Hubungan antara Ukuran Genom dan Karakter Agronomi, Morfologi, Fisiologi dengan Produksi pada Mutan Putatif Tebu Hasil Induksi Kolkisin

Abstract

Tebu (Saccharum officinarum L.) dikenal sebagai sumber tanaman pemanis dengan genom yang kompleks, fertilitas rendah, dan umumnya diperbanyak secara vegetatif. Tebu memiliki tiga tipe kemasakan, yaitu masak awal, masak tengah dan akhir. Penataan penananaman ketiga tipe tersebut sangat berpengaruh terhadap kontinuitas produksi. Varietas PS 881 merupakan salah satu tipe tebu masak awal. Varietas dengan tipe kemasakan ini masih terbatas beredar di masyarakat. Peningkatan keragaman genetik tebu dengan tipe masak awal perlu dilakukan, salah satunya dengan induksi mutasi kolkisin Keragaman genetik tebu hasil induksi mutasi kolkisin telah dilakukan dalam penelitian sebelumnya. Namun belum dilakukan seleksi mutan putatif berdasarkan karakter yang mendukung peningkatan produksi tebu. Pemuliaan tebu melalui induksi mutasi kolkisin bertujuan untuk meningkatkan ukuran genom tanaman. Peningkatan ukuran genom diharapkan meningkatkan ukuran diameter batang tebu, sehingga produksi meningkat. Tujuan penelitian adalah untuk mendapatkan informasi perubahan ukuran genom mutan putatif tebu hasil induksi kolkisin varietas asal PS 881 melalui flow cytometry, penampilan karakter agronomi, briks, dan produksi; mendapatkan informasi ketidakmiripan morfologi antara mutan putatif tebu dan varietas asal hasil induksi kolkisin; serta korelasi antara ukuran genom dengan karakter agronomi, sekaligus analisis lintas terhadap produksi mutan putatif tebu. Penelitian ini dilaksanakan pada bulan Juli 2018-April 2019 di Unit Pengelola Benih Unggul Pertanian (UPBUP) dan Balai Besar Penelitian Bioteknologi dan Sumberdaya Genetik Pertanian (BB Biogen), Badan Litbang Pertanian. Rancangan percobaan yang digunakan rancangan augmented dalam rancangan kelompok lengkap teracak. Penelitian ini menggunakan bahan tanam generasi awal 30 mutan putatif tebu (M1V4) dari hasil induksi kolkisin tanpa ulangan dan lima varietas pembanding yaitu PS 881, PS 862, PSJT 941, KK, serta BL lima ulangan. Semakin tinggi ukuran genom maka jumlah kromosom akan semakin besar. Pengamatan perubahan ukuran genom dilaksanakan menggunakan flow cytometry pada daun muda mutan putatif tebu. Kenaikan ukuran genom pada 30 mutan putatif tebu sebesar 5.03-13.64% dibanding varietas asal PS 881, namun hanya 21 mutan putatif yang mempunyai ukuran genom berbeda nyata dengan varietas asal PS 881. Selain ukuran genom perbedaan nyata ditunjukan juga oleh karakter agronomi (bobot batang per meter, panjang batang, diameter batang, jumlah batang, panjang ruas, jumlah ruas, briks, produksi) dan satu karakter fisiologi yaitu aktivitas nitrat reduktase. Mutasi dengan menggunakan senyawa ini menghasilkan tiga mutan putatif yang berpotensi produksi dan briks lebih tinggi dibanding varietas asal yaitu 9A, 6A dan 36B. Penanda morfologi suatu karakter masih digunakan di lembaga penelitian tebu untuk proses identifikasi varietas. Pengamatan perubahan karakter pada daun, pelepah daun, ruas, batang, dan mata dilakukan sebanyak 34 penanda morfologi. Tingkat ketidakmiripan antar mutan putatif dengan varietas asal berdasarkan karakter morfologi sebesar 25%, yang terbagi menjadi dua kelompok besar. Perubahan karakter morfologi mutan putatif tebu dibanding varietas asal yaitu pada daun (lengkung helai, tinggi telinga, kedudukan telinga, warna, warna segitiga, lebar), pelepah daun (lebar daerah bulu bidang punggung, jarak puncak daerah bulu bidang punggung, panjang bulu bidang punggung, kedudukan bulu bidang punggung, kerapatan bulu bidang punggung, sifat lepas pelepah daun kering, lapisan lilin, warna), ruas batang (susunan, penampang melintang, bentuk, panjang, alur mata), batang (jumlah primordia akar, warna, lapisan lilin), dan mata (tepi sayap, pusat tumbuh, rambut jambul). Ini menunjukkan bahwa induksi mutasi menggunakan kolkisin dapat menyebabkan perubahan karakter morfologi tanaman. Perubahan karakter morfologi ini dapat digunakan sebagai penciri spesifik suatu mutan baru yang akan dikembangkan sebagai varietas unggul baru. Perubahan pada ukuran genom dan penampilan karakter agronomi dianalisis korelasinya dan dilakukan analisis lintas pada karakter yang berpengaruh terhadap produksi mutan putatif tebu. Hasil analisis korelasi ukuran genom dengan karakter agronomi (briks, panjang batang, diameter batang, dan produksi) adalah positif nyata. Semakin meningkat ukuran genom pada mutan putatif maka semakin meningkat karakter briks, panjang batang, diameter batang, produksi. Analisis lintas menunjukkan bahwa karakter bobot batang per meter, jumlah batang dan panjang batang mempunyai pengaruh langsung yang besar terhadap produksi tebu. Sedangkan karakter ukuran genom dan diameter batang mempunyai pengaruh langsung kecil terhadap produksi tebu. Karakter ukuran genom dan diameter batang mempunyai pengaruh tak langsung yang cukup besar terhadap produksi melalui karakter bobot batang per meter. Seleksi tak langsung untuk mendapatkan produksi tebu yang tinggi dapat dilakukan melalui karakter bobot batang per meter, jumlah dan panjang batang dengan tetap mempertimbangkan karakter ukuran genom dan diameter batang. Penelitian ini menghasilkan mutan putatif tebu dengan potensi produksi dan briks tinggi di rumah kaca. Diperlukan evaluasi lanjut di tingkat lapang untuk mengetahui potensi produksinya untuk dilepas sebagai varietas unggul baru dengan produktivitas dan rendemen tinggi.

