Introgression of Root-Knot Nematode Resistance into ... - PubAg - USDA

RESEARCH

Introgression of Root-Knot Nematode Resistance into Tetraploid Cottons P. A. Roberts* and M. Ulloa*

ABSTRACT Root-knot nematode (RKN) resistance introgression into tetraploid cotton (Gossypium spp.) and its ancestral genome origin were examined. Resistance sources (‘Acala NemX’, ‘Clevewilt 6’, Auburn 623 RNR) were compared with diverse germplasm using simple sequence repeat (SSR) markers from chromosomes 7, 11, and 14 and DNA sequence information. Differences (P 3) (Fig. 3).

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CROP SCIENCE, VOL. 50, MAY– JUNE 2010

Table 2. Dissimilarities distance from eight simple sequence repeat (SSR) markers (BNL1066, BNL1231, BNL3279, CIR003, CIR069, CIR196, CIR316, and MUCS088) from chromosome 11. Distances were calculated using PAUP* 4.0 beta software (Swofford, 2002). Entries 1 Pimas 2 Acala NemX 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Clevewilt 6 Coker 100 FBCX 2B LARNs Wild Mexico Jack Jones Stoneville 2 A1 A2 D1 D2 D3_d_26 D4 D5 D7 D8

1

–

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

0.299 0.299 0.299 0.313 0.299 0.239 0.284 0.233 0.202 0.306 0.403 0.299 0.388 0.269 0.313 0.388 – 0.000 0.000 0.015 0.000 0.060 0.015 0.271 0.252 0.366 0.343 0.299 0.418 0.299 0.284 0.388 – 0.000 0.015 0.000 0.060 0.015 0.271 0.252 0.366 0.343 0.299 0.418 0.299 0.284 0.388 – 0.015 0.015 0.060 0.015 0.271 0.252 0.366 0.343 0.299 0.418 0.299 0.284 0.388 – 0.030 0.075 0.030 0.286 0.267 0.351 0.328 0.284 0.403 0.313 0.299 0.403 – 0.045 0.000 0.256 0.237 0.351 0.328 0.284 0.403 0.284 0.269 0.408 – 0.045 0.212 0.192 0.321 0.343 0.239 0.388 0.239 0.388 0.358 – 0.256 0.237 0.351 0.328 0.284 0.403 0.284 0.269 0.403 – 0.098 0.341 0.361 0.217 0.326 0.197 0.321 0.445 – 0.309 0.416 0.242 0.322 0.166 0.327 0.431 – 0.336 0.292 0.306 0.396 0.336 0.423 – 0.313 0.313 0.403 0.328 0.522 – 0.343 0.269 0.328 0.478 – 0.418 0.373 0.418 – 0.418 0.358 – 0.373 –

Fig. 3. Neighbor-joining dendogram or tree based on dissimilarity distance from eight simple sequence repeat (SSR) markers (BNL1066, BNL1231, BNL3279, CIR 003, CIR069, CIR196, CIR316, and MUCS088) from chromosome 11 using the numerical taxonomy and multivariate analysis system (NTSYS-pc) version 2.2 (Rohlf, 2002). CROP SCIENCE, VOL. 50, MAY– JUNE 2010

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Fig. 4. DNA sequence alignment from MUCS088 simple sequence repeat (SSR) marker of different cotton backgrounds using Lasergene V 7.2 computer program (DNASTAR, Inc., Madison, WI) and the Jotun Hein (Hein, 1990) method for generating percentage identities.

Sequence of Alleles (DNA Fragments) from Genomic Regions of Resistance Introgression The ancestral introgression of RKN resistance was examined further with DNA sequencing information from alleles (DNA fragment for this section) of two previously reported SSR markers [CIR316, Wang et al. (2006a), and MUCS088, Wang et al. (2008)] linked to RKN resistance genes on chromosome 11. Primer pairs from CIR316 and MUCS088 markers were utilized to amplify genomic DNA fragments from individual plants of selected cotton entries (Tables 3 and 4). After multiple alignments and verification of DNA sequences from all entries, 15 DNA sequences were selected and deposited in Genebank from primer pair-marker MUCS088 (accession Nos. FJ599673–FJ599687), and 11 sequences were selected from primer pair-marker CIR316 (accession Nos. FJ599688–599698). For MUCS088, the 15 selected fragments varied in sizes from 141 to 153 bp (153–147, 145, and 143–141 bp). We selected two fragments with 151 bp and 149 bp from the allotetraploid G. barbadense and three fragments from allotetraploid G. hirsutum with 143, 142, and 141 bp. The range of sequenced DNA fragments from the A and D diploid genome species was 145 bp to 153 bp (Fig. 4). Percentage identity or similarity of DNA sequences calculated by the Jotun Hein method (Hein, 1990) revealed that the G. 946

