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Stephen B Powles - One of the best experts on this subject based on the ideXlab platform.
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no auxinic herbicide resistance cost in wild radish Raphanus raphanistrum
Weed Science, 2019Co-Authors: Danica E Goggin, Hugh J Beckie, Chad Sayer, Stephen B PowlesAbstract:Wild radish ( Raphanus raphanistrum L.) is a problematic and economically damaging dicotyledonous weed infesting crops in many regions of the world. Resistance to the auxinic herbicides 2,4-D and dicamba is widespread in Western Australian R. raphanistrum populations, with the resistance mechanism appearing to involve alterations in the physiological response to synthetic auxins and in plant defense. This study aimed to determine whether these alterations cause inhibition in plant growth or reproduction that could potentially be exploited to manage 2,4-D–resistant populations in cropping areas. Therefore, the morphology and seed production of resistant and susceptible populations were compared in an outdoor pot study, with plants grown in the presence and absence of competition by wheat ( Triticum aestivum L.). The susceptible and resistant R. raphanistrum populations were equally suppressed by wheat competition, with plant growth and seed production being decreased by approximately 50%. Although resistant populations produced less vegetative biomass than susceptible populations, there was no negative association between resistance and seed production. Therefore, it is unlikely that any nonherbicidal management practices will be more efficacious on 2,4-D–resistant than 2,4-D–susceptible R. raphanistrum populations.
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No Auxinic Herbicide–Resistance Cost in Wild Radish (Raphanus raphanistrum)
Weed Science, 2019Co-Authors: Danica E Goggin, Hugh J Beckie, Chad Sayer, Stephen B PowlesAbstract:Wild radish ( Raphanus raphanistrum L.) is a problematic and economically damaging dicotyledonous weed infesting crops in many regions of the world. Resistance to the auxinic herbicides 2,4-D and dicamba is widespread in Western Australian R. raphanistrum populations, with the resistance mechanism appearing to involve alterations in the physiological response to synthetic auxins and in plant defense. This study aimed to determine whether these alterations cause inhibition in plant growth or reproduction that could potentially be exploited to manage 2,4-D–resistant populations in cropping areas. Therefore, the morphology and seed production of resistant and susceptible populations were compared in an outdoor pot study, with plants grown in the presence and absence of competition by wheat ( Triticum aestivum L.). The susceptible and resistant R. raphanistrum populations were equally suppressed by wheat competition, with plant growth and seed production being decreased by approximately 50%. Although resistant populations produced less vegetative biomass than susceptible populations, there was no negative association between resistance and seed production. Therefore, it is unlikely that any nonherbicidal management practices will be more efficacious on 2,4-D–resistant than 2,4-D–susceptible R. raphanistrum populations.
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a novel psba mutation phe274 val confers resistance to psii herbicides in wild radish Raphanus raphanistrum
Pest Management Science, 2019Co-Authors: Huan Lu, Qin Yu, Mechelle J Owen, Stephen B PowlesAbstract:BACKGROUND: Wild radish (Raphanus raphanistrum) is a globally important weed of crops. Two atrazine-resistant wild radish populations (R1 and R2), collected from the Western Australia grain belt, were investigated for resistance to photosystem II (PSII) herbicides. RESULTS: Sequencing of the full-length psbA gene revealed the well-known Ser264-Gly substitution in population R1, whereas population R2 displayed a novel Phe274-Val substitution. Herbicide dose-response studies confirmed that the population with the Ser264-Gly mutation exhibited high-level resistance to atrazine, but super-sensitivity to bromoxynil. Plants possessing the novel Phe274-Val mutation exhibited a modest level of resistance to atrazine, metribuzin and diuron, and were bromoxynil susceptible. Structural modelling of the mutant D1 proteins predicts that the Ser264-Gly mutation endows atrazine resistance by abolishing H-bonds, but confers bromoxynil super-sensitivity by enhancing hydrogen bonding. The Phe274-Val substitution provides resistance to atrazine and diuron by indirectly affecting H-bond formation between the Ser264 residue and the herbicides. CONCLUSION: The results demonstrate that the Phe274-Val mutation is likely responsible for resistance to PSII-inhibiting triazine and urea herbicides. To our knowledge, this is the first evidence of the psbA Phe274-Val mutation in wild radish conferring resistance to PSII herbicides. © 2018 Society of Chemical Industry.
