Pengembangan Karakter Seleksi Ketahanan Cabai (Capsicum annum L.) Terhadap Kutu Kebul Bemisia tabaci Genn. (Hemiptera : Aleyrodidae)

Abstract

Kutu kebul Bemisia tabaci Genn. adalah salah satu hama penting pada tanaman cabai di Indonesia. Pemuliaan ketahanan cabai terhadap kutu kebul masih terus dikembangkan. Identifikasi karakter seleksi yang efektif dan efisien diperlukan dalam pemuliaan tanaman untuk menghasilkan varietas cabai yang tahan terhadap kutu kebul. Tujuan umum penelitian ini untuk mengetahui preferensi kutu kebul B. tabaci Genn pada berbagai tanaman inang dan cabai (Capsicum annum L.) serta kaitannya dengan anatomi dan morfologi daun dalam upaya pengembangan karakter seleksi ketahanan cabai terhadap kutu kebul B. tabaci Genn. Penelitian ini terdiri atas dua bagian besar yaitu (1) preferensi kutu kebul B. tabaci pada berbagai tanaman inang dan kaitannya dengan anatomi dan morfologi daun, (2) skrining pengujian ketahanan berbagai genotipe cabai terhadap kutu kebul B. tabaci. Penelitian skrining terdiri dari tiga penelitian yaitu (a) pengujian tingkat ketahanan berbagai genotipe cabai terhadap kutu kebul B. tabaci dengan infestasi kutu kebul memilih tanaman secara bebas (free choice test), (b) infestasi kutu kebul tidak dapat memilih daun secara bebas (no choice test), (c) identifikasi karakter terkait ketahanan terhadap kutu kebul B. tabaci pada tanaman cabai (anatomi dan morfologi daun, fotosintesis, kandungan fenol dan flavonoid sebelum infestasi kutu kebul). Tujuan khusus penelitian ini yaitu (1) menseleksi genotipe cabai (Capsicum annum L.) lalu mengelompokkannya menjadi 6 kriteria (sangat tahan, tahan, agak tahan, agak rentan, rentan, dan sangat rentan), (2) mengidentifikasi karakter anatomi dan morfologi daun terkait ketahanan terhadap kutu kebul B. tabaci Genn, (3) memperoleh informasi pengaruh warna daun terhadap preferensi kutu kebul terhadap berbagai genotipe cabai, (4) mengetahui korelasi antara respon kutu kebul, dalam hal ini jumlah telur dan jumlah nimfa instar awal, dengan morfologi daun, dan (5) mengetahui kandungan awal fenol dan flavonoid pada cabai genotipe cabai yang tahan dan rentan terhadap kutu kebul (Ungara, C12, dan Landung). Rancangan percobaan yang digunakan adalah rancangan kelompok lengkap teracak dengan tiga ulangan. Tiap genotipe per ulangan terdiri dari dua tanaman. Penelitian dilakukan di dalam kandang serangga di rumah plastik. Cabai yang digunakan adalah cabai Capsicum annum L. koleksi Laboratorium Genetika dan Pemuliaan Tanaman, Departemen Agronomy dan Hortikultura, Fakultas Pertanian, IPB, Bogor. Cabai yang digunakan adalah cabai OP, kecuali cabai varietas Kastilo. Cabai OP (open-pollinated) digunakan dengan pertimbangan bahwa cabai OP dapat langsung dijadikan tetua persilangan untuk studi informasi genetik lebih lanjut. Hasil penelitian “Preferensi kutu kebul B. tabaci pada berbagai tanaman inang” menunjukkan jumlah telur kutu kebul paling tinggi pada timun, diikuti oleh terong, cabai varietas Kastilo, Yuni, okra, tomat, dan cabai varietas Laris. Terdapat korelasi positif yang nyata antara jumlah telur dan jumlah nimfa instar awal dengan jumlah