Rizobakteri Serratia surfactantfaciens dan Enterobacter sichuanensis sebagai Pemacu Tumbuh Padi secara In Vitro

Abstract

Plant Growth-Promoting Rhizobacteria (PGPR) merupakan kelompok bakteri yang berpotensi meningkatkan pertumbuhan tanaman, salah satunya melalui produksi fitohormon indole-3-acetic acid (IAA). Penelitian ini bertujuan menganalisis kemampuan produksi IAA oleh isolat rizobakteri, menguji pengaruhnya terhadap pertumbuhan benih padi secara in vitro, serta mengidentifikasi isolat potensial berdasarkan gen 16S rRNA. Sebanyak sembilan isolat rizobakteri asal rizosfer padi Pulau Enggano diuji kemampuan menghasilkan IAA menggunakan metode kolorimetri Salkowski dan diuji aktivitas pemacu tumbuhnya terhadap benih padi varietas IR64 secara in vitro. Isolat terbaik selanjutnya diidentifikasi berdasarkan karakteristik morfologi dan analisis sekuen gen 16S rRNA. Hasil penelitian menunjukkan bahwa kesembilan isolat mampu menghasilkan IAA dengan konsentrasi bervariasi antara 3,410-21,902 µg/mL. Isolat KF.2.03 (9,283 µg/mL) dan KB.2.11 (3,410 µg/mL) menunjukkan kemampuan terbaik dalam meningkatkan pertumbuhan kecambah padi dibandingkan kontrol, terutama pada parameter panjang radikula (KF.2.03: 10,078 cm; KB.2.11: 10,144 cm; kontrol: 8,985 cm) dan jumlah akar lateral (KF.2.03: 5,37; KB.2.11: 4,926; kontrol: 2,556). Kedua isolat merupakan bakteri Gram-negatif berbentuk basil pendek dengan ukuran sel masing-masing 1,7 × 0,6 µm (KF.2.03) dan 2,2 × 0,8 µm (KB.2.11). Analisis sekuen gen 16S rRNA menunjukkan isolat KF.2.03 berkerabat dengan Enterobacter sichuanensis strain WCHECL1597 (similaritas 94%, bootstrap 95%) dan isolat KB.2.11 berkerabat dekat dengan Serratia surfactantfaciens strain YD25 (similaritas 98%, bootstrap 66%). Kedua isolat berpotensi dikembangkan sebagai PGPR untuk mendukung pertumbuhan tanaman padi.

Plant Growth-Promoting Rhizobacteria (PGPR) are a group of bacteria that have the potential to enhance plant growth, in part through the production of phytohormone indole-3-acetic acid (IAA). This study aimed to analyze the IAA production capacity of rhizobacterial isolates, evaluate their effect on rice seedling growth in vitro, and identify potential isolates based on the 16S rRNA gene. A total of nine rhizobacterial isolates from the rice rhizosphere on Enggano Island were tested for their ability to produce IAA using the Salkowski colorimetric method, and their growth-promoting activity was assessed on IR64 rice seeds in vitro. The best isolates were then identified based on morphological characteristics and 16S rRNA gene sequence analysis. The results showed that all nine isolates were capable of producing IAA at concentrations ranging from 3.410 to 21.902 µg/mL. Isolates KF.2.03 (9.283 µg/mL) and KB.2.11 (3.410 µg/mL) showed the greatest ability to enhance rice seedling growth compared to the control, particularly in terms of radicle length (KF.2.03: 10.078 cm; KB.2.11: 10.144 cm; control: 8.985 cm) and the number of lateral roots (KF.2.03: 5.37; KB.2.11: 4.926; control: 2.556). Both isolates were Gram-negative, short rod-shaped bacteria, with cell sizes of 1.7 × 0.6 µm (KF.2.03) and 2.2 × 0.8 µm (KB.2.11). Analysis of the 16S rRNA gene sequence showed that isolate KF.2.03 was related to Enterobacter sichuanensis strain WCHECL1597 (94% similarity, 95% bootstrap), whereas isolate KB.2.11 was closely related to Serratia surfactantfaciens strain YD25 (98% similarity, 66% bootstrap). Both isolates have the potential to be developed as PGPR candidates to promote rice growth.