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identity and activity of 2 4 dichlorophenoxyacetic acid metabolites in wild radish Raphanus raphanistrum
Journal of Agricultural and Food Chemistry, 2018Co-Authors: Danica E Goggin, Stephen B Powles, Gareth L Nealon, Gregory R Cawthray, Adrian Scaffidi, Mark J Howard, Gavin R FlemattiAbstract:Synthetic auxin herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D), are widely used for selective control of broadleaf weeds in cereals and transgenic crops. Although the troublesome weed wild radish (Raphanus raphanistrum) has developed resistance to 2,4-D, no populations have yet displayed an enhanced capacity for metabolic detoxification of the herbicide, with both susceptible and resistant wild radish plants readily metabolizing 2,4-D. Using mass spectrometry and nuclear magnetic resonance, the major 2,4-D metabolite was identified as the glucose ester, and its structure was confirmed by synthesis. As expected, both the endogenous and synthetic compounds retained auxin activity in a bioassay. The lack of detectable 2,4-D hydroxylation in wild radish and the lability of the glucose ester suggest that metabolic 2,4-D resistance is unlikely to develop in this species.
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A novel psbA mutation (Phe274–Val) confers resistance to PSII herbicides in wild radish (Raphanus raphanistrum)
Pest Management Science, 2018Co-Authors: Huan Lu, Qin Yu, Mechelle J Owen, Stephen B PowlesAbstract:BACKGROUND: Wild radish (Raphanus raphanistrum) is a globally important weed of crops. Two atrazine‐resistant wild radish populations (R1 and R2), collected from the Western Australia grain belt, were investigated for resistance to photosystem II (PSII) herbicides. RESULTS: Sequencing of the full‐length psbA gene revealed the well‐known Ser264–Gly substitution in population R1, whereas population R2 displayed a novel Phe274–Val substitution. Herbicide dose–response studies confirmed that the population with the Ser264–Gly mutation exhibited high‐level resistance to atrazine, but super‐sensitivity to bromoxynil. Plants possessing the novel Phe274–Val mutation exhibited a modest level of resistance to atrazine, metribuzin and diuron, and were bromoxynil susceptible. Structural modelling of the mutant D1 proteins predicts that the Ser264–Gly mutation endows atrazine resistance by abolishing H‐bonds, but confers bromoxynil super‐sensitivity by enhancing hydrogen bonding. The Phe274–Val substitution provides resistance to atrazine and diuron by indirectly affecting H‐bond formation between the Ser264 residue and the herbicides. CONCLUSION: The results demonstrate that the Phe274–Val mutation is likely responsible for resistance to PSII‐inhibiting triazine and urea herbicides. To our knowledge, this is the first evidence of the psbA Phe274–Val mutation in wild radish conferring resistance to PSII herbicides. © 2018 Society of Chemical Industry
Allison A Snow - One of the best experts on this subject based on the ideXlab platform.
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long term persistence of crop alleles in weedy populations of wild radish Raphanus raphanistrum
New Phytologist, 2010Co-Authors: Allison A Snow, Lesley G Campbell, Patricia M Sweeney, S G Hegde, Theresa M. Culley, Norman C EllstrandAbstract:Summary • Hybridization allows transgenes and other crop alleles to spread to wild ⁄ weedy populations of related taxa. Researchers have debated whether such alleles will persist because low hybrid fitness and linkage to domestication traits could severely impede introgression. • To examine variation in the fates of three unlinked crop alleles, we monitored four experimental, self-seeding, hybrid populations of Raphanus raphanistrum · Raphanus sativus (radish) in Michigan, USA, over a decade. We also compared the fecundity of advanced-generation hybrid plants with wild plants in a common garden experiment. • Initially, F1 hybrids had reduced fitness, but the populations quickly evolved wild-type pollen fertility. In Year 10, the fecundity of plants from the experimental populations was similar to that of wild genotypes. Crop-specific alleles at the three loci persisted for 10 yr in all populations, and their frequencies varied among loci, populations and years. • This research provides a unique case study of substantial variation in the rates and patterns of crop allele introgression after a single hybridization event. Our findings demonstrate that certain crop alleles can introgress easily while others remain rare, supporting the assumption that neutral or beneficial transgenes that are not linked to maladaptive traits can persist in the wild.
