PATOGENISITAS DUA ISOLAT LOKAL JAMUR Nomuraea rileyi (FARLOW) SAMSON TERHADAP Helicoverpa armigera HUBNER (LEPIDOPTERA: NOCTUIDAE)

ABSTRAK Epizootik Nomuraea rileyi telah berkembang secara alami dalam populasi lebih dari 30 spesies serangga inang, termasuk H. armigera. Penelitian ini dilakukan di Laboratorium Patologi Serangga Balai Penelitian Tanaman Pemanis dan Serat Malang mulai Januari hingga Desember 2011, tujuannya untuk mengetahui patogenisitas dua isolat lokal jamur entomopatogen N. rileyi terhadap larva H. armigera. Penelitian terdiri atas dua faktor perlakuan, faktor 1 adalah dua isolat lokal N. rileyi, yaitu ML 01 dan LG 02, dan faktor 2 adalah konsentrasi konidia, yaitu: 2,2 x 10 5 ; 4,5 x 10 5 ; 2,2 x 10 6 ; 4,5 x 10 6 ; 2,2 x 10 7 ; 4,5 x 10 7 ; 2,2 x 10 8 ; 4,5 x 10 8 konidia/ml, dan kontrol. Setiap perlakuan disusun dalam Rancangan Acak Kelompok Faktorial dengan tiga kali ulangan. Aplikasi jamur pada larva H. armigera dilakukan dengan metode kontaminasi permukaan media yang berupa daun kapas muda (1cm 2 ) di dalam ruangan bersuhu 25±1⁰C dan kelembapan 75-80%. Parameter yang diamati adalah mortalitas larva, LC 50 dan LT 50 , serta bobot larva. Hasil penelitian menunjukkan bahwa tingkat patogenisitas isolat ML 01 terhadap larva H. armigera lebih tinggi dibandingkan dengan isolat LG 02. Isolat ML 01 menyebabkan mortalitas larva H. armigera antara 51,13-85,56% (LC 50  = 2,5 x 10 2  Konidia/ml) dan isolat LG 02 antara 43,36-78,90%, (LC 50  = 5x10 6  Konidia/ml). LT 50 isolat ML 01 antara 5,2-5,5 hari, sedangkan isolat LG 02 antara 6,8-7,0 hari, terutama pada konsentrasi 2,2-4,5 x 10 8 konidia/ml. Terdapat korelasi positif yang erat antara konsentrasi konidia dan mortalitas larva baik pada isolat ML 01 (r=0,975) maupun LG 02 (r=0,980), demikian pula antara konsentrasi konidia dan kehilangan bobot larva pada isolat ML 01 (r=0,982) dan LG 02 (r=0,972). Kata kunci: Helicoverpa armigera, Nomuraea rileyi, patogenisitas, isolat, mortalitas ABSTRACT The epizootic of the fungi Nomuraea rileyi has naturally developed in more than 30 species of insect host population, including cotton bollworm, H. armigera. A study on pathogenicity of two local isolates of Nomuraea rileyi (Farlow) Samson fungi against Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) was conducted at Insect Pathology Laboratory of Indonesian Sweeteners and Fibers Crops Research Institute (ISFCRI) in Malang from January to December 2011 in order to find out the pathogenicity of the isolates against H. armigera larvae. This study consists of two factors as treatment. The first factor was N. rileyi isolates, e.g. ML 01 and LG 02, and the second factor were eight conidia concentrations, viz. 2.2 x 10 5 ; 4.5 x 10 5 ; 2.2 x 10 6 ; 4.5 x 10 6 ; 2.2 x 10 7 ; 4.5 x 10 7 ; 2.2 x 10 8 ; 4.5 x 10 8 conidia/ml, and one untreated control. Treatments were arranged in Factorial Randomized Block Design with three replications. Suspense of conidia was applied by surface contamination method of cotton leaf as medium at 25±1⁰C of temperature and 75-80% of humidity. Parameter observed were larval mortality, LC 50 , LT 50 , and larval weight. Result showed that ML 01 isolate was more pathogenic against H. armigera larvae than LG 02 isolate based on larval mortality, LC 50 , and LT 50 . Percentage of mortality of H. armigera larvae due to ML 01 and LG 02 infection were 51.1- 85.56% and 43.36-78.90%, respectively. The LC 50 of ML 01 and LG 02 isolates was 5.2-5.5 days and 6.8-7.0 days, respectively.There are closest positive correlation between conidia concentration and percentage of mortality on ML 01 (r = 0.975) and LG 02 (r = 0.980) isolates as well as between conidia concentration and larval weight loss on ML 01 (r = 0.982) and LG 02 (r = 0.972) isolates. Key words: Helicoverpa armigera, Nomuraea rileyi, pathogenicity, isolate, mortality