Evaluasi Famili F3 Hotong (Setaria italica L. Beauv) Hasil Persilangan Botok-4 x ICERI-6 Berbantu Marka SNAP Berbasis Gen SiDREB2

Abstract

Hotong (Setaria italica L. Beauv.) adalah tanaman potensial untuk dibudidayakan di lahan marginal dan dijadikan pangan fungsional karena memiliki adaptasi luas terhadap lingkungan marginal dan nilai gizi yang baik. Hotong memiliki karbohidrat setara dengan beras, indeks glikemik rendah, dan kandungan gizi dan manfaat kesehatan yang baik. Hotong dapat menjadi makananan diet bagi penderita diabetes, mengurangi faktor resiko kardiovaskular, dan berpotensi sebagai agen terapi terhadap sejumlah jenis kanker. Hotong memiliki adaptasi yang baik pada lahan marginal, termasuk lahan salin. Marka single nucleotide amplified polymorphism (SNAP) berbasis gen SiDREB2 (Setaria italica Dehydration Responsive Element Binding) telah dikembangkan berdasarkan variasi pada basa ke 558, dimana alel A diasosiasikan dengan toleransi terhadap cekaman kekeringan atau salinitas dan alel G diasosiasikan dengan kepekaan terhadap kedua cekaman tersebut. Perakitan varietas unggul hotong perlu dilakukan, terutama karena di Indonesia yang belum ada varietas unggul hotong yang dilepas. Idiotipe varietas unggul hotong yang diharapkan adalah produktivitas tinggi, umur panen cepat, habitus tanaman ideal, dan toleran terhadap salinitas. Penelitian ini terdiri atas dua percobaan. Percobaan pertama dilakukan dari bulan Desember 2022 hingga Februari 2023 di Rumah Kaca Kebun Percobaan Cikabayan Bawah, Departemen Agronomi dan Hortikultura, Fakultas Pertanian, Institut Pertanian Bogor. Percobaan ini menggunakan rancangan kelompok lengkap teracak (RKLT) dengan dua faktor dan tiga ulangan. Faktor pertama adalah lima belas famili F3 hasil persilangan Botok-4 x ICERI-6 dan lima genotipe pembanding. Faktor kedua adalah tingkat cekaman salinitas yang terdiri atas konsentrasi 0 dan 75 mM NaCl. Pengamatan dilakukan pada beberapa karakter pertumbuhan hingga 21 hari setelah tanam (HST). Hasil penelitian menunjukkan bahwa variasi pada basa ke-558 gen SiDREB2 berpengaruh pada respon famili F3 hasil persilangan Botok-4 x ICERI-6 terhadap cekaman salinitas 75 mM NaCl. Famili F3 dengan nomor B4I6-11-342 yang memiliki genotipe A/A diduga paling toleran terhadap cekaman salinitas, berdasarkan beberapa indeks toleransi seperti MP, GMP, STI, YI, HM, K1STI, dan K2STI yang dihitung berdasarkan bobot kering tanaman. Beberapa nomor famili F3 dengan genotipe G/G, seperti B4I6-11-451, B4I6-11-486, B4I6-11-436, dan B4I6-11-370, juga menunjukkan toleransi terhadap cekaman salinitas berdasarkan beberapa indeks toleransi yang diamati. Percobaan kedua dilakukan dari bulan Januari hingga Mei 2023 di Kebun Percobaan Cikabayan Bawah. Percobaan ini bertujuan untuk melakukan studi genetik dan seleksi pada famili F3 hasil persilangan Botok-4 x ICERI-6 dengan bantuan marka SNAP berbasis gen SiDREB2. Percobaan ini menggunakan rancangan kelompok lengkap teracak augmented dengan lima kelompok. Materi genetik yang digunakan terdiri atas 50 famili F3 hasil persilangan Botok-4 x ICERI-6 dengan genotipe A/A (berdasarkan marka SNAP berbasis gen SiDREB2), dua genotipe tetua (Botok-4 dan ICERI-6), dan tiga genotipe lokal (Mauliru-2, NTB-1, dan Toraja) sebagai pembanding. Tiga karakter utama yang diamati, yaitu bobot biji per tanaman, umur berbunga, dan tinggi tanaman, menunjukkan nilai heritabilitas yang sedang hingga tinggi, serta memiliki keragaman fenotipik dan genetik yang sempit hingga luas. Bobot biji per tanaman juga memiliki korelasi positif nyata terhadap tinggi tanaman dan umur berbunga. Seleksi indeks terboboti yang dilakukan berdasarkan tiga karakter target dengan intensitas seleksi 20% dari individu terbaik dalam 20% famili F3 terbaik menghasilkan 37 individu F3 terbaik dari sepuluh famili F3 terbaik. Nilai duga kemajuan seleksi berdasarkan indeks seleksi terboboti menunjukkan adanya peningkatan produktivitas, peningkatan tinggi tanaman, dan penurunan umur berbunga pada generasi berikutnya.

