Preliminary study on embryo rescue to address embryo abortion in different ploidy hybrids of daylilies

Plants in the genus Hemerocallis not only have ornamental value, but are also adaptable to different environmental conditions. Therefore, they have been widely used in landscaping. These plants can be easily crossed and many new cultivars are released with different flower colors, shapes and sizes. Studies have found that the crossing between diploid and tetraploid may produce triploid Hemerocallis. Moreover, the resistance and adaptability of triploid Hemerocallis are much stronger than those of diploid and tetraploid plants. However, the crossing between diploids and tetraploids is not easy and the abortive rate is high. In this study, the immature embryos were collected from the ovaries at 5, 7 and 9 d after pollination. Sampling time, hormone type and concentration for embryos rescue medium were taken as variables. In addition, a small amount of embryos were collected from the first day of embryo rescue, and paraffin sections were made and compared with untreated embryos. Five types of culture medium were used differing in the concentrations of NAA and BA. The results showed that the highest survival rate (31.68%) was obtained with ovaries 7 days after pollination, with the medium that contained MS + 0.01 mg L^-1 NAA + 0.032 mg L^-1 6BA. Overall, 21 cross combinations were made between diploids and tetraploids, 22 between tetraploids and diploids, eight between diploids and triploids and nine between triploids and tetraploids, and crosses between triploids and tetraploids displayed the highest survival rate (38.57%).