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Nuclear ribosomal DNA
diversity of a cotton pest (Rotylenchulus reniformis)
in the United States
Yonathan Tilahun1*, Khairy Soliman1,
Kathy S. Lawrence 3, Leland J. Cseke2
and Joel W. Ochieng4
1Natural
Resources and Environmental Sciences, Alabama A and M
University, P.O. Box 1927 Normal, AL 35762, U.S.A.
2Department
of Biological Sciences, University of Alabama in Huntsville,
Huntsville, AL 35899, U.S.A.
3Department
of Entomology and Plant Pathology, Auburn University,
Auburn, AL 36049, U.S.A.
4Centre
for Plant Conservation Genetics, Southern Cross University,
Lismore, NSW 2480 Australia.
*Corresponding author. E-mail:
yontil@gmail.com. Tel:
+ 1-256-372-4547. Fax: + 1-256-372-8404.
Accepted
1 August, 2008 |
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The reniform nematode (Rotylenchulus reniformis) has
emerged as a major cotton pest in the United States. A
recent analysis of over 20 amphimictic populations of this
pest from the US and three other countries has shown no
sequence variation at the nuclear ribosomal internal
transcribed spacer (ITS) despite the region’s usual
variability. We investigated this unexpected outcome by
amplifying, cloning and sequencing two regions of the
nuclear ribosomal DNA (18S, ITS1) to ascertain whether any
variation occurred within and among populations of reniform
nematodes in Alabama, US. Both the nrITS1 and the relatively
conserved 18S region showed a fairly substantial amount of
variation among populations. The identity among ITS
sequences ranged from 1.00 to 0.86, while sequence identity
at the 18S ranged from 1.00 to 0.948. We conclude that
variation does exist in these sequences in reniform
nematodes, and the earlier report showing no ribosomal ITS
variation in this pest might have been caused by
preferential amplification of a conserved ITS paralog.
Current and future application towards resistance in cotton
varieties to this pest requires reliable information on the
molecular variability of the nematode in cotton-growing
areas.
Key
words:
Ribosomal DNA, ITS, 18S, reniform nematode. |
