Phytophthora Antagonism of Endophytic Bacteria Isolated from Roots of Black Pepper (Piper nigrum L.)

Van Anh Ngo,Van Bon Nguyen,Trung Dzung Tran,Thi Ngoc Tran,Chien Thang Doan,Anh Dzung Nguyen,San-Lang Wang,Dinh Minh Tran

doi:10.3390/agronomy10020286

Van Anh Ngo, Van Bon Nguyen + Show 6 more

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https://doi.org/10.3390/agronomy10020286

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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.

Highlights

Endophytic bacteria belong to a bacterial group living in the tissues of plants, including roots, shoots, leaves, and even fruits
The results showed 106 endophytic bacteria isolated from the root collected in Gia Lai Province; 186 isolates from Dak Lak province and 60 isolates from Dak Nong province
93.57 ± 1.04ab the results show a positive correlation between chitinase activity and the Phytophthora antagonism activity (r = 0.36, n = 18), but a negative correlation between protease activity and the Phytophthora antagonism activity (r = −0.23, n = 18)

Summary

Introduction

Endophytic bacteria belong to a bacterial group living in the tissues of plants, including roots, shoots, leaves, and even fruits. Endophytic bacteria interact with the host in growth promotion, nutrition uptake, pathogenic fungal antagonism, and nematode resistance [1,2,3,4,5,6]. Phytophthora is a pathogenic fungus causing diseases and serious damage to the growth and productivity of agricultural crops. Phytophthora is the most common fungus associated with root rot disease of agricultural crops, such as tomato, potato, onion, coffee, rubber, pepper, and black pepper [13,14,15]. Root rot disease caused by Phytophthora is one of the sources of serious production reduction in black pepper in Vietnam, India, Malaysia, and other countries [16,17]. Using chemical fungicides to manage Phytophthora in black pepper production is the most common application

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