Stigma Receptivity Research Articles

Effect of gradual pollen presentation on pollination efficiency and reproduction of Vaccinium corymbosum Berkeley in two habitats

IntroductionGradual pollen presentation is a reproductive strategy for plants to improve the efficiency and accuracy of pollen export and acceptance as well as to promote outcrossing. Vaccinium corymbosum Berkeley has a typical mechanism of gradual pollen presentation.MethodsIn this study, we used indoor and outdoor observations to investigate the floral characteristics, pollination characteristics and breeding system of this species in open ground and greenhouse.ResultsThe results showed that the single white, inverted bell-shaped flower of V. corymbosum was able to effectively avoid the negative effects of rainfall, nectar dilution and pollen removal by wind, and improved pollen viability and the duration of stigma receptivity. The setting rate of ‘Northland’ is higher than open ground by artificial pollination in greenhouse, therefore, greenhouses are more suitable for ‘Northland’ reproduction. The gradual pollen presentation prolongs dispersal time, promotes pollinator participation in the pollination process, increases staminate fitness, and provides for nectar feeding by pollinators as well as pollen export. Bombus spp. and A. m. ligustica were effective pollinators in the open ground and greenhouse, and the pollination efficiency of Bombus spp. was higher than that of A. m. ligustica, and greenhouse pollination is more efficient than open ground. The coincidence of the peak period of pollinator visits with the period of highest pollen viability and optimal pollination of stigmas, as well as the high nectar production, could maximize the frequency of pollinator visits and increase the chances of successful pollination as well as the pollination efficiency.DiscussionTherefore, it is important to study the floral characteristics of V. corymbosum Berkeley and the mechanism of gradual pollen presentation in order to improve the pollination efficiency and promote the success of outcrossing, which can provide a theoretical basis for the breeding of V. corymbosum.

Aspects of the reproductive biology of sympatric Myrtaceae: <i>Myrceugenia euosma</i> and <i>Siphoneugena reitzii</i> in southern Brazil

Background: The Myrtaceae family represents one of the most diverse groups in South America. Yet, there are few studies on their reproductive characteristics. Among the species with limited information on their reproductive behavior are Myrceugenia euosma (O. Berg) D. Legrand and Siphoneugena reitzii D. Legrand. Questions: What are the floral attractions and resources of M. euosma and S. reitzii for pollinators? Who are the pollinators of these species? What is the predominant reproductive system in both species? Studied species: M. euosma and S. reitzii, two sympatric Myrtaceae from southern Brazil. Study site and dates: Urubici, Painel, and Rio Rufino, Santa Catarina state, southern Brazil. November 2021 - February 2022. Methods: Information was obtained on morphological aspects, anthesis time, stigmatic viability, floral resources, structures attractive to visitors, olfactory testing, observation and identification of floral visitors, and reproductive system testing. Results: The flowers of M. euosma opens between 11 am and 17 pm (- 20 pm), with full opening occurring mostly at night; S. reitzii flowers open between 4 a.m. and 6 a.m., with a highest peak by 8 a.m. Flowers of both species have receptive stigmas until senescence. Pollen is the primary floral reward and the scent coming from the anthers combined with the floral display attract native bees and Apis mellifera, legitimate pollinators of both species. The lack of fruit development in the self-pollination tests support cross reproduction in both taxa. Conclusions: Both species exhibit traits consistent with melittophily syndrome and potential self-incompatibility. These results are essential for conservation efforts.

Pollen viability, stigma receptivity and reproduction mode of spineless cactus (Nopalea cochenillifera Salm-Dyck) accessions

Forage cactus (Opuntia spp. and Nopalea spp.) have great potential for animal feed and human consumption due to their adaptability to semi-arid conditions. This study evaluated six accessions of N. cochenillifera, analyzing pollen viability, stigma receptivity and reproduction mode. Four types of pollination were tested: spontaneous self-pollination, manual self-pollination, natural pollination and cross-pollination. The results indicated high pollen viability and stigma receptivity in some accessions during flower bud development, allowing for self-pollination and controlled hybridization. After 24 hours of anthesis, pollen viability decreased, but stigma receptivity reached 100%. Fruiting occurred via natural pollination in all accessions, and by self-pollination and cross-pollination in accessions ac-02 and ac-03, which showed a mixed reproductive system. These results are essential for breeding programs, contributing to sustainable agriculture in semi-arid regions.

