Resistance against Fusarium oxysporum f.sp. cubense in banana cv. Ampyang (Musa acuminata, AAA, subgroup non-Cavendish) through induced mutation and in vitro selection.

Abstract

Fusarium wilt caused by Fusarium oxysporum Schlecht f.sp. cubense (EF Smith) Snyd & Hans (Foc) is one of the most important disease infecting root of banana and plantain (Musa spp.). This disease reported has become a primary constrain in banana production and lost of some banana germplasm, including in banana cv. Ampyang. Chemical control of this disease is economically impractical, and to widen banana genetic diversity is also a difficult task because most of edible banana are either triploid, male sterility and partenocarp. Therefore conventional breeding approach for resistance to Fusarium wilt for this crop is difficult. The objectives of this research were (1) to increase phenotypic diversity of banana cv. Ampyang through induced mutation; (2) to obtain banana cv. Ampyang resistant to Fusarium wilt. Explants of in vitro grown shoots were exposed to gamma irradiation at 0, 20, 25, 30, 35, 40, 45, 50 Gy to determine its the radiosensitivity. The CurveExpert ver. 1.4 analysis results indicated that lethal doses of irradiation reducing 20% to 50% of shoot growth (LD20-50) were 51.07-64.54 Gy. After 10 months of proliferation and regeneration periods, all regenerated plantlets from irradiated explants produced less numbers of roots, and some of regenerated plantlets, showed significantly less plantlet fresh weight and height, and longer leaves. Glasshouse evaluation indicated that banana plant regenerated from gamma irradiated explants to exhibit lower plant height, shorter leaf, and leaf lenght by leaf width ratio than from non-irradiated ones. Population of banana cv. Ampyang gamma irradiated at 30, 40, 45 and 50 Gy showed wider variation in qualitative characters than that treated with 0 Gy. Field evaluation showed that a number of variants (12 clones) regenerated from gamma irradiated 25, 30, 45, 50 Gy and non-irradiated one identifying as a positive variant. This charachterize were based on agronomyc charachter and quality of fruit. Improvement program to banana cv. Ampyang resistant to Fusarium wilt requiring some previous study in virulences and effectiveness Foc of Banyuwangi isolate as an selective agent. This research showed that Foc of Banyuwangi isolate were virulent to banana cv. Ampyang, and culture filtrate of Foc concentration 40-60% (v/v) was an effective concentration to obtain banana shoots insensitive to culture filtrate of Foc. This experiment also showed that inoculation methods by dipping banana roots for 2 hours into Foc conidial suspensión 2.5 x 107 conidial mL-1 is the most effective methods to identifying banana cv. Ampyang resistant to Fusarium wilt. Several banana clones resistance to Fusarium wilt was obtain. Induced mutation followed by in vitro selection procedures found that 48 clones (40.7%) indicated resistant to Fusarium wilt, most of them originated from gamma irradiated explants of 30 and 50 Gy. Glasshouse evaluation of banana variant regenerated from induced mutation without in vitro selection produced 5 clones (13.8%) and evaluation of banana variant in endemic Fusarium wilt found that 5 clones (4.9%) indicated resistant to Fusarium wilt.

Pisang dan plantain (Musa spp) merupakan komoditas utama untuk ketahanan pangan, walaupun dalam kondisi lingkungan yang buruk tanaman pisang dapat berperan sebagai tanaman pangan yang bermanfaat. Pisang terdiri dari banyak species dan kultivar, diantaranya pisang cv. Ampyang (Musa acuminata, AAA, subgrup non-Cavendish). Pisang cv. Ampyang merupakan pisang meja (dessert banana) yang sudah sulit dijumpai di pasar tradisional maupun modern, diduga pisang ini sudah jarang dibudayakan oleh petani lokal. Keberadaan pisang cv. Ampyang yang sulit dijumpai ini diduga karena pisang cv. Ampyang rentan terhadap penyakit layu Fusarium yang disebabkan oleh cendawan Fusarium oxysporum f.sp. cubense (Foc). Tujuan umum penelitian ini adalah untuk (1) meningkatkan keragaman tanaman pisang (Musa acuminata, AAA) cv. Ampyang melalui teknik mutasi induksi dengan iradiasi gamma secara in vitro; (2) mendapatkan klon-klon dari kultivar pisang (Musa acuminata, AAA) cv. Ampyang yang resistensi terhadap layu Fusarium yang disebabkan oleh cendawan Fusarium oxysporum f.sp. cubense. Percobaan tahap awal dilakukan untuk menentukan radiosensitivitas tunas pisang cv Ampyang (Musa acuminata, AAA) terhadap perlakuan iradiasi gamma yang ditentukan berdasarkan dosis yang mereduksi pertumbuhan tanaman sebesar 20-50% (LD20-50), dan LD20-50 berada dikisaran 51.07-64.54 Gy dengan dosis optimum untuk pertumbuhan tunas pisang aseptis berada pada dosis 30 Gy. Secara fenotipik tunas yang diradiasi cenderung menghasilkan plantlet dengan keragaman karakter kuantitatif (jumlah akar, tinggi plantlet, bobot segar plantlet) yang lebih rendah, dan bentuk daun yang lebih panjang dari tanaman kontrol. Evaluasi di rumah kaca menunjukkan, tanaman yang diradiasi dengan dosis iradiasi yang lebih tinggi, menghasilkan rataan tinggi tanaman dan panjang daun yang makin rendah,. Tanaman yang diradiasi memiliki bentuk daun yang cenderung lebih lebar dari tanaman kontrol. Tanaman yang diradiasi dengan dosis diatas 30, 40, 45 dan 50 Gy) menghasilkan jenis varian karakter kualitatif yang lebih banyak dibandingkan dengan dosis yang lebih rendah. Evaluasi keragaman terhadap densitas stomata memperlihatkan bahwa tanaman kontrol dan tanaman hasil iradiasi 45 Gy memiliki densitas stomata yang nyata lebih tinggi dari tanaman 20, 25 dan 30 Gy.