<p>ABSTRAK<br />Hingga kini teknik perakitan varietas kapas tahan hama masih<br />dilakukan secara konvensional berdasarkan beberapa karakter morfologi<br />tanaman, seperti: bulu daun, daun okra, braktea berpilin, nektar, dan<br />gosipol tinggi. Karakter-karakter ini diketahui erat hubungannya dengan<br />ketahanan terhadap hama, khususnya H. armigera. Berkaitan dengan<br />serangan H. armigera pada buah, diduga ada bagian-bagian buah kapas<br />yang berkontribusi secara langsung pada serangan hama ini, misalnya<br />braktea buah. Namun demikian, besarnya pengaruh braktea terhadap<br />kerusakan buah kapas perlu dipelajari dalam upaya meminimalkan<br />kerusakan. Penelitian ini bertujuan untuk mengetahui pengaruh ukuran<br />braktea terhadap tingkat kerusakan buah oleh H. armigera pada beberapa<br />aksesi kapas. Penelitian dilaksanakan di Kebun Percobaan Balai Penelitian<br />Tanaman Tembakau dan Serat, di Asembagus, Situbondo, Jawa Timur<br />mulai bulan Januari hingga Desember 2006. Sebanyak 18 aksesi dari 50<br />aksesi kapas dengan berbagai variasi ukuran braktea digunakan sebagai<br />perlakuan. Setiap perlakuan (aksesi) disusun dalam rancangan acak<br />kelompok (RAK), dengan tiga kali ulangan. Lima tanaman kapas dari<br />masing-masing aksesi ditentukan secara acak, dan sebanyak 5 buah kapas<br />muda (diameter ± 4 cm) dipetik dari masing-masing tanaman sampel,<br />kemudian dibawa ke laboratorium untuk diukur luas braktea dan buahnya.<br />Selain itu dilakukan pula pengamatan kerusakan buah dan hasil kapas<br />berbiji di lapang. Hasil penelitian menunjukkan bahwa ukuran braktea<br />berkorelasi positif dengan tingkat kerusakan buah (R 2 = 0,9014), sehingga<br />braktea berukuran besar dan lebar serta menutupi buah secara total<br />berpotensi mengalami kerusakan akibat serangan H. armigera lebih tinggi<br />dibanding braktea berukuran kecil dan sempit. Ukuran panjang dan lebar<br />braktea pada 18 aksesi kapas bervariasi antar aksesi dan masing-masing<br />berkorelasi positif dengan luas (R 2 = 0,876; R 2 = 0,894). Hasil penelitian<br />ini dapat dimanfaatkan dalam merakit varietas tahan hama, dan<br />kombinasinya dengan karakter-karakter morfologi kapas yang sudah ada<br />untuk menghasilkan varietas kapas baru dengan tingkat ketahanan yang<br />lebih tinggi terhadap hama penggerek buah H. armigera.<br />Katakunci : Braktea, Helicoverpa armigera, aksesi kapas, karakter<br />morfologi.</p><p><br />ABSTRACT<br />Effects of bract size of several cotton accessions to<br />American bollworm injury level<br />Conventional method by crossing technique based on<br />morphological characters of plant is now still used in providing resistant<br />varieties of cotton against insect bollworms. A number of genetic<br />characters are now available and have been studying for their assosiation<br />with insect pests resistance such as hairiness, okra leaf, frego bract,<br />nectariless, and high gossypol. Regarding to boll damage by H. armigera,<br />it can be mentioned that there are many other morphological characters of<br />cotton attributable to bollworm damage, such as floral bract. As a part of<br />boll, it is estimated that bracts assosiated with bollworm attacked due to<br />their larger size compared with boll size. Objective of the study was to find<br />out the effect of bract size in relation to bollworm damage on cotton<br />accessions. The study was conducted at Experimental Station of<br />Indonesian Tobacco and Fiber Crops Research Institute in Asembagus,<br />Situbondo, East Java from January to December 2006. Eighteen of fifty<br />cotton accessions were used as treatment and they were arranged in<br />Randomized Block Design (RBD) with three replications. Five randomly<br />cotton plants from each accession and five young bolls were sampled<br />from the selected plant with about 4 cm of diameter were brought in the<br />laboratory to collect information on bract and boll sizes. Bollworm<br />damage was determined by counting the damaged bolls in the field as well<br />as the seed cotton yield. Result showed that bract size was positively<br />correlated with boll damage (R 2 = 0.9014). Higher damaged bolls occured<br />on bolls which is covered completely by bracts. There is variation between<br />length and wide size of bracts among cotton accessions and both showed<br />positive correlation to bract area (R 2 = 0.876; R 2 = 0.894). Based on this<br />study, higher resistance of cotton variety against H. armigera will<br />possiblly be provided through combination between bract size and any<br />other morphological characters of cotton.<br />Key words : Floral bract, Helicoverpa armigera, cotton accession,<br />morphological character</p>
COMPARATIVE EFFICACY OF FOUR INSECTICIDES AGAINST AMERICAN BOLLWORM (Helicoverpa armigera) UNDER FIELD CONDITIONS