Floral Morphological Variation in Black Pepper (Piper nigrum L.) Varieties and Hybrid Lines

The inter-variety crossing is a promising approach to increase black pepper production. However, successful hybridization hinges on floral characteristics. This study investigated the floral morphology of diverse pepper varieties and their hybrid offspring. Eighteen genotypes, including parent varieties and F1 hybrids, were cultivated in pots under greenhouse conditions at the Indonesian Spice and Medicinal Crops Research Institute, Bogor. Flower and fruit traits were observed. Results indicated variability in spike morphology. While most ripe spikes were yellowish-green, exceptions included LH 20-1 and LH 22-1. Ciinten and LH 4-5 displayed superior spike length and fruit set, contrasting with the shorter, less productive spikes of 20-1, 22-1, and 455-N2-97. Stigma receptivity and another dehiscence coincided in Ciinten, N2BK, LH 6-2, and LH 4-5, simplifying the hybridization process. Conversely, earlier stigma receptivity in Petaling 1, Petaling 2, Natar 1, Natar 2, LH 44-9, LH 20-1, and LH 22-1 facilitated castration procedures. These findings offer valuable insights for optimizing pepper breeding programs.

Pollen morphology, viability, and stigma receptivity of Hohenbergia (Bromeliaceae) species occurring in the Atlantic forest biome with potential for landscaping and cut flowers

Pollen morphology, viability, and stigma receptivity of Hohenbergia (Bromeliaceae) species occurring in the Atlantic forest biome with potential for landscaping and cut flowers

Achieving hybridisation between Miscanthus species: Commercially-scalable methods to manipulate flowering synchronisation and maximise seed yield

Miscanthus is a high-yielding lignocellulosic perennial biomass crop. The low multiplication rate of clonal rhizome propagation is a bottleneck to upscaling plantation areas of feedstock needed to supply and expand the bioeconomy. Novel seeded Miscanthus hybrids are currently being developed to overcome this bottleneck by increasing annual multiplication rates from approximately 10 to over 1000 times. We describe a series of field experiments in southern Italy using agronomic methods to optimise multiplication rates through (i) planting configurations and densities, (ii) ratio of seed parents to pollen parents (iii) supplemental pre-dawn misting to increase humidity during pollination. In these trials the seed-bearing M. sinensis started flowering 2–3 weeks earlier than the M. sacchariflorus pollen parent. Earlier experiments indicated that flowering in M. sacchariflorus was mostly determined by photoperiod while in M. sinensis it was modulated by endogenous signals. Consequently, a second set of experiments were conducted to delay flowering time in M. sinensis: (iv) mid-season stem cut back, (v) oversupply of nitrogen, and (vi) undersupply of water. Across all treatments and years, the multiplication rates varied from 140 to 1300 seeds m². Reducing the proportion of the pollen parent plants (M. sacchariflorus) from 50 % to 25 % did not reduce seed yield per plant. This therefore increases the seed yield per m² and reduces seed production upscaling costs. Flowering time and duration in M. sinensis was significantly impacted by mid-season cutting and water stress, but not by nitrogen supply rates. Mid-season shoot cutting reduced number of flowers per plant (77 %), seed quantity (47 %), seed size (46 %), and resulted in seeds with a low germination rate of 39 %. High M. sinensis planting densities produced higher seed yields in the first year. However, in subsequent years higher density plots were more susceptible to autumn lodging lowering seed production by loss of panicles. Pre-dawn misting to prolong pollen life and stigma receptivity had no significant effects on seed production. This study demonstrates the importance of flowering time synchronization in the open field for commercial seed production. The limited effect of agronomic efforts to reduce the interspecies flowering time gap emphasises the importance of genetic factors in controlling flowering time. The most impactful intervention to change flowering time and improve parental synchronisation was mid-season cutting, while this method reduced seed production when applied to the seed parent it could be ideal for pollen parents.

