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

ABSTRAKHingga kini teknik perakitan varietas kapas tahan hama masihdilakukan secara konvensional berdasarkan beberapa karakter morfologitanaman, seperti: bulu daun, daun okra, braktea berpilin, nektar, dangosipol tinggi. Karakter-karakter ini diketahui erat hubungannya denganketahanan terhadap hama, khususnya H. armigera. Berkaitan denganserangan H. armigera pada buah, diduga ada bagian-bagian buah kapasyang berkontribusi secara langsung pada serangan hama ini, misalnyabraktea buah. Namun demikian, besarnya pengaruh braktea terhadapkerusakan buah kapas perlu dipelajari dalam upaya meminimalkankerusakan. Penelitian ini bertujuan untuk mengetahui pengaruh ukuranbraktea terhadap tingkat kerusakan buah oleh H. armigera pada beberapaaksesi kapas. Penelitian dilaksanakan di Kebun Percobaan Balai PenelitianTanaman Tembakau dan Serat, di Asembagus, Situbondo, Jawa Timurmulai bulan Januari hingga Desember 2006. Sebanyak 18 aksesi dari 50aksesi kapas dengan berbagai variasi ukuran braktea digunakan sebagaiperlakuan. Setiap perlakuan (aksesi) disusun dalam rancangan acakkelompok (RAK), dengan tiga kali ulangan. Lima tanaman kapas darimasing-masing aksesi ditentukan secara acak, dan sebanyak 5 buah kapasmuda (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 kapasberbiji di lapang. Hasil penelitian menunjukkan bahwa ukuran brakteaberkorelasi positif dengan tingkat kerusakan buah (R 2 = 0,9014), sehinggabraktea berukuran besar dan lebar serta menutupi buah secara totalberpotensi mengalami kerusakan akibat serangan H. armigera lebih tinggidibanding braktea berukuran kecil dan sempit. Ukuran panjang dan lebarbraktea pada 18 aksesi kapas bervariasi antar aksesi dan masing-masingberkorelasi positif dengan luas (R 2 = 0,876; R 2 = 0,894). Hasil penelitianini dapat dimanfaatkan dalam merakit varietas tahan hama, dankombinasinya dengan karakter-karakter morfologi kapas yang sudah adauntuk menghasilkan varietas kapas baru dengan tingkat ketahanan yanglebih tinggi terhadap hama penggerek buah H. armigera.Katakunci : Braktea, Helicoverpa armigera, aksesi kapas, karaktermorfologi.ABSTRACTEffects of bract size of several cotton accessions toAmerican bollworm injury levelConventional method by crossing technique based onmorphological characters of plant is now still used in providing resistantvarieties of cotton against insect bollworms. A number of geneticcharacters are now available and have been studying for their assosiationwith 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 ofcotton attributable to bollworm damage, such as floral bract. As a part ofboll, it is estimated that bracts assosiated with bollworm attacked due totheir larger size compared with boll size. Objective of the study was to findout the effect of bract size in relation to bollworm damage on cottonaccessions. The study was conducted at Experimental Station ofIndonesian Tobacco and Fiber Crops Research Institute in Asembagus,Situbondo, East Java from January to December 2006. Eighteen of fiftycotton accessions were used as treatment and they were arranged inRandomized Block Design (RBD) with three replications. Five randomlycotton plants from each accession and five young bolls were sampledfrom the selected plant with about 4 cm of diameter were brought in thelaboratory to collect information on bract and boll sizes. Bollwormdamage was determined by counting the damaged bolls in the field as wellas the seed cotton yield. Result showed that bract size was positivelycorrelated with boll damage (R 2 = 0.9014). Higher damaged bolls occuredon bolls which is covered completely by bracts. There is variation betweenlength and wide size of bracts among cotton accessions and both showedpositive correlation to bract area (R 2 = 0.876; R 2 = 0.894). Based on thisstudy, higher resistance of cotton variety against H. armigera willpossiblly be provided through combination between bract size and anyother morphological characters of cotton.Key words : Floral bract, Helicoverpa armigera, cotton accession,morphological characte