Cross compatibility and endogenous phytohormone profiles in interspecific hybridization between Iris tectorum and Iris germanica

In order to introduce new valuable trait to other species, the interspecific hybridization is used in ornamental breeding. The success of interspecific hybridization is hindered by incompatibility occurring at various stages of hybridization. To character the barriers of interspecific hybridization between Iris tectorum and Iris germanica cultivars, this study investigated the compatibility of pre-fertilization and post-fertilization, and profiles of endogenous phytohormones in ovary of self-pollination and interspecific hybridization. After pollination, pollen tubes germinated, grew through style, and entered ovules in both self-pollination and interspecific hybridization. Thus, the interspecific incompatibility between I. tectorum and I. germanica cultivars were not caused by pre-fertilization barrier. The observations of embryo and endosperm development revealed that incompatibility of interspecific-hybridization occurred at post-fertilization stage during the development of the embryo. The degeneration of endosperms was observed at 15 days after pollination and no embryo was observed in the interspecific hybridization. The abnormal development of embryos and endosperms indicates that reproductive barriers between I. tectorum and I. germanica cultivars happened at post-fertilization stage. To character the profiles of endogenous phytohormones in the ovary of self-pollination and interspecific hybridization, concentration of auxins, cytokinins (CKs), gibberellins (GAs), abscisic acid (ABA), Jasmonate (JA), salicylic acid (SA), and their derivatives were analyzed by UPLC-ESI-MS/MS. The results showed concentrations of indole-3-acetic acid (IAA) and bioactive free based of CKs were highest in ovary of I. tectorum self-pollination (IT-Self), which has normally developed embryos and endosperms. Four bioactive forms of GAs were identified in this study, while the patterns of their concentration changes were not constant among different materials. Besides, the concentration of ABA was highest in unfertilized ovary of I. tectorum (IT-CK). According to the profiles of endogenous phytohormones, the abnormal development of embryos in interspecific hybridization might be caused by the low concentration of IAA and CKs, proper concentration of these phytohormone could be added into in vitro culture medium to rescue embryos of interspecific hybridization. The investigation of cross compatibility and endogenous phytohormone profiles in this study will provide insight for overcoming the barrier of interspecific hybridization and embryo rescue in Iris genus.