In Vitro Evaluation of Extracellular Enzyme Activity and Its Biocontrol Efficacy of Bacterial Isolates from Pepper Plants for the Management of Phytophthora capsici

Abstract

Phytophthora capsici is one of the most devastating fungal pathogens, causing severe diseases that lead to economic loss in the pepper industry. As a result of the infections, the chemical approach is becoming more popular. Biological control, on the other hand, is better suited to controlling fungal pathogens. The biological control approach significantly reduces the problems associated with chemical applications while restoring natural environmental balance. As a result, the overall findings indicate that certain bacterial isolates play a beneficial role in lytic enzyme production and biocontrol activities against P. capsici. Bacterial isolates obtained from the pepper plants were screened for lytic enzyme and anti-oomycete activity against Phytophthora capsici in Ethiopia. Sixty bacterial isolates were isolated and tested against Phytophthora capsici. From these bacterial isolates, different inhibition zones and hydrolytic enzyme production were detected. Biochemical tests using an automated machine (MALDI-TOF, VITEK 2 compact and 16S rRNA) revealed that three of them, AAUSR23, AAULE41, and AAULE51, showed a high inhibition zone and high production of hydrolytic enzymes and were identified as Enterobacter cloacae (AAUSR23), Pseudomonas fluorescens (AAULE41), and undetermined (AAULE51). The effects of diffusable metabolite isolate AAULE51 has a 66.7% inhibition zone against Phytophthora capsici, followed by AAULE41 and AAUSR23, which have 59.7% and 14.1% inhibition zones, respectively. These bacterial isolates showed high production of hydrolytic enzymes like protease, cellulase, chitinase, and lipase (5-34 diameter of inhibition zone). As a result, the overall findings show that selected bacterial isolates play a beneficial role in lytic enzyme production and for their biocontrol activities against P. capsici.

Figure 1

The maximum likelihood tree showed that the three strains AAUSR23, AAUFE29, and AAULE41 were closely related to Enterobacter hormaechei, Rhizobium sp, and Pseudomonas fluorescens, respectively, and had 100% identity.

Figure 2

Radii of inhibition zone in spore germination test.

Figure 3

Agar well diffusion test for antifungal activity of crude extracts of selected bacterial isolates against P. capsici.

Figure 4

(a) The antioomycete effect of volatile compounds produced by the bacterial isolates AAULE41 and AAULE51 against the phytopathogen P. capsici. (b) Effect of diffusible compounds produced by selected bacterial isolates on P. capsici mycelial growth of AAUSR23, AAUFE29, AAULE41, and AAULE51. (c) Percentage growth inhibition of volatile compounds released by the isolates AAUSR23, AAUFE29, AAULE41, and AAULE51 on P. capsici. Represent the mean ± SE values (n = 3). Different letters above the bar indicate statistically significant differences compared to the control (Tukey-Kramer's HSD test, P < 0.05).

Figure 5

In vitro evaluation of different bacterial isolates on Petri dishes with colonies surrounded by zones of extracellular enzymatic activity: (a) protease, (b) cellulase, (c) chitinase, (d) Lichtinase, and (e) Lipase.

Figure 6

Shows the percentage of bacterial isolates (out of a total of 60) that produce individual hydrolytic enzymes.