1 Zhejiang Provincial Key Laboratory of Germplasm Innovation and Utilization for Garden Plants, Zhejiang A&F University, Hangzhou 311300, China; 2 Key Laboratory of Germplasm Innovation and Utilization of Southern Landscape Plants, State Forestry and Grassland Administration, Zhejiang A&F University, Hangzhou 311300, China; 3 College of Landscape and Architecture, Zhejiang A&F University, Hangzhou 311300, China
Abstract：Rhododendron resources are abundant in China and have a long history of cultivation. Hybridization breeding technology can greatly enrich Rhododendron resources. Rhododendron subgen. Tsutsusi, subgen. Azaleastrum and subgen. Pentanthera belong to the same evolutionary branch of hairy Rhododendron. In order to explore the compatibility of hybridization and the stages of hybridization barriers among 3 genus, Rhododendron simsii, R. pulchrum and 8 cultivars of subgen. Tsutsusi, R. ovatum of subgen. Azaleastrum, R. molle and 2 cultivars of subgen. Pentanthera were studied. The cross compatibility between subgenera was analyzed from the aspects of style length ratio, pollen germination, pollen tube growth, ovary and embryo development. The results showed that there was obvious prezygotic unidirectional discompatibility among subgen. Tsutsusi, subgen. Azaleastrum and subgen. Pentanthera. All pollen combinations could germinate in large quantities in stigma. The pollen tubes of subgen. Tsutsusi × subgen. Pentanthera, subgen. Azaleastrum × subgen. Pentanthera, and subgen. Azaleastrum × subgen. Tsutsusi reached the base of the style in large numbers and were able to set fruit. Reciprocal cross pollen tubes mostly stop growing in the middle of the style, a few reach the base of the style, and could not set fruit. The embryo development of subgen. Azaleastrum × subgen. Pentanthera and subgen. Azaleastrum × subgen. Tsutsusi were slower than that of subgen. Tsutsusi × subgen. Pentanthera, and the capsule dehiscent time was also late, most embryos of mature seeds in each hybridization direction were incomplete. The results of compatibility experiments showed that the cross barriers appeared in pollen tube growth, double fertilization and embryo development. The present study explored the law of cross compatibility and could provide reference for cross breeding of Rhododendron subgenera.
[1] 陈晓阳, 沈熙环. 2020. 林木遗传育种学[M]. 北京: 中国林业出版社, pp. 156-157. (Chen X Y, Shen X H.2020. Genetic Breeding of Forest Trees[M]. China Forestry Publishing House, Beijing, China, pp. 156-157.) [2] 耿兴敏, 张超仪, 尹增芳. 2014. 部分野生杜鹃杂交授粉后花粉管生长状况分析[J]. 安徽大学学报(自然科学版), 38(4): 94-101. (Geng X M, Zhang C Y, Ying Z F.2014. Analysis of pollen tube growth of some wild rhododendrons after cross-pollination[J]. Journal of Anhui University (Natural Science Edition), 38(4): 94-101.) [3] 耿兴敏, 赵红娟, 吴影倩, 等. 2017. 野生杜鹃杂交亲和性及适宜的评价指标[J]. 广西植物, 37(8): 979-988. (Geng X M, Zhao H J, Wu Y Q, et al.2017. Compatibility and suitability evaluation indexes of wild rhododendron hybrids[J]. Guangxi Botany, 37(8): 979-988.) [4] 李西时, 巴春影, 曹后男, 等. 2015. 长白山杜鹃花属种间杂交亲和性的研究[J]. 农业科学技术, 16(8): 1617-1620. (Li X S, Ba C Y, Cao H N, et al.2015. Studies on cross-species compatibility of Rhododendron in Changbai Mountain[J]. Agricultural Science and Technology, 16(8): 1617-1620.) [5] 李叶芳, 尹杨萍, 杜娟, 等. 2019. 比利时杜鹃与几种野生杜鹃杂交亲和性研究[J]. 西南林业大学学报(自然科学), 39(05): 177-181. (Li Y F, Yin Y P, Du J, et al.2019. Studies on cross compatibility between Rhododendron hybrida and several wild rhododendrons[J]. Journal of Southwest Forestry University (Natural Science), 39(05): 177-181.) [6] 宋明波, 穆立蔷. 2022. 