The Potential of Bacillus subtilis subsp. subtilis RJ09 as a Biological Control Agent Against Leaf Spot Diseases on Clove

Cloves is one of the main plantation commodities and is native to Indonesia. Leaf spot disease with necrosis symptom is often found in clove plants. Interferences to photosynthesis caused by leaf spot disease can cause plant death. Bacillus is known to inhibit the development of pathogens through nutrient competition and antibiosis mechanism. This study aims to identify Bacillus sp. RJ09 through molecular approach and determine its potential in suppressing the development of Pestalotiopsis sp., the cause of clove leaf spot by in vitro examination. Identification of the fungus was carried out by observing the morphology which included the color of the colony, the shape and size of the conidium of the isolated fungus. Identification of Bacillus sp. RJ09 was performed by polymerase chain reaction (PCR) using a pair of primers that amplified gyrB gene region of ±1400 bp, followed by sequence analysis. The ability of Bacillus sp. RJ09 as a biological agent against fungi associated with leaf spot was determined using an in vitro double culture method. Pestalotiopsis sp. was found as the fungus associated with leaf spot disease and can cause black necrotic spots on the leaves. Molecular identification of Bacillus sp. RJ09 showed the highest similarity value of 99.40% with B. subtilis subsp. subtitles. In vitro dual culture showed B. subtilis subsp. subtilis RJ09 can inhibit the growth of Pestalotiopsis sp. colonies by 75%.