Different breeding systems of three varieties of Bidens pilosa in Taiwan

Three varieties of the introduced Bidens pilosa (Hairy beggar‐ticks; Asteraceae) co‐exist in Taiwan. Bidens pilosa var. minor and var. pilosa are naturalised, while only var. radiata is invasive. Differences in seed set in bagged versus open‐pollinated capitula, pollen–pistil interactions and the pollen/ovule (P/O) ratio were investigated among these three varieties. In contrast with the resulting 45–55% seed set in each bagged capitulum of var. minor and var. pilosa, almost no mature seeds (1–2 seeds) were found in bagged capitula of var. radiata, showing that var. radiata has a low capability of autonomous seed production. In bagged capitula, only 1.5% of pistils of var. radiata, but 76% and 52% of those of var. minor and pilosa, respectively, had pollen tubes penetrating into their styles, suggesting that var. radiata has strong self‐incompatibility mechanisms preventing autonomous autogamy. The P/O ratio, with mean values of 8189, 2053 and 1613 for var. radiata, var. minor and var. pilosa, respectively, were counted. These results support the hypothesis that the three varieties bear different breeding systems; the invasive var. radiata is highly self‐incompatible, whereas the other two naturalised varieties are self‐compatible.     

Genetic diversity and population genetic differentiation in the endangered annual weed,Bidens cernua (Compositae), and two common congeners in Japan

In this study, we examined the genetic diversity in three populations of the critically endangered annual, Bidens cernua, in Japan by using inter‐simple sequence repeat markers and compared our data with those from two common congeners: Bidens radiata var. pinnatifida and Bidens tripartita. In contrast to our expectations, the degree of genetic diversity at the species level was higher in B. cernua than in B. radiata var. pinnatifida or B. tripartita. At the population level, the degree of genetic diversity was highest in B. cernua. These results may be ascribed to the mating system and method of seedbank formation in B. cernua. An analysis of molecular variance revealed relatively high genetic differentiation among the populations of all three species. We concluded that the distribution width could not be an index of genetic variability in Bidens examined in this study.     

Utilization of Bidens pilosa var. radiata (Sch. Bip.) Sherff integrated with water irrigation for paddy weed control and rice yield production

The application of allelopathic plant materials combined with an agricultural production method is a concept that can be used to manage weeds during rice production. This research investigated the effects of the utilization of Bidens pilosa var. radiata integrated with water irrigation for weed control and rice production. B. pilosa and water extract exerted more toxicity against Echinochloa crus‐galli than the extracted residue applied at the same rates, suggesting that weed control was caused by compounds extracted from B. pilosa. The changes in water properties after the application of B. pilosa were explored. Dissolved oxygen was rapidly reduced after application and then slowly increased within 3–5 days after application (DAA), while the pH also decreased at the early stage and then increased back to normal values within 1–3 DAA. Electrical conductivity increased with increasing rates of application, suggesting that allelochemicals were released from B. pilosa. The concept was studied under field conditions. B. pilosa was applied along with irrigation at 7 days after sowing (DAS) on a direct wet seed system. The results showed that application rates of 2, 4 and 6 tons ha^?1 decreased the number of weeds by 52.16, 86.73 and 95.18% at 30 DAA and reduced dried weight of weeds by 17.65, 34.69 and 86.82%, respectively. The rice yield showed an increase of 72.73, 81.03 and 73.66% when compared with the nonweeded crop, while herbicide treatment increased by 84.68%. The findings demonstrate that the application of B. pilosa integrated with water irrigation was able to control weeds in a direct seeded rice production system.     

Potential gene flow from transgenic rice (Oryza sativa L.) to different weedy rice (Oryza sativa f. spontanea) accessions based on reproductive compatibility

BACKGROUND: The possibility of gene flow from transgenic crops to wild relatives may be affected by reproductive capacity between them. The potential gene flow from two transgenic rice lines containing the bar gene to five accessions of weedy rice (WR1–WR5) was determined through examination of reproductive compatibility under controlled pollination. RESULTS: The pollen grain germination of two transgenic rice lines on the stigma of all weedy rice, rice pollen tube growth down the style and entry into the weedy rice ovary were similar to self‐pollination in weedy rice. However, delayed double fertilisation and embryo abortion in crosses between WR2 and Y0003 were observed. Seed sets between transgenic rice lines and weedy rice varied from 8 to 76%. Although repeated pollination increased seed set significantly, the rank of the seed set between the weedy rice accessions and rice lines was not changed. The germination rates of F₁ hybrids were similar or greater compared with respective females. All F₁ plants expressed glufosinate resistance in the presence of glufosinate selection pressure. CONCLUSIONS: The frequency of gene flow between different weedy rice accessions and transgenic herbicide‐resistant rice may differ owing to different reproductive compatibility. This result suggests that, when wild relatives are selected as experimental materials for assessing the gene flow of transgenic rice, it is necessary to address the compatibility between transgenic rice and wild relatives. Copyright © 2009 Society of Chemical Industry     

