Potensi Bakteri Endofit untuk Pengendalian Bean common mosaic virus Strain Blackeye cowpea (BCMV-BlC) dan Aphis craccivora Koch. pada Kacang Panjang.

Abstract

Bean common mosaic virus strain Blackeye cowpea (BCMV-BlC) dan vektornya, Aphis craccivora Koch, merupakan salah satu kendala utama dalam produksi kacang panjang di Indonesia. Pengelolaan virus tular serangga umumnya secara kimiawi untuk mengendalikan serangga vektor virus untuk menekan penularan dan penyebaran virus. Pengelolaan hama dan penyakit saat ini perlu dipilih cara yang aman bagi lingkungan dan berkelanjutan. Potensi bakteri endofit untuk mengendalikan patogen cendawan, nematoda, dan bakteri telah banyak dilaporkandiantaranya AC112 (Bacillus toyonensis), APE35 (B. siamensis), dan BAT27 (B. toyonensis). Namun, potensi pemanfaatan bakteri endofit untuk mengendalikan infeksi virus dan vektornya masih belum banyak diteliti. Penelitian bertujuan untuk mengkaji potensi bakteri endofit dalam menekan penularan dan infeksi BCMV-BlC serta serangga vektornya A. craccivora Koch. Penelitian ini terdiri dari tiga percobaan utama; Perbanyakan inokulum BCMV-BlC, bakteri endofit (BE), kutu daun, (1) Kemampuan bakteri endofit terhadap pertumbuhan benih kacang panjang. Benih kacang panjang direndam dengan isolat APE35, BAT27, AC112, LCA19, dan kontrol. Perlakuan yang diuji menggunakan kerapatan 108 CFU mL-1 Peubah yang diamati daya berkecambah dan indeks vigor. (2) Efikasi bakteri endofit (BE) dalam menghambat penularan BCMV-BlC dengan kutu daun. Perlakuan yang diuji menggunakan kerapatan 108 CFU mL-1 isolat APE35, BAT27, AC112, dan LCA19, kontrol sehat dan kontrol sakit tanpa BE. Perlakuan BE terdiri dari perendaman benih dan penyemprotan daun. Peubah yang diamati terdiri dari peubah penyakit termasuk titer virus dan aktivitas enzim polifenol oksidase (PPO). Peubah agronomi yang diamati antara lain tinggi tanaman, jumlah daun dan kadar klorofil a dan b. (2) Pengaruh bakteri endofit terhadap mortalitas dan preferensi makan kutu daun. Sebanyak 25 imago kutu daun diinfestasikan ke daun kacang panjang sehat dan diletakkan dalam cawan petri, kemudian kutu daun disemprot suspensi BE dan kontrol disemprot akudes steril. Peubah yang diamati persentasi mortalitas kutu daun. Preferensi makan 25 ekor kutu daun diuji dengan metode choice test. Peubah yang diamati jumlah kutu daun pada tanaman uji setelah infestasi 1, 3, 6, dan 12 jam. (3) Pengaruh BE terhadap kemampuan kutu daun generasi ke-3 dalam menularkan BCMV-BlC. BE diaplikasikan dengan perlakuan benih dan penyemprotan daun. Kutu daun dipelihara pada tanaman perlakuan dan kontrol tanpa BE. Imago kutu daun dari generasi ke-3 diberi makan akuisisi dan makan inokulasi pada tanaman sehat. Peubah yang diamati insidensi, waktu inkubasi, keparahan penyakit dan titer virus. Perlakuan BE meningkatkan perkecambahan dan indeks vigor benih kacang panjang. Semua perlakuan bakteri endofit dapat meningkatkan pertumbuhan dengan perlakuan terbaik isolat B. siamensis-APE35 dan B. toyonensis-BAT27 dibandingkan kontrol. Efikasi BE untuk mengendalikan BCMV-BlC melalui A. craccivora mampu menekan transmisi virus dengan memperpanjang masa inkubasi, menyebabkan gejala yang lebih ringan, serta menurunkan titer virus dibandingkan kontrol tanpa perlakuan. Perlakuan B. toyonensis-AC112 dan B. toyonensis-BAT27 terbukti efektif dalam menghambat kutu daun menularkan BCMV-BlC yang dibuktikan dengan titer virus terdeteksi positif BCMV pada kutu daun, namun negatif terdeteksi negatif BCMV pada tanaman. Perlakuan bakteri endofit meningkatkan pertumbuhan tanaman dan menginduksi enzim PPO serta peningkatan total kadar klorofil dibandingkan kontrol sakit tanpa perlakuan. Semua isolat bakteri endofit menunjukkan efek insektisidal terhadap kutu daun dengan mortalitas berkisar 31%-49%, tergantung spesies bakteri endofit. Diantara BE, isolat B. toyonensis-BAT27 menyebabkan mortalitas kutu daun tertinggi sebesar 49% pada 48 jam setelah perlakuan. Pengujian choice test, menunjukkan bahwa jumlah kutu daun pada tanaman kacang panjang yang diberi perlakuan bakteri endofit nyata lebih sedikit dibandingkan kontrol. Namun, antar perlakuan BE tidak berbeda nyata; semua isolat bakteri endofit berpengaruh terhadap preferensi makan kutu daun sejak awal perlakuan. Kutu daun generasi ketiga yang dipelihara pada tanaman perlakuan bakteri endofit menurunkan kemampuannya menularkan BCMV-BlC. Hal ini ditunjukkan dari masa inkubasi lebih lama, insidensi, keparahan penyakit dan titer virus lebih rendah. Perlakuan bakteri endofit menurunkan efisiensi kutu daun dalam mengakuisisi dan mentransmisikan virus ke tanaman. Titer virus perlakuan B. toyonensis-BAT27 terdeteksi negatif BCMV-BlC pada tanaman, namun terdeteksi positif BCMV pada kutu daun, hal ini mengindikasikan B. toyonensis-BAT27 mampu menghambat kutu daun menularkan virus karena aktivitas antifeedant yang kuat menghambat makan inokulasi pada tanaman.