barbadense fragments were closest to G. arboreum (A2) and G. thurberi (D1) diploid species (Table 3). The sequences were also used to construct phylogenetic trees. The neighbor-joining phylogenetic tree (Fig. 5A) showed the presence of two broad clades in the phylogram, one for G. barbadense and one for G. hirsutum cottons (Fig. 5A). All the sequences (Fig. 4) from an individual clade of the neighbor-joining tree were aligned and compared to detect the putative SNP. These sequences were also checked for variation in base pair number in the SSR motif repeats or number variation of two or three bp at a single position between two entries. The alignment and comparison of all sequences did not reveal a clear distinction between A and D genome species for the origin of introgression into the allotetraploid DNA cottons (Fig. 4). With the strategy of identifying sequence differences in an individual clade, we were able to detect a putative SNP (C) in the TC motif only present in the D1 genome, G. thurberi (148 and 152 bp) and G. barbadense (AD2) (149 bp). In addition, a putative SNP (C) in the G. hirsutum (AD1) fragments (141, 142, and 143 bp) was observed to be present in the D genome G. raimondii Ulbr. (D5) (data not shown). For CIR316, the 11 sequenced fragments varied in size from 189 to 207 bp (Fig. 6). We selected two fragments with 190 and 200 bp from G. barbadense and three fragments from G. hirsutum entries with 197, 199, and 207 bp. For the allele closely linked to the rkn1 locus (Wang et al., 2006a), we harvested fragments ranging from 204 to 207

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Table 3. Percentage identity (similarity) of different cotton backgrounds from DNA sequence information obtained from selected allele-amplicons for each entry from MUCS088 simple sequence repeat (SSR) marker. Lasergene V 7.2 computer program (DNASTAR, Inc., Madison, WI) and the Jotun Hein Method (Hein, 1990) were used for generating percentage identities.

Entries

1 2 3

CMD MUCS088 (153) Pima 3-79 (151) Pima S-6, Pima S-7, Pima 3-79 (149)

4

Auburn 634 RNR, Clevewilt6, Acala NemX, Wild Mexico Jack Jones, TM-1 (143)

5 6 7 8 9 10 11 12 13 14 15 16

Auburn 634 RNR (142) Wild Mexico Jack Jones (141) A1-18, A 2-30 (149) A1-18 (147) A1-18, A 2-30 (145) A 2-194 (150) A 2-30 (147) D1 (152) D1, D8 (150) D1 (148) D8 (151) D5 (148)

2

3

98.7 98.7 – 100.0 –

4

5

6

7

8

9

10

11

12

13

14

15

16

97.9 99.3 99.3

98.6 98.6 98.6

97.2 98.6 98.6

99.3 98.0 98.0

98.6 97.3 97.3

99.3 97.9 97.9

98.0 98.7 98.7

99.3 97.9 97.9

98.0 98.7 98.7

98.0 98.7 98.7

98.0 98.0 98.0

98.6 97.3 97.3

97.3 97.3 97.3

–

99.3

99.3

98.6

97.9

98.6

97.9

98.6

97.9

97.9

97.2

97.9

97.9

–

98.6 –

99.3 97.9 –

98.6 99.3 97.2 97.9 99.3 100.0 – 99.3 –

98.6 99.3 98.6 98.6 97.2 97.9 97.2 97.2 98.0 100.0 98.0 98.0 97.3 98.6 97.3 97.3 97.9 100.0 97.9 97.9 – 97.9 100.0 100.0 – 97.9 97.9 – 100.0 –

