Molecular and morphometric characterisation of Xiphinema ...

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Molecular and morphometric characterisation of Xiphinema ...

C. Cantalapiedra-Navarrete et al.

have significantly improved and facilitated the routine

identification of these nematodes. In addition, molecular

approaches using ribosomal DNA (rDNA) sequences

from partial 18S, ITS regions and the D2 and D3 expansion

segments of the 28S have been shown to be a useful

diagnostic tool in the characterisation and phylogenetic

relationships within plant-parasitic nematodes such

as Longidoridae, especially in cases where morphological

characters may lead to ambiguous interpretation (Ye et al.,

2004; He et al., 2005; Barsi & De Luca, 2008; Pedram et

al., 2009).

The objectives of this work were: i) to characterise morphologically

and morphometrically the Spanish population

of X. globosum and compare with previous descriptions;

ii) to characterise molecularly the Spanish population

using the D2-D3 28S rRNA, ITS1 and partial 18S

rRNA gene sequences; and iii) to study their phylogenetic

relationships with other Xiphinema species.

Materials and methods

NEMATODE POPULATIONS

The Spanish population of X. globosum was collected

in sandy soil around the roots of black alder, Alnus glutinosa

(L.) Gaertn., and river bank grapevine, Vitis riparia

Michx, in the canuto of Valdeinfierno in the Los Alcornocales

Regional Park, Alcalá de los Gazules, Cádiz

Province, southern Spain. The nematodes used in this

study were extracted from soil by centrifugal flotation

(Coolen, 1979) and by a modification of Cobb’s decanting

and sieving (Flegg, 1967) methods. Specimens for light

microscopy were killed by gentle heat, fixed in a solution

of 4% formaldehyde + 1% propionic acid and processed

to pure glycerin using Seinhorst’s (1966) method. Specimens

were examined using a Zeiss III compound microscope

with Nomarski differential interference contrast at

powers up to 1000× magnification. Measurements were

done using a drawing tube. Morphometric data were

processed using Statistix 9.0 (NH Analytical Software,

Roseville, MN, USA). Nematodes were compared with

type specimens (female paratype, slide T-2088p) kindly

provided by Dr Z. Handoo, from the USDA Nematode

Collection (Beltsville, MD, USA).

DNA EXTRACTION, PCRAND SEQUENCING

Nematode DNA was extracted from single individuals

and protocols for PCR as described by Castillo et al.

(2003) and Tanha Maafi et al. (2003) were followed. The

D2-D3 expansion segments of 28S rDNA were amplified

using the forward D2A (5 ′ -ACAAGTACCGTGAGGG

AAAGTTG-3 ′ ) and reverse D3B (5 ′ -TCGGAAGGAACC

AGCTACTA-3 ′ ) primers (Castillo et al., 2003; He et al.,

2005; Palomares-Rius et al., 2008). The forward primer

S-ITS (5 ′ -TTGATTACGTCCCTGCCCTTT-3 ′ ) and the

reverse primer A-ITS1 (5 ′ -ACGAGCCGAGTGATCCA

CCGATAAG-3 ′ ) were used for amplification of ITS1rDNA

region (Wang et al., 2002). The partial 18S rDNA

was amplified using forward primer SSU_F_04 (5 ′ -GCTT

GTCTCAAAGATTAAGCC-3 ′ ) and the reverse primer

SSU_R_81 (5 ′ -TGATCCWKCYGCAGGTTCAC-3 ′ )

(Griffiths et al., 2006). PCR products were purified

with a gel extraction kit (AccuPrep ® Gel Purification

Kit, Bioneer, Munpyeong-Dong, South Korea) according

to the manufacturer’s instructions, quantified using

a Nanodrop spectrophotometer (Nanodrop Technologies,

Wilmington, DE, USA) and used for direct DNA sequencing.

For the 18S gene the internal primer SSU_R_13 (5 ′ -

GGGCATCACAGACCTGTTA-3) (sequence available

online at http://www.nematodes.org/barcoding/sourhope/

nemoprimers.html) was also used. DNA fragments from

two independent PCR amplifications from two different

nematodes were sequenced in both directions using the

same primers with a terminator cycle sequencing ready

reaction kit (BigDye; Perkin-Elmer Applied Biosystems,

Warrington, UK) according to the manufacturer’s instructions.

The resulting products were purified and run on

a DNA multicapillary sequencer (Model 3130XL genetic

analyser; Applied Biosystems, Foster City, CA,

USA) at the Stabvida sequencing facilities (Oeiras, Portugal).

Sequences were deposited in GenBank under accession

numbers GU549474 for D2-D3 expansion segments

of 28S rDNA, GU549475 for the ITS1-rDNA and

GU549476 for partial 18S rDNA regions.

PHYLOGENETIC ANALYSES

D2-D3 expansion segments of 28S, ITS1 and partial

18S rDNA sequences of different Xiphinema spp. from

GenBank were used for phylogenetic reconstruction. Outgroup

taxa for each dataset were chosen according to previous

published data (Pedram et al., 2009). The newly

obtained and published sequences for each gene were

aligned using ClustalW (Thompson et al., 1994) with

default parameters. Sequence alignments were manually

edited using BioEdit (Hall, 1999). Phylogenetic analysis

of the sequence data sets was performed with maximum

likelihood (ML) using PAUP* 4b10 (Swofford, 2003) and

Bayesian inference (BI) using MrBayes 3.1.2 (Huelsen-

18 Nematology

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