SNP markers linked to sex in dioecious Rosa setigera Michx

Rosa setigera is the only dioecious rose species and displays cryptic dioecy. There is increased interest to use R. setigera in breeding programs due to its resistance to rose rosette disease. Expanded understanding of the reproductive biology of R. setigera can help breeders more efficiently introgress disease resistance and other desirable traits from it into cultivated roses. We previously reported that sex in R. setigera is controlled by a single gene (males are heterozygous and females are homozygous recessive). In 2008, a male genotype (19670317-2) unexpectedly produced a limited crop of undersized fruit resulting in 20 seedlings. Seedlings segregated 16 males: 4 females, consistent with a 3:1 male:female ratio expected from crossing two males (males possess at least one dominant allele). The twenty seedlings, 19670317-2, male genotype 19670317-1, and two additional females were analyzed using the WagRhSNP Axiom ^® rose SNP array in order to identify markers that segregated with sex and to identify the paternal parent(s) of the 20 seedlings. SNP markers are consistent with 19 seedlings originating from self-fertilization and one seedling being sired by neighboring 19670317-1. Eleven markers were identified that fit the single gene genetic model for sex determination and were identified by females being homozygous for one of the two SNP alleles and males being either homozygous for the other allele or heterozygous. Candidate SNP markers with their flanking sequences were searched using BLAST and no candidate genes for sex were found in the Rosaceae family. Eight of the SNP markers reveal the same six male seedlings as homozygous for the male associated allele and suggest these plants may be supermales; homozygous dominant. Test crosses of putative supermales onto female R. setigera are being pursued to confirm their genotype for their functional sex. Future work will focus on mapping this sex gene and understanding its function.