POPULATION GENETIC ANALYSIS OF BRAZILIAN PEACH BREEDING GERMPLASM

1/14 ISSN 0100-2945 http://dx.doi.org/10.1590/0100-29452017166 POPULATION GENETIC ANALYSIS OF BRAZILIAN PEACH BREEDING GERMPLASM 1 LIANE BAHR THUROW2, MARIA DO CARMO BASSOLS RASEIRA3, SANDRO BONOW3, LUIS WILLIAN PACHECO ARGE4, CAROLINE MARQUES CASTRO3 ABSTRACT - Peach has great economic and social importance in Brazil. Diverse sources of germplasm were used to introduce desirable traits in the Brazilian peach breeding pool, composed mainly by local selections and accessions selected from populations developed by the national breeding programs, adapted to subtropical climate, with low chill requirement, as well as accessions introduced from several countries. In this research, we used SSR markers, selected by their high level of polymorphism, to access genetic diversity and population structure of a set composed by 204 peach selected genotypes, based on contrasting phenotypes for valuable traits in peach breeding. A total of 80 alleles were obtained, giving an average of eight alleles per locus. In general, the average value of observed heterozygosity (0.46) was lower than the expected heterozygosity (0.63). STRUCTURE analysis assigned 162 accessions splitted into two subpopulations based mainly on their flesh type: melting (96) and non-melting (66) flesh cultivars. The remaining accessions (42) could not be assigned under the 80% membership coefficient criteria. Genetic variability was greater in melting subpopulation compared to non-melting. Additionally, 55% of the alleles present in the breeding varieties were also present in the founder varieties, indicating that founding clones are well represented in current peach cultivars and advanced selections developed. Overall, this study gives a first insight of the peach genetic variability available and evidence for population differentiation (structure) in this peach panel to be exploited and provides the basis for genome-wide association studies. Index terms: Prunus persica, genetic diversity, population structure, low chill germplasm, genetic resources. ESTRUTURA GENÉTICA DO GERMOPLASMA DE MELHORAMENTO DE PESSEGUEIRO NO BRASIL RESUMO - O pessegueiro tem grande importância econômica e social no Brasil. Diversas fontes de germoplasma foram utilizadas para a introdução de caracteres desejados no pool gênico de pessegueiro do Brasil, constituído principalmente de seleções naturalizadas e de acessos selecionados a partir de populações desenvolvidas pelos programas de melhoramento, adaptadas às condições de clima subtropical, de baixa exigência em frio, bem como acessos introduzidos de diversos países. Neste estudo, foram utilizados marcadores SSR, selecionados por seu elevado nível de polimorfismo, com o objetivo de acessar a variabilidade genética e a estrutura populacional de um painel composto por 204 genótipos de pessegueiro, selecionados com base em fenótipos contrastantes para importantes caracteres no melhoramento do pessegueiro. Um total de 80 alelos foram identificados, com média de oito alelos por loco. Em geral, o valor médio da heterozigosidade observada (0,46) foi menor do que a heterozigosidade esperada (0,63). Análises do STRUCTURE atribuíram 162 acessos em duas subpopulações, majoritariamente com base em caracteres relativos ao fruto: cultivares fundentes (96) e não fundentes (66). Os acessos restantes (42) foram considerados não estruturados, utilizando um coeficiente de adesão de 80%. A variabilidade genética foi maior na subpopulação fundente em comparação com a não fundente. Além disso, 55% dos alelos presentes nas cultivares e seleções do programa de melhoramento também estão presentes nos clones de fundação, indicando que estes clones estão bem representados nas cultivares de pessegueiro e em seleções avançadas desenvolvidas. Este estudo apresenta uma primeira percepção da variabilidade genética disponível e evidências para a diferenciação da população (estrutura) neste painel de pessegueiro, que pode ser explorada e servir como base para estudos de mapeamento associativo. Termos para indexação: Prunus persica, variabilidade genética, estrutura de população, germoplasma de baixo frio, recursos genéticos. (Paper 093-16). Received July 27, 2016. Accepted December 13, 2016. Eng. Agr., MSc., Doutoranda do Programa de Pós-Graduação em Agronomia/Fitomelhoramento, Universidade Federal de Pelotas, Bolsista CAPES. Pelotas-RS. E-mail: 3 Eng. Agr., Dr., Pesquisador da Embrapa Clima Temperado, Pelotas-RS. E-mails: ; ; 4 Tecg. Fruticult., Dr., Pós-doutorando do Laboratório Nacional de Computação Científica, Petrópolis-RJ. E-mail: 1 2 Rev. Bras. Frutic., v. 39, n.5: (e-166) DOI 10.1590/0100-29452017166 Jaboticabal - SP L. B. THUROW et al. 2 INTRODUCTION Peach [Prunus persica (L.) Batsch] is considered an important agricultural crop worldwide, becoming the third most produced temperate tree fruit species, after apple and pear (BYRNE et al., 2012; FONT I FORCADA et al., 2013). The world production of peach and nectarine was approximately 22.8 million tons in 2014 whereas in Brazil was approximately 211 thousand tons (FAOSTAT, 2017). Peach is native of China where it was domesticated 4,000–5,000 years ago, and later spread around the world (FAUST; TIMON, 1995). For centuries, seed propagation was the main source of plants and consequently landrace genotypes resulted from this movement. This germplasm became the base of productive hybrids adapted to a wide range of different climate regions throughout the world (BYRNE, 2005a; BIELENBERG et al., 2009). In the Americas, peach was introduced by the Spanish and Portuguese during the sixteenth century, where it was quickly adopted by the native people and spread to a wide variety of environments (BYRNE et al., 2012). According to historical records, peach was introduced in Brazil in 1532 by Martim Afonso de Souza, through seedlings brought from Madeira Island and planted in São Vicente, where it is currently the state of São Paulo (RASEIRA; NAKASU, 2002). In the 1950s, two breeding programs - one in São Paulo and the other in Rio Grande do Sul state – started in Brazil, aiming the development of fresh market and processing peach cultivars adapted to mild winter regions. Local cultivars were then used as founding clones and had great importance for the breeding programs. All this germplasm probably arrived in Brazil several hundred years ago. Since this initial material was propagated by seed, only the most productive and adapted genotypes were maintained. In this way, locally adapted peaches were developed (BYRNE, 2003). Among them it should be cited the non-melting varieties ‘Aldrighi’, ‘Ambrosio Perret’, ‘Abóbora’, and ‘Intermediário’, used mainly in the breeding program for processing cultivars and ‘Delicioso’, ‘Precoce Rosado’, ‘Admirável’, and ‘15 de Novembro’, local cultivars used intensively in southern Brazil breeding program for development of fresh market peach cultivars (BYRNE; BACON, 1999). The low chill germplasm composed initially by local (...truncated)