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

IG.A.A. INDRAYANI, SIWI SUMARTINI

Abstract


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


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DOI: http://dx.doi.org/10.21082/jlittri.v13n4.2007.125-129

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