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pollinator preferences and the persistence of crop genes in wild radish populations Raphanus raphanistrum brassicaceae
American Journal of Botany, 1998Co-Authors: Allison A SnowAbstract:Crop‐weed hybridization can potentially influence the evolutionary ecology of wild populations. Many crops are known to hybridize with wild relatives, but few studies have looked at the long-term persistence of crop genes in the wild. This study investigated one factor in the hybridization process in radish: differential pollinator visitation to wild radish ( Raphanus raphanistrum) vs. crop‐wild F 1 hybrids (R. sativus 3 R. raphanistrum). Wild genotypes had yellow flowers, a recessive single-locus trait, whereas hybrids always had white or pale pink flowers. In experimental arrays in northern Michigan, total pollinator visitation was significantly biased toward wild plants when the frequencies of wild and hybrid plants were equal. Syrphid flies, the most frequent visitors, preferred wild plants while bumble bees showed no preference. This pattern was also observed when hybrid plants were overrepresented in the array (12 hybrid : 2 wild). In contrast, when hybrid plants were rare (2 hybrid : 12 wild), neither morph was preferred by any pollinator group. Later in the summer, pollinators were also observed in a large experimental garden with nearly equal frequencies of wild and hybrid plants. Cabbage butterflies (Pieris rapae) strongly overvisited wild plants, while bumble bees showed a slight preference for hybrids. Taken together, these studies suggest that F 1 hybrids may not be at a disadvantage with regard to pollinator visits when they occur at low frequencies or when bumble bees are frequent flower visitors. Thus, variation in the proportion of white-flowered morphs among wild radish populations could be influenced by different histories of crop-to-wild hybridization, as well as by variation in the composition of local pollinator taxa.
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heritable variation in stomatal responses to elevated co2 in wild radish Raphanus raphanistrum brassicaceae
American Journal of Botany, 1998Co-Authors: Allison A Snow, Andrea L Case, Peter S CurtisAbstract:Rising atmospheric carbon dioxide may affect plant populations in the short term through effects on photosynthesis and carbon allocation, and over the long term as an agent of natural selection. To test for heritable effects of elevated CO 2 on stomatal responses and plant fecundity in Raphanus raphanistrum, we grew plants from 12 paternal families in outdoor open-top chambers at ambient (35 Pa) or elevated (67 Pa) CO2. Contrary to results from a previous study of this species, total flower and fruit production were marginally lower under elevated CO 2. Across families, stomatal index and guard cell length showed little response to CO2 enrichment, but these characters varied significantly among paternal families in both the direction and magnitude of their response to changing CO2. Although these family-by-CO2 interactions suggest that natural selection might affect stomatal characters when ambient CO2 levels increase, we found no significant correlation between either character and flower or fruit production. Therefore, our data suggest that while heritable variation for stomatal index and guard cell length exists in this population, selection due to increasing CO 2 is not likely to act on these traits because they had no detectable effect on lifetime fecundity.
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genotype specific effects of elevated co2 on fecundity in wild radish Raphanus raphanistrum
Oecologia, 1994Co-Authors: Peter S Curtis, Allison A Snow, Amy S MillerAbstract:Rising atmospheric CO2 may lead to natural selection for genotypes that exhibit greater fitness under these conditions. The potential for such evolutionary change will depend on the extent of within-population genetic variation in CO2 responses of wild species. We tested for heritable variation in CO2-dependent life history responses in a weedy, cosmopolitan annual, Raphanus raphanistrum. Progeny from five paternal families were grown at ambient and twice ambient CO2 using outdoor open-top chambers (160 plants per CO2 treatment). Elevated CO2 stimulated net assimilation rates, especially in plants that had begun flowering. Across paternal families, elevated CO2 led to significant increases in flower and seed production (by 22% and 13% respectively), but no effect was seen on time to bolting, leaf area at bolting, fruit set, or number of seeds per fruit. Paternal families differed in their response to the CO2 treatment: in three families there were no significant CO2 effects, while in one family lifetime fecundity increased by >50%. These genotype-specific effects altered fitness rankings among the five paternal families. Although we did not detect a significant genotype x CO2 interaction, our results provide evidence for heritable responses to elevated CO2. In a subset of plants, we found that the magnitude of CO2 effects on fecundity was also influenced by soil fertility.
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effects of pollen load size and number of donors on sporophyte fitness in wild radish Raphanus raphanistrum
The American Naturalist, 1990Co-Authors: Allison A SnowAbstract:Competition among pollen tubes within styles sometimes results in progeny with enhanced growth rates, presumably resulting from selection for superior pollen genotypes. Although such gametophytic selection is often invoked as an agent of evolution, its importance in existing natural populations is unknown. I tested for the effects of past and current pollen competition on sporophytic fitness in wild radish (Raphanus raphanistrum). The intensity of previous pollen competition had no overall effect on progeny characteristics such as seed size, germination rate, plant size, or fecundity, as measured in both field and greenhouse environments. Using pollen from "intense" previous competition, I also tested for separate effects of pollen-load size (60 vs. 300 grains) and number of pollen donors per stigma (one vs. three). Again, these pollination treatments had no consistent effects of progeny fitness. In a few cases, plants resulting from three pollen donors were smaller than those from one. My results do not ...
Roger D Cousens - One of the best experts on this subject based on the ideXlab platform.