PENGARUH WAKTU PENYERBUKAN TERHADAP KUALITAS HASIL TANAMAN MELON (Cucumis melo L) DENGAN PERKAWINAN SILANG TANAMAN SEMANGKA (Citrullus vulgaris L)

Decreased production of melon (Cucumis melo L) which is due to constraints in fruit quality decreases due to the ability of fruit formation is naturally low due to a failure in the process of pollination. The success of pollination it self is influenced by the maturity of the male flowers and female flowers itself. Therefore we need a suitable time to perform pollination to see the stigma receptivity and pollen viability at the same level. To overcome these problems need to develop crops melon (Cucumis melo L) through the technique of cultivation is called plant breeding to obtain the production of melon (Cucumis melo L) qualified by determining the time of pollination and crossed with a watermelon (Citrullus vulgaris L). This research is experimental research design using a randomized block design (RAK) 1 factor with 5 treatment combinations and each treatment using 10 replications. The treatment factors are as follows: PA = at 05:00 to 06:00, PB = at 07:00 to 08:00, PC = at 09:00 to 10:00, PD = at 11 : 00 to 12:00 and PE = at 13:00 to 14:00. The data were collected and presented in tables and statistical analysis of test One-Way ANOVA (Analysis Of Variance). If there is a real difference followed by testing of LSD (Least Significant Difference) (p <0.05). Statistical analysis One-Way ANOVA test and LSD show that there is the influence of pollination time on the fruit weight, average fruit diameter and weight of seed resulting from cross-breeding melon (Cucumis melo L) and watermelon (Citrullus vulgaris L). Data show that the PA treatment is the best treatment compared with other treatments. This happens Because the quality of pollen in the morning are of better quality compared to during the day so that pollen powderd in the morning better able to fertilize the pistil to the maximum.

The fertility research of "Huajin 6", a new variety of honeysuckle

The aim of this study was to investigate the fertility of "Huajin 6" and the effect of exogenous methyl jasmonate on its fertility. In this study, "Huajin 6", "Huajin 6" treated with methyl jasmonate and "Damaohua" were used as the research objects, the stamen phenotypes and the shape of pollen grains were observed, pollen viability and stigma receptivity were measured. The results showed that the pistil structure and function were normal, and although the stamen anthers did not dehisce, they were still capable of producing pollen with a certain amount of vigor. Methyl jasmonate could promote the opening of the flowers of "Huajin 6" and improve the development of pollen grains to a certain extent, but it could not promote anthers dehiscence of "Huajin 6". This study can provide theoretical guidance for the cultivation of new honeysuckle varieties using "Huajin 6".

Evaluation of Blackgram (Vigna mungo L.) Genotypes for Dry Matter Partitioning, Reproductive Efficiency and Yield under High Temperature Stress

Background: In the present climate change scenario, the rising temperatures are imposing severe threat to blackgram production leading to marked reduction in yield potential.The reduction in the yield potential is mainly due to reproductive failures caused by heat stress. Keeping this in view, the present study was carried out to find out the reasons behind reproductive failures and identify the genotypes that yield better under heat stress. Methods: Thirty blackgram genotypes selected from temperature induction response technique were evaluated for reproductive efficiency under natural high temperature conditions. Field experiment was conducted at Agricultural College Farm, Acharya N.G Ranga Agricultural University, Agricultural College, Bapatla. Dry matter partitioning, reproductive efficiency and yield traits were recorded at flowering and the data were analyzed statistically and pooled. Result: Genetic variability was observed among the blackgram genotypes with respect to dry matter partitioning, reproductive efficiency and yield traits under high temperature stress conditions. Among the 30 genotypes tested for thermotolerance, the genotypes TBG-129, PU-1804 and LBG-1015 were found to withstand high temperature stress at reproductive stage by possessing higher dry matter, number of flowers per plant, pollen viability, pollen germination percentage, pollen load on stigma, stigma receptivity, flower to pod setting percentage and higher yield. Correlation analysis revealed a strong positive association of total dry matter and all the reproductive efficiency characteristics with seed yield under heat stress conditions. The PCA results revealed considerable variability among the traits accounting for 86.6% of total variability. The genotypes TBG-129, PU-1804 and LBG-1015 can be potentially used as donors in the breeding programmes for the development of heat tolerant genotypes.

