PENGARUH UKURAN BRAKTEA BEBERAPA AKSESI KAPAS TERHADAP TINGKAT SERANGAN HAMA PENGGEREK BUAH Helicoverpa armigera (HUBNER)

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