Microsatellitebased genetic diversity among ... - Wiley Online Library

Hereditas 150: 53–59 (2013)

Microsatellite-based genetic diversity among accessions of maize landraces from Sinaloa in México KAREN V. PINEDA-HIDALGO1,2, KARLA P. MÉNDEZ-MARROQUÍN1, ELTHON VEGA ALVAREZ1, JEANETT CHÁVEZ-ONTIVEROS1, PEDRO SÁNCHEZ-PEÑA2, JOSE A. GARZÓN-TIZNADO2, MISAEL O. VEGA-GARCÍA1 and JOSE A. LÓPEZ-VALENZUELA1,2 1

Maestría en Ciencia y Tecnología de Alimentos, Facultad de Ciencias Químico-Biológicas, Universidad Autónoma de Sinaloa, Culiacán, Sin., México 2 Programa Regional del Noroeste para el Doctorado en Biotecnología, Facultad de Ciencias Químico-Biológicas, Universidad Autónoma de Sinaloa, Culiacán, Sin., México Pineda-Hidalgo, K. V., Méndez-Marroquín, K. P., Alvarez, E. V., Chávez-Ontiveros, J., Sánchez-Peña, P., Garzón-Tiznado, J. A., Vega-García, M. O. and López-Valenzuela, J. A. 2013. Microsatellite-based genetic diversity among accessions of maize landraces from Sinaloa in México. – Hereditas 150: 53–59. Lund, Sweden. eISSN 1601-5223. Received 29 September 2013. Accepted 20 October 2013. In the state of Sinaloa México, traditional farmers still cultivate maize accessions with a wide diversity of morphological characteristics, but the gene reservoir maintained in these populations has been poorly studied and it is being lost due to changes in land use and the adoption of hybrid commercial varieties. The aim of this study was to evaluate the genetic diversity of some of these maize populations to contribute to their preservation. Twenty eight accessions were used for the analysis. DNA was extracted from 396 individuals and probed with 20 microsatellites distributed across the maize genome. A total of 121 alleles were obtained (average of 6.1 alleles per locus) and a total genetic diversity of 0.72. The UPGMA-cluster analysis, model-based population structure and principal component analysis revealed three major groups, one formed mainly by accessions of races typical of the Northwestern lowlands (Chapalote, Dulcillo del Noroeste, Tabloncillo Perla, Blando de Sonora and Elotero de Sinaloa) and the other two with accessions mainly from Tabloncillo and Tuxpeño. The high number of alleles per locus and total genetic diversity found in this study demonstrate a broad genetic basis of the accessions of maize landraces from Sinaloa, representing a gene reservoir useful in breeding programs. José A. Lopez-Valenzuela, Facultad de Ciencias Químico Biológicas, Universidad Autónoma de Sinaloa, Culiacán, Sin., México. E-mail: [email protected]

México is the center of origin of maize (Zea mays L.) and the evidence suggests this crop originated from its wild progenitor teosinte Zea mays ssp. parviglumis (DOEBLEY 2004) in a single domestication event that occurred in southern México about 9000 years ago (MATSUOKA et al. 2002). This domestication event reduced the genetic diversity of maize resulting in a small group of ancient landraces that subsequently diversified and adapted to a wide range of climatic and geographic conditions around the world. In México, maize has diversified into a huge number of populations with adaptations to different growing conditions and characteristics that allow their use in a great diversity of meal products (ORTEGA PACZKA 2003). Several studies have focused on the description and relationships among the Mexican landraces. One of the first reports classified 25 races into five major groups based on cytological, physiological and agronomic characteristics (WELLHAUSEN et al. 1952). The first two groups were classified as Ancient Indigenous or Pre-Columbian exotic, while the third group (Prehistoric Mestizos) resulted of the hybridization between ancient races and © 2013 The Authors. This is an Open Access article.

teosinte; the races of the fourth group (Modern Incipient) were created after the conquest in the 16th century and they have not yet reached a state of racial stability, while the fifth group (Poorly Defined Races) included recent collections with little information for their classification. The analysis of the associations between these races based on microsatellite data (REIF et al. 2006) supported the relationships proposed by WELLHAUSEN et al. (1952). Other authors used numerical taxonomy to classify the Mexican landraces based on genotype by environment interactions (CERVANTES et al. 1978) and morphological traits (SÁNCHEZ and GOODMAN 1992). A more complete classification of Mexican maize germplasm was proposed by SÁNCHEZ et al. (2000), who collected accessions from 50 landraces and classified them into four major groups on the basis of morphological and isozyme markers: 1) central and northern highlands group, composed of 15 landraces that grow at elevations higher than 2000 m; 2) eight-rowed, with 12 landraces distributed in western (1000–1800 m) and northwestern (100–500 m) México; 3) late maturity and tropical dents, composed of seven and 12 landraces, DOI: 10.1111/j.1601-5223.2013.00019.x