Bean common mosaic virus strain Blackeye cowpea (BCMV-BlC) and its vector, Aphis craccivora Koch, are significant constraints to yardlong bean production in Indonesia. Insect-borne viruses are generally managed chemically to control the insect vectors, thereby suppressing the transmission and spread of the virus. Currently, pest and disease management requires environmentally safe and sustainable methods. The potential of endophytic bacteria to control fungal, nematode, and bacterial pathogens has been widely reported, including AC112 (Bacillus toyonensis), APE35 (B. siamensis), and BAT27 (B. toyonensis). However, the potential use of endophytic bacteria to control viral infections and their vectors remains understudied. This study aims to assess the potential of endophytic bacteria to suppress transmission and infection of BCMV-BlC and its insect vector, A. craccivora Koch. This study consisted of three main experiments; (1) Efficacy of endophytic bacteria (BE) in inhibiting BCMV-BlC transmission by aphids. The treatments tested used a density of 108 cfu/mL isolates APE35, BAT27, AC112, and LCA19, healthy controls and diseased controls without BE. BE treatment consisted of seed soaking and foliar spraying. Observed variables consisted of disease variables including virus titre and polyphenol oxidase (PPO) enzyme activity. Agronomic variables observed included germination capacity and vigor index, plant height, number of leaves and plant physiology by measuring chlorophyll a and b levels. (2) Effect of endophytic bacteria on mortality and feeding preferences of aphids. A total of 25 imago aphids were infested into healthy long bean leaves and placed in a petri dish, then the aphids were sprayed with a suspension of endophytic bacteria and the control was sprayed with sterile distillate water. Observed variables were the percentage of aphid mortality. The feeding preferences of 25 aphids were tested using the choice test method. The variables observed were the number of aphids on the test plants after 1, 3, 6, and 12 hours of infestation. (3) The effect of endophytic bacteria on the ability of 3rd generation aphids to transmit BCMV-BlC. Endophytic bacteria were applied by seed treatment and foliar spraying. Aphids were reared on treatment and control plants without the addition of BE. Aphid adults from the 3rd generation were fed acquisition on infected plants and inoculation feed on healthy plants. The variables observed were incidence, incubation period, disease severity, and virus titre. Endophytic bacterial treatment increased germination and vigour index of yardlong bean seeds. All endophytic bacterial treatments increased growth, with the best results achieved with the B. siamensis-APE35 and B. toyonensis-BAT27 isolates compared to the control. The efficacy of BE in controlling BCMV-BlC through A. craccivora was demonstrated by suppressing virus transmission; extending the incubation period, causing milder symptoms, and reducing virus titers compared to the untreated control. Bacillus toyonensis-AC112 and Bacillus toyonensis-BAT27 treatments were proven effective in inhibiting aphids from transmitting BCMV-BlC, as evidenced by positive virus titres detected for BCMV in aphids, but negative for BCMV detected in plants. Endophytic bacterial treatment increased plant growth and induced PPO enzymes, as well as increased total chlorophyll levels, compared to diseased controls without treatment. All endophytic bacterial isolates exhibited insecticidal effects against aphids, with mortality ranging from 31% to 49%, depending on the endophytic bacterial species. Among the endophytic bacterial isolates, B. toyonensis-BAT27 caused the highest aphid mortality, at 49% 48 hours after treatment. A choice test showed significantly fewer aphids on yardlong bean plants treated with endophytic bacteria than on control plants. However, there was no significant difference between the endophytic bacterial isolates; all endophytic bacterial isolates affected aphid feeding preferences from the beginning of treatment. The third generation of aphids reared on endophytic bacterial plants had a reduced ability to transmit BCMV-BlC. This was demonstrated by a more extended incubation period, a lower incidence, decreased disease severity, and lower virus titer. The endophytic bacterial treatment reduced the efficiency of aphids in acquiring and transmitting the virus to plants. The virus titre of B. toyonensis-BAT27 treatment was detected as negative for BCMV-BlC in plants, but was detected as positive for BCMV in aphids. This suggests that B. toyonensis-BAT27 can prevent aphids to transmitting the virus, as its vigorous antifeedant activity inhibits inoculation feeding on plants.