QTL name extensions, '.1', '.2' etc. are based on publication date, then by chromosome position.
Reference
Rostoks N et al. (2005) Genome-wide SNP discovery and linkage analysis in barley based on genes responsive to abiotic stress. Molecular Genetics and Genomics 274:515-527.
Ellis RP et al. (1997) Mapping physiological traits in barley. New Phytologist 137:149-157.