Isolasi Bakteri Bacillus thuringiensis dari Tanah dan Pengujian Toksisitasnya terhadap Ulat Grayak (Spodoptera litura)

Abstract

Bacillus thuringiensis (Bt) is known to inhibit growth of Lepidoptera larvae such as armyworm (Spodoptera litura) larvae which cause many problem in agriculture. Inhibition activity of Bt due to protein crystal toxin produced during sporulation phase. This study was aimed to isolate Bt from various soil samples and to test its toxicity to the armyworm fifth instar larvae. Two isolates was isolated from soil samples i.e. 47 and Lot 2 isolates. The isolates are Gram positive rod-shaped, had subterminal endospores and crystals of proteins. Colony morphology of the isolates was round, white, and corrugate edge. Both of isolates were tested to the fifth instars of armyworm larvae by immersion method. The toxicity of isolates was higher however it was not significantly different with positive control (Bt subsp. aizawai) and the negative control. The negative control had high percentage of mortality up to 72.5%.

Bacillus thuringiensis (Bt) diketahui dapat menghambat pertumbuhan larva Lepidoptera seperti ulat grayak (Spodoptera litura), yang menyebabkan banyak masalah di bidang pertanian. Penghambatan aktivitas Bt disebabkan racun protein kristal yang diproduksi selama fase sporulasi. Penelitian ini bertujuan untuk mengisolasi Bt dari berbagai contoh tanah dan uji toksisitas terhadap larva ulat grayak instar kelima. Dua isolat berhasil diisolasi dari sampel tanah yaitu isolat 47 dan Lot 2. Isolat-isolat termasuk bakteri Gram positif, berbentuk batang, memiliki endospora subterminal, dan kristal protein. Morfologi koloni isolat berbentuk bulat, berwarna putih, dan tepian berkerut. Kedua isolat diuji dengan ulat grayak instar kelima dengan metode celup. Toksisitas isolat lebih tinggi tetapi tidak berbeda secara signifikan jika dibandingkan dengan Bt pembanding subsp. aizawai dan kontrol negatif. Kontrol negatif memiliki persentase kematian yang cukup tinggi yaitu 72,5%.