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respectively, adapted from low to medium elevations; and 4) Chapalote, with four races from the lowlands of northwestern México that were difficult to find (SÁNCHEZ et al. 2000). In addition to morphological and isozyme studies, microsatellite markers have been used to analyze the genetic structure of maize landraces from the Valley of Oaxaca in México (PRESSOIR and BERTHAUD 2004) and the relationships between accessions of 24 Mexican races (REIF et al. 2006) described by WELLHAUSEN et al. (1952). Other studies have extended these analyses to additional races of the Americas to elucidate their genetic diversity and historical spread throughout the continent (MATSUOKA et al. 2002; VIGOUROUX et al. 2008). Despite extensive research on maize germplasm, few molecular genetic diversity studies have included cultivated materials from northwestern México, with sampling limited to a small number of individuals or accessions (MATSUOKA et al. 2002; REIF et al. 2006; VIGOUROUX et al. 2008). In the state of Sinaloa, traditional farmers still cultivate maize landrace accessions with a wide range of phenotypic characteristics that have been preserved from generation to generation. Recent collections of maize accessions from northwestern México have revealed that up to 12 different maize landraces can be found in Sinaloa (P. Sanchez pers. comm.). However, the gene reservoir maintained in these accessions is being lost, mainly because of the destruction of their habitat and the introduction of genetically uniform materials. The comprehensive study of the genetic variability in different landraces and regions is required for the implementation of effective programs of genetic conservation and exploitation. The aim of this study was to analyze the molecular genetic diversity within and among selected accessions of maize landraces from Sinaloa, which may contribute to defining strategies for their conservation and use in breeding programs.

MATERIAL AND METHODS Genetic materials A set of 396 individuals representing 28 maize accessions were included in this study (Table 1). Samples were collected from open-pollinated populations maintained by traditional farmers at their villages in Sinaloa. Racial identification was mainly based on the following morphological characters: ear length, ear diameter, kernel row number, kernel dimensions and 100-kernel weight. The selected accessions correspond to typical regional races of Sinaloa: Chapalote, Blando de Sonora, Dulcillo del Noroeste, Reventador, Tabloncillo and Tabloncillo Perla, while almost 50% of the accessions were identified as Tuxpeño, a tropical dent race used to develop a number of

Hereditas 150 (2013) outstanding varieties during the 1960s by the International Maize and Wheat Improvement Center (TIMOTHY et al. 1988). This race has the greatest adaptability among Mexican races since it has been found in 19 climatic types (RUIZ CORRAL et al. 2008). Microsatellite genotyping Genomic DNA was extracted from leaf tissue according to SHEN et al. (1994) and diluted to a final concentration of 50 ng ml1 for polymerase chain reactions (PCR). All individuals were genotyped using 20 microsatellites distributed across the maize genome (Table 2). Microsatellite primer sequences and chromosomal locations are available in the Maize Genome Database (www.maizegdb. org.ssr.php). PCR reactions contained 50 ng of genomic DNA, 1 PCR reaction buffer, 1.7 mM MgCl2, 100 μM dNTPs, 20 pmol of forward and reverse primers, 1 unit of Taq DNA polymerase (Invitrogen, Carlsbad, CA, USA) and sterile deionized water to a final volume of 15 μl. The reactions were conducted in a Mastercycler Gradient 5331 (Eppendorf, Hamburg, Germany) and were initiated by denaturing the DNA at 95°C for 5 min, followed by 30 cycles as follows: 94°C, 1 min; 52–58°C (depending of the locus), 1 min; and 72°C, 1.5 min; with a final extension period at 72°C for 5 min. PCR products were separated by electrophoresis using 15% (w/v) polyacrylamide gels with 0.5 TBE (90 mM boric acid, 2 mM EDTA, pH 8.0) under non-denaturing conditions (WANG et al. 2003). Gels were stained with ethidium bromide (1 μg ml1) and photographed under UV light with a Chemidoc XRS system (BioRad, Hercules, CA, USA). Allele sizes were estimated from digitalized gel images by comparison to molecular size markers (100 bp ladder) using the Quantity One software (BioRad). Data analysis The number of alleles per locus was determined for the entire set of 396 individuals, as well as for each accession separately. The total gene diversity (HT) across all accessions and the gene diversity within each accession (HS), as well as the coefficient of genetic differentiation (GST) or relative differentiation of the accessions, were determined according to Nei and Kumar (NEI and KUMAR 2000). The fixation index (FIS) was estimated separately for each accession as one minus the observed heterozygosity divided by the expected heterozygosity under Hardy–Weinberg equilibrium (HWE) (NEI and KUMAR 2000). All the analyses were carried out with the software PowerMarker ver. 3.25 (LIU and MUSE 2005). Deviations from HWE at individual loci were tested with an exact test described by GUO and THOMPSON (1992) using GENEPOP (RAYMOND and ROUSSET 1995). Associations between landraces were graphically depicted by principal

