Genetic diversity of sulfonylurea-resistant and -susceptible Monochoria vaginalis populations in Japan

Monochoria vaginalis is one of the most serious weeds of rice fields in Asia. The species is predominantly selfing. To reveal the potential for multiple mutational events, outcrossing and gene flow in the sulfonylurea‐resistant (SU‐R) M. vaginalis populations, we investigated (i) if each SU‐R population was a single SU‐R biotype or a mixture of several SU‐R biotypes using restriction analysis or direct sequencing of acetolacatate synthase (ALS) genes and (ii) genetic diversity of SU‐R and ‐susceptible (S) populations using amplified fragment length polymorphism (AFLP) analysis. Nineteen or 20 individuals were sampled from four SU‐R and five SU‐S populations respectively. Amino acid substitutions conferring resistance in the SU‐R populations were Pro₁₉₇Ser in the ALS1 or ALS3, or Asp₃₇₆Glu in the ALS1 and each SU‐R population was composed of a single SU‐R biotype. In cluster analysis each SU‐R individual formed a cluster, whereas the individuals from a SU‐S population belonged to different clusters. Some SU‐R populations showed polymorphic AFLP loci. The results indicated that these SU‐R biotypes emerged from a single mutational event and any gene flow of SU‐R genes from adjacent populations did not occur. A low level of outcrossing and recombinations of SU‐R genes occurred within some SU‐R populations of M. vaginalis.     

Flowering behaviors of the inflorescences of an alien plant (Plantago asiatica), an alpine plant (Plantago hakusanensis), and their hybrids on Mt. Hakusan,Japan

In the subalpine zone on Mt. Hakusan, Japan, Plantago asiatica, an alien plant, and Plantago hakusanensis, a native alpine species, grow sympatrically along with their putative hybrids. Here, their flowering behavior, which affects the frequency of hybridization and the colonizing ability of P. asiatica and its hybrids, is described. The flowering behavior of each species and of two F₁ hybrids from different seed parents was determined based on the position of the flower in the inflorescence by using a generalized linear mixed model. The percentage fruit set of individually bagged inflorescences was calculated to corroborate the assumptions of the opportunities for self‐pollination. All the flowers were protogynous; however, many P. asiatica anthers dehisced before browning of the stigma in the flower and the sex presentations in the inflorescence were asynchronous. The percentage of fruit set was high. Consequently, P. asiatica has the opportunity for self‐pollination within the flower and in the inflorescence. In contrast, the P. hakusanensis anthers dehisced after browning of the stigma in the flower; their sex presentation was synchronous in the inflorescence, showing negligible opportunities for self‐pollination, and the fruit set was low. Accordingly, in the field, P. hakusanensis might require pollination among the inflorescences for seed production and be actively outcrossed, while P. asiatica is able to outcross in the early flowering phase. Therefore, P. asiatica and P. hakusanensis have opportunities for hybridization. The F₁ hybrids exhibited intermediate flowering behavior and produced fruits, demonstrating the potential to reproduce by selfing.     

Virus infection and reproductive losses in faba bean (Vicia faba L.)

The viruses, bean yellow mosaic ( BYMV ), Echtes Ackerbohnenmosaik (EAMV) and bean (pea) leaf roll ( BLRV ) reduced seed yield in faba bean particularly when plants were infected at the pre-and mid-bloom stage. EAMV and BYMV , but not BLRV , delayed senescence and increased branching on glasshouse-grown plants so that more inflorescences were produced on diseased plants; most of the additional flower buds necrosed. All three viruses increased the proportion of flower buds that became necrotic thus reducing the number of mature flowers available for pollination. This, together with enhanced abscission of recently set flowers, diminished pod production. Flower set per se was unaffected by infection. The number of ovule sites per pod and weight of individual mature seeds were also unaffected by these diseases but productivity per pod declined because of increased ovule abortions. Patterns of pod production on the inflorescence and location of mature seeds within the pod were unaffected by virus infection.     

