DIVERSITY OF PGPR (PLANT GROWTH PROMOTING RHIZOBACTERIA) RHIZOBACTERIA IN THE VERTICAL RHIZOSPHERE OF COCOA PLANTATIONS (THEOBROMA CACAO L.) IN POSO, CENTRAL SULAWESI

• Main Author: Rabia Adawiya, Puti
• Format: Final Project
• Language: Indonesia
• Subjects: Ilmu hayati ; Biologi
• Online Access: https://digilib.itb.ac.id/gdl/view/83021
• Institution: Institut Teknologi Bandung

Cocoa (Theobroma cacao L.) is an important commodity in the country's economy, used in the food, beverage, pharmaceutical, and cosmetic industries. Indonesia ranks third in cocoa bean production, with Central Sulawesi being a major production center. From 2005 to 2019, Indonesia experienced an average increase of approximately 6.52% in cocoa export value and a 0.93% increase in export volume. Climate change and natural disasters in Sulawesi Province have led to changes in agricultural land conditions and increased incidence of pests and diseases, resulting in plant mortality. This can be addressed by improving soil quality, particularly through the presence of rhizobacteria. Rhizobacteria, also known as Plant Growth Promoting Rhizobacteria (PGPR), are beneficial bacteria that actively colonize the rhizosphere soil and function as plant growth enhancers by solubilizing complex minerals into ions that can be absorbed by plant roots, thus promoting soil ecosystem sustainability. The objective of this research is to compare the vertical profile of rhizobacteria from the cocoa tree rhizosphere at soil depths of 0-30 cm, 30-60 cm, and 60-90 cm in the Bariri Village plantation, Poso, Central Sulawesi, and assess their potential as PGPR to stimulate plant growth. Rhizosphere microbes were isolated and their abundance was determined using Nutrient Agar (NA) after 24 hours of incubation at 25°C, Reasoner’s 2A Agar (R2A) after 3-5 days of incubation at 25°C, and Mannitol Free Nitrogen (MFN) Agar after 7 days of incubation at 25°C. Furthermore, PGPR capabilities were evaluated through cellulase activity, phosphate solubilization, nitrogen fixation, and Indole Acetic Acid (IAA) production. The abundance per gram (CFU/gr) at depths of 0-30 cm, 30-60 cm, and 60-90 cm respectively for fastidious bacteria were 9 x 10^6, 7.11 x 10^6, and 6.04 x 10^6; for non-fastidious bacteria were 3.51 x 10^6, 5.38 x 10^6, and 9.84 x 10^6; and for nitrogen-fixing bacteria were 2.03 x 10^6, 1.82 x 10^6, and 1.03 x 10^6. The study identified a total of 61 isolates comprising 27 fastidious, 29 non-fastidious, and 5 nitrogen-fixing bacteria. Based on diversity indices, the highest diversity was observed at a depth of 60-90 cm (H’=2.19), followed by 0-30 cm (H’=2.04), and the lowest at 30-60 cm; the highest dominance index was at 30-60 cm (D=0.34), followed by 0-30 cm (D=0.17), and the lowest at 60-90 cm (D=0.15). Isolates capable of cellulase degradation included 14 fastidious, 24 non-fastidious, and 2 nitrogen-fixing bacteria; phosphate-solubilizing bacteria comprised 14 fastidious, 16 non-fastidious, and 3 nitrogen-fixing isolates; nitrogen-fixing bacteria producing ammonia were represented by 4 fastidious, 7 non-fastidious, and 3 nitrogen-fixing isolates; and bacteria capable of converting tryptophan to IAA were found in 1 fastidious isolate. Isolate N1 showed the highest potential as a PGPR due to positive results in all PGPR screenings. Through Sanger Sequencing of 16S rRNA, isolate N1 was identified as Priestia aryabhattai strain 062606B-3.