Reproductive biology of the rare and endangered Banksia brownii Baxter ex R. Br. (Proteaceae)

Abstract Banksia brownii is an endangered species, now limited to ～ 15 disjunct populations in southwestern Western Australia. Data on flowering phenology, plant size, fruit set, pollination and the mating system were gathered for two of these populations between March and October 1993. Flowering for both populations followed a similar pattern, with open flowers first evident in April, and the number of inflorescences with open flowers peaking in June. At both locations, trees differed considerably with respect to their size, the total number of inflorescences produced and the length of their flowering season. Fruiting success was typically low, with approximately half of all inflorescences failing to develop into infructescences. Only 1. 8% of the flowers originally present on inflorescences developed into follicles. The distribution of follicles along each infructescence was non-random, with most forming in the middle third of the infructescence for reasons relating to nutrient supply and pollinator behaviour. More flowers opened during the day than at night, although pollen was lost from individual flowers during both periods. Honeyeaters such as Phylidonyris novaehollandiae were common at the two study sites, and often carried large loads of B. brownii pollen. Though less frequently caught, the nocturnal mammals Rattus fuscipes and Tarsipes rostratus also bore substantial amounts of pollen. Most inflorescences from which these mammals and birds were excluded remained barren. Fruiting success was further reduced when invertebrates such as Apis mellifera were also prevented from visiting inflorescences. The ability of B. brownii to set at least some fruit in the absence of biotic poli-nators indicates that the species is partially self-compatible. Honeyeaters foraged preferentially at inflorescences with one to two thirds of their flowers open, probing mainly along the ‘advancing front’ of open flowers. These animals moved more frequently between inflorescences on the same plant than between those on different plants, and were often recaptured in the same locations. Mammals also appeared to be sedentary. Both B. brownii populations had mixed mating systems, with genetically determined outcrossing rates of ～0.7. The unusually high level of selfing in each population is presumably a reflection of the species’ self-compatibility and the foraging behaviour of its pollinators.     

Reproductive biological characteristics potentially contributed to invasiveness in an alien invasive plant Bidens frondosa

Bidens frondosa L. (Asteraceae) is a widespread invasive weed in China. By experimental observation and bagging treatment, the reproductive biological characteristics of this species, such as phenology of flowering, floral syndrome, breeding system and seed germination characteristics, were studied to assess the association of these reproductive characteristics with invasiveness. Flowers of B. frondosa bloom from September to October every year in Ji'an city, Jiangxi province. The lifespan of a single capitulum is approximately 4 to 5 days, with 30 to 60 florets per capitulum. The capitulum diameter, anthocaulus length, floret length and width, stamen length and pistil length were 6.1, 30.9, 2.2, 0.6, 3.0 and 2.7 mm, respectively. The seed set percentage of 48.5% in the treatment of bagging flowers without emasculation suggests B. frondosa is self‐compatible; meanwhile, the percentage of 63.1% in the treatment of bagging with emasculation and manual xenogamy suggests it also is cross‐compatible. P/O ratio per capitulum of this species was 450.5, which suggests that the breeding system of B. frondosa is facultative xenogamous, and it needs pollinators to some degree. The main floral visitors were insects of Hymenoptera, Diptera and Lepidoptera. The 1000‐achenes weight was 1.97 g. The achenes emerged as a small germination peak from the fourth to fifth day, and had a high accumulated germination rate of up to 84.0% on day 20 after sowing. Our experimental findings suggested that the reproductive biological characteristics, such as the versatile mating system of self‐ and cross‐pollination, high seed production, a special method of achene dispersal and germination peak, accompanied by a high accumulated germination rate, might contribute to the invasive ability of B. frondosa.     

