Genetic Variation Within Population of Yellow-Berried Arabica Coffee Cultivars at Farmers Field Based on SSRs Markers

Abstract
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Identification of the genetic diversity within populations of yellow-berried Arabica coffee cultivar based on morphological characters faced an obstacle in finding identical environmental conditions at farmers field. Therefore, an approach which is not influenced by differences in environmental conditions is required, for instance based on DNA polymorphism. The research aimed to analyze genetic variation within populations of yellow-berried Arabica coffee cultivar based on SSRs markers. The research was conducted in the Integrated Laboratory, Indonesian Industrial and Beverage Crops Research Institute, Sukabumi, from April until June 2015. The leaf samples for DNA extraction were obtained from yellow-berried Arabica coffee cultivar (AGK-1) and two red-berried cultivars  as controls, namely  ABP-1 (dwarf type) and Typica (tall type). AGK-1 and ABP-1 cultivars consisted of 17 and 5 individual numbers, respectively, whereas Typica cultivar comprised three individuals. PCR amplification was carried out using 12 SSR primers. Four primers (M24, SSRCa052, M32, and M42) produced polymorphic band. The binary data obtained in this research was subsequently processed using NTSYS-PC program version 2.1. The genotypes were grouped  based on a genetic similarity matrix using the unweighted pair group method arithmetic mean (UPGMA). The result showed the existence of genetic variation among individual of AGK-1 cultivars, which forming three clusters at the genetic similarity value of 67%. One cluster exhibited close genetic relationships between some individuals within the population of AGK-1 cultivar and Typica cultivar. Meanwhile, the other two clusters showed high genetic similarity between AGK-1 cultivar and ABP-1 cultivar. The result demonstrated the possibility of gene flow between genotypes or residual heterozygosity within the population of  AGK-1 cultivar at farmers field, which required a further study.
Identifikasi keragaman genetik dalam kultivar kopi Arabika berbuah kuning berdasarkan karakter morfologi tanaman dihadapkan pada kendala sulitnya menemukan kondisi lingkungan yang seragam di lahan petani. Oleh sebab itu, diperlukan pendekatan lain yang tidak dipengaruhi perbedaan kondisi lingkungan, yaitu berdasarkan polimorfisme DNA. Tujuan penelitian adalah menganalisis variasi genetik dalam populasi kultivar kopi Arabika berbuah kuning berdasarkan penanda SSRs. Penelitian dilakukan di Laboratorium Terpadu Balai Penelitian Tanaman Industri dan Penyegar (Balittri), Sukabumi, mulai bulan April sampai Mei 2015. Sampel daun untuk ekstraksi DNA diambil dari kultivar kopi Arabika berbuah kuning (AGK-1) dan dua kultivar berbuah merah sebagai pembanding, yaitu ABP-1 (tipe katai) dan Typica (tipe tinggi). Kultivar AGK-1 dan ABP-1 masing-masing terdiri dari 17 dan 5 nomor individu, sedangkan kultivar Typica terdiri dari 3 individu. Amplifikasi PCR menggunakan 12 primer SSR yang telah dirancang untuk mengidentifikasi keragaman genetik kopi Arabika. Empat primer SSR di antaranya, yaitu M24, SSRCa052, M32, dan M42, menghasilkan pola pita DNA polimorfik. Data biner diolah menggunakan program NTSYS-PC versi 2.1. Pengelompokan genotipe berdasarkan matriks kesamaan genetik menggunakan unweighted pair group method with arithmetic average (UPGMA). Hasil analisis menunjukkan adanya variasi genetik antar nomor/individu kultivar AGK-1 sehingga membentuk tiga klaster pada nilai kesamaan genetik 67%. Salah satu klaster menunjukkan kedekatan jarak genetik antara beberapa individu dalam populasi kultivar AGK-1 dengan kultivar Typica. Dua klaster lainnya menggambarkan kemiripan genetik yang tinggi antara kultivar AGK-1 dengan kultivar ABP-1. Dugaan adanya aliran gen antar kultivar dan atau residu heterozigositas dalam populasi kultivar AGK-1 di lahan petani perlu dibuktikan lebih lanjut.
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