Fruit set and the diurnal pollinators of the invasive Lantana camara and the endemic Lantana peduncularis in the Galapagos Islands

Fruit set is highly relevant to a plant's reproductive success. Fruit set can vary due to predation on flowers, pollinator services and/or resource availability. Reproductive success, measured as the fruit set of the invasive Lantana camara and the endemic Lantana peduncularis in the cool–dry season and the warm–wet season of the Galapagos Islands, was studied. Also, autonomous self‐pollination ability and seed viability were probed for both species. Furthermore, flower visitors and their activity were registered for both species during the warm–wet season. Lantana peduncularis produced fewer flowers per inflorescence, but had a higher fruit set in the cool–dry season, compared to the warm–wet season. In contrast, the fruit set in L. camara did not change seasonally. The fruit set in L. camara was higher than in L. peduncularis in the warm–wet season. Moreover, ～18% of the bagged flowers of the invasive Lantana produced fruits by autonomous self‐pollination, while for the endemic Lantana, the rate of autonomous self‐pollination was very low. More than 80% of the fruits for both species had at least one viable seed per fruit. The number of pollinators and their frequency, inflorescence‐ and flower‐visiting rates and the duration of the visit per flower were higher in the invasive Lantana than in the endemic one. The endemic Lepidoptera Urbanus galapagensis (the main pollinator of both Lantana species) and the introduced Hymenia perspectalis were observed pollinating both Lantana species. These results indicate that the alien L. camara is more attractive to pollinators and it has reproductive advantages regarding fruit set in comparison with L. peduncularis, factors that contribute to the colonization pattern of this invasive species.     

Biology of Commelina benghalensis L. in south-eastern Queensland. 1. Growth, development and seed production

Experiments conducted at Kingaroy in southeastern Queensland, investigated growth, development and seed production of Commelina benghalensis L. a weed of field crops, which produces aerial and underground flowers. Plants were grown from four seed types (large and small seeds from the two types of flowers) in pots exposed to the weather and in the field. Development was faster, and growth and seed production were greater in the field than in pots. Plants grown from aerial seeds were smaller, developed aerial flowers earlier, and produced more aerial fruits than plants grown from underground seeds. Rhizomes and underground flowers began to develop 6 weeks after emergence on plants from all seed types, prior to the development of aerial flowers. Seed production in the field was 8000 m^?2 for plants grown from underground seeds and 12000 m^?2 for plants grown from aerial seeds. Small aerial seeds represented 73–79% of the total seed production, large aerial seeds 19–22%, and underground seeds only 1–3%.     

Self-incompatibility in Mikania micrantha in South China

Mikania micrantha is a successful invasive weed in many parts of the world, but we do not know how its mating system may have contributed to this. Therefore, its mating system was studied in an open M. micrantha population during the flowering seasons of 2004 and 2005. Pollen/ovule ratio was determined and pollination treatments were applied on entire inflorescences to estimate the seed/ovule ratio. The pollen/ovule ratio of M. micrantha was 4008, and seed/ovule ratio was 0.56 for open pollination and 0.0034 and 0.0038 for wind pollination and selfing respectively. These data indicate that the weed is self‐incompatible and needs insect pollination.     

Time of emergence impacts the growth and reproduction of silverleaf nightshade (Solanum elaeagnifolium Cav.)

Silverleaf nightshade is one of the worst agricultural weeds on a worldwide basis. Improved understanding of its life cycle will be useful for weed management. This research showed that the growth and reproduction of silverleaf nightshade were affected significantly by the time of emergence. Plants (both root‐ and seed‐generated) that emerged early in the growing season, such as in September or November (spring), were significantly taller and produced more biomass and fruit than plants that emerged in January (summer) and March (autumn). Delayed emergence resulted in a shorter vegetative phase and less fruit production. As a result, the silverleaf nightshade plants that emerged in September produced a large amount of seeds, while the plants that emerged later in the season did not flower. Thus, control of early‐emerging plants is important. The dynamics of fruit production indicated that silverleaf nightshade fruit formed in December and peaked in March, which suggests that a control action is required before December to control the soil seed bank.     

