A new robust codominant sex-linked STS marker for asparagus

Abstract

A new sex-linked codominant STS marker useful for discriminating between normal males (Mm), supermales (MM) and females (mm) is described. Primers for this marker were designed based on a reference sequence provided by an internationally funded asparagus genome sequencing consortium. According to this reference sequence, the marker is located approximately 1.3 Kb downstream from the 5’ end of the putative non-recombining sex determination region. Four female (mm) plants lack a 26 bp sequence that is present in four supermale (MM) plants aligned to the reference sequence. The primer combination RM17 surrounds this region and amplifies a 189 bp marker in plants with the m allele and a 215 bp marker in plants with the M allele. Serial dilutions of Qiagen-purified DNA from spears indicated both bands could be resolved with template concentrations ranging from 0.5 to 2000 ng of template per 10 ul reaction. We have tested this marker in numerous plants from UC Riverside asparagus germplasm, which includes material derived from ‘Mary Washington’ (selections from Hanna, Ellison and Takatori) and old Dutch and German cultivars. We found one diploid plant with an apparent crossover between the marker and the sex locus, but plan to confirm this with a new test cross. An initial survey of plants from the UC Riverside Third International Cultivar Trial indicated that at least one possible crossover event between the marker and the sex locus likely occurred in an ancestor of ‘Purple Passion’, ‘Sweet Purple’, ‘NJ1016’ and ‘Pacific Purple’. These cultivars all share ‘Violetto d'Albenga’ as a common ancestor, and this marker highlights the divergence between the tetraploid and diploid Asparagus varieties. This marker is simple to use and very robust.