Analisis Genetik dan Interaksi Genotipe × Lingkungan untuk Perbaikan Periode Panen Kacang Hijau (Vigna radiata L. Wilczek)
Date
2021Author
Marwiyah, Siti
Sutjahjo, Surjono Hadi
Trikoesoemaningtyas
Wirnas, Desta
Suwarno, Willy Bayuardi
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Periode panen pendek dapat mendukung panen serempak pada kacang hijau, meningkatkan efesiensi panen, dan mendukung pemanfaatannya sebagai tanaman sela musim (catch crops). Akan tetapi, periode panen pendek menyebabkan penurunan hasil. Pemuliaan kacang hijau perlu mengupayakan ideotipe periode panen pendek dan potensi hasil yang tetap tinggi. Seleksi karakter yang dikendalikan secara aditif dapat dilakukan di generasi awal, sebaliknya disarankan menunda seleksi bila terdapat peran gen non aditif.
Penelitian bertujuan melakukan analisis pengaruh interaksi genotipe × lingkungan dan analisis genetik karakter periode panen, serta pola panen genotipe kacang hijau. Studi interaksi genotipe dan lingkungan dilakukan terhadap 10 genotipe kacang hijau dengan periode panen berbeda di empat unit lingkungan yaitu musim hujan monokultur, musim hujan tumpangsari, musim kemarau monokultur, dan musim kemarau tumpangsari. Studi genetik periode panen menggunakan rancangan persilangan line × tester terhadap 10 line, 3 tester, dan 30 genotipe F1. Tetua line Lombok 2, Kaur, Kefa, Lombok 1, VR60, VR82, VR10, VR416, VR422H, VR480B merupakan kultivar lokal dan introduksi dengan periode panen pendek hingga panjang. Tetua tester No.129, Vima 1, dan Vima 2 merupakan varietas nasional panen serempak. Lima genotipe F1 dengan periode panen ≤20 hari, dan tetuanya memiliki daya gabung umum dan daya gabung khusus negatif dan nyata dilanjutkan untuk evaluasi F2, dengan 900 individu per populasi F2. Konfirmasi segregan transgresif dilakukan terhadap masing-masing 124 famili populasi F2 yang memiliki indeks transgresif katogeri tinggi dan sedang F2:3. Rancangan kelompok lengkap teracak (3 ulangan) diterapkan pada percobaan interaksi genotipe dan lingkungan dan line × tester, sedangkan augmented design kelompok lengkap teracak (4 ulangan) pada pengujian F2 dan F2:3. Pengamatan meliputi karakter periode panen dan keserempakan panen, fenologi, dan agronomi kacang hijau.
Interaksi genotipe dan lingkungan berpengaruh terhadap karakter periode panen dan seluruh karakter yang dipelajari, kecuali derajat indeterminasi periode panen, kehijauan daun, dan panjang polong. Faktor genetik berkontribusi besar terhadap fenotipe seluruh karakter yang diamati berdasarkan nilai heritabilitas arti luas kategori tinggi (59,83 – 98,32%), kecuali derajat indeterminasi tinggi tanaman dan bobot biji per tanaman. Kesepuluh genotipe kacang hijau menunjukkan perbedaan respon stabilitas. Kefa, Lombok 2, Kaur, VR480B, MLB tergolong stabil untuk sifat periode panen pendek berdasarkan pendekatan regresi serta GGE biplot. Karakter periode panen dapat diseleksi secara langsung pada lingkungan spesifik yaitu di lingkungan monokultur musim kemarau. Seleksi tidak langsung perlu mempertimbangkan karakter derajat indeterminasi periode panen karena berkorelasi sangat nyata terhadap periode panen, memiliki heritabilitas kategori tinggi, dan tidak dipengaruhi oleh interaksi genotipe dan lingkungan.
Studi genetik pada populasi line × tester memberikan informasi kendali gen-gen non aditif pada periode panen dan seluruh karakter yang dipelajari sehingga sesuai untuk menunda seleksi hingga generasi lanjut. Berdasarkan rataan periode panen pendek (≤ 20 hari), daya gabung umum tetua sangat nyata bernilai negatif (rendah × rendah), dan daya gabung khusus sangat nyata bernilai negatif, maka dapat memprioritaskan genotipe F1 VR10 × Vima 1, VR480B × Vima 1, Lombok 2 × Vima 1, Lombok 2 × No.129, VR422H × 129 sebagai populasi seleksi.