Genetic diversity among accessions of maize landraces

Hereditas 150 (2013)

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Table 1. Accessions of maize landraces from Sinaloa used in this study. Collection

Code

Common name

Collection county

Latitude

Longitude

Landracea

No. ind.

FAUAS-364 FAUAS-358 FAUAS-339 FAUAS-221 FAUAS-482 FAUAS-220 FAUAS-240 FAUAS-387 FAUAS-303 FAUAS-01 FAUAS-05 FAUAS-07 FAUAS-37 FAUAS-540 FAUAS-471 FAUAS-23 FAUAS-79 FAUAS-11 FAUAS-94 FAUAS-82 FAUAS-12 FAUAS-93 FAUAS-42 FAUAS-97 FAUAS-206 FAUAS-43 FAUAS-98 FAUAS-295

CH DN RE BS1 BS2 ES1 ES2 ES3 TAP TA1 TA2 TA3 TA4 TA5 TA6 TA7 TA8 TU1 TU2 TU3 TU4 TU5 TU6 TU7 TU8 TU9 TU10 TU11

Maíz Chapalote Maíz Dulce Maíz reventador Maíz Blando Maíz Blando Maíz Breve Maíz de Ocho Negro Jazmín Zorrita Zorrita Zorrita Zorrita Maíz de Ocho Blanco de 8 Blanco de 8 Blanco de 8 Serrano Blanco Serrano Blanco Blanco de 8 Hibrido Blanco Hibrido Blanco Breve San Juan Breve San Juan Breve San Juan Pinto Amarillo Pinto Amarillo Pinto Amarillo

El Fuerte El Fuerte Choix Culiacán El Fuerte Badiraguato San Ignacio Cosala El Rosario Elota Elota Elota San Ignacio Concordia Culiacán San Ignacio Culiacán El Rosario Concordia Culiacán El Rosario Concordia Mocorito Concordia Culiacán Badiraguato Concordia Concordia

26.25262 26.233556 26.25426 25.05026 26.233556 25.18333 24.68334 24.2944 22.86674 24.054634 24.054634 24.054634 24.035174 23.21057 25.47100 23.524239 24.480842 23.041142 23.155879 24.480842 23.041142 23.234643 25.075945 23.155879 25.08342 25.255688 23.233933 23.40019

108.31025 108.21486 108.13054 107.45343 108.21486 107.48333 107.08360 106.4329 105.96683 106.404842 106.404842 106.404842 106.383275 106.07003 106.07003 106.192546 107.082376 105.310824 105.572204 107.082376 105.310824 105.560164 107.372377 105.572204 107.45012 107.342116 106.100678 106.06689

Chapalote Dulcillo del Noroeste Reventador Blando de Sonora Blando de Sonora Elotero de Sinaloa Elotero de Sinaloa Elotero de Sinaloa Tabloncillo Perla Tabloncillo Tabloncillo Tabloncillo Tabloncillo Tabloncillo Tabloncillo Tabloncillo Tabloncillo Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño Tuxpeño

17 20 16 17 20 17 17 20 17 15 11 17 10 20 17 10 17 10 10 11 10 10 10 10 17 10 10 10

a

Classification based on morphological criteria.

