wheat NIAB MAGIC population (+2.1 SPS) compared to the spring wheat CSIRO MAGIC population (+1.1 SPS) and an epistatic interaction between WAPO-A1, VRN-D3, PPD-B1 and Qsn.csu-6B has been described 45 . These data together support the conclusion that the phenotypic effect of WAPO-A1 alleles on SPS is finetuned by the timing of developmental transitions and the genetic constitution of PPD1 and VRN1.…”

“…PPD1, VRN1 and VRN3 all influence the timing of transition from vegetative to inflorescence meristem (IM) and from IM to terminal spikelet [3][4][5]53 . Later transitions are associated with increased SPS 53 , either linked to the duration or resources available for development.…”