Abstract:【Objective】Pollen is the genetic carrier of the male parent in plant sexual reproduction, of which germination and insemination on the stigma of female flower is the prerequisite depends successful reproduction for plants. Therefore, the determination of pollen morphological differencesis the basis for plant hybridization and breeding. According to morphology, pomegranate flowers are divided into two types: Bisexual flowers and functional male flowers. Bisexual flowers, also known as "tubular flowers", have normal pistil and eventually develop into fruit. Functional male flowers, which also known as "bell-shaped flowers", have aborted pistil fall off eventually. Pollen characteristics plays a critical role in pomegranate production, influencing the fruit sets. The objectives of this study were to explore the effects of anther quality, pollen germination rate and different culture conditions on pollen germination rate of different pomegranate varieties for bisexual flowers and functionally male flowers, which will provide a basis for pollen selection and preservation in the process of pomegranate genetic breeding. 【Methods】Pollen samples were collected from the National Horticultural Germplasm Resource Center. The number of anthers of bisexual flowers and functionally male flowers was analyzed by using Suanmeiren, Mollar, Tianshihong, Zhongshiliu4, Huaguang and Turkmenistan as test materials. On June 8th, 2022, at the initial period of the flowering, 50 flower buds of uniform size that were about to open were selected and sampled. Peel the anthers in a dry carton indoors, remove the filaments, put them in a room temperature and dark ventilation place to make the anthers fully cracked, and when the pollen is completely dispersed, the dried pollen of each variety is packed into a dry small glass bottle and sealed for the determination of each index. Anther quality and pollen germination rate of bisexual flowers and functionally male flowers of different pomegranate varieties were analyzed. The differences of anther number, single anther yield, stigma, pollen tube and pollen germination rate between bisexual flowers and functionally male flowers were analyzed. The effects of sucrose concentration on germination rate and storage temperature on pollen viability were also compared. 【Results】When the sucrose concentration was 300 g×L-1, the pollen germination rate reached 83.5%, exhibiting no significant difference when compared to the treatment with a sucrose concentration of 250 g×L-1. Sucrose concentrations of both 250 g×L-1 and 300 g×L-1 are beneficial for the germination of pomegranate pollen. There was no significant difference in the number of stamens between bisexual flowers and functionally male flowers of the same cultivar. The number of stamens of Turkmenistan in fertile flowers was significantly lower than that of Suanmeiren, Mollar, Tianshihong, Zhongshiliu4 and Huaguang (P<0.05). The pollen amount of each anther of bisexual flowers (31~48) was significantly lower than that of functionally male flowers (85~91), otherwise, the pollen germination rate of bisexual flowers (90%~93%) was significantly higher than that of functionally male flowers (41%~43%). Pollen tube growth of bisexual flowers is faster than that of functionally male flowers, and the length of pollen tube is higher than that of functionally male flowers. There was no correlation between the number of stamens, the number of pollens produced by anthers and the pollen germination rate of bisexual flowers and functionally male flowers. Bisexual pollen began to germinate 12 hours after pollination, and the number of germinations was less at 24 hours, and some of the pollen had begun to grow in the flower column. By 36 hours, the bisexual pollen germinates in large quantities and extends into the flower column to grow. In contrast, functionally male pollen did not germinate at 12 h and 24 h incubation time until 36 h and 48 h, and only partial pollen germination was observed on the stigma surface, and only a very small amount of pollen was able to protrude into the columella to grow. Although functionally male flowers can accept pollen and the pollen on the stigma surface can germinate, only a few pollens can successfully reach into the flower column and elongate. The large germination of pollen from bisexual flowers at 36 h post-pollination indicates that pollen needs at least 36 h of contact time to fully interact with the flower column to ensure successful and reliable pollination. Different storage temperatures had different effects on pomegranate pollen activity, and the pollen germination rate was significantly higher at -20°C than at 4°C and 25°C. The pollen was completely inactivated after 3 days of storage at 25°C, but it could maintain pollen viability for a longer time when stored at -20°C The pollen germination rate of different varieties was different, with the highest germination rate of Tianshihong pollen being 93.3% and the lowest germination rate of Zhongshiliu4 being 82.7%.【Conclusion】There were differences in anther quality and pollen germination rate between bisexual flowers and functionally male flowers of different cultivars. But there was no significant difference in the number of stamens between bisexual flowers and functionally male flowers of the same cultivar, the functionally male flowers has a large amount of pollen but a low germination rate, the storage conditions of -20°C could maintain higher pollen viability, which provided a theoretical basis for pollen selection and storage conditions for pomegranate genetic breeding.
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