Reproductive biology in an invasive plant Solidago canadensis

Solidago canadensis,a perennial Compositae plant originating from North America,was introduced into China as a horticultural plant in 1935.Under natural conditions,S.canadensis allocates large amounts of energy to sexual reproduction and produces many seeds,which reflects an r-strategy with high seed number and small seed size.In addition,naturalized populations have a great capacity to grow clonally with underground stems.S.canadensis has become an invasive weed in eastern China,and has caused serious damages to agricultural production and ecosystems in several provinces in China.In order to understand the reproductive characteristics of S.canadensis and effectively control its spread,we examined soil conditions,seed characteristics,seed germination and the capacity for asexual reproduction in different plant parts.We investigated the population dispersion of S.canadensis in fixed sites for three years,and analyzed the seasonal dynamics of the morphological parameters of the underground parts and the caloric values of different organs of S.canadensis.We also compared differences in the root systems of S.canadensis and composite exotic weeds.The following results were obtained:1)Under natural conditions,the germination season of S.canadensis lasts from March to October,with a peak from April to May.Vegetative growth and asexual reproduction are especially vigorous during summer due to high temperatures and soil drought stress.On the other hand,the rainy season proves suitable for seed germination.Most S.canadensis flower between September and January,and fruit in late October.A mature plant can produce about 20000 seeds.The mean weight of 1000 seeds ranges from 0.045 g to 0.050 g,and the mean seed moisture content ranges from 60% to 80%.The light-winged seeds disperse readily by air,water,vehicles,human activity or through livestock.2)S.canadensis seeds have a wide tolerance for different values of pH,salinity and soil moisture.The mean percent germination of seeds is 30% under suitable conditions.The results of seed germination under various environmental stresses and investigation of soil conditions indicate that well-aerated,slightly acidic soils with low salinity are suitable for the growth of S.canadensis.Additionally,S.canadensis has a high tolerance for contamination by heavy metal elements including Zn,Cu and Pb,but has low accumulation coefficients for these elements.3)S.canadensis reproduces asexually via underground rhizomes and nodes on the stem base to recruit new individuals,and in plants that experience mechanical damage,this reproductive strategy is used to produce clonal shoots.The capacity for asexual reproduction among different plant parts rank as follows:underground parts＞stem-base (20 cm)＞stem-base (30 cm)＞stem-base (45 cm)＞stem.Further,with increasing mechanical damage,the quantity of shoots produced by the plant decreases.4)The morphological parameters of the root system of S.canadensis including length,surface area,volume,and average diameter are greater than for composite exotic weeds.These parameters indicate that S.canadensis has the physiological potential to widely invade China.5)The aboveground growth rate and most of the underground morphological parameters vary remarkably among the seasons,with a peak normally occurring in September.In August,a fraction of the energy in leaves and stems is allocated underground to increase fine root growth and water uptake during hot weather.Additionally,the seasonal dynamics of the underground morphological parameters and the caloric values of different organs of S.canadensis enhance its reproductive ability.Based on the results above,we conclude that S.canadensis has great invasive potential in China.We suggest that urgent measures should be taken to control its further spread,and to minimize its impact on local plant diversity.     

Reproductive biology in an invasive plant Solidago canadensis

Solidago canadensis, a perennial Compositae plant originating from North America, was introduced into China as a horticultural plant in 1935. Under natural conditions, S. canadensis allocates large amounts of energy to sexual reproduction and produces many seeds, which reflects an r-strategy with high seed number and small seed size. In addition, naturalized populations have a great capacity to grow clonally with underground stems. S. canadensis has become an invasive weed in eastern China, and has caused serious damages to agricultural production and ecosystems in several provinces in China. In order to understand the reproductive characteristics of S. canadensis and effectively control its spread, we examined soil conditions, seed characteristics, seed germination and the capacity for asexual reproduction in different plant parts. We investigated the population dispersion of S. canadensis in fixed sites for three years, and analyzed the seasonal dynamics of the morphological parameters of the underground parts and the caloric values of different organs of S. canadensis. We also compared differences in the root systems of S. canadensis and composite exotic weeds. The following results were obtained:

Hydrous characteristics of pearl millet (Pennisetum glaucum (L.) R. Br.) under drought

The variations in the hydrous characteristics - leaf water potential (psi(F)) and relative water content (TRE) - of plants indicate their hydrous status and also their capacity to incorporate water, particularly in situations of hydrous stress. These characteristics were used to differentiate the behaviour of six autochthonous ecotypes of pearl millet (Pennisetum glaucum (L.) R. Br.) subjected to various hydrous modes. The results showed that the psi(F) and the TRE evolve in the same direction and decrease in the presence of hydrous stress. These hydrous characteristics are also very important, since they condition the yield. The study also showed that the six pear millet ecotypes present two standard behaviours: the first type is characterized by an important fall of the psi(F) and TRE, representing an osmotic adjustment of adaptive type, whereas the second group showed a weak reduction of leaf water potential while maintaining a TRE appreciably higher, which could be the result of an important reduction of the osmotic potential due to an active accumulation of solutes (constitutive osmotic adjustment). Moreover, the genetic variability of ecotypes with respect to the hydrous stress does not seem related to the geographical origin of the millet ecotypes, but rather to their phenology and their morphology.     

Reproductive biology of Aechmea bracteata (Sw.) Griseb. (Bromelioideae: Bromeliaceae)

• Individuals of Aechmea bracteata show inflorescences with red scape bracts and odourless, yellow, tubular diurnal flowers, with closely arranged sexual organs, producing a large amount of fruits.
• In order to investigate the reproductive system of this species, a suite of characters was assessed: phenology, floral morphology and biology, nectar production dynamics, and fruit and seed production and germination, as a result of controlled pollination crosses. The study was conducted during two flowering seasons in wild populations in Yucatán, Mexico.
• Results suggest an annual flowering pattern with one flowering peak; flowers were diurnal, showing partial dichogamy (protandry)‐herkogamy, anthers and stigma become mature before floral aperture, which could lead to self‐pollination, nectar is produced during anthesis, varying in volume and total sugar concentration during the day; fruits and seeds were produced in all experimental crosses (cross‐pollination, obligated cross‐pollination, assisted and unassisted selfing, geitonogamy and apomixis), as well as high percentage seed germination.
• Several species of Aechmea are reportedly self‐compatible and autogamous, as suggested by results of selfing and non‐assisted selfing crosses, but these results are negated by the presence of apomixis, indicating that the species is apomictic. This is the first report of this breeding system for subgenus Aechmea and the sixth for Bromeliaceae. Polyembryony is here suggested for the first time in this genus and family based on the fact that more seeds were recorded that expected based on ovule numbers. Finally, when performing experimental crosses, estimating reproductive success based on number of seeds is a better approach than number of fruits, due to the effect of pseudogamy.

     

The role of seed germination in the invasion process of Honey locust (Gleditsia triacanthos L., Fabaceae): comparison with a native confamilial

Identifying plant traits that promote invasiveness has been a major goal in invasion ecology. Germination plays a central role in the life cycle of plants and therefore could be a key trait in determining species invasiveness. In this study, seed germination of two confamilial, co‐occurring species that share ecological characteristics, the exotic invasive Gleditsia triacanthos L and the native Acacia aroma Gillies ex. Hook. & Arn., was compared. Seeds were obtained from individuals of three localities in the Chaco Serrano region of Córdoba, Argentina. Percent of seed germination and mean germination time were recorded in chemically and mechanically scarified seeds, and the former variable was also recorded in seeds subjected to: passage through the digestive tract of dispersers, fire simulations, fire simulation plus mechanical scarification, seed longevity, and dormancy break over time. In general, both species showed similar germination percentage. However, non‐scarified seeds of the exotic species lost physical dormancy when subjected to experiments of dormancy break over time, whereas, the native species had shorter mean germination time. The greater percentage of seed germination over time of the exotic species than of the native one might be triggering the spread of the former, whereas the shorter mean germination time might be hindering its expansion to more arid regions. The study of different mechanisms for achieving seed germination, particularly in hard seed species, could provide important information on the expansion of invasive species as well as useful knowledge for their management.     