trikhoma. Tidak terdapat korelasi antara jumlah telur dan jumlah nimfa instar awal per tanaman dengan panjang palisade dan tebal daun. Skoring genotipe cabai dilakukan berdasarkan jumlah telur (7 hari setelah infestasi) dan jumlah nimfa instar awal (10 hari setelah infestasi) dari hasil pengujian tingkat ketahanan berbagai genotipe cabai terhadap kutu kebul B. tabaci. Terdapat 6 kriteria genotipe cabai yaitu sangat tahan, tahan, agak tahan, agak rentan, rentan, dan sangat rentan. Warna daun cabai berdasarkan software ImageJ (berdasarkan warna merah, hijau, dan biru) berbeda nyata pada berbagai genotipe cabai, namun tidak ada penciri yang khas untuk membedakan genotipe tahan dan rentan. Warna daun mempengaruhi ketertarikan kutu kebul terhadap cabai. Daun cabai dengan warna keunguan kurang disukai oleh kutu kebul. Kutu kebul lebih menyukai daun cabai yang berwarna hijau muda atau hijau kekuningan. Kerapatan trikhoma non-kelenjar per 10mm2, ketebalan epidermis (µm), panjang palisade (µm), kerapatan sel palisade per 100 µm dan tebal daun (µm) pada berbagai genotipe cabai berbeda nyata. Demikian juga dengan panjang trikhoma. Anatomi dan morfologi daun mempengaruhi imago kutu kebul meletakkan telur. Parameter fotosintesis yang diukur sebelum infestasi kutu kebul yaitu laju fotosintesis, konduktansi stomata, CO2 internal dan laju transpirasi menggunakan Li-Cor. Konduktansi stomata pada genotipe rentan lebih tinggi dibandingkan genotipe tahan dan sangat tahan. Demikian juga dengan CO2 internal. Laju transpirasi pada genotipe rentan lebih rendah dibandingkan genotipe tahan dan sangat tahan. Konduktansi stomata, CO2 internal dan laju transpirasi mempengaruhi imago kutu kebul dalam meletakkan telur secara tidak langsung. Stomata cabai genotipe sangat tahan dan tahan lebih besar dibandingkan dengan genotipe rentan. Terdapat korelasi positif yang signifikan antara jumlah telur dengan jumlah nimfa instar awal per tanaman dengan jumlah trikoma non-kelenjar. Disamping itu trikhoma berkorelasi negatif dengan laju transpirasi. Trikoma non-kelenjar mendukung iklim mikro yang menguntungkan untuk perkembangan telur dan nimfa. Tebal epidermis tidak memiliki korelasi dengan jumlah telur. Panjang dan kerapatan palisade berkorelasi negatif signifikan dengan jumlah telur dan jumlah nimfa instar awal tanaman. Ketebalan daun berkorelasi negatif signifikan dengan jumlah nimfa instar awal tanaman. Heritabilitas (dalam arti luas) memiliki memiliki nilai >60% (tinggi) yaitu jumlah trikhoma non-kelenjar, panjang trikhoma non-kelenjar, ketebalan epidermis, panjang palisade, kerapatan palisade, tebal daun, jumlah stomata, warna daun (merah, hijau, dan biru), laju fotosintesis, konduktivitas stomata, CO2 internal, dan laju transpirasi kecuali karakter panjang dan lebar stomata. Karakter anatomi daun, khususnya trikhoma dan palisade dapat dikembangkan menjadi karakter seleksi pada awal skrining. Fenol dan flavonoid adalah senyawa metabolit sekunder yang memiliki fungsi yang beragam. Tidak terdapat perbedaan yang signifikan kandungan total fenol dan flavonoid pada genotipe cabai tahan (genotipe Ungara) dan cabai rentan (genotipe Landung).

