Optimation of In Vitro Shoot Proliferation Medium for Diploid and Tetraploid Kaliurang Taro (Colocasia esculenta L.) Taro cv. Kaliurang has a good taste and is tolerant to certain pests and diseases but its development is hampered by insufficient number of good quality plant materials. Quality improvement has been carried out through polyploidization. Shoot multiplication is an important step in micropropagation, which often needs specific formulation of culture medium. This study aimed to obtain an optimum formulation of in vitro shoot-inducing medium of taro cv. Kaliurang. Explants from one diploid and three tretraploid clones were subjected to six treatments of medium formulations with various concentrations of thiamine and adenine in BAP-containing MS media. Shoots were then rooted, followed by plantlet acclimatization. Ploidy level was measured using flow cytrometry. The rooting medium was ½ MS without growth hormones, whereas acclimatization medium was a mixture of sterile soil, husk, and cocopeat. The results showed that MS + 2 mg L-1 BAP + 4 mg L-1 thiamine + 2 mg L-1 adenine was the optimum medium with an average 3.45 shoots per explant. Plantlet acclimatization was successful with 99.1% survival. Flow cytometry measurement confirmed tetraploidy level of the regenerants from 3 tetraploid clones. Keywords: adenine, acclimatization, benzyl amino purine, shoot proliferation, thiamine ABSTRAK Talas Kaliurang memiliki rasa yang enak dan toleran terhadap hama dan penyakit tertentu, namun pengembangannya terkendala oleh ketercukupan benih bermutu. Upaya perbaikan mutu tanaman telah dilakukan sebelumnya melalui poliploidisasi. Perbanyakan tunas merupakan langkah penting, yang membutuhkan formula spesifik untuk media kultur. Penelitian ini bertujuan untuk mengoptimasi medium perbanyakan tunas in vitro dari satu klon diploid dan tiga klon tetraploid, yang dikulturkan pada enam konsentrasi tiamin dan adenin dalam media MS yang mengandung BAP. Tunas kemudian diinduksi akar, lalu diaklimatisasi, dan pengukuran tingkat ploidi menggunakan flow cytometry. Media pengakaran adalah ½ MS tanpa ZPT, media aklimatisasi adalah campuran tanah steril, sekam dan kokopit. Hasil penelitian ini menunjukkan bahwa medium MS + 2 mg L-1 BAP + 4 mg L-1 tiamin + 2 mg L-1 adenin merupakan medium optimum dengan rata-rata 3,45 tunas per-eksplan. Hasil aklimatisasi menunjukkan bahwa 99,1% tanaman dapat bertahan hidup. Analisis ploidi dengan flow cytometry menunjukkan bahwa tanaman hasil regenerasi tunas talas Kaliurang tetraploid memiliki tingkat ploidi yang stabil.