Floral biology and reproductive potential of Annona hybrid Arka Sahan

Annona hybrid Arka Sahan has become a commercially important fruit in recent times and it needs an assisted pollination to get good size. Studies on floral biology of Annona hybrid Arka Sahan revealed that major bloom occurs during March-April. Most of the flowers start opening during the afternoon and continued till 7.00 pm, while, pollen dehiscence mainly occurred in early morning in the following day. The maximum stigma receptivity was recorded on the day of anthesis. Completely pendulous petal was more common in Arka Sahan flowers resulting = improper pollination. The minimum number of beetles and bees were observed between 7.00 to 8.00 am. Pollen germination and viability were lower at anthesis (5.8% and 44%, respectively) and declined as the day progressed. The pendulous nature of petals eventually brings some un-pollinated stigmas potentially resulting in delayed selfing leading to misshaped fruits.

Floral biology and reproductive potential of Annona hybrid Arka Sahan

Annona hybrid Arka Sahan has become a commercially important fruit in recent times and it needs an assisted pollination to get good size. Studies on floral biology of Annona hybrid Arka Sahan revealed that major bloom occurs during March-April. Most of the flowers start opening during the afternoon and continued till 7.00 pm, while, pollen dehiscence mainly occurred in early morning in the following day. The maximum stigma receptivity was recorded on the day of anthesis. Completely pendulous petal was more common in Arka Sahan flowers resulting = improper pollination. The minimum number of beetles and bees were observed between 7.00 to 8.00 am. Pollen germination and viability were lower at anthesis (5.8% and 44%, respectively) and declined as the day progressed. The pendulous nature of petals eventually brings some un-pollinated stigmas potentially resulting in delayed selfing leading to misshaped fruits.

Morphology, Reproductive Biology and Anatomy of the Foxtail Orchid, Rhynchostylis retusa (L.) Blume

Background: Rhynchostylis retusa (L.) Blume, commonly known as the fox-tail orchid, is a promising epiphytic native species for breeding programs. Its’ population is diminishing in the native habitat due to unscrupulous overexploitation and habitat destruction. Hence, conservation of this species attains prime importance. To achieve the foregoing task, phenotypic traits in relation to adaptation are to be elucidated. Methods: In the present investigation, the morphological characters were documented and the correlation between each trait was determined. Furthermore, the anatomy of leaves and roots was documented, as was the stomatal structure and distribution on the abaxile and adaxile surfaces of the leaves. Biometric features of floral characters and reproductive biology such as anthesis, stigma receptivity, pollen production per pollinium, pollen viability, pollination mechanisms, self and cross-compatibility; male sterility, etc. were studied and documented. Observations on capsule development, nature of seeds, seed viability, etc. were also determined. Result: The seed viability tests revealed that about 40% of the seeds are viable. The observations gathered during this investigation can be used to develop conservation, sustainable utilization and genetic improvement strategies for this crop.

Effects of ecological factors on the pollination biology and seed production of Salvia daiguii: A critically endangered ornamental species from China

