Stigmatic Surface Research Articles

Synthesis of aspartic acid and tyrosine by the fire blight pathogen Erwinia amylovora is not required for proliferation on apple flower stigmas or virulence in fruitlets.

The Gram-negative bacterium Erwinia amylovora (Ea) is the causal agent of fire blight, a devastating disease of apples and pears. In the fire blight disease cycle, Ea grows in different plant tissues, each presenting a distinct nutrient environment. Here, we investigate the ability of aspartate and tyrosine double auxotroph Ea lines to proliferate on apple flower stigma surfaces representing the epiphytic growth stage of Ea and in developing fruitlets representing one endophytic growth stage of Ea. Heterologous complementation studies in an Escherichia coli aspartate and tyrosine auxotroph verify that Ea aspartate aminotransferase (AspC) and tyrosine aminotransferase (TyrB) act as aspartate and tyrosine amino transferases. Growth analysis reveals that Ea aspC tyrB mutants multiply to near-wild-type levels on apple flower stigmas and immature fruitlets. Ea AspC and TyrB are reciprocally complementing for aspartate and tyrosine synthesis in Ec and in Ea. Ea aspC and tyrB mutants obtain sufficient aspartate and tyrosine to support multiplication on stigma surfaces and virulence in immature fruitlets.

Transcriptome Analysis of Stigmas of Vicia faba L. Flowers.

Pollination in angiosperms depends on complex communication between pollen grains and stigmas, classified as wet or dry, depending on the presence or absence of secretions at the stigma surface, respectively. In species with wet stigma, the cuticle is disrupted and the presence of exudates is indicative of their receptivity. Most stigma studies are focused on a few species and families, many of them with self-incompatibility systems. However, there is scarce knowledge about the stigma composition in Fabaceae, the third angiosperm family, whose stigmas have been classified as semidry. Here we report the first transcriptome profiling and DEGs of Vicia faba L. styles and stigmas from autofertile (flowers able to self-fertilize in the absence of manipulation, whose exudate is released spontaneously) and autosterile (flowers that need to be manipulated to break the cuticle and release the exudates to be receptive) inbred lines. From the 76,269 contigs obtained from the de novo assembly, only 45.1% of the sequences were annotated with at least one GO term. A total of 115,920, 75,489, and 70,801 annotations were assigned to Biological Process (BP), Cellular Component (CC), and Molecular Function (MF) categories, respectively, and 5918 differentially expressed genes (DEGs) were identified between the autofertile and the autosterile lines. Among the most enriched metabolic pathways in the DEGs subset were those related with amino acid biosynthesis, terpenoid metabolism, or signal transduction. Some DEGs have been related with previous QTLs identified for autofertility traits, and their putative functions are discussed. The results derived from this work provide an important transcriptomic reference for style-stigma processes to aid our understanding of the molecular mechanisms involved in faba bean fertilization.

Reproductive biology of Capparis decidua (Kair): A potential underutilized multipurpose plant of arid and semi arid region

Foliation and flowering of Capparis decidua occurs three times a year i.e. from January to November months. Flowers are bracteate, pedicellate, complete, hermaphrodite, zygomorphic, hypogynous with slender pedicel, usually light red, scarlet red and yellow in colour. Anthesis was maximum between 4.00 p.m. to 8.00 PM and 6.00 to 10.00 AM. Pollen grains are prolate, tricolporate, trilobed, with costae, colpal membrane sparsely granulated. Anther dehiscence takes place after 20–30 minutes of anthesis at 6.00 to 8.00 PM by the time the flowers starts antehsizing, the anthers are almost mature. The viability of pollen grains ranges from 38–52%, and starts decreasing in the stored pollen. The percentage fruit set decreases with the collection time of the pollen grains and plant type. According to visual observation stigmatic surface change in the appearance i.e. green coloured stigma was considered receptive while dull and brown was accounted non-receptive. Pollen germination in-vivo showed 80 per cent stigma receptive and 90 percent of fruit set in the flowers pollinated on the time of anthesis. Pollen grains per anther were ranging from 331–369, fully developed and mature anthers differing significantly among the plant types. The mean number of pollen grains per ovule was 4309 thus the pollen-ovule ratio was 431:1. There is 17–23% fruit set observed under self pollination (autogamy and geitonogamy) and 52–72% as a result of cross pollination. The cross pollinated nature of C. decidua is due to entomophilic nature of flowers, insect visitors which play the main role of pollination are from Apidae and Papilionidae.

