WAPO1 (Triticum) has been curated with links to the MASWheat page describing the protocol to distinguish alleles.

From MASWheat: "Achieving higher grain yields is a difficult task due to the number of genes involved, their interactions and the importance of environmental effects. This complexity determines that taken as a single trait, yield shows low heritability. Instead of improving overall yields, a more effective strategy is to focus on yield components, such as grain weight, spikes per unit area, grain number per spikelet and spikelet number per spike (SNS). Among these, SNS is an attractive trait for wheat breeders because it shows a higher heritability compared to the other yield components."

GWAS revealed a candidate gene, TraesCS7A02G481600, that was later validated and named WAPO1. WAPO1 is an acronym for wheat ortholog for the rice ABERRANT PANICLE ORGANIZATION 1 (APO1) gene. Of the four alleles described to date, the WAPO-A1b allele coincides with high SNS and has an amino acid change in a conserved region.