Salvia constitutes one of the largest genera in the Lamiaceae, with approximately 1,000 species found worldwide, and is recognized for its high ornamental and medicinal value. Salvia daiguii is a multipurpose perennial herb that grows on cliffs in the Zhangjiajie City, Hunan Province, China. Nevertheless, the pollination biology of vulnerable plants on cliffs, specifically the effects of abiotic factors on flower visitation and seed set, remains poorly understood. In this study, we observed the effects of biotic factors: flowering phenology and flower characteristics, flower longevity, nectar volume and concentration, pollen viability and stigma receptivity, pollinator visitation frequency, pollen remaining and deposition, and breeding systems, as well as abiotic factors: habitat fountain, temperature, and humidity, on the pollination and seed production of S. daiguii in two populations in Zhangjiajie City. The pollination biology results reveal that S. daiguii has a mixed mating system that depends on pollinators. The flower visitation and seed set of S. daiguii in the absence of natural fountain areas in Tianmenshan National Forest Park was scarcely affected by biotic factors. However, we observed a significant reduction in pollinator types, visitation frequency, and natural seed set of this population owing to abiotic factors, including the presence of a fountain habitat and increased humidity. Further, seed set in the Zhangjiaxi Ecological Forest Reserve was affected by both biotic (serious pollen limitation) and abiotic (higher population temperature) factors. We considered that pollinators types, flower visitation frequency, and natural seed set are vulnerable to the influence of ecological factors in fragmented habitats. Our results reveal the mechanisms contributing to the endangerment of species exemplified by S. daiguii and underscore the significance of conservation efforts for the sustainable use of other endangered species.

Analyses of the sexual reproductive traits for conservation and sustainable utilization of Dactylorhiza hatagirea – A critically endangered medicinal orchid of North-western Himalaya

To undertake scientifically appropriate management and conservation practices, understanding the reproductive biology of endemic and threatened species is critical. Dactylorhiza hatagirea is an important medicinal plant whose reproductive strategies and adaptive evolution mechanisms are still not fully clear. The present study was conducted in the North-western Himalaya of India to understand the reproductive biology, breeding system and pollination ecology of D. hatagirea; an endemic and critically endangered orchid. It is a perennial herb that grows along the altitudinal gradients of 2100–3107 m.a.s.l. and overcomes harsh winters through underground perrenating tubers. The flowering commences from May to July and the flowers are completely zygomorphic with male and female reproductive organs fused to constitute gynostemium. Analysis of variance (ANOVA) show significant statistical difference (p < 0.05) between the floral traits for most of the characters. Each flower bears two dark green colored pollinaria with an average of 212.14 ± 14.4 pollinia. Pollen occur as tetrads and polyads in massulae and their viability was greater than 95 ± 4.2 %. Stigma receptivity was confirmed on the day of anthesis and reaches its peak on 5–6th day. Cruden outcrossing index (5), asynchronous anthesis, conspicuous inflorescences, nectaries, presence of rostellum and herkogamy points towards outcrossing nature while pollen ovule ratio (1.27 ± 0.4) and the greater value of self-incompatibility (0.9) reflect that plants are potent cross-breeders. Pollination treatments significantly impacted seed set in D. hatagirea (one-way ANOVA; F = 23.14; p = 0.001) with an average seed set of 92.75 % ± 0.95 for manual xenogamy (p < 0.01), 89.5 % ± 2.38 for geitonogamy (p < 0.01) and 17 % ± 2.2 for bagged inflorescences (p<0.05). Pollination syndrome is exclusively entomophilly. Insignificant difference was reported in the timining for the insect visitation to flowers (calculated value = 3.4; critical value = 5.1; p < 0.01), however different environmental factors created a significant impact on the frequency of insect visitation (calculated value = 9.7; critical value = 4.3; p < 0.01). Apis cerana, Apis mellifera and Bombus asiaticus show highest pollination indices (p < 0.01) and were characterized as dominant pollinators. This study provides a detailed explanation and substantial understanding regarding operative reproductive mechanism of this threatened medicinal plant and can be used by conservation biologists to develop holistic and effective conservation strategies and address the unique challenges that this threatened species face in the wild.

The genetic control of herkogamy.

Herkogamy is the spatial separation of anthers and stigmas within complete flowers, and is a key floral trait that promotes outcrossing in many angiosperms. The degree of separation between pollen-producing anthers and receptive stigmas has been shown to influence rates of self-pollination amongst plants, with a reduction in herkogamy increasing rates of successful selfing in self-compatible species. Self-pollination is becoming a critical issue in horticultural crops grown in environments where biotic pollinators are limited, absent, or difficult to utilise. In these cases, poor pollination results in reduced yield and misshapen fruit. Whilst there is a growing body of work elucidating the genetic basis of floral organ development, the genetic and environmental control points regulating herkogamy are poorly understood. A better understanding of the developmental and regulatory pathways involved in establishing varying degrees of herkogamy is needed to provide insights into the production of flowers more adept at selfing to produce consistent, high-quality fruit. This review presents our current understanding of herkogamy from a genetics and hormonal perspective.