Seed biology of Mikania micrantha in Viti Levu,Fiji

Mikania micrantha (mile‐a‐minute) reproduces both by seed and vegetatively. A study to determine the possible pollinators, seed production rates, temperature and salinity limitations to germination and its seedbank size and persistence was conducted in Viti Levu, Fiji. Representatives of the Diptera had the greatest percentage of all floral visits (38%), followed by Hymenoptera (34%) and Lepidoptera (27%), while the honeybee was the most recurring visitor (18% of all visits). Flower heads (capitula) within the inflorescence commonly formed four viable seeds, resulting in 60 820 filled seed being produced per m². However, the seedbanks formed were not massive (600 seed m^?2) and they were moderately persistent (T₅₀: 1–3 years). Seed germination from both high and moderate rainfall regions occurred rapidly, under a wide range of temperature regimes, with no primary dormancy being observed. This study indicates that the seed reproductive success of M. micrantha in the two rainfall regions of Fiji is due to a number of factors, including the production of large numbers of flowers, successful pollination by local insects and the subsequent production of a large number of viable seeds. These seeds have high viability, no dormancy and are capable of forming small‐to‐medium seedbanks that are moderately long‐lived. In addition, seeds can germinate under a wide range of temperature and salinity conditions. This knowledge on seed production, biology, longevity and salt tolerance is vital in the development of management plans of M. micrantha in Fiji.     

Relationships Between Blueberry Flower Age, Pollination, and Conidial Infection by Monilinia vaccinii-corymbosi

ABSTRACT Monilinia vaccinii-corymbosi infects open blueberry flowers via the gynoecial pathway, leading to mummification of the developing fruit. To determine the effect of flower age on infection, stigmata were inoculated with conidia of M. vaccinii-corymbosi between 0 and 5 days after anthesis, fungal growth rates through the stylar canal were measured in detached flowers in the laboratory, and fruit disease incidence was determined in plants grown in the greenhouse. Hyphal growth rates were greatest in flowers inoculated on the day of anthesis, declined linearly with increasing flower age at inoculation (r = 0.921; P < 0.0001; n = 12), and were unaffected by the presence or absence of pollen applied at the time of inoculation. In greenhouse-grown plants, the percentage of infected fruit decreased exponentially with increasing flower age at inoculation (R = 0.878; P = 0.0057; n = 10), with disease incidence ranging from 76.4% for flowers inoculated on the day of anthesis to 15.5% for those inoculated 4 days later. Fruit disease incidence in the greenhouse was linearly correlated with hyphal growth rates in detached flowers (r = 0.985; P < 0.0001; n = 9), justifying the use of detached flowers when investigating gynoecial infection by M. vaccinii-corymbosi. In separate experiments, the effects of timing and sequence of pollination and inoculation on hyphal growth rates through the stylar canal and on disease incidence were investigated. Application of pollen to detached flowers 1 or 2 days before inoculation reduced hyphal growth rates by between 14.0 and 42.9% compared with flowers that received pollen and conidia simultaneously. Similarly, reductions in fruit disease incidence by between 9.5 and 18.3% were observed on greenhouse-grown plants for pollination-to-inoculation intervals ranging from 1 to 4 days. These results document that newly opened flowers are most susceptible to infection by M. vaccinii-corymbosi and that fruit disease incidence is reduced if pollination occurs at least 1 day before inoculation. Strategies that lead to early pollination of newly opened flowers may be useful for managing mummy berry disease in the field.     

The Relationship Between Wheat Seed Weight, Infection by Fusarium culmorum or Microdochium nivale, Germination and Seedling Disease

The distribution of seeds by weight for three lots of winter wheat cv. Avalon infected by Fusarium culmorum and three lots of winter wheat cv. Riband infected by Microdochium nivale was determined. The distribution of infected seeds within each seed lot was then determined by isolating F. culmorum from seeds on moist filter paper and M. nivale from seeds on potato dextrose agar. The distribution of M. nivale infected seeds between seeds of different weight was similar to that of the seed lot as a whole, whereas the distribution of F. culmorum was greater in light seeds than heavy seeds. The percentage germination of infected seeds decreased with seed weight. A similar situation was found with respect to seedling emergence in compost for F. culmorum infected seeds. However, with M. nivale infection, similar numbers of seedlings emerged from both light and heavy infected seeds. Seed treatment with guazatine increased seedling emergence for both light and heavy seed infected by M. nivale. However, seedling emergence from F. culmorum infected seed was poor even following treatment with guazatine. Poor emergence was most evident from light seed.     