杜鹃属植物资源及园林应用[J]. 特种经济动植物, 25(02): 103-104. (Song M B, Mu L Q.2022. Rhododendron resources and garden applications[J]. Special Economic Animals and Plants, 25(02): 103-104.) [7] 王文鹏. 2013. 蜡梅科植物远缘杂交亲和性及其组织学机理[D]. 硕士学位论文, 浙江农林大学, 导师: 赵宏波, pp. 15-16. (Wang W P.2013. Affinity and histological mechanism of distant hybridization in Schizocarpaceae plants [D]. Thesis for M.S., Zhejiang A&F University, Supervisor: Zhao H B, pp. 15-16.) [8] 解玮佳, 李世峰, 瞿素萍, 等. 2019. 常绿杜鹃不同杂种群间杂交的可育性分析[J]. 园艺学报, 46(5): 910-922. (Xie W J, Li S F, Qv S P, et al.2019. Fertility analysis of cross between different hybrid populations of evergreen azalea[J]. Acta Horticulturae Sinica, 46(5): 910-922.) [9] 郑硕理, 易陈燃, 刘巧, 等. 2016. 云南几种杜鹃杂交育种初探[J]. 云南农业大学学报(自然科学), 31(6): 1052-1057. (Zheng S L, Yi C R, Liu Q, et al.2016. Preliminary study on cross breeding of several rhododendrons in Yunnan[J]. Journal of Yunnan Agricultural University (Natural Sciences), 31(6): 1052-1057.) [10] 庄平. 2018a. 杜鹃花属植物杂交不亲和与败育分布研究[J]. 广西植物, 38(12): 1581-1587. (Zhuang P.2018a. Distribution of hybrid incompatibility and abortion in Rhododendron[J]. Journal of Guangxi Botany, 38(12): 1581-1587.) [11] 庄平. 2018b. 32种杜鹃花属植物亚属间杂交的可育性研究[J]. 广西植物, 38(12): 1566-1580. (Zhuang P.2018b. Study on fertility of 32 species of Rhododendron intersubgeneric hybridization[J]. Journal of Guangxi Botany, 38(12): 1566-1580.) [12] Barragan A C, Collenberg M, Wang J, et al.2021. A truncated singleton NLR causes hybrid necrosis in Arabidopsis thaliana[J]. Molecular Biology and Evolution, 38(2): 557-574. [13] Chen T, Xie M, Jiang Y, Yuan T.2022. Abortion occurs during double fertilization and ovule development in Paeonia ludlowii[J]. Journal of Plant Research, 135(2): 295-310. [14] Eeckhaut T, De Keyser E, Van Huylenbroeck J, et al.2007. Application of embryo rescue after interspecific crosses in the genus Rhododendron[J]. Plant Cell, Tissue and Organ Culture, 89(1): 29-35. [15] Kobayashi N, Matsunaga M, Nakatsuka A, et al.2013. Chimeric inheritance of organelle DNA in variegated leaf seedlings from inter-subgeneric crossing of azalea[J]. Euphytica, 191(1): 121-128. [16] Kobayashi N, Mizuta D, Nakatsuka A, et al.2007.Attaining inter-subgeneric hybrids in fragrant azalea breeding and the inheritance of organelle DNA[J]. Euphytica, 159(1-2): 67-72. [17] Kuligowska K, Lütken H, Christensen B, et al.2016. Interspecific hybridization among cultivars of hardy Hibiscus species section Muenchhusia[J]. Breeding Science, 66(2): 300-308. [18] Okamoto A, Ureshino K.2015. Pre- and post-fertilization barriers in interspecific hybridization between evergreen azalea species and Rhododendron uwaense H. Hara & T. Yamanaka[J]. Horticulture Journal, 84(4): 355-364. [19] Sakai K, Ozaki Y, Ureshino K, et al.2008. Interploid crossing overcomes plastome-nuclear genome incompatibility in intersubgeneric hybridization between evergreen and deciduous azaleas[J]. Scientia Horticulturae, 115(3): 268-274. [20] Ureshino K, Kawai M, Miyajima I.2000. Factors of intersectional unilateral cross incompatibility between several evergreen azalea species and Rhododenron japonicum f. fllavum[J]. Journal of the Japanese Society for Horticultural Science, 69(3): 261-265. [21] Williams E G, Rouse J L.1990. Relationships of pollen size, pistil length and pollen tube growth rates in Rhododendron and their influence on hybridization[J]. Sexual Plant Reproduction, 3: 7-17.