Overcompensation of seed production caused by clipping of Bidens pilosa var. radiata (Compositae): Implications for weed control on Iriomote‐Jima Island,Japan

The invasion of natural ecosystems by exotic species is a major threat to biodiversity on a local, regional, and global scale. Endemic island flora are particularly vulnerable to invasive species. Bidens pilosa var. radiata is a common invasive weed of roadsides, which are subject to clipping, on Japanese subtropical islands. To assess compensation by the weed to damage by clipping, a pot experiment was conducted under common garden conditions. The above‐ground parts were clipped with pruning shears at various frequencies, ranging from no clipping (the control) to clipping at 4–16 week intervals for 32 weeks in summer. The clipped individuals regenerated new branches from the axillary buds and flowered for ≤12 weeks after the clipping. The regeneration after the clipping gave rise to secondary reproduction, whereas minimal regeneration occurred in the unclipped individuals after the maturation of the fruit. Consequently, the total flower head mass, represented by the dry weight of the inflorescences throughout the experiment, was higher on the individuals that were clipped at 12 and 16 week intervals than on the unclipped individuals, suggesting overcompensation in fecundity. At the higher frequencies of above‐ground clipping, the flower head mass was suppressed at 8 week clipping intervals, while both the flower head mass and the productive biomass were suppressed at 4 week clipping intervals. This indicates that clipping at intervals of ≤8 weeks is required to prevent the reproduction of this weed.     

Agronomic performance of F1, F2 and F3 hybrids between weedy rice and transgenic glufosinate-resistant rice

BACKGROUND: Studies of hybrid fitness, of which agronomic performance may be an indicator, can help in evaluating the potential for introgression of a transgene from a transgenic crop to wild relatives. The objective of this study was to assess the agronomic performance of reciprocal hybrids between two transgenic glufosinate‐resistant rice lines, Y0003 and 99‐t, and two weedy rice accessions, WR1 and WR2, in the greenhouse. RESULTS: F₁ hybrids displayed heterosis in height, flag leaf area and number of spikelets per panicle. The agronomic performance of F1 between WR1 and Y0003 was not affected by crossing direction. The tiller and panicle numbers of F1 individuals were higher than their F2 counterparts. However, these traits did not change significantly from the F2 to the F3 generation or in hybrids with weedy rice as maternal or paternal plants. For all hybrids, the in vitro germination rates of fresh pollen were similar and significantly lower than those of their parents, seed sets were similar to or of lower value than those of weedy rice parents and seed shattering characteristics were partially suppressed, but the survival of hybrids over winter in the field was similar to that of weedy rice parents. All F1, F2 and F3 hybrids had similar composite agronomic performance to weedy rice parents. CONCLUSION: There was no significant decrease in the composite agronomic performance of any of the hybrids compared with weedy rice. This implies that gene flow from transgenic cultivated rice to weedy rice could occur under natural conditions. Copyright © 2011 Society of Chemical Industry     

Pink‐awned weedy rice (Oryza sativa): a potential conduit for gene exchange in rice agro‐ecosystems

Hybridisation between genetically distinct lineages results in increases in overall genetic diversity and is a potential mechanism for the origin and spread of adaptive alleles. Weed and crop hybridisation may result in weedy ecotypes, which have, in addition to classic weedy traits such as seed shattering and long seed dormancy, crop traits that enhance weediness, such as adaptation to field cultivation and harvest strategies. Weedy rice (Oryza sativa) hybridises with cultivated rice and, in the process, may produce new (pink‐awned) weedy rice varieties. Pink‐awned (PA) weedy rice plants have been observed in rice fields in Arkansas. We explored the genetic relationships between PA weedy rice, crop rice, global rice accessions and other weedy rice ecotypes present in the southern United States. Gene sequencing of 48 sequence‐tagged sites (STS loci) revealed a pattern of hybridisation and gene flow between blackhull weedy rice and tropical japonica rice (O. sativa subsp. japonica) cultivars. Our data suggest that PA rice originates from hybridisation between blackhull weedy rice and tropical japonica rice. PA rice offspring segregate phenotypic traits associated with weediness in rice. This segregation could lead to adaptive allele combinations in PA rice, which could potentially move into other weedy rice types through subsequent hybridisation events.     

