Screening of pollen viability test methods and comparative analysis of pollen viability and stigma acceptability from 25 species of Passiflora L.

Abstract: 【Objective】The study aimed to test the pollen viability and stigma receptivity of 25 species [including 8 local varieties are Tainong (TN), Xintainong (XTN), Qinmi No. 9 (QM No. 9), Fengmihuangjinbaixiangguo (FMHJ), Yuanyangmi (YYM), Juwubabaixiangguo (D1- A1), Tianhuangxing (THX), Zhuangxiangmibao (ZXMB), 15 introduced varieties/strains are Guanhua (GH), Kangsitansi (KSTS), W- 1, Honghuaxifanlian (XG), Jingchixifanlian (MGMX), Ruixiang (RX), Zilian (ZL), Zhangyexifanlian (JMCH), Lüpi (LP), Qingpi (QP), Hongguan (HG), ZZ-B1, Lüpixifanlian (Ⅱ-Y), Wulaguireqingguo (ULGRQG), Lanxiang (LX), and 2 selected varieties/strains are Huangxiang No. 1 (HX No. 1), Xiaohuagnjin (D2-11).] of Passiflora L., and provide theoretical basis for the selecting parents for crossing in Passiflora L.【Methods】Using six representative species of Passiflora L. as test materials, including TN, HX No. 1, GH, W-1, XG and KSTS a single-factor experiment was conducted usinga basic medium containing 0.02% boric acid (H3BO3), 15% sucrose, 15% PEG-4000, 0.08% calcium nitrate [Ca(NO3)2 ·4H2O], and 0.02% MgSO4 ·7H2O to screen optimal conditions for pollen viability test in vitro. The 25 species of Passiflora L. were used as materials, the basic floral morphological parameters were measured. Pollen vitality was detected using pollen culture in vitro, TTC staining, and I2-KI staining methods to compare differences of pollen vitality of different species with different detection methods. Additionally, the stigmatic receptivity of the 25 species of Passiflora L. was compared and analyzed using the benzidine-hydrogen peroxide method.【Results】The results showed that all the 25 species of Passiflora L. exhibited different stigma receptivity. Among them, the 19 species including TN, HX No. 1, W-1, XG, XTN, QM No. 9, MGMX, LP, QP, FMHJ, HG, YYM, ZZ-B1, D1-A1, THX, ZXMB, D2- 11, Ⅱ- Y and ULGRQG exhibited strong stigma receptivity. The 3 species, GH, KSTS and JMCH had moderate stigma receptivity, while another 3 species, RX, ZL and LX showed weaker stigma receptivity. Only the optimal sucrose concentration for different species was different in pollen culture in vitro. Aong the 6 species tested, the optimal sucrose concentration for TN, HX No. 1, GH and KSTS was 15%, while the optimal sucrose concentration for W-1 and XG was 10%. The optimal concentrations of boric acid, PEG-4000, and calcium nitrate were 0.02%, 15%, and 0.08%, respectively, with an optimal incubation temperature of 25 ℃ . The pollen culture in vitro was the most effective method for demonstrating the pollen vitality of the 25 species, followed by TTC staining, which could serve as a rapid detection method. The I2-KI staining was not suitable for detecting the pollen vitality of Passiflora L. Based on pollen culture in vitro and TTC staining methods, the 25 species of Passiflora L. was classified into three groups by cluster analysis. GroupⅠ consisted of 21 species, including FMHJ, ZXMB, W-1, Ⅱ-Y, LP, XTN, TN, THX, QM No. 9, ULGRQG, HX No. 1, D1-A1, D2-11, YYM, XG, MGMX, QP, HG, ZZ-B1, KSTS and JMCH with pollen vitality above 70%, being considered as normally fertile. Group Ⅱ consisted of only one species, GH with pollen vitality between 50% and 70%, also being considered as normally fertile. Group Ⅲ included three species, ZL, LX and RX which belonged to the high sterile category.【Conclusion】Among the three detection methods, pollen vitro-culture is the most effective method for evaluating the pollen vitality of the 25 species of Passiflora L., while the TTC staining method could serve as a rapid alternative. Among the 25 species (varieties) of Passiflora L., ZL, LX and RX could be only used as female parents for hybridization, while the other 22 species could be used as either male or female parents for hybridization.