Table 2. Allelic variation and polymorphic information content (PIC) of the 20 SSR markers used in this study. Marker

Bina

Repeatb

Allele number

Allele size range (pb)

PIC

Phi097 Bnlg439 Bnlg2248 Bnlg1633 Bnlg2136 Bnlg1496 Phi072 Bnlg1755 Dupssr10 Umc1019 Phi078 Bnlg1740 Phi034 Phi114 Phi119 Bnlg666 Bnlg244 Bnlg1129 Phi059 Bnlg1074 Mean

1.01 1.03 2.03 2.07 3.04 3.09 4.01 4.05 5.04 5.06 6.05 6.07 7.02 7.03 8.02 8.05 9.02 9.08 10.02 10.05

Tri Comp. Di Di Di Di Tetra Di Di Di Tetra Di Tri Tetra Di Comp. Comp. Di Tetra Di

2 7 7 8 6 7 4 6 8 5 7 7 8 5 6 6 6 6 5 5 6.1

99–150 192–277 200–300 75–222 85–223 159–266 156–172 95–171 145–252 55–234 125–241 109–247 120–250 136–238 100–208 114–200 124–214 116–249 153–300 175–257

0.23 0.76 0.79 0.75 0.71 0.78 0.66 0.77 0.82 0.61 0.67 0.82 0.68 0.49 0.67 0.72 0.76 0.62 0.74 0.63 0.68

a

Chromosomal location. Repeat unit of the simple sequence repeat; Comp: consisting of more than one repeat type.

b

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component analysis (PCA) based on allele frequency using STATA ver. 11.1 (Stata Corp, College Station, TX, USA). The genetic distance between accessions was determined using the coefficient of NEI (1972) based on the allele frequencies. Associations among the accessions were revealed using the unweighted pair-group method with arithmetic mean (UPGMA) available in PowerMarker. Standard errors of Nei distance were estimated by a bootstrap procedure with resampling (1000) across markers and individuals. The correlation between genetic and geographical distance was tested with a Mantel-test (LEGENDRE and LEGENDRE 2012). Genetic relationships among individual genotypes from the accessions were analyzed with a model-based clustering approach using the Software package STRUCTURE (PRITCHARD et al. 2000). The number of clusters (k) was varied from 1 to 10 and five runs of STRUCTURE were performed per k, setting the burn-in time to 100 000 and replication number to 1 000 000. The results were visualized with the DISTRUCT program (ROSENBERG 2004).

RESULTS AND DISCUSSION Genetic diversity The 20 microsatellites were polymorphic across the 396 individuals analyzed and detected a total of 121 alleles; the number of alleles varied from two to eight per locus with an average of 6.1 (Table 2). This average value of total alleles per locus was similar to that found by REIF et al. (2005a) who analyzed 150 maize plants from five European populations using microsatellites, but it was slightly lower than the 6.5 alleles obtained by LABATE et al. (2003) in a study of the genetic diversity of 461 plants representing the germplasm of the United States. REIF et al. (2006) reported an average of 7.8 alleles per locus in a study including 25 accessions from 24 Mexican races. The average PIC value for the 20 SSR was 0.68; the lowest value was found in the Phi097 marker (0.23), which corresponds to the fact that this locus showed only 2 alleles, while the highest value was obtained by the Dupssr10 marker (0.82), a dinucleotide repeat that allowed the amplification of 8 alleles. These values were similar to those found by XU et al. (2004), who reported PIC values from 0.28 to 0.81 with a mean value of 0.63 in fifteen Chinese maize inbred lines. SMITH et al. (1997) also reported a mean PIC value of 0.62 for SSR in a collection of US maize inbreds. The average number of alleles per locus within the accessions was 4.06, with a range from 3.15 (TU1) to 5.05 (TA8) (Table 3). The gene diversity values within accessions (Hs) varied from 0.49 (TU11) to 0.67 (TA8), with a mean of 0.60. The total genetic diversity value was 0.72, which is similar to the 0.71 found by PRESSOIR and

Hereditas 150 (2013) Table 3. Genetic diversity within 28 accessions of maize landraces from Sinaloa. Code CH DN RE BS1 BS2 ES1 ES2 ES3 TAP TA1 TA2 TA3 TA4 TA5 TA6 TA7 TA8 TU1 TU2 TU3 TU4 TU5 TU6 TU7 TU8 TU9 TU10 TU11 Average total

Average no. of Gene diversity Fixation index alleles per locus (Hs) (FIS) 4.35 3.95 3.55 4.65 4.75 4.30 4.55 4.10 4.30 4.25 3.75 4.60 3.20 4.05 4.45 4.45 5.05 3.15 3.75 3.90 3.55 3.85 3.90 3.60 4.40 4.20 3.85 3.35 6.1

0.59 0.56 0.58 0.66 0.59 0.58 0.65 0.63 0.62 0.61 0.53 0.64 0.54 0.60 0.65 0.62 0.67 0.51 0.61 0.57 0.54 0.64 0.58 0.60 0.66 0.61 0.60 0.49 0.72

