Genome size, cytogenetic data and transferability of EST-SSRs markers in wild and cultivated species of the genus Theobroma L. (Byttnerioideae, Malvaceae).

Rangeline Azevedo Da Silva,Lívia Santos Lima Lemos,Rafael Moysés Alves,Lucília Helena Marcellino,Didier Clement,Fabienne Micheli,Karina Peres Gramacho,Nara Geórgia Ribeiro Braz Patrocínio,Gustavo Souza,Uilson Vanderlei Lopes

doi:10.1371/journal.pone.0170799

Abstract

The genus Theobroma comprises several trees species native to the Amazon. Theobroma cacao L. plays a key economic role mainly in the chocolate industry. Both cultivated and wild forms are described within the genus. Variations in genome size and chromosome number have been used for prediction purposes including the frequency of interspecific hybridization or inference about evolutionary relationships. In this study, the nuclear DNA content, karyotype and genetic diversity using functional microsatellites (EST-SSR) of seven Theobroma species were characterized. The nuclear content of DNA for all analyzed Theobroma species was 1C = ~ 0.46 pg. These species presented 2n = 20 with small chromosomes and only one pair of terminal heterochromatic bands positively stained (CMA+/DAPI− bands). The small size of Theobroma ssp. genomes was equivalent to other Byttnerioideae species, suggesting that the basal lineage of Malvaceae have smaller genomes and that there was an expansion of 2C values in the more specialized family clades. A set of 20 EST-SSR primers were characterized for related species of Theobroma, in which 12 loci were polymorphic. The polymorphism information content (PIC) ranged from 0.23 to 0.65, indicating a high level of information per locus. Combined results of flow cytometry, cytogenetic data and EST-SSRs markers will contribute to better describe the species and infer about the evolutionary relationships among Theobroma species. In addition, the importance of a core collection for conservation purposes is highlighted.

Highlights

The 22 species ascribed to the genus Theobroma L. (Malvaceae s.l.) are typically Neotropicals and distributed in the Amazon Tropical Forest
Nuclear DNA content (1C values) in the studied Theobroma species ranged from 0.41 pg in T. microcarpum to 0.49 pg in T. speciosum and T. subincanum, with an average of 0.46 pg (Table 2)
This trend was observed in this study, wherein the genome sizes estimated in this study for species of the Theobroma genus (T. cacao, T. grandiflorum, T. microcarpum, T. speciosum, T. bicolor, T. subincanum and T. obovatum) did not differ statistically

Summary

Introduction

The 22 species ascribed to the genus Theobroma L. (Malvaceae s.l.) are typically Neotropicals and distributed in the Amazon Tropical Forest. Nine species of Theobroma are present in the Brazilian Amazon, among them- cupuassu (T. grandiflorum Schum.) and cacao (T. cacao L.). The latter considered the most important species in the genus due to its economic value for providing raw material for production of chocolate and derivatives, cosmetics and pharmaceuticals [1, 6]. T. grandiflorum, one of the main tree crops in the Amazon region, has its pulp as the principal product, being used in juices, ice creams, yogurts and cosmetics. Their seeds can be used for cupulate production, an alternative to chocolate. Recent studies highlight the potential of cupuassu fruit extracts for medicinal use in gastrointestinal treatments [9]

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