Enhanced resistance of Vigna unguiculata to Fusarium oxysporum via Rubia cordifolia extract and growth-promoting endophytic Bacillus amyloliquefaciens DW6

The current study investigated how well an aqueous extract of Rubia cordifolia and a Bacillus amyloliquefaciens bacterium strain (DW6 OR083409) protected Vigna unguiculata L. plants from Fusarium oxysporum infection. In vitro study revealed that Rubia cordifolia aqueous extracts at 10% and 30% did not exhibit antifungal activity against F. oxysporum isolate, likewise no inhibition towards F. oxysporum as a presence of B. amyloliquefaciens DW6. Molecular identification characteristics confirmed the fungal pathogen being F. oxysporum AWEKA, based on the 18s rRNA sequence. B. amyloliquefaciens was found to produce indole-3-acetic acid, gibberellic acid, and hydrogen cyanide at concentrations being 203.67 ± 5.6, 335.6 ± 7.5, and 218 ± 6.4 µg/ml, respectively. In vivo, the growth of plants enhanced the induced resistance of cowpea plants against F. oxysporum during treatments with the biotic agents. The activity of defense-related enzymes was also enhanced, where Bacillus culture showed the highest increase, followed by the R. cordifolia at 30% extract and bacterial supernatant, respectively. SEM investigation of infected cowpea roots revealed notable differences in xylem vessels, including tylose formation and obstruction of vessels. Plasmolysis of parenchymal cells and hydrolysis of some cells were observed following the fungicide treatment. Both Bacillus amyloliquefaciens DW6 and the 30% aqueous extract of R. cordifolia proved effective in enhancing the induced resistance of cowpea against F. oxysporum, leading to a reduction in the damage caused by Fusarium root infection. Interestingly, this is the first report attaining the boosting of Vigna unguculata’s immune system towards F. oxysporum using aqueous extract of R. cordifolia and endophyte bacterium; B. amyloliquefaciens.

Graphical Abstract