Unlocking a ‘lock–key’ mechanism governing pollen–pistil interactions

Pollen–pistil interactions ensure genetic diversity and shape the reproductive success of plants. Lan et al. recently revealed that the interaction among various receptor-like kinases, cell-wall proteins, and stigmatic RALF peptides (sRALFs) or pollen RALF peptides (pRALFs) on the stigma surface govern the penetration of pollen tubes in members of the Brassicaceae.

Synergid cell calcium oscillations refine understanding of FERONIA/LORELEI signaling during interspecific hybridization

Key messagePollen tubes from closely related species and mutants lacking pollen tube MYB transcription factors are able to initiate FER/LRE-dependent synergid cell calcium oscillations.Reproductive isolation leads to the evolution of new species; however, the molecular mechanisms that maintain reproductive barriers between sympatric species are not well defined. In flowering plants, sperm cells are immotile and are delivered to female gametes by the pollen grain. After landing on the stigmatic surface, the pollen grain germinates a polarized extension, the pollen tube, into floral tissue. After growing via polar extension to the female gametes and shuttling its cargo of sperm cells through its cytoplasm, the pollen tube signals its arrival and identity to synergid cells that flank the egg. If signaling is successful, the pollen tube and receptive synergid cell burst, and sperm cells are released for fusion with female gametes. To better understand cell–cell recognition during reproduction and how reproductive barriers are maintained between closely related species, pollen tube-initiated synergid cell calcium ion dynamics were examined during interspecific crosses. It was observed that interspecific pollen tubes successfully trigger synergid cell calcium oscillations—a hallmark of reproductive success—but signaling fails downstream of key signaling genes and sperm are not released. This work further defines pollen tube–synergid cell signaling as a critical block to interspecific hybridization and suggests that the FERONIA/LORELEI signaling mechanism plays multiple parallel roles during pollen tube reception.

Stigmas of holoparasitic Phelipanche arenaria (Orobanchaceae) – a suitable ephemeric flower habitat for development unique microbiome

BackgroundMicrobial communities have occasionally been observed in part of the ephemeric reproductive structure of floral stigmas, but their prevalence, phylogenetic diversity and ecological roles are understudied. This report describes the first study of bacterial and fungal communities in immature and mature stigma tissue of the endangered holoparasitic plant Phelipanche arenaria. Culture-dependent methods coupled with next-generation sequencing indicated that a small surface of the flower stigma was an unexpectedly rich and diverse microhabitat for colonization of microbial. We also compared the enzymatic activity of the bacterial communities between immature and mature stigmas samples.ResultsUsing high-throughput sequencing methods, we identified and classified 39 to over 51 OTUs per sample for bacterial OTUs represented by Pantoea agglomerans and P. ananatis, comprising 50.6%, followed by Pseudomonas, Luteibacter spp., Sphingomonas spp. with 17% of total frequency. The bacterial profile of immature stigmas of P. arenaria contained unique microorganisms (21 of the most numerous OTUs) that were not confirmed in mature stigmas. However, the enzymatic activity of bacteria in mature stigmas of P. arenaria showed more activity than observed in immature stigmas. In the fungal profile, we recorded even 80 OTUs in mature stigmas, consisting of Capnodiales 45.03% of the total abundance with 28.27% of frequency was created by Alternaria eichhorniae (10.55%), Mycosphaerella tassiana (9.69%), and Aureobasidium pullulans (8.03%). Additionally, numerous putative plant growth-promoting bacteria, fungal pathogens and pathogen-antagonistic yeasts were also detected.ConclusionsOur study uncovered that P. arenaria stigmas host diverse bacterial and fungal communities. These microorganisms are well known and have been described as beneficial for biotechnological and environmental applications (e.g., production of different enzymes and antimicrobial compounds). This research provided valuable insight into the parasitic plant–microbe interactions.

