Biotecnología

 

Molecular diversity and genetic relationships of mango germplasm from Chiapas, Mexico

 

Diversidad molecular y relaciones genéticas de germoplasma de mango de Chiapas, México

 

Didiana Gálvez–López¹, Miguel Salvador–Figueroa², Enrique N. Becerra–Leor³, Maurilio González–Paz¹, Sanjuana Hernández–Delgado¹, Netzahualcóyotl Mayek–Pérez^1*

 

¹ Centro de Biotecnología Genómica, Instituto Politécnico Nacional. Bulevard Del Maestro s/n esquina Elias Piña, Colonia Narciso Mendoza, 88710. Reynosa, México. Autor responsable: (nmayek@ipn.mx)

² Área de Biotecnología, Universidad Autónoma de Chiapas. Carretera a Puerto Madero km 2. 30700, Tapachula, México.

³ Campo Experimental Cotaxtla–INIFAP. Carretera Veracruz–Córdoba km 34, A. Postal 429. 91700. Veracruz, México.

 

Received: October, 2009.
Approved: October, 2010.

 

Abstract

Most of mango (Mangifera indica L.) production in Chiapas, México is located at Soconusco region where a large morphological and genetic diversity have been detected due the free–pollination among plants. The characterization and identification of outstanding plants can be useful for mango diversity conservation as well as the use for mango breeding. Forty–one local mango accessions collected in five locations (Huehuetán, Pijijiapan, Tuxtla Chico, Tapachula, Escuintla) in the state of Chiapas, México, were subjected to AFLP analysis and then compared with 19 mango cultivars. AFLP analysis indicated high levels of polymorphisms among accessions (> 84 %). AMOVA analysis indicated significant genetic differentiation (F_ST = 0.23743) among and within mango accessions. Cluster analysis showed two groups: accessions from Chiapas and Ataulfo mangos closely related to Manila, Carabao, Amini and Cambodiana cultivars native from Asia; and Mexican and non–Mexican bred mangos from Germplasm Bank. Mangifera odorata was different than all other M. indica accessions. The highest heterozygosity were found in mangos from Tuxtla Chico (0.260) and Escuintla (0.254). Genetic differences among accessions and cultivars were associated with their geographical origin and indicated new genetic diversity of mangos from Chiapas due to free–pollination and the use of recombinant plants.

Keywords: Mangifera indica L., M. odorata, AFLPs, genetic relationships, Soconusco.

 

Resumen

La mayor parte de la producción de mango (Mangifera indica L.) en Chiapas, México, se localiza en la región Soconusco, donde se ha detectado una gran diversidad morfológica y genética, que se debe a la polinización libre entre plantas. La caracterización e identificación de plantas excepcionales puede ser útil para la conservación de la diversidad del mango, así como para su uso en el cultivo del mango. Se recolectaron 41 accesiones de mango en cinco localidades (Huehuetán, Pijijiapan, Tuxtla Chico, Tapachula, Escuintla) en el estado de Chiapas, México, que se sometieron a análisis AFLP y después se compararon con 19 variedades cultivadas de mango. El análisis AFLP indicó altos niveles de polimorfismo entre las accesiones (> 84 %). El análisis AMOVA indicó una diferenciación genética significativa (F_ST = 0.23743) entre y dentro las accesiones de mango. El análisis de agrupamiento arrojó dos grupos: las accesiones de Chiapas y los mangos Ataulfo se relacionan cercanamente a los cultivares Manila, Carabao, Amini y Cambodiana, nativas de Asia; y los mangos mexicanos y no mexicanos cultivados a partir del Banco de Germoplasma. Mangifera odorata fue distinta a todas las otras muestras de M. indica. La heterocigosidad más alta se encontró en mangos de Tuxtla Chico (0.260) y Escuintla (0.254). Las diferencias genéticas entre accesiones y cultivares se asociaron con su origen geográfico e indicaron nueva diversidad genética de los mangos de Chiapas debido a la polinización libre y el uso de plantas recombinantes.

Palabras clave: Magnifera indica L., M. odorata, AFLP, relaciones genéticas, Soconusco.

 

Introduction

Mango (Mangifera indica L.) is a major crop for the state of Chiapas, México, where 26,000 ha were planted and 176 000 t produced during 2008. Most of the mango production (≈95 %) is located at a southern region (Soconusco) which comprises 17 municipalities, and where Tapachula produces nearly one third of the state's mango production (SIAP, 2010).