Foxtail millet (Setaria italica L. Beauv.) is a potential functional food in marginal areas due to its broad adaptation to adverse environments and good nutritional value. The nutritional properties of foxtail millet include its comparable carbohydrate content with rice, low glycemic index, high protein and dietary fiber content, and antioxidant potential. Hypertension prevention, cardiovascular risk factors reduction, and its potential as a therapeutic agent against several types of cancer are some of the reported health benefits of foxtail millet. The broad adaptability of the species to adverse environmental conditions includes drought, salinity, and limited nutrient availability. Single nucleotide amplified polymorphism (SNAP) marker based on the SiDREB2 (Setaria italica Dehydration Responsive Element Binding) was developed based on nucleotide variation at base 558, where the A allele was associated with tolerance to drought/salinity stress while the G allele was associated with sensitivity to both stresses. The development of superior foxtail millet varieties needs to be conducted, especially in Indonesia, where there are no released superior foxtail millet varieties yet. The desired ideotype of superior foxtail millet varieties includes high productivity, early maturity, ideal plant habitus, and tolerance to salinity. This research consisted of two experiments. The first experiment was conducted from December 2022 to February 2023 in the Cikabayan Bawah Experimental Greenhouse, Department of Agronomy and Horticulture, Faculty of Agriculture, IPB University. The experiment was arranged in a randomized complete block design (RCBD) with two factors and three replications. The first factor consisted of 15 F3 families derived from Botok-4 and ICERI-6 cross and five check genotypes. The second factor was the level of salinity stress, comprised of 0 and 75 mM NaCl. Observations were made on several growth characteristics up to 21 days after planting (DAP). The research results indicated that variations at base 558 of the SiDREB2 gene influenced the response of F3 families derived from Botok-4 and ICERI-6 cross to 75 mM NaCl salinity stress. The F3 family with the number B4I6-11-342 (A/A genotype) was presumed to be the most salinity tolerant based on several tolerance indices such as MP, GMP, STI, YI, HM, K1STI, and K2STI calculated from the plant's dry weight. Some F3 family numbers with the genotype G/G, such as B4I6-11-451, B4I6-11-486, B4I6-11-436, and B4I6-11-370, also showed tolerance to salinity stress based on several observed tolerance indices. The second experiment was conducted from January to May 2023 at the Cikabayan Bawah Experimental Field. This research aimed to conduct genetic studies and perform selection on F3 families derived from Botok-4 and ICERI-6 cross assisted by the SiDREB2-based SNAP marker. The experiment was arranged in an augmented randomized complete block design with five blocks. The genetic material used consisted of 50 F3 families derived from Botok-4 and ICERI-6 cross with the A/A genotype (based on SNAP markers of the SiDREB2 gene), two parental genotypes (Botok-4 and ICERI-6), and three local genotypes (Mauliru-2, NTB-1, and Toraja) as check genotypes. The three main traits observed, namely grain weight per plant, heading time, and plant height, showed moderate to high heritability values and had varying degrees of phenotypic and genetic coefficient of variation. Grain weight per plant showed a significant positive correlation with plant height and heading time. The weighted selection index based on these three target traits, with a selection intensity of 20% from the top individuals within the top 20% of the best F3 families, resulted in the selection of 37 best F3 individuals from the top 10 F3 families. The estimated predicted selection response based on the weighted selection index indicated an increase in productivity, an increase in plant height, and a decrease in heading time in the subsequent generations.