The reproductive biology of &lt;em&gt;Marathrum rubrum Novelo &amp; C. T. Philbrick&lt;/em&gt;: morphological and anatomical changes during flower development

Background: Podostemaceae is the largest family of strictly aquatic angiosperms. Species of this family possess unusual morphological and reproductive characters, grow attached to rocks in rivers with strong currents, and have a life cycle tightly linked to seasonality. Due to its reduced floral structures, which characterizes most species, the analysis of developmental stages and events such as anthesis or stigma receptivity has proven difficult.&#x0D; Question: How floral morphology, floral development and stigma receptivity of different stages of flower development of Marathrum rubrum Novelo &amp; C. T. Philbrick are related among them?&#x0D; Studied species: Marathrum rubrum Novelo &amp; C. T. Philbrick.&#x0D; Study site and dates: Horcones River, Jalisco, Mexico. January, 2014 and 2015.&#x0D; Methods: We made an in situ and lab analyses of flower morphology to assess the relationships between flower morphology, stages of development, reproductive structures, and stigma receptivity, during different stages of flower development.&#x0D; Results: When flowers emerge from the spathella, both the ovules and pollen grains are fully developed, implying that sporogenesis and gametogenesis take place within the stem while the plant is still submerged.&#x0D; Conclusions: The morphological changes observed in the flowers of M. rubrum during the analyzed stages are related only to events associated with fertilization and fruit development. The time-course of morphological changes in the flowers, from anthesis to fruit formation, lasts 20 to 30 days. The detailed observation of the aerial reproductive biology of M. rubrum bears important implications to the genetic structure of populations, plant fitness and conservation biology in threatened environments.

First evidence of late-acting self-incompatibility in the Aristolochiaceae.

Most Aristolochiaceae species studied so far are from temperate regions, bearing self-compatible protogynous trap flowers. Although self-incompatibility has been suggested for tropical species, the causes of self-sterility in this family remain unknown. To fill this gap, we studied the pollination of the tropical Aristolochia esperanzae, including the physical and physiological anti-selfing mechanisms. Floral visitors trapped inside flowers were collected to determine the pollinators. Protogyny was characterized by observing the temporal expression of sexual phases and stigmatic receptivity tests. The breeding system was investigated using hand-pollination treatments. Pollen tube growth was observed using epifluorescence to identify the self-incompatibility mechanism. Flies were the most frequent visitors found inside A. esperanzae trap flowers, with individuals from the family Ulidiidae being potential pollinators since they carried pollen. The characteristic flower odour and presence of larvae indicate that A. esperanzae deceives flies through oviposition-site mimicry. Although this species showed incomplete protogyny, stigmatic receptivity decreased during the male phase, avoiding self-pollination. Fruits developed only after cross- and open pollination, indicating that the population is non-autonomous, non-apomictic, and self-sterile. This occurred through a delay in the growth of geitonogamous pollen tubes to the ovary and lower ovule penetration, indicating a late-acting self-incompatibility mechanism. Our findings expand the number of families in which late-acting self-incompatibility has been reported, demonstrating that it is more widespread than previously thought, especially when considering less-studied tropical species among the basal angiosperms.