A broad morphological and genetic diversity of mango has emerged at southern Chiapas due to free sexual recombination, continuous grafting of outstanding plants produced by seeds from commercial cultivars (cv.) cultivated or consumed in the state, or both. For example, the cv. Ataulfo (Manila fruit type) originated in Soconusco region was dispersed throughout México and worldwide (Gálvez–López et al., 2007a, Gálvez–López et al. 2007b). This genetic diversity need to be analyzed in order to increase our knowledge about Mexican plant genetic resources and then used to design strategies for conservation and use of germplasm for breeding and production purposes.

Several procedures for the identification and characterization of mango genotypes have been developed based on morphological, biochemical, agronomical or genetic traits (Krishna et al., 2007; Gálvez–López et al., 2009). Mango cultivars and species from México and other countries have been characterized based on morphological traits and isozyme patterns (Gálvez–López et al., 2007b; 2010). In addition, germplasm have been analyzed by using RAPD (Karihaloo et al., 2003; Anju et al., 2008; Rajwana et al., 2008), AFLP (Kashkush et al., 2001; Yamanaka et al., 2006; Gálvez–López et al., 2009), SSR (Schnell et al., 2005; Viruel et al., 2005; Hirano et al., 2010); and ISSR (Pandit et al., 2007; Anju et al., 2008). Overall results indicate clearly the differentiation of mango accessions regardless the marker system use to fingerprint based on type of embriony (mono– or poly–embryonic), geographical origin or genetic status (cultivars, landraces, species). The aim of this study was to characterize mango landraces present in southern Chiapas, México, by means of AFLP in the end to determine the genetic relationships among native and bred mango genotypes from México and other countries.

 

MATERIALS AND METHODS

Gemplasm

Forty–one mango accessions from the Soconusco region in southern Chiapas, Mexico were collected during 2005 (Table 1) by Drs. Ma. Lourdes Adriano–Anaya and Miguel Salvador–Figueroa (Universidad Autónoma de Chiapas, Tapachula, México). We did not know if the accessions were originated by direct planting of one seed of mango cultivar grown at Chiapas or originated from grafting of outstanding local mangos as well as cultivars planted throughout the Soconusco region. One M. odorata accession as well as six introduced mango cultivars from Florida, USA, six cultivars from other countries and six mango cultivars from other regions of México were included as out–groups (Table 1). Out–groups are included in the Mango Germplasm Bank of the Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP) located in Cotaxtla, Veracruz, México.

Genetic analysis

Genetic analysis consisted of DNA genomic isolation (Doyle and Doyle, 1987) and AFLP analysis using the protocol described by Vos et al. (1995). After the evaluation of amplified products and polymorphisms generated by eight AFLP primer combinations in five randomly selected accessions, four combinations of selective oligonucleotides EcoRI / Msel were selected: AGG/AAA, AGG/AGG, AGG/ATG, AGG/AAG. Amplified products were separated by electrophoresis in 6.5 % acrylamide gels and visualized in real–time using an automated sequencer model (LICOR*; Lincoln, NE, USA) (Gálvez–López et al., 2009).

Statistical analysis

AFLP bands were numbered based on their migration in gels. The band with the highest molecular weight was numbered 1, and subsequent bands were numbered in order of decreasing weight. We assumed that two bands with the same migration in different sample gels were identical (Gálvez–López et al., 2009). A zero–ones matrix was used to estimate simple matching coefficients (Nei and Li, 1979). Coefficients were used to estimate genetic similarities between genotypes, and a single dendrogram was then constructed based on the Neighbor–Joining (NJ) method (Felsenstein, 2004), using the software programs Phylip, NJ–Plot andTreeView 1.6.6 (Perrière and Gouy, 1996; Felsenstein, 2005). Genetic diversity within populations was measured using average heterozygosity (H) and percentages of polymorphic loci (P), with Excel version 2000 for Windows. A similarity matrix was also used to perform a hierarchic analysis of molecular variance (AMOVA) (Huff et al., 1993) using Arlequín 3.1 (Excoffier et al., 2005). The number of permutations to AMOVA's significance tests was 1000 (Felsenstein, 2004). For AM OVA, two hierarchies were assessed: groups (Mexican and no–Mexican mangos) and accessions within groups (mangos from five Chiapas locations; Mexican mangos from the Germplasm Bank; mangos from Florida; and mangos from other countries).