Aspidistra shimentaiensis (Asparagaceae), a new species from Guangdong, China

Aspidistra shimentaiensis, a new species of Asparagaceae from Guangdong, southern China, is described and illustrated. The new species is similar to A. nankunshanensis, but differs by the narrowly lanceolate leaf blade, purplish red pistil, slightly convex upper surface of stigma with a white triangular speckle and three inconspicuous Y-shaped wavy lines at center. Colour plates of the two similar species are provided for comparison.

Reproductive systems and hybridization of Lymania species (Bromeliaceae) endemic to Northeast Brazil threatened with extinction

Reproductive systems among the Bromeliaceae family are very diverse at the species level, including allogamous, autogamous, cleistogamous, agamospermic or mixed plants. Hybridization allows the creation of new genotypes with different combinations of shapes and colors to meet the ornamental plant market's demand for novelty. Knowing the reproductive strategies of the species makes it possible to obtain these new materials with ornamental potential, in addition to being essential to define better conservation strategies. Little is known about the reproductive biology of Lymania species. In addition, at least 60% of these species are on the Brazilian National List of Species Threatened with Extinction. The purpose of this study was to identify the reproductive systems, the possible interspecific hybridizations, and the possible reproductive barriers of nine Lymania species based on the germination of pollen grains and the corresponding growth of the pollen tube in the pistil by using fluorescence microscopy with ultraviolet filtering. Natural and controlled pollinations of the nine species were carried out. The reproductive strategy was defined according to the autogamy index (AI), self-incompatibility index (SII), and reproductive efficiency index (REI). All species were self-incompatible except for L. smithii, which was autogamous. Agamospermy was not observed in any of the studied species. Forty-one hybridization combinations between species were performed, resulting in a 54% success rate, with incongruity in only 12 combinations. The main incongruence phenomena identified after interspecific crosses were: poor germination of pollen grains on the stigma surface; inhibition of pollen tube growth along the style; coiling of pollen tubes along the style; pollen tubes inside the ovary but without penetration into the micropyle; and reticulate deposition of callose in the pollen tube, among others. We suggest that self-incompatibility of the species is gametophytic, preventing self-fertilization. Results showed that it is possible to perform hybridization with some species. However, morphological, genetic, and molecular studies are needed to confirm the potential of these species. Seeds generated in the different reproductive systems, as well as in the hybridizations, had germination rates above 94%. The results presented here make important contributions to the conservation of species, seed generation, and hybridization of Bromeliaceae.

Effect of elevated temperature on the rate of flowering anthesis and seed set in Olea ferruginea

Plant reproduction and climate are strongly correlated with each other in various aspects, as climate change is the main cause of biotic and abiotic stresses, which adversely affect plant reproductive biology. We conducted a field experiment over two consecutive years to record how warming temperature affects flowering anthesis within inflorescence and the relationship between the flowers with anther dehiscence before anthesis (ADBA) and fruit set with maximum and minimum temperature in Olea ferruginea. The results of linear regression analysis show that there is increase in the rate of ADBA by 0.846 times per unit increase in maximum temperature and 0.789% per unit increase in minimum temperature. Also, there is decrease in fruit set by 0.933% and 0.743% when compared with maximum and minimum temperature respectively. The fruit set was found to be decreased by 0.81% when flowers undergo ADBA. Since the species is self-incompatible, cross pollination and pollen germination becomes impossible after anthesis due to the presence of self-pollen on the stigmatic surface. Our study results suggest that temperature fluctuations could affect rate of anthesis in flowering and reduce seed production under higher temperature. Thus, the impacts of climate extremes on plant life cycles may be as influential as gradual warming. In particular, it appears that throughout the anthropocene, temperature regime fluctuation had a bigger impact on flowering dynamics.

The fertilization process in Lithocarpus dealbatus (Fagaceae) and its implication on the sexual reproduction evolution of Fagales.

