3 results
Dormancy-linked Population Structure of Weedy Rice (Oryza sp.)
- Te-Ming Tseng, Vinod K. Shivrain, Amy Lawton-Rauh, Nilda R. Burgos
-
- Journal:
- Weed Science / Volume 66 / Issue 3 / May 2018
- Published online by Cambridge University Press:
- 09 May 2018, pp. 331-339
-
- Article
- Export citation
-
Seed dormancy allows weedy rice (Oryza sp.) to persist in rice production systems. Weedy and wild relatives of rice (Oryza sativa L.) exhibit different levels of dormancy, which allows them to escape weed management tactics, increasing the potential for flowering synchronization, and therefore gene flow, between weedy Oryza sp. and cultivated rice. In this study, we determined the genetic diversity and divergence of representative dormant and nondormant weedy Oryza sp. groups from Arkansas. Twenty-five simple sequence repeat markers closely associated with seed dormancy were used. Four populations were included: dormant blackhull, dormant strawhull, nondormant blackhull, and nondormant strawhull. The overall gene diversity was 0.355, indicating considerable genetic variation among populations in these dormancy-related loci. Gene diversity among blackhull populations (0.398) was higher than among strawhull populations (0.245). Higher genetic diversity was also observed within and among dormant populations than in nondormant populations. Cluster analysis of 16 accessions, based on Nei’s genetic distance, showed four clusters. Clusters I, III, and IV consisted of only blackhull accessions, whereas Cluster II comprised only strawhull accessions. These four clusters did not separate cleanly into dormant and nondormant populations, indicating that not all markers were tightly linked to dormancy. The strawhull groups were most distant from blackhull weedy Oryza sp. groups. These data indicate complex genetic control of the dormancy trait, as dormant individuals exhibited higher genetic diversity than nondormant individuals. Seed-dormancy trait contributes to population structure of weedy Oryza sp., but this influence is less than that of hull color. Markers unique to the dormant populations are good candidates for follow-up studies on the control of seed dormancy in weedy Oryza sp.
EPSPS Gene Amplification Primarily Confers Glyphosate Resistance among Arkansas Palmer amaranth (Amaranthus palmeri) Populations
- Shilpa Singh, Vijay Singh, Amy Lawton-Rauh, Muthukumar V. Bagavathiannan, Nilda Roma-Burgos
-
- Journal:
- Weed Science / Volume 66 / Issue 3 / May 2018
- Published online by Cambridge University Press:
- 26 January 2018, pp. 293-300
-
- Article
- Export citation
-
Research was conducted to determine whether resistance to glyphosate among Palmer amaranth (Amaranthus palmeri S. Watson) populations within the U.S. state of Arkansas was due solely to increased EPSPS gene copy number and whether gene copy number is correlated with resistance level to glyphosate. One hundred and fifteen A. palmeri accessions were treated with 840 g ae ha−1 glyphosate. Twenty of these accessions, selected to represent a broad range of responses to glyphosate, underwent further testing. Seven of the accessions were controlled with this dose; the rest were resistant. The effective dose to cause 50% injury (ED50) for susceptible accessions ranged from 28 to 207 g ha−1. The glyphosate-resistant (GR) accessions had ED50 values ranging from 494 to 1,355 g ha−1, a 3- to 48-fold resistance level compared with the susceptible standard (SS). The 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene relative copy number was determined for 20 accessions, 4 plants accession−1. Resistant plants from five GR accessions (38% of resistant plants tested) did not have increased EPSPS gene copies. Resistant plants from the remaining eight GR accessions (62% of resistant plants tested) had 19 to 224 more EPSPS gene copies than the SS. Among the accessions tested, injury declined 4% with every additional EPSPS copy. ED50 values were directly correlated with EPSPS copy number. The highly resistant accession MIS11-B had an ED50 of 1,355 g ha−1 and 150 gene copies. Partial sequences of EPSPS from GR accessions without EPSPS amplification did not contain any of the known resistance-conferring mutations. Nearly 40% of GR accessions putatively harbor non–target site resistance mechanisms. Therefore, elevated EPSPS gene copy number is associated with glyphosate resistance among A. palmeri from Arkansas.
Agricultural Weed Research: A Critique and Two Proposals
- Sarah M. Ward, Roger D. Cousens, Muthukumar V. Bagavathiannan, Jacob N. Barney, Hugh J. Beckie, Roberto Busi, Adam S. Davis, Jeffrey S. Dukes, Frank Forcella, Robert P. Freckleton, Eric R. Gallandt, Linda M. Hall, Marie Jasieniuk, Amy Lawton-Rauh, Erik A. Lehnhoff, Matt Liebman, Bruce D. Maxwell, Mohsen B. Mesgaran, Justine V. Murray, Paul Neve, Martin A. Nuñez, Anibal Pauchard, Simon A. Queenborough, Bruce L. Webber
-
- Journal:
- Weed Science / Volume 62 / Issue 4 / December 2014
- Published online by Cambridge University Press:
- 20 January 2017, pp. 672-678
-
- Article
- Export citation
-
Two broad aims drive weed science research: improved management and improved understanding of weed biology and ecology. In recent years, agricultural weed research addressing these two aims has effectively split into separate subdisciplines despite repeated calls for greater integration. Although some excellent work is being done, agricultural weed research has developed a very high level of repetitiveness, a preponderance of purely descriptive studies, and has failed to clearly articulate novel hypotheses linked to established bodies of ecological and evolutionary theory. In contrast, invasive plant research attracts a diverse cadre of nonweed scientists using invasions to explore broader and more integrated biological questions grounded in theory. We propose that although studies focused on weed management remain vitally important, agricultural weed research would benefit from deeper theoretical justification, a broader vision, and increased collaboration across diverse disciplines. To initiate change in this direction, we call for more emphasis on interdisciplinary training for weed scientists, and for focused workshops and working groups to develop specific areas of research and promote interactions among weed scientists and with the wider scientific community.