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plants as populations of release sites for seed dispersal a structural statistical analysis of the effects of competition on Raphanus raphanistrum
Journal of Ecology, 2013Co-Authors: Natalie Kelly, Mohammad Sadegh Taghizadeh, Roger D Cousens, Jim Hanan, David MouillotAbstract:Trajectories of dispersing seeds begin at the positions of their fruits on the maternal plant. Mechanistic simulation models usually assume that seed release is restricted to a characteristic, species-specific height. However, real canopies constitute distributed rather than point sources, which may have important consequences for dispersal kernels. Fruit positions are determined by plant architecture, which is under both genetic control and environmental influence. Competition with other plants has a major modifying influence on canopy structure. We used quantitative methods to describe the positions of fruits on plants of Raphanus raphanistrum L., examined how fruit spatial distributions change when plants grow under interspecific competition and explored how this is related to changes in the structural geometry and topology of the plant. Raphanus raphanistrum was grown either as individual plants or in a wheat crop. Branching structures and fruit positions were captured using a three-dimensional digitizer. Propagule locations were also mapped on the ground after dispersal. Fruit distributions pre-dispersal were analysed using various statistical approaches; plant topological and geometrical indices were calculated for the branching structures. Plants grown under competition were smaller, but the reduced size was because fewer modules were produced rather than because individual branches were in some way different. The distribution of these branches was also different under competition, with more apical dominance resulting in less branching along dominant modules. Under competition, fruits were concentrated in the upper parts of the canopy and closer, in the horizontal plane, to the base of the plant. This resulted in much more restricted local seed shadows post-dispersal. Synthesis. The effect of competition on plant size is primarily a result of a reduction in initiation of branches. For species with limited dispersal ability, this results in a greatly modified seed shadow at short distances. In the case of agricultural weeds, the concentration of fruits at greater heights when competing with a crop might result in a greater proportion being dispersed long distances by harvesting machinery, but they would be fewer in number. © 2013 The Authors. Journal of Ecology
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Plants as populations of release sites for seed dispersal: a structural‐statistical analysis of the effects of competition on Raphanus raphanistrum
Journal of Ecology, 2013Co-Authors: Natalie Kelly, Roger D Cousens, Jim Hanan, M. S. Taghizadeh, David MouillotAbstract:Trajectories of dispersing seeds begin at the positions of their fruits on the maternal plant. Mechanistic simulation models usually assume that seed release is restricted to a characteristic, species-specific height. However, real canopies constitute distributed rather than point sources, which may have important consequences for dispersal kernels. Fruit positions are determined by plant architecture, which is under both genetic control and environmental influence. Competition with other plants has a major modifying influence on canopy structure. We used quantitative methods to describe the positions of fruits on plants of Raphanus raphanistrum L., examined how fruit spatial distributions change when plants grow under interspecific competition and explored how this is related to changes in the structural geometry and topology of the plant. Raphanus raphanistrum was grown either as individual plants or in a wheat crop. Branching structures and fruit positions were captured using a three-dimensional digitizer. Propagule locations were also mapped on the ground after dispersal. Fruit distributions pre-dispersal were analysed using various statistical approaches; plant topological and geometrical indices were calculated for the branching structures. Plants grown under competition were smaller, but the reduced size was because fewer modules were produced rather than because individual branches were in some way different. The distribution of these branches was also different under competition, with more apical dominance resulting in less branching along dominant modules. Under competition, fruits were concentrated in the upper parts of the canopy and closer, in the horizontal plane, to the base of the plant. This resulted in much more restricted local seed shadows post-dispersal. Synthesis. The effect of competition on plant size is primarily a result of a reduction in initiation of branches. For species with limited dispersal ability, this results in a greatly modified seed shadow at short distances. In the case of agricultural weeds, the concentration of fruits at greater heights when competing with a crop might result in a greater proportion being dispersed long distances by harvesting machinery, but they would be fewer in number. © 2013 The Authors. Journal of Ecology
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effects of relative emergence time and water deficit on the timing of fruit dispersal in Raphanus raphanistrum l
Crop & Pasture Science, 2012Co-Authors: Mohammad Sadegh Taghizadeh, Marc E Nicolas, Roger D CousensAbstract:Seed dispersal is both a spatial and a temporal phenomenon, although most studies focus on spatial aspects. Seed initiation on the maternal plant may occur over a considerable period, especially in indeterminately flowering species, and thus seeds may be exposed to a wide range of environmental conditions during their development. The result is variation in the timing of seed development, the anatomy of structures related to the dispersal process, and the behaviour and fate of seeds post-dispersal. A key resource during the growth and development of summer-maturing species in most areas, and one that is thus likely to modify these processes, is water. Two experiments were therefore undertaken to describe (i) the development of Raphanus raphanistrum fruits and the timing of fruit dispersal, and (ii) the effects of water availability on the timing of fruit dispersal. Fewer seeds were produced and subsequently dispersed by later emerging plants. The duration of fruit dispersal became shorter when the plants emerged progressively later than the crop, and the time of maximum dispersal was later. For cohorts of fruits initiated at the same time, those that developed under mild and severe water deficit reached their final length sooner, and were dispersed sooner, than those receiving a plentiful supply of water. Thus, the phenology of the maternal plant and the nature of its environment can modify the timing of propagule maturity and consequently dispersal. Such information may provide an opportunity for managers to reduce weed seed return to their field or, conversely, to regulate the amount of contaminated grain or reduce dispersal to other locations.