The pistillate flowers of Lithocarpus dealbatus show two pollen tube (PT) arresting sites (the style-joining and micropyle) within the pistil during the postpollination-prezygotic stage. The PT, arrested at the pre-ovule stage, enhanced PT competition allowing the most compatible PTs to enter the ovary to ensure the highest fertilization success. During the shift from animal pollination to wind pollination, plants require a series of changes in reproductive traits. The mode of pollination is striking labile in Fagaceae. Lithocarpus is insect pollinated and is closely related to wind-pollinated Quercus. Little is known about the sexual reproduction of Lithocarpus. This study aimed to reveal the sexual reproduction of Lithocarpus dealbatus and to explore the evolutionary pattern of the key sexual reproduction traits to better understand their possible role in labile pollination. We found that after pollination, L. dealbatus PTs grew slowly in the style reaching style-joining in mid-January of the second year; then PT growth was arrested at style-joining for four months. Only two to three PTs resumed growth in mid-May to reach the micropyle, where PT growth ceased for one month before one PT resumed growth and passed through the micropyle to the embryo sac. Fagaceae showed a generalized mating system. Vast pollen production, small-sized pollen grains, long stigmatic receptive time, and reduced perianth were compatible with beetle pollination syndrome, representing the plesiomorphic status in Fagaceae. A large stigmatic surface and dry pollen grains linked to wind pollination might be independently derived several times in fagaceous lineages. Beetle pollination syndrome can cope with the uncertainty of pollinators to ensure conspecific pollen capture, which represents pre-adaptation status and has a selective advantage when conditions change, favouring wind pollination. The arrest of the PT at style-joining is a unique mechanism in later derived fagaceous lineages to enhance PT competition and promote outcrossing.

Parallel developments in floral adaptations to obligate moth pollination mutualism in tribe Phyllantheae (Phyllanthaceae).

Several groups within tribe Phyllantheae (Phyllanthaceae) formed, independently, an (obligate) pollination mutualism with Epicephala moths, which originally had been parasitic. In this pollination system, female moths actively collect pollen from staminate flowers and deposit it on the stigma of pistillate flowers, after which they place at least one egg in or against the ovary. The high pollination rate makes the system beneficial for the plants, whereas the larvae are provided with food (part of the developing seeds) and some protection against predation. Qualitative comparisons are made between non-moth-pollinated lineages, used as outgroups and various, independently moth-pollinated Phyllantheae clades, used as ingroups, thereby looking for parallel developments. The flowers of both sexes of various groups display similar, convergent morphological adaptations to the pollination system, likely to secure the obligate relationship and to improve efficiency. Sepals in both sexes, free or partly to highly connate, are commonly upright and form a narrow tube. The staminate flowers often have united, vertical stamens with the anthers along the androphore or on top of the androphore. Pistillate flowers generally reduce the stigmatic surface, either by making the stigmas shorter or by uniting them into a cone with a small opening at the top for pollen deposition. Less obvious is the reduction of the stigmatic papillae; these are often present in non-moth-pollinated taxa, but absent in the moth-pollinated species. The most diverging, parallel adaptations to moth pollination are currently found in the Palaeotropics, whereas in the Neotropics, some groups continue to also be pollinated by other insect groups and are morphologically less changed.

Active pollination in a functionally dioecious Ficus species: An interplay between pollinator behaviour and floral morphology

Active pollination has evolved four times in brood site pollination mutualisms. When pollination is active, the pollinator's behaviour specifically evolves to ensure flower fertilisation. In functionally dioecious Ficus species, the male figs host pollinating wasp larvae, while wasps cannot breed in the female figs because the styles are longer than the wasp ovipositor. Here we investigate the dioecious Ficus hispida. We show that in male figs, every time the wasp has laid an egg into a pistillate flower, it removes one pollen grain from its pollen pockets and places it on the hypopygium. When the wasp inserts its ovipositor into the next flower, the pollen grain is deposited deep within the style. Each ovipositor insertion results in flower pollination and insect oviposition. Because of systematic pollination of the flowers into which the eggs are laid, the wasp larvae benefit from feeding on fertilised endosperm while no seed are produced. In female figs, after probing a flower, the wasp presents pollination behaviour only every five visits. However, if it does occur, this behaviour lasts longer than in male figs and results in the deposition of on average 10 pollen grains on the hypopygium. The exposed sticky papillae on the stigmatic surface collect pollen from the hypopygium and pollen tubes may grow to neighbouring stigmas, ensuring secondary dispersal and efficient ovule fertilisation. Overall, our study demonstrates that the floral morphology of male figs facilitates precise pollen deposition, beneficial for the wasp progeny, while the floral morphology of female figs compensates for wasp pollination behaviour that is not selected in those figs. We conclude that the morphology of the arena in which interactions with its pollinator are played out is the result of selection on the plant to maximize its male and female fitness. Incidentally, this morphology stabilises the mutualistic interaction.

