Inflorescence type marker in a polyploid F1 population of Hydrangea macrophylla

Diploid and triploid plants of the ornamental crop Hydrangea macrophylla develop either lacecap (wild type) or mophead inflorescences. These inflorescence types differ in the number and position of decorative flowers. The inflorescence type is inherited in a monogenic, dominant-recessive manner, in which the mophead type is recessive and the lacecap type dominant. In order to identify markers linked with the INFLORESCENCE TYPE LOCUS (INF), we used a F-1 population consisting of 424 plants. These plants segregated into 25% diploid and 75% triploid mophead and lacecap plants, although both, the mophead and the lacecap parent, were diploid. However, the lacecap parent produced predominantly unreduced pollen. We used pooled restriction site associated (RAD) DNA sequencing data of 380 F-1 plants and identified 2 INF markers by bulk sequence analysis. Both of these markers explained 99.7% of the inflorescence phenotype. In addition, we found a co-segregation between the mophead and the non-flowering trait independently of ploidy (Trankner et al., 2019). Here, we present marker data of the INF marker A133A134 with regard to the gamete contribution to triploid F-1 plants. Out of 314 analyzed triploids, 74 were homozygous (aaa), whereas 240 were heterozygous (aab or abb) at marker locus A133A134. We suggest that the triploid F-1 plants are largely the product of sexual polyploidization caused by unreduced pollen from the lacecap parent. Furthermore, we assume that meiotic restitution underlies the formation of unreduced pollen.