Whitefly Bemisia tabaci Genn. is one of the important pests on chilli in Indonesia. Breeding resistance of chili on whitefly is still being developed. Identification of the right selection character is needed in plant breeding to produce chili varieties that are resistant to whitefly. The general purpose of this study were to determine the preference of whitefly B. tabaci Genn on various host plants and chili (Capsicum annum L.) and its relation to leaf morphology in an effort to develop the selection character of chili resistance against whitefly B. tabaci Genn. This study consisted of two parts: (1) preference of whitefly B. tabaci on various host plants and correlation with leaf anatomy and morphology, (2) screening resistance of chili pepper (Capsicum annum L.) genotypes on whitefly B. tabaci. Screening research consisted of (1) screening on various genotypes of chili with whitefly infestation free-choosing plants, (2) screening on various genotypes of chili with whitefly infestations no-choose, (3) study of leaf anatomy and morphology, photosynthesis, phenol and flavonoid content before whitefly infestation. The specific objectives of this study were (1) screening chili pepper (Capsicum annum L.) genotypes and grouping them into 5 criteria (very resistant, resistant, moderately resistant, moderately susceptible, susceptible, and very susceptible), (2) identifying leaf anatomical and morphological characters related to resistance. against whitefly B. tabaci Genn, (3) determine whether there is an effect of leaf color on whitefly preferences for various chili genotypes, (4) see the correlation between whitefly responses, in this case number of eggs and number of early instar nymphs, and leaf anatomy and morphology , and (5) knowing the initial content of phenols and flavonoids in chili genotypes Ungara, C12, and Landung. The experimental design used was a complete randomized group design with three replications. Each genotype per replication consisted of two plants. The research was conducted in a plastic housing. The chili used was Capsicum annum L. collection of the Laboratory of Genetics and Plant Breeding, Department of Agronomy and Horticulture, Faculty of Agriculture, IPB, Bogor. The chilies used are OP chilies, except for the Kastilo variety. OP (open-pollinated) chili was used with the consideration that OP chili could be directly used as the parent of crosses for further genetic information studies. The results of the study "Preference of whitefly B. tabaci on various host plants" showed the highest number of eggs in cucumber, followed by eggplant, chili varieties of Kastilo, Yuni, okra, tomatoes, and chili varieties of Laris. Likewise with the number of early instar nymphs. B. tabaci prefer cucumber and eggplant. There is a significant positive correlation between the number of eggs and the number of early instar nymphs and the number of trichomes. There was no correlation between the number of eggs and the number of early instar nymphs per plant with palisade length and leaf thickness. The correlation between the number of eggs and the number of early instar nymphs per plant with a positive palisade density with P<0.05 with a low correlation value. Chili genotype scoring was carried out based on the number of eggs (7 days after infestation), the number of early instar nymphs (10 days after infestation) and the percentage of eggs that hatched (10 days after infestation) from the results of studies 2 and 3. There were six class of Chili: very resistant, resistant, moderately resistant, moderately susceptible, susceptible, and very susceptible. Chili leaf color based on ImageJ software was significantly different for various chili genotypes, but there were no distinctive features to distinguish resistant and susceptible genotypes. Analysis of leaf color conversion to CIE Lab (L, a, and b) showed that Ungara (very resistant) and Adelina (resistant) genotypes had lower b values compared to susceptible genotypes. The purplish color of the Ungara and Adelina genotypes was indicated by a low b value. Leaf color affects the attraction of whitefly to chili. Trichoma non-glandular density per 10mm2, epidermal thickness (µm), palisade length (µm), palisade cell density per 100 m and leaf thickness (µm) in various chili genotypes were significantly different. Likewise with the length of the non-glandular trichomes. Leaf anatomy and morphology affected whitefly imago laying eggs. Photosynthetic parameters measured before whitefly infestation were photosynthesis rate, stomatal conductance, internal CO2 and transpiration rate using Li-cor. Stomata conductance in susceptible genotypes was higher than resistant and highly resistant genotypes. Likewise with internal CO2. Transpiration rate in susceptible genotypes was lower than resistant and highly resistant genotypes. Stomata conductance, internal CO2 and transpiration rate affected whitefly imago in laying eggs indirectly. Chilli stomata of resistant and very resistant genotypes were bigger than susceptible genotypes. There was a significant positive correlation between the number of eggs and the number of early instar nymphs per plant and the number of trichomes. In addition, trichomes were negatively correlated with the rate of transpiration. Non-glandular trichomes supported a favorable microclimate for egg and nymph development. The epidermis had no correlation with the number of eggs. The length and density of palisade were significantly negatively correlated with the number of eggs and the number of early instar nymphs of the plant. Leaf thickness was significantly negatively correlated with the number of early instar nymphs of the plant. Heritability (in the broad sense), except for the character of the length and width of the stomata, has a value of >60% (height). The meaning of this heritability value is that there is diversity in the population. This diversity comes from the plant's internal (genetic). Various genotypes of chili used in this study can be used as parental for further research. Leaf morphological characters, especially trichomes and palisade can be developed into selection characters at the beginning of screening. Phenols and flavonoids are secondary metabolites that have various functions. Phenols and flavonoids play a key role in plant resistance to insects, but on the other hand they can also be stimulants for insects. There was no significant difference in the total phenol and flavonoid content in the resistant chili genotype (Ungara) and susceptible chili (Landung).