Estratégias para os próximos ciclos do melhoramento intrapopulacional do maracujazeiro-azedo

ABSTRACT In breeding programs, the identification of genetic variability and knowledge of genetic constitutions existing within segregating populations are of fundamental importance for the success and continuation of the program. The present study aimed to quantify the genetic diversity among progenies of a sour passion fruit population based on morphoagronomic variables of flowers and fruits using the Ward-MLM (modified location model) procedure, which was efficient in quantifying genetic diversity and allowed the identification and consistent formation of three groups within the population. Among the groups formed, group I presented the highest means for the variables related to flowers, group II presented the highest values for the variables related to yield, and group III presented the highest means for the variables related to fruit quality. The androgynous length, nectariferous chamber length, anther surface, nectareous chamber length, and stigma surface were the variables that most contributed to the divergence between the evaluated genotypes. Crosses between groups II and III genotypes are promising for the next cycle, contributing to increased production and improvement of the physical and chemical quality of fruits.

Gynoecium structure and pollen tube pathway in the cactus family with emphasis on tribe Trichocereeae (Cactaceae: Cactoideae)

Abstract The structural details of the gynoecium are key to understanding the reproductive systems and successful diversification of flowering plants. However, the gynoecium morpho-anatomy in South American species of Cactaceae that evolved in the Andean region remains largely unknown. Here we selected 18 species, most of them of evolutionarily related genera of Cactaceae tribe Trichocereeae, to conduct a detailed comparative study. Observations were made using light, fluorescence, differential interference contrast and scanning electron microscopy. Most of the characters of the ovary and ovule were typical of the family, except for the nucellar beak in Echinopsis aurea and E. haematantha, here reported for the first time in cacti. We found evidence suggesting that the stigmatic surface covered with multiseriate trichomes, the semi-closed style type and the pollen tube transmitting tract are conserved characters among species of Trichocereeae; this finding may be explained by a phylogenetic conservatism of the investigated genera of the tribe. We integrated the available information about structural and histological characters of the gynoecium in the family, taking into account the current phylogenetic context of the examined genera. Our results reinforce the significance of floral anatomical traits for the systematics of Cactaceae.

Development of Quercus acutissima (Fagaceae) pollen tubes inside pistils during the sexual reproduction process.

Extensive histology of pistillate flowers revealed two pollen tube arresting sites (the style-joining and micropyle) within the pistil of Quercus acutissima during the postpollination-prezygotic stage, which reflects a unique female and male gametophyte recognition/selection mechanism. Sexual reproduction is among the most delicate and essential stages in plant life cycles and involves a series of precise interactions between pistils and male gametophytes. Quercus is a woody genus that dominates Northern Hemisphere forests and is notorious for interspecific hybridization, but its sexual reproduction is poorly understood, especially its pollen tube (PT) growth dynamics within pistils. This study used microtome techniques and scanning electron microscopy to observe the postpollination-prezygotic process in the biennially fruiting oak Quercus acutissima. Many pollen grains germinated at anthesis instantly, and PTs penetrated stigmatic surfaces and elongated through the stylar transmitting tissue, then arrested at style-joining for about 12-13months. Few PTs resumed growth along the compitum in the upper ovarian locule wall in the subsequent April, concurrent with the rapid growth of rudimentary ovules. PTs arrived in the micropyle, and upper septum during megaspore mother cell meiosis, then arrested again for 7-10days waiting for the embryo sac maturation. Fertilization occurred one week later. Our study shows a clear female dominant crosstalk growth pattern between PT and the ovule. The intermittent PT growth might reflect a unique male gametophyte recognition/selection mechanism to avoid self-pollination and enhance PT competition while increasing interspecific hybridization.