Effects of host plant genotype and seedbank density on Striga reproduction

Prevention of seed input to the seedbank of Striga hermonthica‐infested fields is an important objective of Striga management. In three consecutive years of field experimentation in Mali, Striga reproduction was studied for 10 sorghum genotypes at infestation levels ranging from 30 000 to 200 000 seeds m^?2. Host resistance was identified as an important determinant of Striga reproduction, with the most resistant genotypes (N13, IS9830 and SRN39) reducing Striga reproduction by 70–93% compared with the most susceptible genotype (CK60‐B). Seedbank density had a significant effect on Striga seed production. Higher seedbank density resulted in more Striga plants, which led to increased intra‐specific competition and consequently a reduced level of reproduction per plant. For the most susceptible sorghum genotypes, density dependence also occurred in the earlier belowground stages. Striga reproduction continued beyond harvest. At the high infestation level just 8% of the total reproduction was realised after harvest, whereas at the low infestation level 39% was attained after harvest. Even though host‐plant genotype plays a significant role in Striga reproduction, calculations indicated that only at very low infestation levels the use of the most resistant genotype was able to lower the Striga seedbank.     

Are road verges corridors for weed invasion? Insights from the fine‐scale spatial genetic structure of Raphanus raphanistrum

Raphanus raphanistrum (Brassicaceae) is considered amongst the world's worst agricultural weeds. We address critical issues in its management by studying the pathway of colonisation at local scales. For this, we assessed the small‐scale spatial genetic structure of 231 samples collected from three different sites across the Cape Floristic Region, South Africa, using 11 nuclear microsatellite markers. Although natural pollen and seed dispersal were expected to be restricted, we found no significant relationship between genetic and geographical distance within sites. Instead, our results suggest that R. raphanistrum had colonised new habitats via jump dispersal, rather than through natural diffusive dispersal at local scales. We did not find evidence for road verges as dispersal corridors, as evidenced by a lack of isolation‐by‐distance at local scales. Instead, the absence of spatial genetic structure suggests that R. raphanistrum had rapidly spread throughout its current range, possibly facilitated by human‐mediated actions. Management plans addressing containment or suppression of the weedy species R. raphanistrum (and possibly other weedy species) should take the high degree of connectivity between distant geographical localities into account.     

Impacts of mowing and bud destruction on Centaurea solstitialis growth,flowering, root dynamics and soil moisture

Centaurea solstitialis (yellow starthistle) has invaded rangelands and natural areas in the western USA. There is evidence that mowing is a more effective method of reducing growth and seed production, compared with the well‐established and distributed bioagents. To test this hypothesis we measured C. solstitialis's growth and reproduction following two treatments (late spring and early summer bud/capitula destruction and shoot mowing) and measured C. solstitialis's growth and reproduction. We measured changes in soil moisture content to test the hypothesis that these manipulations differentially affect water usage by the invasive plant. Mowing produced shorter plants that weighed less. Bud damaged plants were not statistically different from untreated controls. The number of developed capitula was reduced 67% by mowing but was unaffected by bud damage. Mowed plants redistributed resources from root to flower production. Both treatments reduced mean capitulum diameter. This resulted in reductions of 76% and 21% in estimated seed number for mowed and bud damaged plants respectively. Root abundance decreased and root life‐span was reduced by both treatments. Soil moisture depletion was greatest from mid‐May to mid‐July (from 21% to 9%) and occurred after maximum root abundance. Mowing resulted in a delay in soil moisture depletion compared with the bud damaged plants or the untreated controls. Bud/capitula damage did not affect C. solstitialis's requirement for soil water. Overall, this study supported the hypothesis that mowing reduced C. solstitialis growth and reproduction more than bud damage alone. This information will aid managers in selecting a strategy for managing C. solstitialis in a particular habitat.     

