Study on interspecific hybridization between tulip cultivars and wild species native to China

The interspecific hybridization was performed between five tulip cultivars, including ‘Judith Leyster,’ ‘World’s Favorite,’ ‘Heart of Poland,’ ‘Crispa Fabio’ and ‘Jumbo Pink,’ and five wild species, including Tulipa thianschanica Regel, T. sinkiangensis Z. M. Mao, T. altaica Pall. ex Spreng, T. buhseana Boiss. and T. schrenkii Regel., to explore the cross-compatibility between tulip cultivars and wild species. In this experiment, pollen size and germinability, pollen storage life, stigma receptivity, fruit-setting, hybrid seed germination and bulblet formation were observed. The chromosome count and karyotype of hybrids were also examined. The results showed that T. altaica and five cultivars had closer genetic relationship than the other four wild species. Among the five wild Tulipa species T. altaica has the largest pollen and the highest germination rate (65.23%) compared with any other four species. The pollen viability of all five pollen parents decreased slowly across all stages at − 20 °C and decreased rapidly at 25 °C and 4 °C. A total of 1066 hybrids were obtained from interspecific hybridization combinations, including ‘Heart of Poland’ × T. thianschanica, ‘Heart of Poland’ × T. altaica, ‘Crispa Fabio’ × T. altaica, ‘Jumbo Pink’ × T. altaica, ‘Crispa Fabio’ × T. schrenkii and ‘Jumbo Pink’ × T. schrenkii. According to the chromosome count, approximately 20% and 12% aneuploidy hybrids were produced from ‘Heart of Poland’ (2n = 3x = 36) × T. thianschanica (2n = 2x = 24) and ‘Heart of Poland’ (2n = 3x = 36) × T. altaica (2n = 2x = 24), respectively, and the any other hybrids were diploid (2n = 24) in these two crosses. All the hybrids from crosses of diploid parents were diploid (2n = 24). Meanwhile, the karyotype characteristics of six parents and their six progenies were also elaborated, which had similar 3A and 3B karyotypes. The results of this study may facilitate tulip interspecific hybridization in the future.