Light and scanning electron microscopy observations on morphological diversity of Rosaceae stigma and its taxonomic significance

The stigma morphology can provide a reference for exploring plant systematics and pollination biology. In this study, we observed the stigma morphological characteristics of Rosaceae in Beijing urban area in detail using light microscopy and scanning electron microscopy. The stigma of Rosaceae is entire or bilobed and mostly baculate, crateriform, cristate, discoid, or flattened. The stigma surface may have irregular, strongly raised ridges; or flat without papillae; or composed of densely or loosely arranged papillary cells. Surface ornamentation includes fossulate, psilate, psilate-striate, rugulate, scabrate, striate, and striate-rugulate. There are similarities in stigma morphology among genera and differences in stigma morphology among species within genera. The stigma shape supports the view of molecular systematic classification, that is, the former subfamilies Maloideae, Prunoideae, and Spiraeoideae are grouped into subfamily Amygdaloideae. RESEARCH HIGHLIGHTS: Scanning electron microscopy (SEM) was used to provide high-quality figures for observing stigma morphology. The data on the morphological diversity of stigma were provided to further explore the systematics and pollination biology of Rosaceae.

Fine‐tuned spatiotemporal dynamics of sporophylls in movement‐assisted dichogamy: A study on Clerodendrum infortunatum

AbstractHermaphroditism is cost‐effective because a common investment in reward and attractive structures yields benefits through both male and female reproductive success. However, the advantage is accompanied by an increased risk of self‐pollen deposition, which is generally disadvantageous. Hermaphroditic plants reduce self‐pollen deposition by separating sporophylls (a term applied to the stamens and carpels) either spatially (herkogamy) or temporally (dichogamy). In movement‐assisted dichogamy, both sporophylls show coordinated motion in opposite directions. However, the effectiveness of this movement in reducing self‐pollen deposition may be compromised at the point when the sporophylls cross each other and are close enough to interfere, resulting in a transition phase problem. The solution to this problem lies in the details of the spatiotemporal dynamics of the sporophylls in relation to their reproductive maturity. We studied these details across the floral lifetime of a protandrous shrub, Clerodendrum infortunatum (Lamiaceae), in rainforest fragments of the Western Ghats, India. We took photos of flowers at regular time intervals and measured sporophyll angles from the images. We also carried out a field experiment to determine stigma receptivity. We found that the stigma lobes remained narrowly opened at transition, and the stigma surfaces remained non‐receptive. Our findings suggest that the effectiveness of dichogamy is maximized through two properties of the transition phase: physical resistance to self‐pollen deposition by narrow stigma lobe opening and chemical non‐receptivity of the stigma during this phase. This study emphasizes the importance of accessory adaptations in movement‐assisted dichogamy to tackle the transition phase problem.

Micromorphology of endemic Centaurea glaberrima subsp. divergens (Asteraceae)

In this study, the micromorphology of the vegetative and reproductive structures of the endemic Centaurea glaberrima Tausch subsp. divergens (Vis.) Hayek (Asteraceae), using scanning electron microscope (SEM), is presented for the first time. Uniseriate whip-like non-glandular and biseriate glandular trichomes are found on the surface of all aboveground parts (stem, leaves, peduncles, involucral bract). On the adaxial leaf epidermis ribbed thickenings (striation pattern) of outer periclinal cell walls, slightly curved anticlinal cell walls and anomocytic stomata are noticed. Rugose abaxial surface with thorny protuberances of the involucral bract is documented. Corolla is glabrous with longitudinally parallel epidermal cells with distinct straight outline. Isopolar, radially symmetric and tricolporate microechinate pollen grains are seen. Short stylar hairs, without cuticular striations, are present along the outer sides of the style, while the inner sides (abaxial surface) constitute the papillate stigmatic surface. Microcharacters found in cypsela are as follows: slightly ribbed body; rotund base; lateral and concave insertion; short, unicellular curly acute trichomes; smooth epidermis; fine-sulcate ornamentation; rod shaped epidermal cells with short, obtuse end walls and straight anticlinal walls; poorly developed minutely dentate pericarp rim; and dimorphic pappus with bristles of different length and morphology, with pinnules restricted to the margins of the bristles. The results obtained contribute to knowledge about the micromorphology of the studied endemic species and provide features for its better identification. The taxonomic significance of the analyzed characters is discussed. Some well defined microcharacters of the studied species might have taxonomic value.

