KORELASI ANTARA AGRESIVITAS INOKULUM SPORANGIA DENGAN TOKSISITAS FILTRAT Phytophthora capsici ASAL TANAMAN LADA (Piper nigrum L.)

CHAERANI CHAERANI, DYAH MANOHARA

Abstract


ABSTRAK
Penggunaan varietas lada tahan penyakit paling praktis dan efektif
untuk menekan serangan Phytophthora capsici, penyebab penyakit busuk
pangkal batang (BPB) lada, tetapi varietas lada tersebut belum tersedia.
Seleksi dini ketahanan lada dapat dilakukan di laboratorium menggunakan
inokulum sporangia atau filtrat biakan P. capsici. Tujuan penelitian ini
ialah membandingkan agresivitas inokulum sporangia dengan toksisitas
filtrat biakan (FB) P. capsici. Penelitian dilakukan dari bulan Juni sampai
September 2009 di laboratorium Biokimia BB Biogen dan Hama dan
Penyakit Balittro. Penelitian menggunakan 50 isolat P. capsici dari
berbagai 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 dengan
potongan agar mengandung sporangia atau 20 µl FB P. capsici. Percobaan
dilakukan secara faktorial (2 varietas × 50 isolat) dengan rancangan acak
kelompok dan tiga ulangan. Derajat agresivitas isolat dan toksisitas FB
diukur berdasarkan luas bercak nekrotik. Hasil penelitian menunjukkan
bahwa agresivitas inokulum sporangia dan toksisitas FB bervariasi antar
isolat P. capsici. Bercak nekrotik yang disebabkan oleh inokulum
sporangia 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 dipengaruhi
oleh asal isolat (P<0,0001), tetapi tidak dipengaruhi oleh varietas dan
interaksi isolat×varietas (P>0,05). Derajat ketahanan pada varietas tahan
Natar-1 diduga tidak berbasis genetik dan tidak berbeda nyata dari varietas
rentan Petaling-1 sehingga kedua metode seleksi ketahanan tidak dapat
dibedakan keefektifannya. Luas bercak nekrotik yang diinduksi oleh FB
tidak berkorelasi nyata dengan yang ditimbulkan oleh inokulum sporangia
(R 2 =0,002; P>0,05), sehingga secara umum FB P. capsici tidak dapat
digunakan sebagai standar pengujian ketahanan lada. Oleh karena itu
masih perlu dikembangkan metode inokulasi yang konsisten untuk seleksi
dini ketahanan lada.
Kata kunci: lada, penyakit busuk pangkal batang, Phytophthora capsici,
agresivitas, filtrat biakan, seleksi dini

ABSTRACT
Resistant varieties are the most practical and effective means to
control Phytophthora capsici, the pathogen of foot rot disease of black
pepper. However, no resistant cultivars are available. Early selection of
black pepper resistance can be performed in laboratory using P. capsici
inocula or culture filtrate. The objective of this study was to compare P.
capsici isolate aggressiveness with culture filtrate (CF) toxicity. The study
was conducted from June until September 2009 at the Biochemistry
Laboratory of the Indonesian Center for Agriculutral Biotechnology and
Genetic Resources Research and Development and the Plant Pest and
Disease Laboratory of the Indonesian Research Institute of Spice and
Medicinal Crops. The study used 50 P. capsici isolates collected from
various black pepper plantations during 1982 until 2009. Detached leaves
of two black pepper cultivars, i.e. moderately resistant cv. Natar-1 and
susceptible cv. Petaling-1, were inoculated with agar blocks containing
sporangia or 20 µl CF of P. capsici. The experiments were designed as
factorial experiments (2 cultivars × 50 isolates) under a randomized
completely block design. Isolate aggressiveness and CF toxicity were
measured based on the necrotic area of the inoculated leaves. The results
from the two inoculation methods showed varying levels of aggressiveness
and CF toxicity among isolates. Necrotic lesions incited by sporangial
inoculum were more extensive (0.0-2,535.2 mm 2 ) than those induced by
CF (0.7-233.0 mm 2 ). Degree of isolate aggressiveness and CF toxicity
were significantly affected by origins of isolate (P<0.0001), but not by
cultivar and isolate×cultivar interaction (P>0.05). Resistance degree in the
moderately resistant cv. Natar-1 was presumably not genetically based and
was not different to that in the susceptible cv. Petaling-1, and hence both
selecting agents were unable to discriminate resistance level between the
two cultivars. Necrotic sizes induced by CF did not well correlate with
those incited by sporangial inocula (R 2 =0.002; P>0.05), indicating that CF
is generally not suitable to be used as early selection agent of resistant
plants. Therefore, further study is justified to find more reliable inoculation
method for early detection of resistant black pepper.
Key words: black pepper, foot rot disease, Phytophthora capsici,
aggressiveness, culture filtrate, early selection in laboratory


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DOI: http://dx.doi.org/10.21082/jlittri.v18n4.2012.173-182

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