Quantifying the dormancy of Alopecurus myosuroides seeds produced by plants exposed to different soil moisture and temperature regimes

In pot studies, seeds of Alopecurus myosuroides were less dormant when produced under warm and dry, than under cool and wet conditions. The temperature to which plants were exposed had a greater effect on seed dormancy than soil moisture. The timing of temperature stress had a big impact on initial seed dormancy. The critical period was during seed maturation, irrespective of temperature conditions during the earlier phase of panicle emergence and anthesis. A much higher proportion (57–62%) of seeds collected from fields in 2001, 2003 and 2005 were non‐dormant than in 2002 and 2004 (22–28%). Meteorological records showed that the mid‐June to mid‐July periods in England for 2001, 2003 and 2005 were warmer than average but in 2002 and 2004 were cooler than average. Consequently, results for samples collected from fields support those from experiments conducted under more controlled conditions. Studies in outdoor micro‐plots showed that the differences in seed dormancy recorded with freshly produced seed did affect the rate of germination in the field, 2–3 months after shedding.     

Growth and reproductive success of the seed‐derived plants of Sagittaria trifolia emerging at different times

In order to clarify the growth and reproductive success of seed‐derived Sagittaria trifolia individuals emerging at different times within a season, seeds were sown on May 16, June 16 and July 22 2010 and allowed to grow in pots under shaded and unshaded conditions. The timing of when the first inflorescence of each seedling appeared was recorded, as well as the number of seeds and tubers produced and the dry weight of each organ. In total, 220 seedlings were used, 23–59 in each treatment. As the sowing time was delayed, so too was the appearance of the first inflorescence. Additionally, the number of inflorescences, fruits and seeds produced by the unshaded plants significantly decreased with the sowing time. The total dry weight was significantly greater in the unshaded than in the shaded plants: the July‐sown, shaded plants grew very poorly. The relative resource allocation to the tubers was greater in the late‐emerging, shaded seedlings. Even in the shaded groups, except for the July‐sown plants, most of the plants set seed. Therefore, when addressing weed control in paddy fields, one should keep seedlings in mind, in addition to plants that have grown from tubers.     

Influences of herbicides, uprooting and use as cut flowers on sexual reproduction of Solidago canadensis

Solidago canadensis is a noxious invasive species in China. We examined the influences of herbicides on pollen germination and pollen tube growth and the effects of cutting flowers and herbicides on seed production and quality. We also determined the seed production and resource allocation to different organs of S. canadensis after uprooting the plants during their reproductive periods. The main results were as follows: (i) 49% pollen of S. canadensis was able to germinate on an appropriate medium; (ii) compared with paraquat, ethephon and 2,4-D, glyphosate had an ideal inhibitory effect on pollen germination and the formation of seeds of S. canadensis ; (3) cut flowering branches, when placed in water or nutrient solution, were still able to produce viable seeds; (4) resources were allocated more to the inflorescences to facilitate seed maturation after plants were uprooted at the flowering stage. Uprooted flower branches were still able to produce viable seeds, especially those in full flower. Therefore, in order to reduce the seed production of S. canadensis and spread of the species we suggest: (i) apply glyphosate at the flower bud stage, (ii) completely destroy uprooted plants at flowering stages and (iii) avoid using the flowering branches as ornamental materials.     

Some studies on the competition between Avenu fatua L. and spring barley.II. Variation of A. fatua emergence and development and its influence on crop yield.

The emergence and development of A fatua were studied in 23 spring barly fields in 1972 and nine in 1973 nautarally infested with yhe weed. Emergence occurred up to the four-leaf stages of the crop. The mean number of days from drilling to 50% emergence of A fatua plants was 22 in 1972 and 36 in 1973.The majority of seeds were shed by early emerging plants in 1972, 79% and in 1973. 59% of A fatua plants had emerged by the two-leaf stage of the crop and these plants produced 97 and 89% respectively of all the seed shed. In both years, A fatua plants emerging before the crop produced five times as many seeds per plant as those emerging between the crop two and three-leaf stages. The earliest emerging plants were also the heaviest and had most stems per plant.In both years there was a significant relationship between the density of A fatua plants in the crop in spring and their mortality.A large variation occured between the sites in the number of A fatua plants that emerged by a given crop leaf stage. In 1973.insufficient numbers of sites were investigatesd to derive a relationship between time to A fatua emergence and crop yield loss, but in 1972, a given density of A fatua plants emerging at an early stage caused agreater crop yields loss than the same density emerging later. This was also evident to aleser extent in data derived from a similar series of 15 experiments in 1971.     