97.9 96.5 97.3 96.6 97.2 99.3 97.2 99.3 99.3 –

98.6 97.2 99.3 98.6 99.3 97.3 99.3 97.3 97.3 96.6 –

98.6 97.2 97.9 97.3 97.9 97.3 97.9 97.3 97.3 96.6 97.3 –

bp from the three major G. hirsutum germplasm sources of RKN resistance (N901, Acala NemX, Clevewilt 6, and Auburn 634 RNR). The size variation was the result of missing nucleotides (A) at bp positions 49 to 51. However,

the Clevewilt 6 DNA fragment (207 bp) was observed with a G nucleotide at bp position 49 (Fig. 6). Sequenced fragments from A and D diploid genome species ranged from 189 to 216 bp (Fig. 6). We only sequenced DNA fragments

Fig. 5. Neighbor-joining dendograms or trees from DNA sequence information. 5A) Neighbor-joining tree of different cotton backgrounds from DNA sequence information obtained from selected allele-amplicons for each entry from MUCS088 simple sequence repeat (SSR) marker. Lasergene V 7.2 computer program (DNASTAR, Inc., Madison, WI) and the Jotun Hein (Hein, 1990) method were used for generating percentage identities. 5B) Neighbor-joining tree of different cotton backgrounds from DNA sequence information obtained from selected allele-amplicons for each entry from CIR316 SSR marker. Lasergene V 7.2 computer program (DNASTAR, Inc., Madison, WI) and the ClustalV (Higgins and Sharp, 1989) method were used for generating percentage identities. CROP SCIENCE, VOL. 50, MAY– JUNE 2010

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Fig. 6. DNA sequence alignment of different cotton backgrounds from CIR316 simple sequence repeat (SSR) marker. Lasergene V 7.2 computer program (DNASTAR, Inc., Madison, WI) and the ClustalV (Higgins and Sharp, 1989) method were used for generating percentage identities.

from G. trilobum (D8) for CIR316 because this species was the one showing similar fragment sizes to the allotetraploid species. Percentage identity calculated by the ClustalV (Higgins and Sharp, 1989) method from DNA sequences revealed that the G. barbadense cottons and G. hirsutum Clevewilt 6 (207 bp) were closest to G. herbaceum (A1) and G. arboreum (A2) as well to G. trilobum (D8) diploid species. The other G. hirsutum DNA fragments were closer to G. raimondii (D5) (Table 4). The neighbor-joining phylogenetic tree had two broad clades, one for G. barbadense and one for G. hirsutum (Fig. 5B). Alignment and comparison of all sequences did not reveal a clear distinction between A and D genome species for the origin of introgression into allotetraploid cottons (Fig. 6). For sequence differences in an individual clade, two putative SNPs (A) were present in the G. trilobum D8 genome (200 bp) and AD2 G. barbadense cottons (190 bp). In addition, we detected putative SNPs (T) in AD1 G. hirsutum Clevewilt 6 (207 bp), A2 G. arboreum (200 bp), D8 G. trilobum (200 bp), and AD2 G. barbadense (200 bp) (data not shown). Additional analyses for specific alleles (206–207 bp linked to resistance and 199 bp linked 948

to susceptibility) of CIR316 marker located on chromosome 11 revealed a putative haplotype between resistant and susceptible entries calculated by the Jotun Hein method (Hein, 1990). The haplotype SNP positions for the resistant/susceptible state were observed at the base positions: G/A 88 bp, T/G 91 bp, T/C 93 bp, T/G 105 bp, and T/A 110 bp (data not shown).

DISCUSSION To examine the introgression of RKN resistance and its ancestral genome origin, we compared the three major germplasm sources (Acala NemX, Clevewilt 6, and Auburn 623 RNR) of RKN resistance and diverse germplasm, using selected SSR markers from chromosomes 7, 11, and 14 and sequence DNA information. The RKN resistance phenotyping results confirmed previous reports of the resistance levels in most of the modern RKN resistant germplasm sources and their derivatives, as illustrated in the pedigrees in Fig. 1, and identified a set of RKN resistant germplasm lines for the DNA marker and sequence analysis. This included the high resistance levels in Acala NemX

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Table 4. Percentage identity (similarity) of different cotton backgrounds from DNA sequence information of single sequence repeat (SSR) marker CIR316 obtained from selected allele-amplicons for each entry. Lasergene V 7.2 computer program (DNASTAR, Inc., Madison, WI) and the ClustalV Method (Higgins and Sharp, 1989) were used for generating percentage identities. Entries 1 2 3 4 5 6 7 8 9 10 11 12

