Indonesia merupakan negara penghasil karet alam terbesar kedua di dunia setelah Thailand. Namun, penyakit gugur daun Pestalotiopsis mulai menyerang perkebunan karet di Sumatera Utara, Indonesia pada tahun 2016. Penyakit tersebut mampu menurunkan produksi lateks hingga lebih dari 45%. Pengendalian PGDP saat ini yang dilakukan secara kimiawi belum dapat menyelesaikan permasalahan dengan baik. Oleh karena itu, pemilihan klon unggul yang resistan terhadap PGDP baik secara agronomi maupun molekuler perlu dilakukan. Penelitian ini bertujuan menganalisis karakter agronomi dan keparahan penyakit dari klon karet RRIC 100, PB 260, BPM 24, dan GT 1 serta mengetahui profil ekspresi gen dan Hevea brasiliensis Pathogenesis-Related 4 (HbPR4) dan Hevea brasiliensis Pathogenesis-Related 10 (HbPR10) pada klon karet RRIC 100 yang terserang PGDP. Karakter agronomi yang diamati, yaitu pertambahan tinggi tanaman, pertambahan diameter batang, jumlah daun tumbuh, dan jumlah daun gugur selama 16 minggu pengamatan setelah inokulasi Pestalotiopsis. Kedua gen tersebut berkaitan dengan ketahanan tanaman, yaitu HbPR4 dengan kemampuan mendegradasi kitin Pestalotiopsis, sedangkan gen HbPR10 dengan kemampuan mendegradasi RNA Pestalotiopsis. Ekspresi gen HbPR4 dan HbPR10 dianalisis pada waktu pengamatan yang berbeda, yaitu 2,4,6, dan 8 hari setelah inokulasi Pestalotiopsis dengan gen UBC2a sebagai housekeeping gene dengan stabilitas tinggi. Masing-masing klon menunjukkan perbedaan performa karakter agronomi setelah inokulasi Pestalotiopsis. Klon RRIC 100 merupakan klon yang menunjukkan performa terbaik berdasarkan kombinasi hasil analisis karakter agronomi dan keparahan penyakit pada 16 minggu setelah inokulasi Pestalotiopsis, dengan penurunan pertambahan tinggi tanaman sebesar 53,94%, penurunan diameter 44,82%, jumlah daun tumbuh 98,43%, jumlah daun gugur 39,37%, dan keparahan penyakit sebesar 50%. Lebih lanjut, analisis molekuler pada klon RRIC 100 mengungkapkan peningkatan signifikan ekspresi gen HbPR4 pada 4 hari setelah inokulasi (hsi), yaitu 14,23 ± 2,30 kali lipat, yang terjadi lebih awal dibandingkan dengan HbPR10 yang terekspresi signifikan pada 6 hsi dengan peningkatan 11,58 ± 1,39 kali lipat.

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Indonesia is the second largest producing country of natural rubber in the world after Thailand. However, Pestalotiopsis leaf fall disease (PLFD) began to attack rubber plantations in North Sumatra, Indonesia in 2016. This disease can reduce latex production by more than 45%. The current chemical control of PLFD has not been able to solve the problem properly. Therefore, the selection of superior clones that are resistant to PLFD both agronomically and molecularly needs to be done. This study aims to analyze the agronomic traits and disease severity of rubber clones RRIC 100, PB 260, BPM 24, and GT 1 and also to determine the gene expression profile and Hevea brasiliensis Pathogenesis-Related 4 (HbPR4) and Hevea brasiliensis Pathogenesis-Related 10 (HbPR10) in RRIC 100 rubber clones attacked by PLFD. The agronomic traits observed were the increase in plant height, the increase in stem diameter, the number of emerged leaves, and the number of fallen leaves in 16 weeks of observation after Pestalotiopsis inoculation. Both genes are related to plant resistance, namely HbPR4 with the ability to degrade Pestalotiopsis chitin, while the HbPR10 gene with the ability to degrade Pestalotiopsis RNA. The expression of HbPR4 and HbPR10 genes was analyzed at different observation times, namely 2, 4, 6, and 8 days after Pestalotiopsis inoculation with the UBC2a gene as a housekeeping gene with high stability. Each clone showed differences in agronomic character performance after Pestalotiopsis inoculation. Clone RRIC 100 was the best performing clone based on a combination of agronomic traits analysis results and disease severity at 16 weeks after Pestalotiopsis inoculation, with the decrease in plant height of 53.94%, the decrease in diameter of 44.82%, the number of emerged leaves was 98.43%, the number of fallen leaves was 39.37%, and disease severity was 50%. Furthermore, molecular analysis on RRIC 100 clone revealed a significant increase in HbPR4 gene expression at 4 days after inoculation (hsi), which was 14.23 ± 2.30 fold, which occurred earlier than HbPR10 which was significantly expressed at 6 hsi with an increase of 11.58 ± 1.39 fold.