Phytophthora antagonism of endophytic bacteria isolated from roots of black pepper (Piper nigrum L.)

Abstract

In this study, 90 root samples were collected from 30 black pepper farms in three provinces in the Central Highlands of Vietnam. A total of 352 endophytic bacteria were isolated and their morphology described. An in vitro assay on the antifungal activity of these isolates was then conducted and 47 isolates were found to have antagonistic activity on Phytophthora fungi. The antifungal activity of the 47 isolates was evaluated in vivo by shoot assay. Among these 47 isolates, 6 were selected for further investigation. The six isolates were classified and identified by sequencing the 16S RNA gene and phylogeny. The results showed that all six endophytic bacteria belong to the following species of Bacillus genus: B. siamensis, B. amyloliquefaciens, B. velezenis, and B. methylotrophiycus. Enzymatic activity related to the antifungal activity of the six potent isolates was determined; it showed that they possessed high chitinase and protease activities. These isolates were applied for black pepper seedlings in greenhouse. The results showed three promising isolates: B. siamensis EB.CP6, B. velezensis EB.KN12, and B. methylotrophycus EB.KN13. Black pepper seedlings treated with the promising bacteria had the lowest rate of root disease (8.45–11.21%) and lower fatal rate (11.11–15.55%) compared to the control group (24.81% and 24.44%). In addition, the three promising isolates strongly affected the growth of the black pepper seedlings in greenhouse. The plant height, length of roots, and fresh biomass of the seedlings in the treated plots were higher than those in the control plots. Thus, the endophytic bacterial isolates have the potential to act as biocontrol agent for the sustainable production of black pepper.