KORELASI ANTARA AGRESIVITAS INOKULUM SPORANGIA DENGAN TOKSISITAS FILTRAT Phytophthora capsici ASAL TANAMAN LADA (Piper nigrum L.)
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Pusat Penelitian dan Pengembangan Perkebunan
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ABSTRAKPenggunaan varietas lada tahan penyakit paling praktis dan efektifuntuk menekan serangan Phytophthora capsici, penyebab penyakit busukpangkal batang (BPB) lada, tetapi varietas lada tersebut belum tersedia.Seleksi dini ketahanan lada dapat dilakukan di laboratorium menggunakaninokulum sporangia atau filtrat biakan P. capsici. Tujuan penelitian iniialah membandingkan agresivitas inokulum sporangia dengan toksisitasfiltrat biakan (FB) P. capsici. Penelitian dilakukan dari bulan Juni sampaiSeptember 2009 di laboratorium Biokimia BB Biogen dan Hama danPenyakit Balittro. Penelitian menggunakan 50 isolat P. capsici dariberbagai daerah pertanaman lada yang diisolasi tahun 1982 sampai 2009.Daun-daun lada yang diambil dari varietas Natar-1 (agak tahan terhadap P.capsici) dan Petaling-1 (rentan terhadap P. capsici) diinokulasi denganpotongan agar mengandung sporangia atau 20 µl FB P. capsici. Percobaandilakukan secara faktorial (2 varietas × 50 isolat) dengan rancangan acakkelompok dan tiga ulangan. Derajat agresivitas isolat dan toksisitas FBdiukur berdasarkan luas bercak nekrotik. Hasil penelitian menunjukkanbahwa agresivitas inokulum sporangia dan toksisitas FB bervariasi antarisolat P. capsici. Bercak nekrotik yang disebabkan oleh inokulumsporangia lebih luas (0,0–2.535,2 mm 2 ) dibandingkan dengan FB (0,7–233,0 mm 2 ). Derajat agresivitas isolat dan toksisitas FB sangat dipengaruhioleh asal isolat (P<0,0001), tetapi tidak dipengaruhi oleh varietas daninteraksi isolat×varietas (P>0,05). Derajat ketahanan pada varietas tahanNatar-1 diduga tidak berbasis genetik dan tidak berbeda nyata dari varietasrentan Petaling-1 sehingga kedua metode seleksi ketahanan tidak dapatdibedakan keefektifannya. Luas bercak nekrotik yang diinduksi oleh FBtidak berkorelasi nyata dengan yang ditimbulkan oleh inokulum sporangia(R 2 =0,002; P>0,05), sehingga secara umum FB P. capsici tidak dapatdigunakan sebagai standar pengujian ketahanan lada. Oleh karena itumasih perlu dikembangkan metode inokulasi yang konsisten untuk seleksidini ketahanan lada.Kata kunci: lada, penyakit busuk pangkal batang, Phytophthora capsici,agresivitas, filtrat biakan, seleksi diniABSTRACTResistant varieties are the most practical and effective means tocontrol Phytophthora capsici, the pathogen of foot rot disease of blackpepper. However, no resistant cultivars are available. Early selection ofblack pepper resistance can be performed in laboratory using P. capsiciinocula or culture filtrate. The objective of this study was to compare P.capsici isolate aggressiveness with culture filtrate (CF) toxicity. The studywas conducted from June until September 2009 at the BiochemistryLaboratory of the Indonesian Center for Agriculutral Biotechnology andGenetic Resources Research and Development and the Plant Pest andDisease Laboratory of the Indonesian Research Institute of Spice andMedicinal Crops. The study used 50 P. capsici isolates collected fromvarious black pepper plantations during 1982 until 2009. Detached leavesof two black pepper cultivars, i.e. moderately resistant cv. Natar-1 andsusceptible cv. Petaling-1, were inoculated with agar blocks containingsporangia or 20 µl CF of P. capsici. The experiments were designed asfactorial experiments (2 cultivars × 50 isolates) under a randomizedcompletely block design. Isolate aggressiveness and CF toxicity weremeasured based on the necrotic area of the inoculated leaves. The resultsfrom the two inoculation methods showed varying levels of aggressivenessand CF toxicity among isolates. Necrotic lesions incited by sporangialinoculum were more extensive (0.0-2,535.2 mm 2 ) than those induced byCF (0.7-233.0 mm 2 ). Degree of isolate aggressiveness and CF toxicitywere significantly affected by origins of isolate (P<0.0001), but not bycultivar and isolate×cultivar interaction (P>0.05). Resistance degree in themoderately resistant cv. Natar-1 was presumably not genetically based andwas not different to that in the susceptible cv. Petaling-1, and hence bothselecting agents were unable to discriminate resistance level between thetwo cultivars. Necrotic sizes induced by CF did not well correlate withthose incited by sporangial inocula (R 2 =0.002; P>0.05), indicating that CFis generally not suitable to be used as early selection agent of resistantplants. Therefore, further study is justified to find more reliable inoculationmethod for early detection of resistant black pepper.Key words: black pepper, foot rot disease, Phytophthora capsici,aggressiveness, culture filtrate, early selection in laboratory