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the role of the persistent fruit wall in seed water regulation in Raphanus raphanistrum brassicaceae
Annals of Botany, 2010Co-Authors: Roger D Cousens, Kenneth R Young, Ali TadayyonAbstract:†Background and Aims Dry fruits remain around the seeds at dispersal in a number of species, especially the Brassicaceae. Explanations for this vary, but usually involve mechanisms of innate dormancy. We speculate that, instead, a persistent fruit may give additional protection through control of dehydration, to species growing in arid or Mediterranean environments where water is sporadic. †Methods X-rays and weight measurements were used to determine the extent to which Raphanus raphanistrum seeds within mature fruits imbibe water, and germination tests determined the roles of the fruit and seed coat in seed dormancy. Rates of water uptake and desiccation, and seedling emergence were compared with and without the fruit. Finally, germinability of seeds extracted from fruits was determined after various periods of moist conditions followed by a range of dry conditions. †Key Results Most seeds rapidly take up water within the fruit, but they do not fully imbibe when compared with naked seeds. The seed coat is more important than the dry fruit wall in maintaining seed dormancy. The presence of a dry fruit slows emergence from the soil by up to 6–8 weeks. The fruit slows the rate of desiccation of the seed to a limited extent. The presence of the fruit for a few days during imbibition somehow primes more seeds to germinate than if the fruit is absent; longer moist periods within the pod appear to induce dormancy. †Conclusions The fruit certainly modifies the seed environment as external conditions change between wet and dry, but not to a great extent. The major role seems to be: (a) the physical restriction of imbibition and germination; and (b) the release and then re-imposition of dormancy within the seed. The ecological significance of the results requires more research under field conditions.
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water deficit changes the anatomy of the fruit abscission zone in Raphanus raphanistrum brassicaceae
Australian Journal of Botany, 2009Co-Authors: Mohammad Sadegh Taghizadeh, Simon Crawford, Marc E Nicolas, Roger D CousensAbstract:Raphanus raphanistrum L. is an important agricultural weed that often matures at a time of year when water availability is decreasing rapidly. We examined the development of the abscission zone under contrasting soil water treatments and exogenous application of Ethrel. Morphometric analyses of cell traits were used to quantify the effects. Although the abscission zone was visible in sections after 2 weeks under all water regimes, it was more distinctive for pods that had developed under water deficit and Ethrel application. Pod separation began on the outside and gradually extended through the inner cells until the pod was supported only by the xylem elements. The rate of weakening of the cells accelerated where pods developed under water deficit (both mild and severe) or were treated by Ethrel. Water deficit increased the sizes of cells in and adjacent to the abscission zone, doubling their cross-sectional area from well watered to severe water deficit. Ethrel, but not water deficit, significantly increased the thickness and the number of cells across the separation layer. Abscission scar diameter increased by ~50% with increasing water deficit. Notably, we observed some plants in which no abscission zone formed.
Jeffrey K. Conner - One of the best experts on this subject based on the ideXlab platform.