Pathways of bacterial invasion and watermelon seed infection by Acidovorax citrulli

This study explored the pathways of ingress of Acidovorax citrulli, the causal agent of bacterial fruit blotch of cucurbits, into watermelon seeds. Up until 7 days post‐inoculation (DPI), a significantly higher percentage of watermelon seeds was infected with A. citrulli when the bacteria were applied (c. 1 × 10⁶ colony‐forming units) to stigmas versus ovary pericarps of female flowers. Immunofluorescence microscopy showed that, with stigma inoculation, A. citrulli colonized style and ovary tissues by 1 DPI, and the bacteria co‐localized with pollen germ tubes in these tissues. With ovary pericarp inoculation, A. citrulli cells penetrated the epicarp and mesocarp tissues by 1 DPI but did not reach endocarp until 4 DPI. Finally, manual pollination followed by stigma inoculation led to >53% A. citrulli‐infected seed lots, while A. citrulli was not detected in seeds/ovules generated by stigma inoculation without pollination (chemically induced parthenocarpy). These results show that stigma inoculation results in faster colonization of watermelon ovules by A. citrulli than pericarp inoculation, even though there is no difference in the levels of infection in mature seeds. The data also indicate that pollen germ tubes play an important role in A. citrulli ingress into watermelon seeds via stigmas.     

Flower infection of Brassica oleracea with Xanthomonas campestris pv. campestris results in high levels of seed infection

During seed production, Brassica seed may become infected with Xanthomonas campestris pv. campestris after systemic colonization of plants upon leaf infection, or alternatively, after flower infection. Polytunnel experiments were conducted in 2007 and 2008 to study the relative importance of these colonization routes resulting in seed infection. Cauliflower plants (Brassica oleracea) were spray-inoculated at the 8-leaf stage, after formation of cauliflowers or during flowering, at which stage leaves or blossoms were inoculated. Inoculation at all stages resulted in a relatively high percentage of systemic infection; the average estimated infection incidences for stem base and peduncle infections were 16 % and 19 %, respectively. When seed samples were examined by dilution plating for deep-seated infection following hot water treatment, Xcc was detected in 61 % of the 23 seed samples harvested from plants with inoculated flowers. However, symptom development in seedlings raised from the seeds could not be confirmed in a grow-out test under favourable conditions for Xcc infection at a high RH (>95 %) and a relative high temperature (28 °C). Xcc was not detected in 59 seed samples harvested from leaf-inoculated plants with the exception of one sample from plants inoculated at peduncle formation. In a third polytunnel experiment carried out in 2009, the population dynamics of Xcc on inoculated flowers was investigated. Following spray-inoculation of flowers, 52 % of the flowers were infected with Xcc. During development of siliques, infection incidence decreased slowly and at 56 dpi, 20 % of the superficially disinfected siliques were infected with Xcc. It was estimated that 0.18 % of the seeds was infected and that 1–10 % of the infected siliques contained infected seeds. The implications of these results for control of Xcc in a seed production crop are discussed.     

Secondary dispersal, spatial dynamics and effects of herbicides on reproductive capacity of a recently introduced population of Bromus sterilis in an arable field

An arable field was subdivided and subjected to either deep inversion ploughing or non‐inversion cultivation after viable seeds of Bromus sterilis had been sown into oilseed rape stubble. After sowing in isolated plots distributed within the field, sequences of cropping treatments for the establishment of two successive winter wheat crops were applied. Each subfield was split into an uphill and a downhill direction for soil cultivation. The field had a 10° slope. In the season following seed introduction, 2.6% of the introduced seeds had successfully germinated and established in the non‐inversion cultivation regime, when no effective graminicide was applied. Ploughing eradicated B. sterilis. Using differential global positioning system (DGPS) mapping of the whole field population, emerged plants were observed up to 8.7 m (uphill treatment) and 21.3 m (downhill treatment) of their initial source. The median distance seeds were transported was 2.3 m uphill and 4.8 m downhill. Post‐emergence application of the herbicide propoxycarbazone slightly reduced weed density and seed weight, and almost halved weed seed production. Application of fenoxaprop‐P‐ethyl was followed by higher density of plants, tillers and seeds of B. sterilis. Seed viability was unaffected by herbicide use. Thus, in the second wheat crop following seed rain, the weed population was dispersed more widely in the field, such that 20–30% of seeds were dispersed more than 5 m distance from the first year's foci of infestation. The relevance of soil cultivation to secondary dispersal of B. sterilis is discussed.     