CMD CIR316 (200) Clevewilt 6 (207) Auburn 634 RNR, Clevewilt 6, Acala NemX, N901 (199) Clevewilt 6 (197) Wild Mexico Jack Jones (197) Pima S-7 (190) Pima S-7 (200) A1-30 (216) A 2-30 (200) D8-6 (189) D8 (200) D5 (197)

2

3

4

5

6

7

8

9

10

11

12

83.0 –

92.0 87.9 –

89.3 87.8 97.5 –

89.3 88.3 97.5 99.5 –

84.2 90.5 88.9 88.9 88.9 –

84.5 94.5 89.4 89.9 90.4 90.0 –

82.0 93.7 86.9 86.8 87.8 92.6 93.5 –

83.0 94.5 87.9 87.8 87.3 88.4 93.5 93.0 –

84.7 93.7 89.4 89.4 89.4 97.4 90.5 92.6 88.9 –

85.0 95.0 89.9 90.4 90.9 90.5 99.5 94.0 94.0 91.0 –

88.8 87.8 97.0 99.0 99.5 88.4 89.8 87.3 86.8 88.9 90.4 –

and Auburn 623 RNR, and Auburn 634 RNR and M-lines derived from the Auburn source, plus the moderate resistance in Clevewilt 6 and WMJJ, and low resistance in Auburn 56. The recent pedigree relationships of these lines and cultivars are established and indicate the importance of Clevewilt 6 and WMJJ as the resistance donors for the Auburn germplasm sources (Fig. 1B). Screening of the earlier 1900s pedigree lines for the Auburn source of resistance, for which the record is incomplete (Fig. 1B), identified Lone Star, Coker Foster, and Coker 100 as primary resistance donors, while Stoneville 2 and Stoneville 3 were susceptible or with weak resistance, respectively. In the pedigree of Acala NemX (Fig. 1A), the Missouri breeding line FBCX-2 was resistant, and derived line N0044-1 was highly resistant, indicating that FBCX-2 was a key RKN resistance donor, and that AXTE 22, the other parent of the N-line series (which was unavailable for testing), also contributed one or more resistance genes. FBXC-2 and AXTE 22 had complex pedigrees including triple hybrids (G. arboreum-thurberi-hirsutum) (Fig. 1A), among which G. arboreum had close genome association with the RKN resistant G. hirsutum group as indicated by the RKN chromosome 11 markers and sequence data. We scrutinized alleles from the 14 selected SSRs from chromosomes 7 (Shen et al., 2006; Ulloa et al., 2009), 11 (Wang et al., 2006a), and 14 (Ynturi et al., 2006) because of their previously identified association with RKN resistance from our diverse cotton array. Each of these SSR markers amplified novel alleles or DNA fragments in the ancestral A or D genome species not observed in the tetraploid entries. Only the SSR CIR316 allele (206–207 bp) marker located on chromosome 11 was observed on the cotton entries that had resistant phenotypes, confirming the importance of chromosome 11 for RKN resistance. All the other alleles from other SSRs did not associate with the resistance phenotype, indicating that they were not informative as markers linked to major resistance determinants. For some, such as the MUCS088 allele associated with the transgressive resistance CROP SCIENCE, VOL. 50, MAY– JUNE 2010

factor RKN2 in susceptible Pima S-7 (Wang et al., 2008), the association with the resistance phenotype would not be recognized in genetic backgrounds which lacked a primary gene for resistance, because its contribution to resistance is only generated by epistatic interaction between the R genes. When we focused more directly on chromosome 11 to examine the ancestral genome origin of RKN resistance introgression, the closest average genetic relatedness or genetic distances to the allotetraploid RKN resistance backgrounds generated from eight chromosome 11 SSRs were observed with the Asiatic diploid A genome, G. arboreum (A2), indicating it as the probable source of introgression (Table 2; Fig. 2; Wang et al., 2008). A larger distance was found between the tetraploids AD1 and AD2. This observation may have resulted from only targeting this specific region for chromosome 11 and not the entire genome. However, markers based on electrophoretic differences, including restriction fragment length polymorphisms (RFLPs), amplified fragment length polymorphisms (AFLPs), and SSRs can sometimes mask underlying genetic variation. This can complicate marker discovery and application, especially in the complex polyploid cotton genome. Single-nucleotide polymorphism provides access to sequence differences directly by single-base variations in the genetic code usually represented as two, or sometimes three, different bases at a single position (Ulloa et al., 2007). We focused on DNA sequencing information from alleles (DNA fragments) of specific primer pairs from CIR316 (Wang et al., 2006a) and MUCS088 (Wang et al., 2008) markers which are known to be linked to RKN resistance genes, using comparisons of entries from the three major Acala and Upland germplasm sources of RKN resistance, G. hirsutum [Acala NemX (N901), Clevewilt 6, and Auburn 634 RNR], RKN susceptible allotetraploid entries (Pima S-6, Pima S-7, Pima 3-79, TM-1, and moderately tolerant WMJJ), and A and D diploid genome species. After multiple alignments and verification of DNA sequences from all entries, we were able to run different analyses on 15 DNA