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effect of expanded variation in anther position on pollinator visitation to wild radish Raphanus raphanistrum
Annals of Botany, 2017Co-Authors: Yuval Sapir, Heather F Sahli, Vanessa A. Koelling, Keith Karoly, Frances N Knapczyk, Jeffrey K. ConnerAbstract:Background and Aims: Plant-pollinator interactions shape the evolution of flowers. Floral attraction and reward traits have often been shown to affect pollinator behaviour, but the possible effect of efficiency traits on visitation behaviour has rarely been addressed. Anther position, usually considered a trait that influences efficiency of pollen deposition on pollinators, was tested here for its effect on pollinator visitation rates and visit duration in flowers of wild radish, Raphanus raphanistrum . Methods: Artificial selection lines from two experiments that expanded the naturally occurring phenotypic variation in anther position were used. In one experiment, plant lines were selected either to increase or to decrease anther exsertion. The other experiment decreased anther dimorphism, which resulted in increased short stamen exsertion. The hypothesis was that increased exsertion would increase visitation of pollen foragers due to increased visual attraction. Another hypothesis was that exsertion of anthers above the corolla would interfere with nectar foragers and increase the duration of visit per flower. Key Results: In the exsertion selection experiment, increased exsertion of both short and long stamens resulted in an increased number of fly visits per plant, and in the dimorphism experiment bee visits increased with increased short stamen exsertion. The duration of visits of nectar feeders declined significantly with increasing long stamen exsertion, which was opposite to the hypothesis. Conclusions: Until now, anther position was considered to be an efficiency trait to enhance pollen uptake and deposition. Anther position in wild radish is shown here also to have an ecological significance in attracting pollen foragers. This study suggests an additional adaptive role for anther position beyond efficiency, and highlights the multiple ecological functions of floral traits in plant-pollinator interactions.
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consequences of whole genome triplication as revealed by comparative genomic analyses of the wild radish Raphanus raphanistrum and three other brassicaceae species
The Plant Cell, 2014Co-Authors: Gaurav D Moghe, Jeffrey K. Conner, David E Hufnagel, Haibao Tang, Yongli Xiao, Ian Dworkin, Christopher D Town, Shinhan ShiuAbstract:Polyploidization events are frequent among flowering plants, and the duplicate genes produced via such events contribute significantly to plant evolution. We sequenced the genome of wild radish (Raphanus raphanistrum), a Brassicaceae species that experienced a whole-genome triplication event prior to diverging from Brassica rapa. Despite substantial gene gains in these two species compared with Arabidopsis thaliana and Arabidopsis lyrata, ;70% of the orthologous groups experienced gene losses in R. raphanistrum and B. rapa, with most of the losses occurring prior to their divergence. The retained duplicates show substantial divergence in sequence and expression. Based on comparison of A. thaliana and R. raphanistrum ortholog floral expression levels, retained radish duplicates diverged primarily via maintenance of ancestral expression level in one copy and reduction of expression level in others. In addition, retained duplicates differed significantly from genes that reverted to singleton state in function, sequence composition, expression patterns, network connectivity, and rates of evolution. Using these properties, we established a statistical learning model for predicting whether a duplicate would be retained postpolyploidization. Overall, our study provides new insights into the processes of plant duplicate loss, retention, and functional divergence and highlights the need for further understanding factors controlling duplicate gene fate.
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adaptive differentiation of quantitative traits in the globally distributed weed wild radish Raphanus raphanistrum
Genetics, 2008Co-Authors: Heather F Sahli, Jeffrey K. Conner, Frank H Shaw, Stephen Howe, Allison LaleAbstract:Weedy species with wide geographical distributions may face strong selection to adapt to new environments, which can lead to adaptive genetic differentiation among populations. However, genetic drift, particularly due to founder effects, will also commonly result in differentiation in colonizing species. To test whether selection has contributed to trait divergence, we compared differentiation at eight microsatellite loci (measured as FST) to differentiation of quantitative floral and phenological traits (measured as QST) of wild radish (Raphanus raphanistrum) across populations from three continents. We sampled eight populations: seven naturalized populations and one from its native range. By comparing estimates of QST and FST, we found that petal size was the only floral trait that may have diverged more than expected due to drift alone, but inflorescence height, flowering time, and rosette formation have greatly diverged between the native and nonnative populations. Our results suggest the loss of a rosette and the evolution of early flowering time may have been the key adaptations enabling wild radish to become a major agricultural weed. Floral adaptation to different pollinators does not seem to have been as necessary for the success of wild radish in new environments.
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fitness effects of mutation accumulation in a natural outbred population of wild radish Raphanus raphanistrum comparison of field and greenhouse environments
Evolution, 2008Co-Authors: Angela J Roles, Jeffrey K. ConnerAbstract:Spontaneous deleterious mutation has been measured in a handful of organisms, always under laboratory conditions and usually employing inbred species or genotypes. We report the results of a mutation accumulation experiment with an outbred annual plant, Raphanus raphanistrum, with lifetime fitness measured in both the field and the greenhouse. This is the first study to report the effects of spontaneous mutation measured under field conditions. Two large replicate populations (Ne ≈ 600) were maintained with random mating in the greenhouse under relaxed selection for nine generations before the field assay was performed and ten generations before the greenhouse assay. Each generation, every individual was mated twice, once as a pollen donor and once as a pollen recipient, and a single seed from each plant was chosen randomly to create the next generation. The ancestral population was maintained as seeds at 4°C. Declines in lifetime fitness were observed in both the field (1.7% per generation; P = 0.27) and the greenhouse (0.6% per generation; P = 0.07). Significant increases in additive genetic variance for fitness were found for stems per day, flowers per stem, fruits per flower and seeds per fruit in the field as well as for fruits per flower in the greenhouse. Lack of significance of the fitness decline may be due to the short period of mutation accumulation, the use of outbred populations, or both. The percent declines in fitness are at the high end of the range observed in other mutation accumulation experiments and give some support to the idea that mutational effects may be magnified under harsher field conditions. Thus, measurement of mutational parameters under laboratory conditions may underestimate the effects of mutations in natural populations.
