Preliminary screening of rhizosphere bacteria in shallot plants grown in organic field as antagonists against Fusarium oxysporum f.sp. cepae

Fusarium wilt disease, caused by Fusarium oxysporum f. sp. cepae ( Focc ), is a devastating disease affecting shallot plants. This study aimed to screen rhizosphere bacteria isolated from healthy shallot plants cultivated in organic field and to evaluate their antagonistic potential against Focc . A total of 29 rhizosphere bacterial isolates were found from healthy shallot plants in Jember, East Java, Indonesia. These isolates exhibited considerable variation in morphological characteristics, including colony color, shape, and opacity. The bacterial density in the samples generally ranged from 10 7 to 10 9 CFU/ml, with colony numbers differing among isolates. The predominant colony colors were white and yellow, with morphological forms ranging from circular to irregular and serrated. Among these, thirteen isolates (RB1, RG1, RH1, RI1, RJ1, RF2, RA3, RB3, GC3, GD3, GRA4, GRC4, and GRE4) demonstrated strong antagonistic potential against Focc , with inhibition percentages ranging from 56.60 to 68.79%. These findings indicate that rhizosphere bacteria from shallot plants possess antagonistic properties and hold potential as biocontrol candidates against Fusarium wilt. However, further in vitro antagonistic assays and molecular identification are required to confirm the bacterial species involved and to determine their efficacy in suppressing Fusarium wilt while promoting shallot growth.