Develompent of sweet potato varieties tolerance to drought stress

English. Drought stress is considered as one of important factor constraining the productivity of sweet potato in Indonesia. Therefore, research on the development of sweet potato varieties tolerance to drought stress is necessary. Experiments that consisted of selection of parents materials based on dry matter content preliminary and advance yield trials were carried out in dry and wet season of 2000 at Kendalpayak, Muneng, and Ngale experimental farms of RILET and at Blitar and Tumpang. Twenty four lines, including MLG 12664 and MLG 12697, were selected as their high dry matter contents of more than 30 percent. They would then be used as parents for hybridization. Evaluation on 18 genotypes from germplasm collection was yielded of more than 1000 g/5 plants. The highest yield was obtained by MLG 12684 which produced 3475 g/5 plants with approximately 26 percent in dry matter content, followed by MLG 12686 with 3000 g fresh tubers production/5 plants and 28 percent dry matter content. In general, drought stress reduced stem length, canopy weight, root size and root mass production. Drought condition also induced the increase of weevil infestation. Preliminary yield trial at Muneng indicated that drought stress reduced yield up to 46 percent. There were three genotypes: No.544-17, No.508-2 and No.461-42, selected. These genotypes had high productivity and affected by drought stress, with yield losses of only 2.94 percent, 24.76 percent, and 21.54 percent respectively. The fresh tubers yield obtained under an optimum irrigation is 1.5 to 14.63 t/ha, while under limited irrigation is 0.53 to 7.48 t/ha. Root damages caused sweet potato weevil under limited irrigation was up to 100 percent. The average yield of these three genotypes contained from the advance yield trials at Blitar, Ngawi, and Tumpang under optimum irrigation were 23.38 t/ha, 12.44 t/ha and 25.74 t/ha, respectively. Under limited irrigation however, they produced only 17.25 t/ha, 7.01 t/ha and 20.99 t/ha respectively. The average yield loss caused by drought stress were 26.3 percent, 43.7 percent, and 18.5 percent

unknown. Kekeringan merupakan salah satu penyebab menurunnya produksi ubijalar. Penurunan produksi dapat diperkecil dengan menanam varietas yang toleran terhadap cekaman kekeringan. Oleh karena itu pembentukan varietas unggul toleran terhadap cekaman kekeringan perlu dilakukan. Penelitian dilaksanakan di INLITKABI Kendalpayak, Muneng, Ngale, Blitar, dan Tumpang. Penelitian mencakup seleksi tetua persilangan untuk bahan kering tinggi, uji daya hasil pendahuluan dan uji daya hasil lanjutan. Diperoleh tetua yang kadar bahan keringnya di atas 30 percent sebanyak 24 nomor diantaranya adalah MLG 12664 dan MLG 12697. Genotipe-genotipe tersebut dapat digunakan sebagai tetua persilangan. Genotipe plasma nutfah yang menghasilkan umbi di atas 1000 g/5 tanaman sebanyak 18 nomor, dan yang tertinggi adalah MLG 12684 dengan hasil umbi 3475 g/5 tanaman dengan kadar bahan kering 26.0 persen dan MLG 12686 dengan hasil umbi 3000 g/5 tanaman dan kadar bahan kering 28.0 persen. Secara umum deraan kekeringan menurunkan panjang sulur, berat tajuk, ukuran umbi, dan produksi umbi. Kekeringan juga mengakibatkan meningkatnya serangan hama boleng. Pada pengujian daya hasil pendahuluan di Muneng, rataan kehilangan hasil akibat deraan kekeringan sebesar 46,03 persen dengan kisaran 2,94-73,74 persen. Genotipe yang terpilih adalah yang hasilnya tinggi dengan kehilangan hasil rendah antara lain No.544-17, No.508-2, dan No.461-42 dengan kehilangan hasil berturut-turut 2,94 persen, 24,76 persen, dan 21,54 persen, Kisaran produksi umbi pada pengairan optimum antara 1,50 s/d 14,63 t/ha dan pada pengairan terbatas antara 0,53 s/d 7,48 t/ha. Kerusakan umbi akibat serangan hama boleng pada pengairan terbatas mencapai 100 persen pada No.623-3. Rataan produksi umbi segar pada pengujian lanjut di tiga lokasi pada pengairan optimum di Blitar, Ngawi, dan Tumpang berturut-turut adalah 23,38 t/ha; 12,44 t/ha; 25,74 t/ha dan pada pengairan terbatas berturut-turut adalah 17,25 t/ha; 7,01 t/ha; dan 20,99 t/ha. Rataan kehilangan hasilnya berturut-turut adalah 26,26 persen; 43,65 persen; dan 18,45 persen