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visitation effectiveness and efficiency of 15 genera of visitors to wild radish Raphanus raphanistrum brassicaceae
American Journal of Botany, 2007Co-Authors: Heather F Sahli, Jeffrey K. ConnerAbstract:Plant-pollinator interactions are one of the most important and variable mutualisms in nature. Multiple pollinators often visit plants and can vary in visitation rates, pollen removal and deposition, and spatial and temporal distribution, altering plant reproduction and patterns of pollinator-mediated selection. Although some visitors may not be effective pollinators, pollinator effectiveness is rarely estimated directly as seed set resulting from a single visit by each taxon visiting generalist plants. For two years, effectiveness of visitors to wild radish, Raphanus raphanistrum, was quantified by counting seeds set and pollen grains removed as a result of a single visit. We calculated a pollinator's importance to plant reproduction as the product of visitation rate and single-visit seed set, and regressed pollinator body size on pollen-removal and on seed set effectiveness. Although pollinators differed in effectiveness and visitation rates, pollinator importance was primarily determined by visitation rates. In contrast to similar 2-yr studies, pollinator assemblage composition varied little, suggesting pollinator-mediated selection can be consistent across years for this generalist. Larger pollinators were more effective than smaller at effecting seed set, but body size was a poor predictor of pollen removal ability. Instead, pollen-removal effectiveness may be more influenced by foraging behavior than size.
Michael J. Walsh - One of the best experts on this subject based on the ideXlab platform.
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recurrent selection with reduced 2 4 d amine doses results in the rapid evolution of 2 4 d herbicide resistance in wild radish Raphanus raphanistrum l
Pest Management Science, 2016Co-Authors: Michael B. Ashworth, Michael J. Walsh, Ken Flower, Stephen B PowlesAbstract:BACKGROUND When used at effective doses, weed resistance to auxinic herbicides has been slow to evolve when compared with other modes of action. Here we report the evolutionary response of a herbicide-susceptible population of wild radish (Raphanus raphanistrum L.) and confirm that sublethal doses of 2,4-dichlorophenoxyacetic acid (2,4-D) amine can lead to the rapid evolution of 2,4-D resistance and cross-resistance to acetolactate synthase (ALS)-inhibiting herbicides. RESULTS Following four generations of 2,4-D selection, the progeny of a herbicide-susceptible wild radish population evolved 2,4-D resistance, increasing the LD50 from 16 to 138 g ha−1. Along with 2,4-D resistance, cross-resistance to the ALS-inhibiting herbicides metosulam (4.0-fold) and chlorsulfuron (4.5-fold) was evident. Pretreatment of the 2,4-D-selected population with the cytochrome P450 inhibitor malathion restored chlorsulfuron to full efficacy, indicating that cross-resistance to chlorsulfuron was likely due to P450-catalysed enhanced rates of herbicide metabolism. CONCLUSION This study is the first to confirm the rapid evolution of auxinic herbicide resistance through the use of low doses of 2,4-D and serves as a reminder that 2,4-D must always be used at highly effective doses. With the introduction of transgenic auxinic-herbicide-resistant crops in the Americas, there will be a marked increase in auxinic herbicide use and therefore the risk of resistance evolution. Auxinic herbicides should be used only at effective doses and with diversity if resistance is to remain a minimal issue. © 2016 Society of Chemical Industry
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transfer of 2 4 d resistance from Raphanus raphanistrum into brassica napus production of f1 hybrids through embryo rescue
Canadian Journal of Plant Science, 2016Co-Authors: Andrew J Dillon, Michael J. Walsh, Paul Kron, Mithila JugulamAbstract:Development of 2,4-D-resistant Brassica napus varieties is valuable for conservation tillage and post emergence control of broadleaf weeds. This research documents successful production and transfer of 2,4-D resistance from Raphanus raphanistrum (wild radish) into, Brassica napus via embryo rescue.