0.50 0.65 0.54 0.31 0.62 0.40 0.31 0.51 0.48 0.29 0.38 0.39 0.59 044 0.51 0.33 0.53 0.45 0.24 0.20 0.30 0.57 0.31 0.41 0.53 0.35 0.32 0.48 0.17

BERTHAUD (2004) in a study of maize landraces from the high valleys of Oaxaca in México. However, this value was higher than those obtained by REIF et al. (2005a) in five European maize populations and REIF et al. (2006) in the 24 maize Mexican races originally described by WELLHAUSEN et al. (1952). The number of alleles per locus and the gene diversity found in this study (Table 3) demonstrate a broad genetic basis of the maize accessions from Sinaloa. Population structure and genetic relationships The percentage of loci with significant (p 0.01) deviations from HWE varied from 10% (TU3) to 85% (BS2, DN and TU8) with an average of 47%. Most of these loci (95.4%) showed an excess of homozygosity and the fixation index (FIS) values for the accessions ranged from 0.20 (TU3) to 0.65 (DN) (Table 3). The observed deviation from HWE was in close agreement with previous studies using microsatellites with open-pollinated populations (REIF et al. 2005a; QI-LUN et al. 2008) and could be attributed mainly to non random



mating. The coefficient of genetic differentiation (GST) averaged 0.17 (Table 3) and was lower than those reported by REIF et al. (2005a, 2006). This value indicates that 17% of the total variation is due to differences among populations, therefore it was expected they could be differentiated using microsatellites data. This level of differentiation suggests moderate gene flow between the populations, normally associated with pollen contamination of neighbor populations or seed mixing, since it is common that farmers exchange seeds to improve crop performance (LOUETTE et al. 1997). This value is smaller than the 0.21 found by REIF et al. (2006) in 24 races from México, which can be attributed to the fact that the materials used in that study were from a seed bank. Nevertheless, the level of genetic differentiation found in this study is markedly higher than that reported by PRESSOIR and BERTHAUD (2004) for landraces from Oaxaca (FST 0.011). The geographic distance between the accessions could be another influencing factor because they were collected from different counties of Sinaloa. However, a Mantel-test showed no significant association between pairwise genetic distances and pairwise geographic distances, indicating that the pattern of differentiation is not due to isolation by distance. The genetic distance between the 28 accessions was estimated using the allele frequencies with the coefficient

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of NEI (1972). Distance values between accession pairs ranged from 0.15 (BS2 DN) to 0.73 (TA2 TU1) with an average of 0.37. Clustering analysis with the unweighted pair group method with arithmetic mean (UPGMA) separated the accessions in three main groups (Fig. 1a). The main group consisted of accessions that have been previously classified to the eight-rowed and Chapalote groups by SÁNCHEZ et al. (2000) based on morphological and isozymatic markers. BS2 accession (eight-rowed group) was clustered first with DN (Chapalote group), a landrace that originated from Maiz Dulce according to WELLHAUSEN et al. (1952); Dulcillo del Noroeste was previously clustered with landraces of the Chapalote and eight-rowed groups while Maiz Dulce was included into a separate group based on isozymes, morphological and ecological variables (RUIZ-CORRAL et al. 2008; SÁNCHEZ et al. 2000). However, Maiz Dulce has been grouped with landraces typical of northwestern México using microsatellite data (REIF et al. 2006). The next accessions that clustered in the main group were Reventador (RE) and the Tabloncillo landrace TA6. Tabloncillo is considered to be derived from Reventador and Harinoso de Ocho or Blando de Sonora with a great contribution from Chapalote (WELLHAUSEN et al. 1952). BS1 also formed part of this group and was identified as Blando de Sonora; this race was classified together with Tabloncillo Perla in

Fig. 1a–b. Genetic relationships among 28 accessions of maize landraces from Sinaloa. (a) Dendogram was constructed using the UPGMA method based on NEI (1972) distance. Bootstrap values are indicated. (b) Estimated population structure of the maize genotypes (K 3). Each individual is represented by a thin horizontal line, which is partitioned into colored segments that represent the different populations. Population I (blue), population II (red) and population III (yellow).