Sebaran data F2 menunjukkan keterlibatan gen-gen non aditif dengan aksi epistasis duplikat terhadap karakter periode panen dan karakter lainnya, kecuali F2 VR10 × Vima 1 yang dikendalikan secara aditif. Menunda seleksi umum dilakukan ketika terdapat kendali gen non aditif, tetapi seleksi pada generasi awal F2 tetap dilakukan dalam penelitian ini. Pendugaan indeks transgresif berdasarkan perbandingan selisih nilai maksimum dan minimum antara F2 dan tetua berhasil mendeteksi jumlah segregan transgresif 7,19 - 42,45 (kategori sedang hingga tinggi). Segregan transgresif putatif ini menyebar pada tiga kelas periode panen pendek (<14 hari), sedang (14-29 hari), dan panjang (>29 hari).
Pengujian terhadap 124 famili F2:3 segregan transgresif putatif VR10 × Vima 1 (peluang indeks transgresif tinggi) dan Lombok 2 × No.129 (indeks transgresif terendah) berhasil mengidentifikasi 24 famili F2:3 VR10 × Vima 1 sebagai segregan transgresif yaitu 1 famili periode panen pendek (11 hari), 20 famili periode panen sedang (14-27 hari) dan 3 famili periode panen panjang (30-35 hari) dengan ragam ≤ 59,99 (≤ tetua VR10); serta 16 famili Lombok 2 × No.129 yaitu 13 famili periode panen sedang (15-25 hari) dan 3 famili periode panen panjang (30-35 hari) dengan ragam ≤ 45,26 (≤ No.129). Hasil ini mengindikasikan adanya peluang seleksi segregan transgresif untuk sifat periode panen pendek pada generasi awal di bawah kendali gen-gen non aditif. Pengujian famili kandidat di F2:3 berhasil mengurai pengaruh gen-gen non aditif (epistasis). Populasi besar di F2 berhasil menjaring genotipe segregan transgresif diantara segregan non transgresif dan mempertahankannya di F3 setelah satu kali kawin sendiri. Metode seleksi segregan transgresif di generasi awal membantu mengelola populasi bersegregasi yang banyak dan besar serta merupakan upaya percepatan mendapatkan galur-galur homozigot kacang hijau.
Famili segregan transgresif pada F2:3 VR10 × Vima 1 dan Lombok 2 × No.129 menunjukkan pola panen yang mirip yaitu membentuk satu puncak atau beberapa puncak panen. Beberapa famili F2:3 dengan satu puncak panen pada dua minggu setelah polong awal matang penuh memiliki potensi panen 80-100% polong total. Kombinasi pola panen demikian dan kekuatan pecah polong dapat mendukung panen satu kali (panen serempak) pada kacang hijau.
Penelitian ini menghasilkan strategi pemuliaan untuk perbaikan sifat periode panen dalam pengaruh gen-gen non aditif dengan metode seleksi segregan transgresif tanpa harus menunda seleksi. Seleksi langsung periode panen berlaku spesifik lokasi sehingga akan berkaitan dengan ideotipe tertentu di lingkungan berbeda (monokultur dan tumpangsari), salah satunya morfologi daun. Genotipe dengan sifat periode panen pendek dan ideotipe tanaman dengan percabangan sedikit diduga sesuai untuk penanaman rapat (populasi tinggi) sehingga mendukung produktivitas tinggi. Mungbean breeding attempts to achieve short harvest periods and high yield. Short harvest periods on mungbean support synchronous maturity, harvest efficiency, and suitability as a catch crop. However, the challenge is that a shorter harvest period is related to a lower yield. Control of additive genes indicated that selection can be performed in the early generation, and on the contrary, selection should be delayed for several generations if non-additive genes played a role.
The objectives of this study were to analyze the genotype by environment interaction, elucidate the genetics of harvest periods trait, and understand the harvest patterns on mungbean. Study of genotype by environment interaction was carried out on ten mungbean genotypes with different harvest periods at four environments: rainy season-monoculture; rainy season-intercropping; dry season-monoculture; and dry season-intercropping.