Germination ecology, emergence and host detection in Cuscuta campestris

Trials were carried out to study the germination and dormancy of Cuscuta campestris Y. (dodder) seeds and factors influencing the success of early parasitisation of sugarbeet. Primary dormancy can be removed by seed scarification. Germination was negligible at 10°C and optimal at 30°C, while it was not influenced by light. Seed burial induced a cycle of induction and breaking of secondary dormancy. Seedling emergence was inversely proportional to the depth of seed burial and only seed buried within 5 cm of the soil surface emerged. Storage of C. campestris seeds in a laboratory for 12 years resulted in the loss of primary dormancy, enabling the germination of all viable seeds. Host infection (i.e. protrusion of parasite haustoria from host tissue) was heavily influenced by host growth stage. Tropism towards a host was due to the perception of light transmitted by green parts of sugarbeet plants. Insertion of a transparent glass sheet between host leaves and parasite seedlings did not modify this response. This phototropism permitted Cuscuta to identify host plants with high chlorophyll content as a function of the lower red/far red ratio of transmitted light.     

Micro‐elevations in paddy fields affect the efficacy of mechanical weeding: Evaluation of weeding machines to control Monochoria vaginalis in herbicide‐free farming

Differences in local topography (micro‐elevation) within a paddy field that constitute a source of variability in agronomical indicators have not been considered thoroughly as a block factor in weed studies. This study investigated and evaluated the performance of weeding machines (weeders) in two herbicide‐free paddy fields that contained micro‐elevations. The plant density of Monochoria vaginalis, a typical and harmful paddy weed unless controlled with herbicides, was used as the indicator of the efficacy of the weeders. Among the three weeders that were tested, one suppressed M. vaginalis dramatically at low elevations and the others were less sensitive to micro‐elevation. For comparison across the fields, micro‐elevations at weed sampling locations were converted to the initial depth of water by using the records of hydrographs that had been set in each field. The relationship between the initial depth of water and the plant density of M. vaginalis was very clear with the use of the elevation‐sensitive weeder. Moreover, this relationship was valid, even with the less‐sensitive weeders. The finding that the greater the depth of water, the less the plant density was significant, even for M. vaginalis, a difficult aquatic paddy weed that was controlled with any of the weeders tested. Thus, micro‐elevation within a paddy field needs to be treated as a crucial block factor in weed‐sampling studies. A coarse survey of the level of a field and the installation of a hydrograph are recommended for a clear analysis of the background of weed control practices.     

Extreme variation in the reproductive phenology of the weed Ruellia nudiflora

Temporal variation in morphological and life‐history traits is directly linked to phenotypic plasticity in perennial plants. Phenotypic plasticity in reproductive phenology determines colonisation ability and population persistence in invasive weeds. We describe the reproductive phenology of Ruellia nudiflora (a cleistogamous weed) and assess the plasticity of its response to between‐year environmental variation in two contrasting light environments. We recorded the flower and fruit production of focal plants under two experimental levels of light intensity (open vs. shaded) over two years. Our results suggest that light differentially affects the phenology of reproductive structures, but not between‐year variation. Specifically, individual production of chasmogamous structures (flowers and fruit) ended earlier under shaded conditions than in the open, whilst production of cleistogamous fruits was not affected. At the population level, there was between‐year variation in the phenology of chasmogamous structures, which were bimodal and unimodal in the first and second year respectively. At the individual level, we found very low repeatability, suggesting high levels of phenotypic plasticity. Temporal variation in rainfall did not explain phenological variation. Although shade did not affect between‐year variation, it produced a briefer period of production of chasmogamous structures. This effect of shade may have some consequences for the genetic background of R. nudiflora's progeny, because only chasmogamous flowers can be out‐crossed, and this therefore might be an important factor to consider when designing management strategies.