Karyotype analysis of eight wild Tulipa species native to China and the interspecific hybridization with tulip cultivars

The information of ploidy, karyotype and genetic relationship is useful for interspecific hybridization in ornamental plants. For Tulipa species native to China, very limited cytological information is available now. The objective of this study was to verify the chromosome number, karyotype and genetic relationship of the eight Tulipa species: T. edulis , T. schrenkii , T. iliensis , T. thianschanica , T. altaica , T. sinkiangensis , T. heterophylla and T. buhseana . And the interspecific crosses were made between T. altaica and ten tulip cultivars to obtain novel germplasm. The ovary-swelling, fruit-setting and bulblet formation rates were surveyed when different ploidy cultivars were used as female parents. This work confirmed that all eight species collected in China were diploid (2 n = 2 x = 24), among which chromosome numbers of T. thianschanica , T. sinkiangensis and T. heterophylla were firstly reported and the karyotypes of all any other species except for T. edulis were determined for the first time. The karyotypes of eight Tulipa species were classified as 3A, 4A or 3B. The results of interspecific hybridization showed significant difference when different ploidy cultivars were used as female parents. The highest fruit-setting rate was obtained when diploid cultivars were used as female parents crossed with diploid T. altaica , whereas the ovary swelling was observed in two out of four triploid cultivars as female parents, and no seeds were harvested when tetraploid cultivars were used as female parents. Our findings provided an effective means of cultivar improvement in tulip.