Genetic studies were carried out using a line × tester mating design, involving 10 lines, 3 testers, and 30 F1 genotypes. Lines Lombok 2, Kaur, Kefa, Lombok 1, VR60, VR82, VR10, VR416, VR422H, VR480B, were obtained from exploration and introduction with different harvest periods; while tester No.129, Vima 1, Vima 2 were national varieties with synchronous maturity. Five F1 genotypes with a harvest period ≤20 days and a negative and significant general and specific combining ability of their parents proceeded to the F2 generation, and 900 F2 individuals per population were planted. Confirmation of transgressive segregation was carried out of 124 families F2:3 from two F2 populations having high and medium transgressive indexes. The randomized complete block design with 3 replications was applied in the study of genotype by environment interaction and line × tester, while an augmented randomized complete block design with 4 replications was used for the study of F2 and F2:3 populations. The observation was performed on the harvest period and synchronous maturity traits, phenological, and agronomic traits of mungbeans.
Genotype by environment interaction significantly affected harvest period and other traits except for the degree of indetermination of harvest period. High heritability (59,83 – 98,32%) indicated high genetic contribution to all traits except for the degree of indetermination of plant height and seed weight per plant. Ten mungbean genotypes had different harvest period stability. Kefa, Lombok 2, Kaur, VR480B, and MLB were stable based on regression and GGE biplot methods. Direct selection of harvest period traits may be carried out in a specific environment, i.e., in the dry season-monoculture. The degree of indetermination harvest period was significantly correlated to harvest period, had a high heritability, and was not affected by genotype × environment, therefore is recommended as an indirect selection trait for harvest periods.
Study of line × tester showed non-additive genes controlled for harvest period and all studied traits, and therefore selection should be more effective if conducted in the advanced generations. Based on the mean value of harvest period ≤ 20 days, as well as negative and significant general and specific combining ability, the population VR10 × Vima 1, VR480B × Vima 1, Lombok 2 × Vima 1, Lombok 2 × 129, VR422H × 129 populations could be prioritized for selection.
The phenotype distribution of each F2 population showed non-additive genes control for all traits in four populations and additive in F2 VR10 × Vima 1 only. Even though non-additive gene control suggests delayed selection, early selection in the F2 generation was still carried out in this study. Estimation of the transgressive index based on the ratio of the difference between the maximum and minimum values of F2 and the parents succeeded in detecting the number of transgressive segregants from 7,19 to 42,45 (medium to high category). These putative transgressive segregants spread over three classes of short (<14 days), medium (14-29 days), and long (>29 days) harvest periods.
Verification on 124 families of F2:3 putative transgressive segregation VR10 × Vima 1 (high transgressive index) and Lombok 2 × No.129 (medium transgressive index) identified 24 transgressive segregant families of F2:3 VR10 × Vima 1, consisting of one family with a short harvest period (11 days), 20 families with medium harvest period (14-27 days) and three families with long harvest period (30-35 days), with a variance of 59.99 (≤ VR10); and 16 families of Lombok 2 × No.129 consisting of 13 families with medium harvest period (15-25 days) and three families with long harvest period (30-35 days), with a variance of 45.26 (≤ No.129). These results indicated the opportunity for transgressive segregation selection for short harvest period traits in early generations under non-additive genes control. Testing of the F2:3 family perhaps segregated the effect of non-additive genes (epistatic). The considerably large F2 population was able to capture transgressive genotypes and maintain them after one inbreeding generation (F3). The selection of transgressive segregants in early generations would help to manage many segregated populations and accelerates the acquisition of homozygous lines of mungbean.
The transgressive segregant F2:3 families of VR10 × Vima 1 and Lombok 2 × No.129 showed a similar harvest pattern, forming one or several harvest peaks. Several F2:3 families with one peak harvest at two weeks after the early pods ripening had a potential harvest of 80-100% of total pods per plant. The combination of harvest pattern and pod shattering strength can support a one-time harvest of mungbeans.
This study resulted in a breeding strategy for the harvest periods under non-additive genes control by transgressive segregants selection without delaying selection. Direct selection of the harvest period will apply for a specific environment, and therefore will relate to plant ideotypes for each cropping system (monoculture and intercropping); one of which is leaf morphology. Genotypes with a short harvest period and slightly branched may be suitable for planting a dense population to support high productivity.
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