Risk posed to honeybees (Apis mellifera L,Hymenoptera) by an imidacloprid seed dressing of sunflowers

In a greenhouse metabolism study, sunflowers were seed‐treated with radiolabelled imidacloprid in a 700 g kg^?1 WS formulation (Gaucho® WS 70) at 0.7 mg AI per seed, and the nature of the resulting residues in nectar and pollen was determined. Only the parent compound and no metabolites were detected in nectar and pollen of these seed‐treated sunflower plants (limit of detection <0.001 mg kg^?1). In standard LD₅₀ laboratory tests, imidacloprid showed high oral toxicity to honeybees (Apis mellifera), with LD₅₀ values between 3.7 and 40.9 ng per bee, corresponding to a lethal food concentration between 0.14 and 1.57 mg kg^?1. The residue level of imidacloprid in nectar and pollen of seed‐treated sunflower plants in the field was negligible. Under field‐growing conditions no residues were detected (limit of detection: 0.0015 mg kg^?1) in either nectar or pollen. There were also no detectable residues in nectar and pollen of sunflowers planted as a succeeding crop in soils which previously had been cropped with imidacloprid seed‐treated plants. Chronic feeding experiments with sunflower honey fortified with 0.002, 0.005, 0.010 and 0.020 mg kg^?1 imidacloprid were conducted to assess potential long‐term adverse effects on honeybee colonies. Testing end‐points in this 39‐day feeding study were mortality, feeding activity, wax/comb production, breeding performance and colony vitality. Even at the highest test concentration, imidacloprid showed no adverse effects on the development of the exposed bee colonies. This no‐adverse‐effect concentration of 0.020 mg kg^?1 compares with a field residue level of less than 0.0015 mg kg^?1 ( = limit of detection in the field residue studies) which clearly shows that a sunflower seed dressing with imidacloprid poses no risk to honeybees. This conclusion is confirmed by observations made in more than 10 field studies and several tunnel tests. © 2001 Society of Chemical Industry     

Differences in constitutive and inducible defences in pine species determining susceptibility to pinewood nematode

The pinewood nematode, Bursaphelenchus xylophilus, originating from North America (NA), is a major invasive pine pest in Eurasia. It was first detected in Portugal in 1999 associated with maritime pine, Pinus pinaster, and has been differently affecting the main local pine species, P. pinaster and P. pinea. Field studies and direct inoculation experiments in Pinus spp. seedlings, under controlled conditions, were performed to assess whether the differences in constitutive and inducible defences are determining the different susceptibility of pine host species to B. xylophilus. Host co‐evolution with the pathogen was also assessed, including the NA P. radiata, widely used in forestry in the northeast of the Iberian peninsula. Pine mortality in the field was positively related with the abundance of B. xylophilus, and concentration of phenolics and condensed tannins in pines. In the greenhouse assay, seedling tissues were analysed for constitutive investment in defences, as well as the potential inducibility of those defences as driven by B. xylophilus inoculation. Slower growing P. pinea presented higher levels of constitutive defences than faster growing P. pinaster, with only P. pinaster being affected by B. xylophilus. Furthermore, co‐evolution with the pathogen is important, with the fast‐growing NA P. radiata presenting an inducible and effective response to B. xylophilus. Results point to the importance of integrating data on pine life history traits, including growth rate, and production of constitutive and inducible defences, into predictive models for this invasive forest pest.     

Phenology and seed production of variegated thistle, Silybum marianum (L.) Gaertn., in Australia in relation to mechanical and biological control

Production of viable seeds occurred in immature capitula of Silybum marianum following simulated slashing and mowing. In the slashing treatment, capitula with 20 cm or less of stem attached produced viable seeds if cut off when at least half the florets were open, the proportion of viable seeds ranging from 0·3% in capitula at midanthesis to 12% in those at the end of anthesis. Following mowing, viable seeds were produced in full-sized buds which were close to anthesis and in capitula at any stage of anthesis at the time of plant cutting, the proportion increasing from 0·1% in capitula at the start of anthesis to 30% in those at the end. Within a capitulum, anthesis usually lasted five days in irrigated plants. Ripe seeds were released about 17 days later. Seed production averaged 190 seeds for the primary capitulum and 114 in others. In a flowering season starting in early November and lasting about two months, individual plants had the potential to produce an average of 55 capitula, representing an output of 6350 seeds per plant, of which 94% were viable. In view of the prolonged flowering season and the large seed output of S. marianum, it is argued that the restricted period of oviposition by the weevil Rhinocyllus conicus and the low density of larvae per capitulum might limit its impact as a biological control agent for this weed in Australia.     

