Xanthomonas axonopodis pv glycines (Xag) is a pathogen that causes pustule disease in soybeans. Many
techniques for controlling this disease have been widely developed, one of which is the use of biological agents.
Bacillus sp. from the soybean phyllosphere is a biological agent that has the potential to suppress the
development of pustule disease. One of the biological control mechanisms is through biochemical induction
of plant resistance which includes the accumulation of phenols, salicylic acid compounds, and peroxidase
enzymes. Bacillus subtilis JB12 and Bacillus velezensis ST32 are two bacteria isolated from the soybean
phyllosphere which have previously been known to suppress Xag through an antibiosis mechanism. This study
aimed to determine the potential of Bacillus subtilis JB12 and Bacillus velezensis ST32 in inducing soybean
resistance against Xag infection. This research was carried out in two stages, the induction of resistance to
soybean germination and an experiment in a greenhouse. This study consisted of 4 treatments and 5
replications, including P0 (Xag inoculation), P1 (Bacillus subtilis JB12 inoculation), P2 (Bacillus velezensis
ST32), and P3 (Bacillus subtilis JB12 + Bacillus velezensis ST32 inoculation). Observations were made on
the content of phenolic compounds, peroxidase enzyme activity, and the development of soybean pustule
disease. The results showed differences in phenol content and peroxidase activity at the two stages of the study.
Seed treatment with both isolates of Bacillus sp was able to increase the phenol content of soybean sprouts up
to 3 - 5 days after inoculation (dai). Phenol content then decreased and was followed by an increase in the
peroxidase activity up to 7 dai. The application of Xag and two isolates of Bacillus sp. in soybean plants caused
the phenol content to fluctuate and peroxidase activity to decrease. Bacillus subtilis JB12 in general played a
better role in increasing phenol content and peroxidase enzyme activity in soybean than Bacillus velezensis
ST32. The application of two isolates of Bacillus sp. was not able to prolong the incubation period and reduce
the severity of the pustule disease 14 days after inoculation.