Sugarcane (Saccharum officinarum L.) is known as a sweetener plant with a complex genome, low fertility, and generally propagated vegetatively. Sugarcane has three types of maturity, namely early maturity, middle maturity and late maturity. The arrangement of the three types of planting is very influential on the continuity of production. The PS 881 variety is one of the sugarcane with early maturity type. Varieties with this level of maturity are still in short supply. It is necessary to increase the genetic diversity of sugarcane with early maturity type, one of which is by induction of colchicine mutations. The genetic diversity of sugarcane induced by colchicine mutations has been carried out in previous studies. However, the selection of putative mutants has not been carried out based on the characters that support the increase in sugarcane production. The goal of sugarcane breeding via colchicine mutation induction is to increase the size of the plant genome. Sugarcane stalk diameter is projected to increase as genome size increases, resulting in increased production. The objectives of this study were to use flow cytometry to determine changes in genome size of sugarcane putative mutants generated by colchicine from variety PS 881, as well as the performance of agronomic features, brix, and yield, to obtain information on the morphological dissimilarity between sugarcane putative mutants and the original variety induced by colchicine; and the correlation between genome size and agronomic characters, as well as path analysis of the production of sugarcane putative mutants. This study was conducted in July 2018-April 2019 at the Agricultural Superior Seed Management Unit (UPBUP) and the Indonesian Research Center for Biotechnology and Agricultural Genetic Resources (ICABIOGRAD), Indonesian Agency for Agricultural Research and Development. The experimental design used was an augmented design in a randomized complete block design. This study used early generation planting material of 30 sugarcane putative mutants (M1V4) from colchicine induction without replications and five comparison varieties, namely PS 881, PS 862, PSJT 941, KK, and BL replicated five times. The higher the genome size, the greater the number of chromosomes. The observation of changes in genome size was carried out using flow cytometry on young leaves of sugarcane putative mutants. The increase in genome size in 30 sugarcane putative mutants was 5.03-13.64% compared to the PS 881 variety, but only 21 putative mutants had a significantly different genome size from the PS 881 variety. In addition to genome size, the significant difference was also shown by agronomic characters (stem weight per meters, stem length, stem diameter, number of stems, length of internodes, number of internodes, brix, production) and one physiological character, namely nitrate reductase activity. Mutations using this compound resulted in three putative mutants with higher production potential and brix than the original varieties, namely 9A, 6A and 36B. Morphological markers of a character are still used in sugarcane research institutes for the identification of varieties. In this study , observations of character changes in leaves, leaf midrib, internodes, stems, and nodes were carried out as many as 34 morphological markers. The level of dissimilarity between putative mutants and the original variety based on morphological characters was 25%, which was divided into two major groups. Changes in the morphological characters of the putative mutants of sugarcane compared to the original variety, namely in the leaves (curl of strands, ear height, ear position, color, color triangle, width), leaf midrib (width of the dorsal hair area, distance to the top of the dorsal hair area, length of dorsal hairs, position of dorsal hairs, density of dorsal hairs, dry leaf midrib detachment, waxy coating, color), internodes (arrangement, cross section, shape, length, bud grooves), stem (number of root primordia, color, waxy coating), and bud (wing edge, growth center, crested hair). This indicates that mutation induction using colchicine can cause changes in plant morphological characters. This change in morphological characters can be used as a specific characteristic of a new mutant that will be developed as a new superior variety. Changes in genome size and appearance of agronomic characters were analyzed for correlation and path analysis was performed on the characters that the production of sugarcane putative mutants. The genome size was positively correlated with with agronomic characters, namely brix, stem length, stem diameter, and production. The increase in the genome size of the putative mutants is followed by increase in the brix value , stem length, stem diameter, production. The path analysis showed that the character of stem weight per meter, number of stems and stem length had a large direct influence on sugarcane production. The genomic size and stem diameter had a small direct effect on sugarcane production, but has a significant indirect effect on production through the character of stem weight per meter. Indirect selection to obtain high sugarcane production can be done through the character of stem weight per meter, number and length of stems while taking into account the character of genome size and stem diameter. This study resulted in sugarcane putative mutants with high production potential and high brix in the greenhouse. Further evaluation in the field is needed to determine the production potential to be released as new high yielding varieties with high productivity and yield.