Germination of Prosopis juliflora (Sw.) D.C. seeds at different osmotic potentials and temperatures

The effects of osmolytes, osmotic potential (Ψ_s), temperature, and their interactions on the germinability, germination rate, and other germination parameters of the invasive shrub Prosopis juliflora, which grows in the semiarid environmental conditions of the Caatinga in northeast Brazil, were evaluated. To study the effects of polyethylene glycol (PEG) and NaCl stress and temperature on germination, two separate experiments were carried out at the Plant Ecophysiology Laboratory of the Federal University of Pernambuco in 2011. The overall germinability decreased significantly with increases in both PEG (one‐way anova , F_4,75 = 111.21, P ≤ 0.001) and NaCl (one‐way anova , F_4,75 = 12.82, P ≤ 0.001); however, the effects were more accentuated with PEG than NaCl. The PEG‐treated seeds maintained their germinability, even when they were subjected to a Ψ_s = ?1 MPa after being rinsed and allowed to germinate on deionized water. In contrast, NaCl‐treated seeds usually lost their ability to germinate; this fact was possibly linked to the accumulation of Na⁺ and Cl^? in the cells, which may have contributed to a loss of membrane function that led to the death of the embryos. Although numerous studies describing seed germination in the presence of osmolytes have been conducted, studies that show the interactions between osmolytes, osmotic potentials, and temperature are scarce. The present study is the first to describe these interactions for P. juliflora seeds.     

Experimental Droughting of Woodsia ilvensis (L.) R. Br.

Summary

Populations of Woodsia ilvensis Oblong Woodsia have been observed to decline at all the British sites. It has been suggested that drought might have accelerated this decline. In an experiment with cultivated Plants it was found that summer drought had a more severe effect than drought during the spring.     

Long-term storage of Pennisetum glaucum (L.) R. Br. pollen

Summary Pearl millet [Pennisetum glaucum (L.) R. Br.] pollen has been successfully stored for 2,615 and 2,911 days at -18° and -73 °C, respectively, and continues to be viable. Viability of pollen stored at -73 °C appears to be little affected either by pollen storage moisture contents below 7.2% or by storage in glass vial or zip-lock plastic bag containers. Pollen moisture content appears to be more critical for maintaining viability at -18°C than at -73°C. Glass vials appear to be more desirable for longer term (>3 years) storage at -18°C.     

Reproductive ecology of three endangered African violet (Saintpaulia H. Wendl.) species in the East Usambara Mountains, Tanzania

Knowledge of the reproductive biology of endangered plants is essential for their effective conservation. It also provides important information for understanding the evolutionary processes that affect speciation, thus helping the definition of proper units for conservation in endangered plants with problematic taxonomy. We studied the reproductive potential and possibility for hybridization in the endangered genus Saintpaulia (Gesneriaceae) by examining flowering phenology, flower and seed production and pollination of three sympatric cross‐compatible Saintpaulia species in the East Usambara Mts., Tanzania. The synchrony observed in flowering in S. confusa and S. difficilis may enable hybridization between these two species, whereas partial phenological separation may contribute to the integrity of S. grotei. Although the level of flower abortion is high in S. confusa, each pollinated flower yields about 1000 seeds. Saintpaulia confusa produces fruits following both self‐ and cross‐pollination but spontaneous self‐pollination seems not to occur. Thus, seed production depends on sufficient pollinator service. Floral heteromorphy (i.e. enantiostyly) and bee pollination are likely to further enhance cross‐pollination, suggesting that the genus predominantly outcrosses. Thus, Saintpaulia populations are likely to suffer from negative effects of inbreeding if they become small and isolated.     

