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

• Main Author: Tiladera Sihombing, Selicia
• Format: Final Project
• Language: Indonesia
• Subjects: Ilmu hayati ; Biologi
• Online Access: https://digilib.itb.ac.id/gdl/view/83022
• Institution: Institut Teknologi Bandung

Cacao (Theobroma cacao L.) is a plantation commodity whose export rate continues to increase by at least 3% per year. Indonesia is one of the largest cacao producers in the world, with the Indonesian Ministry of Agriculture recording that by 2022, cacao production reached 706 thousand tons, 20.11% of which was produced in Central Sulawesi province. Due to climate change and the increased frequency of earthquakes in Central Sulawesi, cacao production is projected to decline by an average of -0.16% per year until 2026. PGPR (Plant Growth Promoting Rhizobacteria) can be a solution to improve soil nutrient structure in cacao plantations, thus enhancing both the quality and quantity of cacao production. PGPR is a group of soil bacteria that act as biocontrol agents and as sources of plant nutrient enrichment, especially nitrogen, phosphorus, and potassium, thereby enhancing plant quality and productivity. The microbial community structure in the rhizosphere differs horizontally due to root structure. This study aims to (1) compare the profile of PGPR microbes in cacao plantation soil horizontally (at 0 cm, 30 cm, 60 cm, and 90 cm from the main roots); and (2) characterize potential PGPR microbes as a solution to improve soil conditions in cacao plantations in Central Sulawesi. Enumeration and isolation of fastidious bacteria were conducted using Nutrient Agar (NA) incubated at 25°C for 24-36 hours; non-fastidious bacteria using Reasoner's 2A Agar (R2A) at 25°C for 3-5 days; and nitrogen-fixing bacteria using Mannitol Free Nitrogen Agar (MFN) at 25°C for 7 days. The results showed that the abundance of fastidious bacteria at 0 cm, 30 cm, 60 cm, and 90 cm was 5.53×106, 2.31×107, 1.54×107, dan 2.76×106 respectively; non-fastidious bacteria were 3.60×106, 1.22×107, 9.38×106, and 3.42×105 CFU/g; and nitrogen-fixing bacteria were 9.70×105, 1.02×106, 1.87×106, 1.12×106 CFU/g. Based on the Shannon diversity index (H’), it was found that microbial communities with high diversity were at 60 cm (H’=3.45), 30 cm (H’=3.33), and 90 cm (H’=3.20); while at the 0 cm point (H’=2.83), the diversity was moderate. The dominance index (D) at 0 cm (D=0.09), 30 cm (D=0.06), 90 cm (D=0.05), and 60 cm (D=0.04) indicated low dominance. A total of 24 fastidious bacterial isolates, 28 non-fastidious bacterial isolates, and 4 nitrogen-fixing bacterial isolates were obtained. These isolates were identified for their abilities to produce cellulase, solubilize phosphate, fix nitrogen, and produce Indole Acetic Acid (IAA). The results showed that 10 fastidious bacterial isolates, 18 non-fastidious bacterial isolates, and 2 nitrogen-fixing bacterial isolates had cellulolytic activity; 10 fastidious bacterial isolates, 14 nonfastidious bacterial isolates, and 2 nitrogen-fixing bacterial isolates had phosphate solubilizing activity; 3 fastidious bacterial isolates, 5 non-fastidious bacterial isolates, and 3 nitrogen-fixing bacterial isolates had nitrogen-fixing activity; and 2 fastidious bacterial isolates could produce IAA. Among these tests, the isolate N20 (fastidious bacteria) was identified as the most potential PGPR isolate, showing positive results in all four PGPR screening tests.