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sequences of MUCS088 and on 11 sequences of CIR316. DNA sequences between RKN resistant and susceptible entries for CIR316 alleles provide additional information for developing SNP markers to optimize MAS. Tetraploid Acala and Upland (AD1) and Pima (AD2) cottons showing the same SSR marker amplification alleles as G. arboreum (A 2) might suggest that RKN resistance was introduced from the diploid cotton A 2 genome (genetic distance ranging from 0.19 to 0.27 distances) as we have implied previously (Wang et al., 2008). However, DNA sequence differences from PCR amplified products in the tested A and D diploid genomes also suggested a pattern of variation developed during cotton genome evolution. Percentage identity from MUCS088 and CIR316 DNA sequences revealed that the Pima cottons and Upland RKN resistant cotton Clevewilt 6 (206–207 bp) were closer not only to A 2 but also to G. herbaceum (A1), G. thurberi (D1), and G. trilobum (D8) diploid species, while other Upland DNA sequences were closer to G. raimondii (D5). This finding is supported by the DNA sequence information because G. arboreum (A 2) and G. thurberi (D1), which have similar putative SNPs (C) at the DNA level, are not similar to G. raimondii (D5), which is considered to be the closest relative to tetraploid cottons (Wendel and Cronn, 2003). It is possible that D8 (G. trilobum) is the ancestor of G. thurberi (D1) because these two species grown under similar environments and are very similar morphologically, although they have different specific habitats ( J. Stewart and M. Ulloa, personal communication, 2009). D8 is found closer to the equator, therefore we propose that D1 is a dispersed species from D8 that eventually migrated as far north as the Arizona desert. More research is needed to fully understand and determine the ancestral introgression of RKN resistance into Acala and Upland tetraploid cottons. Recently, Ulloa et al. (2009) reported that RKN resistance genes rkn1 and RKN2 were positioned on chromosome 11, and SSR markers CIR316 and MUCS088 on chromosomes 11 and 21 showed the association of two different chromosomes with RKN resistance, supporting that gene interactions occurred in these two chromosomes. Allotetraploid cottons have 26 pairs of chromosomes. Chromosomes 11 and 21 are homeologous and between which locus duplication and gene interactions have occurred (Ulloa et al., 2007; Ulloa et al., 2009). Our results support the view that interaction between these homeologous chromosomes 11 and 21 has contributed to the genetic structure of nematode resistance trait determinants in the Acala and Upland and the Pima or Acala/Upland and Pima cottons. Further fine mapping and physical mapping efforts of these chromosome regions should help to reveal the detailed structure of the nematode resistance gene specificities in this region. Results from this research indicate that the introgression of RKN resistance into Acala and Upland tetraploid cottons occurred 950

by artificial hybridization with ancestral genome origin from G. arboreum (A2) and G. thurberi (D1), and also G. trilobum (D8) diploid species, as outlined in the breeding pedigrees, and not during cotton genome evolution. We conclude that breeding for optimal resistance must be based on selection of progenies with combinations of determinant genes homozygous for RKN resistance. Acknowledgments This study was funded in part by a Cooperative Research Agreement from Cotton Incorporated and a grant from the University of California Discovery Grant (BioSTAR) Program (P.R.). The authors thank Stephen Oakley (California Planting Cotton Seed Distributors), James Starr, (Texas A & M Univ.), and USDA Cotton Germplasm Collection (College Station, TX) for providing cotton seed, and Kathie Carter, Sherry Ellberg, William Matthews, and Teresa Mullens for technical help. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U. S. Department of Agriculture.

