Flowering Biology of Rhododendron pulchrum

Abstract

To study the flowering biology of Rhododendron pulchrum, we used scanning electron microscopy (SEM) and paraffin sectioning to observe the microstructures of its floral organs, a methyl thiazolyl tetrazolium (MTT) colorimetric assay to detect pollen viability in different periods, continuous observations to study flowering phenology, and artificial pollination and a benzidine-hydrogen peroxide method to determine stigma receptivity. R. pulchrum exhibited a centralized flowering phenology. The protogynous stigmas of R. pulchrum were able to receive pollen before flowering. The pollen grains of R. pulchrum fused into tetrads, the average ratio of the polar axis length to the equatorial axis length (P/E) was 1.05, and the pollen viability was highest in the initial flowering period, reaching 88.98%. The pollen/ovule (P/O) ratio was 266–328, and the outcrossing index (OCI) was 4; the vitality of R. pulchrum pollen remained high in the initial flowering and blooming periods. Compared with the lifespan of a single flower, pollen vitality remained high for most of the experimental period, thereby improving male fitness. The P/O ratio suggests that R. pulchrum may have a facultative outcrossing breeding system. The OCI estimation suggests that R. pulchrum is partially self-compatible, most likely requiring pollinators to complete pollination.

Contradistinctive floral attributes, pollination guilds and their consequence on the outcrossing rate in two elevational morphs of Rhododendron arboreum Sm.

“…Although the early onset of the stigma receptivity indicates protogyny, it was incomplete, as the male and female phases overlapped considerably over the lifespan of the flower. Occurrence of incomplete protogyny has been shown in R. pulchrum Sweet ( Qiu et al., 2021 ), in contrast to R. semibarbatum Maxim., which exhibits protandry ( Ono et al., 2008 ). The continuous receptivity of the stigma across the floral life-span could be due to the selective pressure to enhance the likelihood of receiving pollen, rather than aiding in pollen dispersal which in turn determines the longevity of flowers as seen in Flame Azalea ( R. calendulaceum (Michx.)…”

Flower opening dynamics, pollen-ovule ratio, stigma receptivity and stigmatic pollen germination (in-vivo) in Chaenomeles speciosa (Sweet) Nakai

“…During the single-flower lifespan (approximately 8–10 d), the pollen had high stainability for only a short time, leading to low stamen fitness. Stigma receptivity is an important indicator of flower maturation and affects the transmission rate, self-pollination rate and gametophyte selection at different stages after flowering; furthermore, stigma strength is an important prerequisite for pollination and fertilization 45 . The stigma of C. speciosa can accept pollen even before flowering, which is manifested by the observation that the pistil matured before the stamen.…”

Influence of Sucrose, Boric Acid and Calcium Chloride on in vitro Pollen Germination and Tube Elongation of Alfalfa

“…The most suitable medium for in vitro pollen germination varies by species, or even by different flowering states to collect pollen for the same species. Hemerocallis (Qiu et al, 2021) has the highest percentage of in vitro germination occurred with the concentrations of 4 g L agar, 74.6 g L sucrose, 800 mg L boric acid and 590 mg L calcium nitrate; Passiflora spp. Orthogonal experimental design (OED) is a design method for the study of multi-factor and multi-level systems and can find the optimal level combination through a small number of experiments.…”

“…(Batos andMilj ković, 2019) (Beck-Pay, 2012). The most common external factors include incubation time, incubation temperature and storage temperature (Báez et al, 2002;Wang et al, 2021). Many plant biologists and researchers suggested that each species required different growth conditions and culture media.…”