Reproductive barriers in cassava: Factors and implications for genetic improvement.

Cassava breeding is hampered by high flower abortion rates that prevent efficient recombination among promising clones. To better understand the factors causing flower abortion and propose strategies to overcome them, we 1) analyzed the reproductive barriers to intraspecific crossing, 2) evaluated pollen-pistil interactions to maximize hand pollination efficiency, and 3) identified the population structure of elite parental clones. From 2016 to 2018, the abortion and fertilization rates of 5,748 hand crossings involving 91 parents and 157 progenies were estimated. We used 16,300 single nucleotide polymorphism markers to study the parents' population structure via discriminant analysis of principal components, and three clusters were identified. To test for male and female effects, we used a mixed model in which the environment (month and year) was fixed, while female and male (nested to female) were random effects. Regardless of the population structure, significant parental effects were identified for abortion and fertilization rates, suggesting the existence of reproductive barriers among certain cassava clones. Matching ability between cassava parents was significant for pollen grains that adhered to the stigma surface, germinated pollen grains, and the number of fertilized ovules. Non-additive genetic effects were important to the inheritance of these traits. Pollen viability and pollen-pistil interactions in cross- and self-pollination were also investigated to characterize pollen-stigma compatibility. Various events related to pollen tube growth dynamics indicated fertilization abnormalities. These abnormalities included the reticulated deposition of callose in the pollen tube, pollen tube growth cessation in a specific region of the stylet, and low pollen grain germination rate. Generally, pollen viability and stigma receptivity varied depending on the clone and flowering stage and were lost during flowering. This study provides novel insights into cassava reproduction that can assist in practical crossing and maximize the recombination of contrasting clones.

Molecular cloning and yeast two-hybrid provide new evidence for unique sporophytic self-incompatibility system of Corylus.

The Corylus genus contains several important nut producing species and exhibits sporophytic self-incompatibility (SSI). However, the underlying molecular mechanisms of SSI in Corylus remain largely unknown. To clarify whether Corylus and Brassica share the same SSI molecular mechanism. We cloned ChaTHL1/2, ChaMLPK, ChaARC1, ChaEX70A1 genes from Ping'ou hybrid hazelnut using RACE techniques and tested the interaction between the ChaARC1 and ChaSRK1/2. We also examined the pistil-pollen interactions using scanning electron microscopy. We found no differences in the stigma surface within 1 h after compatible or incompatible pollination. Compatible pollen tubes penetrated the stigma surface, while incompatible pollen did not penetrate the stigma 4 h after pollination. Bioinformatics analysis revealed that ChaTHL1/2, ChaMLPK, ChaARC1 and ChaEX70A1 have corresponding functional domains. Quantitative real-time PCR (qRT-PCR) analysis showed that ChaTHL1/2, ChaMLPK, ChaARC1 and ChaEX70A1 were not regularly expressed in compatible or incompatible pollination. Furthermore, the expression patterns of ARC1, THL1/2, MLPK and Exo70A1 were quite distinct between Corylus and Brassica. According to yeast two-hybrid assays, ChaSRK1/2 did not interact with ChaARC1, confirming that the SRK-ARC1 signalling pathway implicated in the SSI response of Brassica was not conserved in Corylus. These results further reinforce the conclusion that, notwithstanding the similarity of the genetic basis, the SSI mechanism of Corylus does not conform in many respects with that of Brassica. Our findings could be helpful to better explore the potential mechanism of SSI system in Corylus.