References Bridge, J., and S.L.J. Page. 1980. Estimation of root-knot nematode infestation levels on roots using a rating chart. Trop. Pest Manage. 26:296–298. Felsenstein, J. 1985. Confidence limits on phylogenies: An approach using the bootstrap. Org. Evolution 39:783–791. Frelichowski, J.E., M.B. Palmer, D. Main, J.P. Tomkins, R.G. Cantrell, D.M. Stelly, J. Yu, R.J. Kohel, and M. Ulloa. 2006. Cotton genome mapping with new microsatellites from Acala ‘Maxxa’ BAC-ends. Mol. Gen. Genomics. 275:479–491. Fryxell, P.A. 1992. A revised taxonomic interpretation of Gossypium L. (Malvaceae). Rheedea 2:108–165. Fryxell, P.A., L.A. Craven, J. McD. Stewart. 1992. A revision of Gossypium sect. Grandicalyx (Malvaceae), including the description of six new species. Syst. Bot. 17:91–114. Hein, J.J. 1990. Unified approach to alignment and phylogenies. Methods Enzymol. 183:626–645. Higgins, D.G., and P.M. Sharp. 1989. Fast and sensitive multiple sequence alignments on a microcomputer. CABIOS 5:151– 153. Hyer, A.H., and E.C. Jorgenson. 1984. Root-knot nematode resistance in cotton breeding: Techniques and results. p. 377–379. In Proc. Beltwide Cotton Conf., Atlanta, GA. 8–12 Jan. 1984. Natl. Cotton Counc. Am., Memphis, TN. Hyer, A.H., E.C. Jorgenson, R.H. Garber, and S. Smith. 1979. Resistance to root-knot nematode in control of root-knot nematode Fusarium wilt disease complex in cotton Gossypium hirsutum. Crop Sci. 19:898–901. McPherson, R.G., J.N. Jenkins, J.C. McCarty, and C. Watson. 1995. Combining ability analysis of root-knot nematode resistance in cotton. Crop Sci. 35:373–375. McPherson, R.G., J.N. Jenkins, C. Watson, and J.C. McCarty. 2004. Inheritance of root-knot nematode resistance in M-315 RNR and M78-RNR cotton. J. Cotton Sci. 8:154–161. Nei, M. 1972. Genetic distance between populations. Am. Nat. 106:283–292. Niu, C., D.J. Hinchliffe, R.G. Cantrell, C. Wang, P.A. Roberts, and J. Zhang. 2007. Identification of molecular markers

WWW.CROPS.ORG


associated with root-knot nematode resistance in upland cotton. Crop Sci. 47:951–960. Oakley, S.R. 1995. CPCSD Acala C-225: A new nematode-resistant Acala variety for California’s San Joaquin Valley. p. 39. In Proc. of Beltwide Cotton Conf., San Antonio, TX. 4–7 Jan. 1995. Natl Cotton Counc. Am., Memphis, TN. Ogallo, J.L., P.B. Goodell, J. Eckert, and P.A. Roberts. 1999. Management of root-knot nematodes with resistant cotton cv. NemX. Crop Sci. 39:418–421. Park, Y.H., M.S. Alabady, M. Ulloa, B. Sickler, T.A. Wilkins, J. Yu, D.M. Stelly, R.J. Kohel, O.M. El-Shihy, and R.G. Cantrell. 2005. Genetic mapping of new cotton fiber loci using ESTderived microsatellites in an interspecific recombinant inbred line cotton population. Mol. Gen. Genomics 274:428–441. Roberts, P.A., M. Ulloa, and C. Wang. 2008. Host plant resistance to root-knot nematode in cotton. In Proc. World Cotton Res. Conf., 4th, Lubbock, TX. 10–17 Sept. 2007 [CD-ROM]. Omnipress, Madison, WI. Robinson, A.F., D.T. Bowman, C.G. Jenkins, J.E. Jones, L.O. May, S.R. Oakley, M.J. Oliver, P.A. Roberts, M. Robinson, C.W. Smith, J.L. Starr, and J.M. Stewart. 2001. Nematode resistance. p. 68–72. In T.L. Kirkpatrick and C.S. Rothrock (ed.) Compendium of cotton diseases. Am. Phytopathological Soc., St. Paul, MN. Rohlf, F.J. 2002. NTSYS-pc: Numerical taxonomy and multivariate analysis system, version 2.2, user guide. Exeter Software, Setauket, NY. Saitou, N., and M. Nei. 1987. The neighbor-joining method: A new method for reconstructing phylogenetic trees. Mol. Biol. Evol. 4:406–425. Sasser, J.N. 1977. Worldwide dissemination and importance of the root-knot nematodes, Meloidogyne spp. J. Nematol. 9:26–29. Shen, X., G. Van Becelaere, P. Kumar, R.F. Davis, L.O. May, and P. Chee. 2006. QTL mapping for resistance to root-knot nematodes in the M-120 RNR Upland cotton line (Gossypium hirsutum L.) of the Auburn 623 RNR source. Theor. Appl. Genet. 113:1539–1549. Shepherd, R.L. 1974a. Registration of Auburn 623 RNR cotton germplasm. Crop Sci. 14:911. Shepherd, R.L. 1974b. Transgressive segregation for root-knot nematode resistance in cotton. Crop Sci. 14:872–875. Smith, C.W., R.G. Cantrell, H.S. Moser, and S.R. Oakley. 1999. History of cultivar development in the United States. p. 99–171. In C.W. Smith and J. Cothren (ed.) Cotton: Origin, history, technology, and production. John Wiley & Sons, New York. Starr, J.L., S.R. Koenning, T.L. Kirkpatrick, A.F. Robinson, P.A.


