Understanding the weedy Chenopodium complex in the north central states

Singh, Sukhvinder

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Description

Title

Understanding the weedy Chenopodium complex in the north central states

Author(s)

Singh, Sukhvinder

Issue Date

2010-08-31T20:01:52Z

Director of Research (if dissertation) or Advisor (if thesis)

Tranel, Patrick J.

Doctoral Committee Chair(s)

Tranel, Patrick J.

Committee Member(s)

• Hudson, Matthew E.
• Levin, Geoffrey A.
• Hager, Aaron G.

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Chenopodium
• glyphosate tolerance
• molecular markers
• DNA content

Abstract

The genus Chenopodium consists of several important weed species, including Chenopodium album, C. berlandieri, C. strictum, and C. ficifolium. All of these species share similar vegetative morphology and high phenotypic plasticity, which makes it difficult to correctly identify these species. All of these weedy Chenopodium species have developed resistance to one or more classes of herbicides. An experiment was conducted to determine if there is variability in response of Chenopodium species present in the North Central states to glyphosate. Our results indicate variable responses within and among the Chenopodium species. Species such as C. berlandieri and C. ficifolium had higher levels of tolerance to glyphosate than did various accessions of C. album. In another experiment, 33 populations of Chenopodium sampled across six North Central states were screened with glyphosate. The results showed variable responses to glyphosate within and among the Chenopodium populations. In general, the Chenopodium populations from Iowa were more tolerant, but some biotypes from North Dakota, Indiana and Kansas also had significantly high tolerance to glyphosate. Given there are species other than C. album that have high tolerance to glyphosate, and there are Chenopodium populations across the North Central states that showed tolerance to glyphosate, one intriguing question was to whether the Chenopodium populations were either biotypes of C. album were or are more closely related to other species such as C. berlandieri, C. strictum or C. ficifolium, which would indicate that there has been a species shift. To investigate which species are prevalent in North Central states, 12 Chenopodium species were investigated using morphological DNA content values and sequence data. With the exception of morphological characters such as pericarp covering the seeds, calyx shape (keeled or not) and DNA content of the species, most of the morphological characters were not phylogenetically informative. The morphological characters were useful in distinguishing some species from others, but with an increase in number of species under investigation, there was overlap of morphological characters within closely related species, and hence one cannot use morphological markers alone to differentiate the Chenopodium species. Three DNA sequence based markers, ITS (nuclear), matK and trnD-trnT (chloroplast) were explored. The sequence data were subjected to maximum parsimony and Bayesian analyses. Irrespective of the method used for tree estimation, all three markers gave similar tree topologies, but ITS markers gave the greatest number of polymorphic sites. The ITS based phylogenetic tree was well resolved. Some closely related species such as C. strictum, C. berlandieri and C. album shared high sequence similarity among homologous genes, but these species were easily differentiated with the support of the genome size data. Samples of C. strictum had a 2C value of 2.0 pg, which was different than C. album (3.6 pg/2C). Chenopodium populations from North Central states were also tested with ITS markers, and DNA content values were also obtained from a few samples. Based on the sequence data, results indicated that all the field samples were closely related to C. album, and also the genome sizes of all the populations were close to the genome size values of different accessions of C. album. In conclusion, all the Chenopodium samples that were sampled for our experiment were closely related to C. album, and the increase in reports of common lambsquarters populations developing tolerance to glyphosate most likely is due to evolution within C. album and not because of a shift in weed species.

Graduation Semester

2010-08

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Copyright and License Information

Copyright 2010 Sukhvinder Singh

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