化学通讯在松材线虫侵染和扩散中的作用

松材线虫为外来入侵种 ,由其引起的松材线虫病正在我国迅速扩散蔓延 ,造成我国部分地区松林资源的毁灭性破坏。松材线虫病的发生和流行与媒介天牛、寄主植物、共生真菌和细菌密切相关 ,松材线虫 -墨天牛 -松树 -共生微生物之间存在着广泛的化学联系 ,它们通过化学互作 ,调控松材线虫的行为 ,影响松材线虫的侵染和扩散     

Reproductive success of a colony of the introduced bumblebee Bombus terrestris (L.) (Hymenoptera: Apidae) in a Tasmanian National Park

Abstract  Ever since a feral population of the bumblebee Bombus terrestris was found in suburban Hobart, on the Australian island of Tasmania, there has been ongoing debate surrounding the capacity of this species to utilise Australian native vegetation. Although several studies have reported B. terrestris foraging on Tasmanian native vegetation, doubts have been raised as to whether this reflects successful breeding in native vegetation. This study documents the success of a colony of B. terrestris in a Tasmanian National Park, isolated from urban and agricultural areas by 10 km of sea. Examination of the larval cocoons revealed that this colony had produced at least 304 new queens and 939 workers and drones. Pollen stores found in the colony were mostly from native plants, particularly Eucalyptus. These results strongly suggest that B. terrestris is able to reproduce successfully in parts of Australia that still support almost exclusively native vegetation.     

Acylated anthocyanins in flowers of Matthiola tricuspidata (L.) R. Br. and Matthiola fruticulosa (L.) Maire (Brassicaceae)

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Reproductive capacities in the sexual forms of the gynodioecious species Thymus vulgaris L.

The reproductive capacities of the females (male-steriles or mS) of Thymus vulgaris L. have been investigated, in terms of size and weight of plants, seed production, germination ability and pollination. The data, collected during nine years under controlled conditions and in natural situations are discussed in comparison with the results known in the literature. It is suggested that the large diversity of characteristics promoting sexual polymorphism could justify the high and variable rates of mS met in natural conditions in T. vulgaris.     

Mitochondrial DNA-RFLP Analysis Distinguishes New CMS Sources in Pearl Millet (Pennisetum glaucum (L.) R. Br.)

Restriction fragment length polymorphism (RFLP) of mitochondrial (mt) DNA provides a rapid and effective method to assess heterogeneity among male sterile cytoplasms. Six isonuclear A-lines (81 A₁, with Tift 23A₁, cytoplasm, ICMA 88001 (= 81A_v) with Violaceum cytoplasm, 81A (=81A₄) with monodli = violaceum cytoplasm, Pb 310A₂ and Pb 311A₂ with A₂ cytoplasm from L 66A, and Pb 406A₃ with A₃ cytoplasm from L 67A), nine cytoplasmic male-sterility sources from Large-Seeded Genepool (LSGP 6, LSGP 14, LSGP 17, LSGP 22, LSGP 28, LSGP 36, LSGP 43, LSGP 55 and LSGP 66) and two each from Early Genepool (EGP 33 and EGP 15) and Population Varieties (PV 1 and PV 2) were characterized for variation in their mitochondrial genomes following Southern blot hybridizations using homologous (pearl millet 13.6 kb, 10.9 kb, 9.7 kb and 4.7 kb clones) and heterologous (maize atp6 and coxl clones) mitochondrial DNA (mtDNA) probes. Following cluster analysis based on similarity indices for the RFLP banding patterns observed, we identified seven cytoplasmic groups within LSGP. Two (LSGP 43 and LSGP 66) of these were quite distinct from each other as well as from other cytoplasms. This clearly indicates that besides serving as a source of diversity for agronomic and adaptation traits, broad-based gene pools can also provide diverse sources of cytoplasmic male sterility. These new CMS sources were also compared with standard CMS systems and cytoplasm-specific restriction fragments were identified.