Pollination of thermogenic inflorescence of Pandanus odorifer by a specialist Amystrops sap beetle that reproduces on the male inflorescence

Abstract Pandanus is a morphologically unique plant group of the Paleotropical flora, with approximately 450 known species occupying diverse habitats. Because the male inflorescences of this genus are pendent and nectarless, they are commonly assumed to be wind-pollinated; however, their floral scent coupled with the observation that female inflorescences mature while still covered by bracts suggest the possibility of an alternative pollination mechanism. We studied the pollination system of Pandanus odorifer in subtropical Japan. A peroxidase assay was conducted to determine the timing of stigma receptivity, which showed that the stigmas were sensitive to peroxidase while the female inflorescences were covered by bracts. We found numerous pollen-bearing adult beetles of the genus Amystrops on both male and female inflorescences. Nitidulid larvae were also found on male inflorescences, and the larvae became adults of the same Amystrops species as found on the inflorescences by feeding only on Pandanus pollen. Last, floral temperature was monitored to test for floral thermogenesis. Both male and female inflorescences were thermogenic at night when insect visitation occurred. This study provides the first examples of insect pollination and floral thermogenesis in Pandanaceae. Most known Amystrops species are associated with Pandanus inflorescences, suggesting a widespread, specialized Pandanus–Amystrops association.

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

Although Chaenomeles is widely used in horticulture, traditional Chinese medicine and landscape greening, insufficient research has hindered its breeding and seed selection. This study investigated the floral phenology, floral organ characteristics, palynology, and breeding systems of Chaenomeles speciosa (Sweet) Nakai. The floral characteristics of C. speciosa were observed both visually and stereoscopically. The microstructures of the flower organs were observed using scanning electron microscopy. Pollen stainability was determined using triphenyl tetrazolium chloride staining. Stigma receptivity was determined using the benzidine-H2O2 method and the post-artificial pollination pollen germination method. The breeding system was assessed based on the outcrossing index and pollen–ovule ratio. The flowers of C. speciosa were bisexual with a flowering period from March to April. The flowering periods of single flowers ranged from 8 to 19 d, and those of single plants lasted 18–20 d. The anthers were cylindrical, with the base attached to the filament, and were split longitudinally to release pollen. The flower had five styles, with a connate base. The ovaries had five carpels and five compartments. The inverted ovules were arranged in two rows on the placental axis. The stigma of C. speciosa was dry and had many papillary protrusions. In the early flowering stage (1–2 d of flowering), the pollen exhibited high stainability (up to 84.24%), but all stainability was lost at 7 d of flowering. Storage at – 20 °C effectively delayed pollen inactivation. The stigma receptivity of C. speciosa lasted for approximately 7 days, and the breeding system was classified as outcrossing with partial self-compatibility.

The reduced growth due to elevated CO2 concentration hinders the sexual reproduction of mature Northern pipevine (Aristolochia contorta Bunge).

The phenology has gained considerably more attention in recent times of climate change. The transition from vegetative to reproductive phases is a critical process in the life history of plants, closely tied to phenology. In an era of climate change, understanding how environmental factors affect this transition is of paramount importance. This study consisted of field surveys and a greenhouse experiment on the reproductive biology of Northern pipevine (Aristolochia contorta Bunge). During field surveys, we investigated the environmental factors and growth characteristics of mature A. contorta, with a focus on both its vegetative and reproductive phases. In its successful flowering during the reproductive phase, A. contorta grew under the conditions of 40% relative light intensity and 24% soil moisture content, and had a vertical rhizome. In the greenhouse experiments, we examined the impact of increased CO2 concentration on the growth and development of 10-year-old A. contorta, considering the effect of rhizome direction. Planted with a vertical rhizome direction, A. contorta exhibited sufficient growth for flowering under ambient CO2 concentrations. In contrast, when planted with a horizontal rhizome direction, it was noted to significantly impede successful growth and flowering under elevated CO2 concentrations. This hindered the process of flowering, highlighting the pivotal role of substantial vegetative growth in achieving successful flowering. Furthermore, we observed a higher number of underground buds and shoots under the conditions of elevated CO2 concentration and a horizontal rhizome direction instead of flowering. Elevated CO2 concentrations also exhibited diverse effects on mature A. contorta's flower traits, resulting in smaller flower size, shorter longevity, and reduced stigma receptivity, and pollen viability. The study shed light on elevated CO2 concentrations can hinder growth, potentially obstructing sexual reproduction and diminishing genetic diversity.