Roberts, and R.L. Nichols. 2007. The future of nematode management in cotton. J. Nematol. 39:283–294. Swofford, D.L. 2002. PAUP*. Phylogenetic analysis using parsimony Version 4b.10. Sinauer Associates, Sunderland, MA. Ulloa, M., C. Brubaker, and P. Chee. 2007. Cotton. p. 1–49. In C. Kole (ed.) Genome mapping & molecular breeding. vol. 6: Technical crops. Springer, Heidelberg, Berlin, New York, Tokyo. Ulloa, M., S. Saha, Z.J. Yu, J.N. Jenkins, W.R. Meredith, and R.J. Kohel. 2008. Lessons learned and challenges ahead for cotton genome mapping. In Proc. World Cotton Res. Conf., 4th, Lubbock, TX. 10–17 Sept. 2007 [CD-ROM]. Omnipress, Madison, WI. Ulloa, M., J.McD. Stewart, E.A. Garcia-C., S. Godoy-A., A. Gaytán-M., and S. Acosta-N. 2006. Cotton genetic resources in the western states of Mexico: in situ conservation status and germplasm collection for ex situ preservation. Genet. Resour. Crop Evol. 53:653–668. Ulloa, M., C. Wang, and P.A. Roberts. 2009. Gene action analysis by inheritance and QTL mapping of resistance to root-knot nematodes in cotton. Plant Breed. DOI: 10.1111/j.14390523.2009.01717.x. Wang, C., W.C. Matthews, and P.A. Roberts. 2006b. Phenotypic expression of rkn1-mediated Meloidogyne incognita resistance in Gossypium hirsutum populations. J. Nematol. 38:250–257. Wang, C., and P.A. Roberts. 2006. Development of AFLP and derived CAPS markers for root-knot nematode resistance in cotton. Euphytica 152:185–196. Wang, K., X. Song, Z. Han, W. Guo, J.Z. Yu, J. Sun, J. Pan, R.J. Kohel, and T. Zhang. 2006c. Complete assignment of the chromosomes of Gossypium hirsutum L. by translocation and fluorescence in situ hybridization mapping. Theor. Appl. Genet. 113:73–80. Wang, C., M. Ulloa, and P.A. Roberts. 2006a. Identification and mapping of microsatellite markers linked to a root-knot nematode resistance gene (rkn1) in Acala NemX cotton (Gossypium hirsutum L.). Theor. Appl. Genet. 112:770–777. Wang, C., M. Ulloa, and P.A. Roberts. 2008. A transgressive segregation factor (RKN2) in Gossypium barbadense for nematode resistance clusters with gene rkn1 in G. hirsutum. Mol. Gen. Genomics 279:41–52. Wendel, J.F., and R.C. Cronn. 2003. Polyploidy and the evolutionary history of cotton. Adv. Agron. 78:139–186. Ynturi, P., J.N. Jenkins, J.C. McCarty, Jr., O.A. Gutierrez, and S. Saha. 2006. Association of root-knot nematode resistance genes with simple sequence repeat markers on two chromosomes in cotton. Crop Sci. 46:2670–2674.

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