Biology and management of barnyardgrass,red sprangletop and weedy rice

About 400 weed species of 73 families have been reported to occur in upland and lowland rice fields in Vietnam. Two important families are Poaceae and Cyperaceae having 42% of weed species with 21% each. The barnyardgrass, Echinochloa crus‐galli (L.) Beauv., is the most important weed in both transplanted and direct‐seeded rice in this country. The competi‐tion of 25 barnyardgrass plants/m² causes approximately 50% yield loss. Red sprangletop, Leptochloa chinensis (L.) Nees., is an emerging major weed in direct‐seeded rice. Weedy rice (Oryza sativa L.) was detected in 1994 and is now a new dangerous pest in rice fields. The main reasons are: herbicides which can kill weedy rice completely are not available in the market, non‐chemical methods are laborious and costly, and weedy rice can develop a new generation from contaminated seeds through rice sowing or emerging from soil seed bank. Research results on the Vietnamese situation of barnyardgrass, red sprangletop and weedy rice in terms of biology and management by chemical and non‐chemical methods have been reviewed in this paper.     

The effects of natural and manipulated density regimes on Alliaria petiolata survival, growth and reproduction

Knowledge of the ecology of Alliaria petiolata, an alien invasive species in the USA, is essential to predict the efficacy of introduced biological control agents. Accordingly, we examined the growth and reproduction of second‐year A. petiolata rosettes under natural and manipulated density regimes. Plant survival was also studied under natural conditions. Similar survivorship patterns were observed for high‐ and low‐density populations, although survival in the low‐density populations was c. 10% higher. Under natural conditions, low‐density plants were larger and more fecund, on average, than high‐density plants; however, on a per‐area basis, high‐density populations were much more productive. When plant density was experimentally reduced, average seed production and plant size increased with thinning intensity, suggesting that thinning released plants from intra‐specific competition. Additionally, plants in thinned plots were able to recover from past competition and could approach production of the plants in un‐thinned lower density plots that had not experienced prior competition. However, seed production per unit area was lower in thinned versus un‐thinned plots of the same initial density. Results suggest herbivore‐induced plant mortality late in the life cycle, as might occur following the introduction of biological control agents, may reduce the contribution to the A. petiolata seedbank.     

High level of variation among Sri Lankan weedy rice populations,as estimated by morphological characterization

Weedy rice (Oryza sativa f. spontanea) is a notorious weed that infests paddy fields worldwide. Understanding the morphological variation pattern of this weed in a given rice‐planting region will facilitate its effective management and use. Here, 29 populations, covering nearly all the rice‐cultivation regions in Sri Lanka, were characterized in a common‐garden cultivation experiment that was based on 13 morphological traits. The variation level of the weedy rice populations was considerably high, as estimated by the Simpson and Shannon–Weaver indices. An ANOVA revealed a higher level of among‐population variation than within‐population variation. Seed shattering was the most variable trait and the seed length and width were the least variable traits, as indicated by their coefficient of variation. The results of the principal component analysis, in which the first two principal components represented 57.5% of the total variation, indicated the important role of such traits as plant height, seed weight and number of tillers and panicles in the divergence of the weedy rice populations. However, the variation was not associated with their geographical locality. Knowledge of such a morphological variation pattern provides opportunities to design strategic management methods for weedy rice control in Sri Lanka, in addition to the proper use of it as a genetic resource for rice improvement.     

Response to flooding intensity in Elytrigia repens, E. intermedia (Poaceae: Triticeae) and their hybrid

Response to flooding intensity in three closely related taxa, Elytrigia repens, E. intermedia and their hybrid was studied. Plants were exposed to three intensities of flooding for a 30‐day period. Response to flooding intensity was estimated by measuring dry mass of the following: total biomass, above‐ground living biomass, above‐ground dead biomass, below‐ground biomass, rhizome and root mass and by the allocation of dry mass into rhizomes and root:shoot ratio. Reduction of nearly all the biomass compartments with increasing flooding intensity was observed in the three taxa. All three taxa can thus be regarded as flood‐intolerant. Based on the parameters measured, E. repens is regarded as the relatively most flooding‐tolerant, E. intermedia as the least tolerant, while the hybrid displayed intermediate flooding tolerance. The higher flooding tolerance in E. repens was likely related to its ability to accumulate a sufficient mass of rhizomes before flooding, due to higher regeneration ability. E. repens also displayed the highest phenotypic plasticity, as deduced from the reaction norms constructed for total biomass and rhizome mass of particular clones of the three taxa studied. This indicates that, on the species level, E. repens is better adapted to changing environmental conditions and it can be expected to colonize flooded soils. Both Elytrigia species also occur as weeds: E. intermedia grows in agricultural environments in warm regions, while E. repens infests many different types of habitats. Where they co‐occur, hybridization between them may lead to the enrichment of their gene pools with genes responsible for survival of the parental species under extreme conditions; their weedy potential may thus be enhanced.     