 

RESULTS AND DISCUSSION

AFLP analysis produced a total of 392 amplified bands and 331 polymorphic bands (84.4 %) (Table 2). AM OVA analysis indicated significant differences for all the hierarchies analyzed, although the higher variance values were found within mango accessions (86.26 %). Fixation indexes for hierarchies (F_SC= 0.0953, F_ST = 0.2374, F_CT = 0.0465, for groups, accessions within groups, and within accessions) indicated significant genetic differentiation among and within populations (Table 3). The dendrogram showed two major groups of accessions. One included accessions from Chiapas, although Ataulfo mangos were closely related to Manila, Carabao, Amini and Cambodiana mangos, which are native to Asia. The second group included Mexican and non–Mexican bred genotypes from the Germplasm Bank. Bred mangos were separated from Chiapas mangos while M. odorata was different from all other M. indica accessions (Figure 1), as was previously found by Yamanaka etal. (2006). Ho values were 0.260 (Tuxtla Chico), 0.134 (Tapachula), 0.178 (Huehuetán), 0.254 (Escuintla) and 0.166 (Pijijiapan).

Broad genetic diversity was found in native mango in Chiapas. We assumed that optimal conditions for free recombination among mangos introduced from other countries were common for farmers in Chiapas. The highest polymorphism detected in mango landraces from Chiapas (84.43 %) compared with breed mangos (López–Valenzuela et al., 1997) (74 %) must be due to the fact that AFLP is a more robust marker methodology than RAPD for plant analysis (Canchignia–Martínez et al., 2007). In addition, landraces are more genetically diverse than breed cultivars despite high levels of coancestry Ediahtong et al. (2000) reported 77 % of polymorphisms in 14 Mangifera species analyzed with AFLPs and Yamanaka et al. (2006) > 96% of polymorphism among and within four Mangifera species. In this sense, Gálvez–López et al. (2009) found >87 % of polymorphisms in mango accessions from México and other countries. Differences in polymorphisms are related to the genetic nature and origins of germplasm, as well as to the high level of coancestry among breed mango cultivars world–wide. Because AMOVA indicated significant differences among and within populations from Chiapas, we assume that differences can be associated with gene exchange resulting from the migration of new populations or recombinants naturally produced in mango orchards in southern Chiapas. Mango populations were introduced from Asia to the Caribbean in the 18^th century (Duval et al., 2009) and to México in the 18^th and 19^th centuries (Gálvez–López et al., 2007a), and they were well adapted to climatic conditions in the country. In southern Chiapas, common practices by farmers consist of allowing mango fruits to germinate and produce sexual plants that are derived from natural and random recombinated–sexual plants. When recombinants show desirable traits, trees are propagated and planted. It is therefore common to see small backyards including a broad range of mango phenotypes (Gálvez–López et al., 2010).

Genetic differentiation (F_ST=0.13743) among populations was moderated and indicated relative coancestry among populations as well as the absence of geographic isolation for recombination. Phylogenetic analysis showed genetic differentiation between mango landraces in Chiapas and accessions from Germplasm Bank. Our results suggest that native mango populations show genetic differences based on geographical origin and their known history (Duval et al., 2009; Hirano et al., 2010) and that genetic exchange persists (Rivera–Ocasio et al., 2002). Similar separations among mango accessions based on geographical origins have been found (Karihaloo et al., 2003; Viruel et al., 2005; Pandit et al., 2007, Rajwana et al., 2008).

Breed mangos from USA and other countries (Australia and Spain) are mono–embryonic while Mexican mangos are commonly poly–embryonic. Mexican mangos are called 'manila' and they have intermediate fruit size, orange or yellow fruit color, low–intermediate fiber density and oblong fruit shape with acute apex; foreign breed mangos are commonly named 'petacones' and they show intermediate to large fruit size, shape from roundish to ovoid, green–red–purple colors, and intermediate–large fiber density (Gálvez–López et al., 2010). Differences between mangos from Chiapas from all other from Germplasm Bank suggest the empirical selection and cultivation of those preferred by local consumers.

 

CONCLUSIONS

Genetic analysis indicated significant genetic diversity in mango germplasm adapted in Chiapas, México, and genetic differentiation among and within mango accessions. Mangos from Chiapas were different to other mangos from México and other countries.

 

ACKNOWLEDGEMENTS

This study was supported by Instituto Politécnico Nacional (grant CGPI–20050084) and Fondo Mixto de Fomento a la Investigación Científica y Tecnológica CONACYT–Gobierno del Estado de Tamaulipas. D. Gálvez–López also grateful to CONACYT (fellow 169661), PIFI–IPN, Club Rotado de Reynosa A. C. and FOMIX–Tamaulipas (grant TAMPS–2003–C02–09) for financial support of her M. Sc. program at CBG–IPN. S. Hernández–Delgado and N. Mayek–Pérez are S.N.I., EDI–IPN and COFAA–IPN scholarship recipients.

 

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