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Identification of glyphosate-resistant Lolium rigidum and Raphanus raphanistrum populations within the first Western Australian plantings of transgenic glyphosate-resistant canola
Crop and Pasture Science, 2015Co-Authors: Michael B. Ashworth, Ken C. Flower, Michael J. Walsh, Stephen B PowlesAbstract:Transgenic glyphosate-resistant canola was first commercially grown in Western Australia (WA) in 2010, providing an opportunity to obtain important baseline data regarding the level of glyphosate resistance in weeds following the exclusive use of glyphosate for in-crop weed control. In this study, two surveys (2010 and 2011) were conducted across the 14Mha of the grainbelt of WA. The 2010 survey was carried out at the late-flowering stage of glyphosate-resistant canola, whereas the 2011 survey was conducted at an earlier growth stage (6-8 leaves), ?2-3 weeks after the second in-crop glyphosate application. During the surveys, 239 fields were visited, representing an estimated combined area of 24000ha. The 2011 survey alone represented a subsample of 23% of the total glyphosate-resistant canola planting in the WA grainbelt for that season. Glyphosate resistance was identified in one population of wild radish (Raphanus raphanistrum L.) and in eight annual ryegrass (Lolium rigidum L.) populations. None of the tested capeweed (Arctotheca calendula (L.) Levyns) populations were glyphosate-resistant. In this survey, no populations of barley grass (Hordeum spp.), brome grass (Bromus spp.), wild oat (Avena spp.) or small-flowered mallow (Malva parviflora L.) survived glyphosate application. Despite a long history of pre-seeding and fallow glyphosate use in WA, this survey found that glyphosate still provides excellent in-crop control of most species; however, some resistance is evident, requiring diverse weed control techniques to limit their spread.
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identification of the first glyphosate resistant wild radish Raphanus raphanistrum l populations
Pest Management Science, 2014Co-Authors: Michael B. Ashworth, Michael J. Walsh, Ken Flower, Stephen B PowlesAbstract:BACKGROUND: In Australia, glyphosate has been used routinely to control wild radish (Raphanus raphanistrum L.) for the past 40 years. This study focuses on two field-evolved glyphosate-resistant populations of wild radish collected from the grainbelt of Western Australia. RESULTS: Two wild radish biotypes were confirmed to be glyphosate resistant by comparing R/S of two suspected populations. Based on R/S from dose–response curves, the R1 and R2 populations were 2.3 and 3.2 times more resistant to glyphosate respectively. Dose response on glyphosate-selected progeny (>1080 g ha −1 ) demonstrated that the glyphosate resistance mechanism was heritable. When compared with the pooled mortality results of three known susceptible populations (S1, S2 and S3), the R1 and R2 subpopulations were 3.4-fold and 4.5-fold more resistant at the LD 50 level respectively. Both populations were found to have multiple resistance to the phytoene desaturase inhibitor; diflufenican, the synthetic auxin; 2,4-D and the ALS inhibitors; chlorsulfuron, sulfometuron-methyl, imazethapyr and metosulam. CONCLUSIONS: This is the first report confirming glyphosate resistance evolution in wild radish and serves to re-emphasise the importance of diverse weed control strategies. Proactive and integrated measures for resistance management need to be developed to diversify control measures away from glyphosate and advance the use of non-herbicidal techniques. © 2014 Society of Chemical Industry Supporting information may be found in the online version of this article.
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Introgression of phenoxy herbicide resistance from Raphanus raphanistrum into Raphanus sativus
Plant Breeding, 2014Co-Authors: Mithila Jugulam, Michael J. Walsh, John Christopher HallAbstract:Phenoxy herbicides such as 2,4-dichlorophenoxy acetic acid (2,4-D) and 4-chloro-2-methylphenoxy acetic acid (MCPA) are selective herbicides used extensively in agriculture for weed control. Wild radish (Raphanus raphanistrum) is a problem weed across the globe and heavily infests crop fields in Australia. Phenoxy herbicides are used to selectively control dicot weeds, including wild radish. As a result of selection, phenoxy-resistant wild radish populations evolved in Western Australia. In this research, introgression of phenoxy resistance from wild radish to cultivated radish (Raphanus sativus) was investigated following classical breeding procedures. F1 progeny were generated by crossing MCPA-resistant R. raphanistrum and MCPA-susceptible R. sativus .F 1 hybrids were screened for MCPA resistance. The MCPA-resistant F1 hybrids were used to produce three generations of backcross progeny. Genetic analyses of F1 and backcross progeny demonstrated introgression of the MCPA-resistant trait from wild radish to cultivated radish. Implications of phenoxy resistance introgression into cultivated radish include potential development of herbicidetolerant radish cultivars or other members of the Brassicaceae family.