Consequences of narrow crop row spacing and delayed Echinochloa colona and Trianthema portulacastrum emergence for weed growth and crop yield loss in maize

Echinochloa colona and Trianthema portulacastrum are weeds of maize that cause significant yield losses in the Indo‐Gangetic Plains. Field experiments were conducted in 2009 and 2010 to determine the influence of row spacing (15, 25 and 35 cm) and emergence time of E. colona and T. portulacastrum (0, 15, 25, 35, 45 and 55 days after maize emergence; DAME) on weed growth and productivity of maize. A season‐long weed‐free treatment and a weedy control were also used to estimate maize yield and weed seed production. Crop row spacing as well as weed emergence time had a significant influence on plant height, shoot biomass and seed production of both weed species and grain yield of maize in both years. Delay in emergence of weeds resulted in less plant height, shoot biomass and seed production. However, increase in productivity of maize was observed by delay in weed emergence. Likewise, growth of both weed species was less in narrow row spacing (15 cm) of maize, as compared with wider rows (25 and 35 cm). Maximum seed production of both weeds was observed in weedy control plots, where there was no competition with maize crop and weeds were in rows 35 cm apart. Nevertheless, maximum plant height, shoot biomass and seed production of both weed species were observed in 35 cm rows, when weeds emerged simultaneously with maize. Both weed species produced only 3–5 seeds per plant, when they were emerged at 55 DAME in crop rows spaced at 15 cm. Infestation of both weeds at every stage of crop led to significant crop yield loss in maize. Our results suggested that narrow row spacing and delay in weed emergence led to reduced weed growth and seed production and enhanced maize grain yield and therefore could be significant constituents of integrated weed management strategies in maize.     

Comparative seed predation of woolly cupgrass (Eriochloa villosa) and yellow foxtail (Setaria pumila) along a field border in Canada

The seed predation of woolly cupgrass (Eriochloa villosa), an invasive weed of East‐Asian origin, was compared to that of yellow foxtail (Setaria pumila), an established and widespread weed, along a field border in Canada. The seeds of both species were glued to sandpaper cards and their removal in field conditions was recorded from July to September during the 3 years of 2009, 2010 and 2011. Predator exclusion cages allowed the evaluation of seed loss to be attributed to invertebrates, vertebrates and total seed loss due to predation for both species. Pitfall traps were installed and collected once in 2010 and during all the seed sampling dates in 2011 in order to evaluate predatory pressure from ground beetles and crickets. The average amount of seed loss that could be attributed to invertebrates was higher for S. pumila than for E. villosa, while the amount of seed loss that could be attributed to vertebrates was higher for E. villosa than for S. pumila in 2009 and 2010. The level of S. pumila seed loss to invertebrates was correlated with the sum of crickets (Gryllus pennsylvanicus) and beetles (Harpalus spp. and Ophonus rufibarbis) trapped during the 2011 season. During the same period, correlations between E. villosa seed loss to invertebrates and trapped insects were not observed. Reduced postdispersal seed predation by invertebrates could increase the local fall survival of the unburied seeds of invasive E. villosa populations, compared to other naturalized, smaller‐seeded weedy grasses.     

A study on seed population dynamics of three weedy species of Eupatorium

The data on seed population dynamics of three weedy species of Eupatorium, viz. E. adenophwrum Spreng., E. riparium Regel and E. odoratum L. have been presented and discussed in the paper. The seed production and seed populations in soil seed bank were estimated, and the fate of buried seeds in soil was followed over a 2-year period. All the three species of Eupatorium produced a large number of seeds. The seed production of E. riparium per unit area was higher than that of the other two species because of its high population density. In all the three species most of the seeds were found to be present in the top 2 cm of the soil. The viable seed population of the three species of Eupatorium declined exponentially alter their burial in soil showing almost similar mortality patterns. A large proportion of seeds of all the Eupatorium spp. remained under enforced dormancy during their burial in soil with only a small fraction exhibiting induced dormancy. The longevity of the buried seeds increased on account of the dormancy imposed on them. The loss of seeds through degeneration and/or decomposition was rather low.