Antagonistic activity of endophytic bacteria isolated from weed plant against stem end rot pathogen of pitaya in Vietnam

Abstract

Background Fungal stem end rot disease of pitaya caused by Alternaria alternata is one of the most destructive diseases in Binh Thuan province, Vietnam. This study aimed to assess the antagonistic effects of some endophytic bacteria isolated from the weed plant (Echinochloa colonum) against A. alternata. Results A total of 19 endophytic bacteria were isolated and 5 of them presented in vitro antagonistic activity against A. alternata. Of five, strain EC80 significantly inhibited the pathogenic growth with a mean inhibition diameter of 11.88 ± 0.08 mm, while the other four (C79, EC83, EC90, and EC97) showed a weak inhibition. Interestingly, the combination of EC79 and EC80 reduced more biomass of pathogenic fungi than the single one did. EC79 showed positive results for amylase, indole acetic acid (IAA), and biofilm production, whereas EC80 presented positive capabilities for IAA and biofilm production and a negative one for amylase production. In addition, the combined filtrate of EC79 and EC80 presented non-antifungal activity on biocontrol tests in vitro, indicating that bacteria cells played a role in defending against the pathogen. Moreover, both isolates EC79 and EC80 significantly increased seedling biomass than the control. Conclusions The results suggest that those two strains in combination had the potential to be used as a biocontrol agent against A. alternata. More studies should be done in the future to evaluate their efficiency under the field conditions.

Endophytic bacteria isolated from a weed plant as a potential biocontrol agent against stem end rot pathogen of pitaya in Vietnam

“…Dual culture assays were used to test the antagonistic activity of isolated bacteria on A. alternata (Luu et al 2021). For each repetition, a cylinder of a 1-cm 2 fungal plug (A. alternata) was placed in the center of a sterile potato dextrose agar (PDA, potato infusion 200 g/l; dextrose 20 g/l; agar 15 g/l; pH = 7.0-7.3) plate and the bacterial isolates were inoculated between the fungal plug and the plate edge.…”

“…The inoculated and control media were incubated at 28 °C for 7 days and observed every 12 h. After that, the biomass of A. alternata was collected by filtrating it through filter paper and oven-dried at 40 °C overnight. The reduction of fungal biomass was calculated by using the following formula (Luu et al 2021): Growth inhibition (%) = [(Growth in control -Growth in treatment)/Growth in control] × 100. The fungal growth inhibition was used as an indicator for the antifungal activity of filtrate.…”

“…Pitaya is an important fruit crop with high economic value and grown well in Nam Dinh, Vietnam. In this region, however, fungal pathogens are widely spreading, particularly from stem end rot (SER) caused by Alternaria alternata YZU, resulting in severe economic losses (Luu et al 2021). Currently, control of SER is highly dependent on the application of agrochemicals resulting in many problems to human health and the environment and especially it might induct the pesticide resistance of phytopathogenic agents (Crane et al 2013).…”

“…They were reported that they not only antagonized the infection, colonization, and development of other plant pathogens but also enhanced plant growth under both abiotic (heat, drought, salinity, heavy metal exposure, etc.) and biotic stresses, including stem end rot (Luu et al 2021). For example, those authors isolated 19 endophytic bacteria from the weed, Echinochloa colonum, and 5 of them presented in vitro antagonistic activity against A. alternata on pitaya.…”

“…The endophytic bacterial associates might play a role in those abilities. While living in the weeds, endophytic bacteria could benefit their weed host in various ways such as the production of bioactive compounds or the generation of induced systemic resistance (Luu et al 2021). Hence, exploiting these interesting bacteria in crop production is getting more interest from scientists (Khan et al 2020).…”