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the eight-rowed group by SÁNCHEZ et al. (2000) based on morphological and isozymatic markers. Three accessions that clustered more distantly within the same group were ES1, ES2 and CH; the first two accessions were identified as Elotero de Sinaloa, a race that according to SÁNCHEZ (1989) more likely resulted from the cross between Chapalote and Blando de Sonora or Harinoso de Ocho. A subcluster within this group was formed by the accessions TU8, TU3 and TU10, which were classified as Tuxpeño, but they also appear to have some kernel characteristics of Blando de Sonora. The second group was formed by accessions TA1, TA2 and TA8, all of them classified as Tabloncillo based on their morphological characteristics. The third main group clustered eleven accessions, most of them classified as Tuxpeño, except for three of them identified as Tabloncillo, which could be explained by genetic flow from different accessions and selection by farmers. A high degree of variability within the same landrace was previously observed by REIF et al. (2006), who obtained a distance of 0.33 between two accessions of the Chalqueño race. It is worth mentioning that those accessions were from seed banks. In the present study, the highest genetic distance between accessions of the same landrace varied from 0.29 (Elotero de Sinaloa) to 0.64 (Tuxpeño). The high genetic diversity of Tuxpeño is likely related to its broad adaptability (RUIZ CORRAL et al. 2008) and the fact that several varieties were developed from this race during the 1960s by the International Maize and Wheat Improvement Center (TIMOTHY et al. 1988). Bayesian analysis of population structure using the model-based approach of PRITCHARD et al. (2000) with the admixture model proposed by FALUSH et al. (2003) provided support for the existence of genetic structure in our sample. The inferred population structure (K 3) is presented in Fig. 1b. Individuals with probability of membership 60% were assigned to the same group, while those with 60% probability membership in any single group were assigned to a mixed group (YANG et al. 2011). This analysis was consistent with the dendogram generated (Fig. 1a). Individuals of the accessions TU8, TU3, ES1, CH, BS1, TAP and ES2 were assigned to the population I (Pop I, blue), while RE, TA6, ES3, TA5, DN, BS2 and TU11 were in pop II (red), and the third population (Pop III, yellow) was comprised mostly by individuals of Tuxpeño and Tabloncillo races (Fig. 1b). Only individuals from TA2 and TU10 were considered as a mixed group since they had 60% membership probability. The structure uncovered by our analysis was similar to that described by REIF et al. (2006), who assumed a K 3 for the population structure of the 24 Mexican races previously described by WELLHAUSEN et al. (1952); one of the populations found by those authors was formed by the races Dulce, Chapalote, Reventador and Harinoso de Ocho, while our study clustered the races Dulcillo del


Fig. 2. Association among 28 accessions of maize from Sinaloa revealed by principal component analysis based on allelic frequencies from 20 SSR markers. Symbols reflect the individuals grouped according to STRUCTURE. Population I (plus), population II (filled triangle) and population III (filled circle).

Noroeste, Blando de Sonora (Harinoso de Ocho), Reventador and Tabloncillo (Reventador Harinoso de Ocho). A principal component analysis (PCA) was performed in order to estimate the distribution of variance and genetic relationships within the 28 accessions. The first two principal components (PC) explained the 19.43% of the total SSR variation among samples. The geometrical distances among samples in the two dimensional plot reflect the genetic distance among them. A plot of PC1 (11.49%) and PC2 (7.94%) revealed three groups (Fig. 2). The grouping patterns were very similar to the model based population established by STRUCTURE, with individuals of mixed groups being intermediate between the three populations. The group on the right side of the plot was formed by individuals of population III (Tabloncillo and Tuxpeño races), while two groups were formed in the upper and lower left plot side, which corresponded to individuals of populations I and II, respectively. Principal component analysis as well as population structure have been shown to be good predictors of grouping patterns and they can be used to complement the clustering method analysis, since different combinations of genetic distance matrices and clustering algorithms can give rise to somewhat different groups (REIF et al. 2005b). In our study, the three grouping methods used showed high concordance in recognizing three principal groups that corresponded to previous reports (SÁNCHEZ et al. 2000; REIF et al. 2006). In summary, the average number of alleles per locus (6.1) and genetic diversity (0.72) found in this study demonstrated a broad genetic base of the accessions of maize landraces from Sinaloa. The observed clustering of the different accessions was in agreement with some of the relationships originally proposed by WELLHAUSEN



et al. (1952). The results of this study will be useful to design strategies that maximize the utility of these genetic resources. Acknowledgements – This work was supported by grants from Consejo Nacional de Ciencia y Tecnología (CONACYT), Programa de Mejoramiento del Profesorado (PROMEP) and Universidad Autónoma de Sinaloa (PROFAPI).

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