Gender inheritance and identification of male sterility gene RSMS1 in intra - And inter-specific crosses of dioecious rosa setigera michaux

Rosa setigera Michaux (prairie or blackberry rose; 2n=2x=14) is the only dioecious rose species and only member of the Synstylae section (=Systylae) native to North America. Although flowers have male and female structures to attract pollinators, only one gender is typically functional per genotype. Intra- and interspecific crosses were made to document gender segregation in progeny. Seventeen of the 19 intraspecific crosses did not deviate from a 1:1 female: male ratio. The remaining two families shared a parent, with one family having significantly more and the other less of each gender. Interspecific crosses were only successful with female R. setigera genotypes, indicating the existence of unilateral interspecific cross incompatibility. All F₁ hybrids were male-sterile and female-fertile. Segregation for male fertility was observed in subsequent generations. Segregation data support the conclusion that a single gene (RSMS1) controls male sterility with a dominant allele needed for the male-sterile phenotype. This gene has high penetrance, but in some interspecific populations has weakened expressivity as seen by very low rates of in vitro pollen germination (<1%) and abnormal pollen tube growth. Potential applications and new research opportunities related to these advancements in understanding interspecific cross compatibility and gender inheritance in R. setigera are discussed.