Bacillus velezensis CE 100 Inhibits Root Rot Diseases (Phytophthora spp.) and Promotes Growth of Japanese Cypress (Chamaecyparis obtusa Endlicher) Seedlings

Abstract

Root rot diseases, caused by phytopathogenic oomycetes, Phytophthora spp. cause devastating losses involving forest seedlings, such as Japanese cypress (Chamaecyparis obtusa Endlicher) in Korea. Plant growth-promoting rhizobacteria (PGPR) are a promising strategy to control root rot diseases and promote growth in seedlings. In this study, the potential of Bacillus velezensis CE 100 in controlling Phytophthora root rot diseases and promoting the growth of C. obtusa seedlings was investigated. B. velezensis CE 100 produced β-1,3-glucanase and protease enzymes, which degrade the β-glucan and protein components of phytopathogenic oomycetes cell-wall, causing mycelial growth inhibition of P. boehmeriae, P. cinnamomi, P. drechsleri and P. erythoroseptica by 54.6%, 62.6%, 74.3%, and 73.7%, respectively. The inhibited phytopathogens showed abnormal growth characterized by swelling and deformation of hyphae. B. velezensis CE 100 increased the survival rate of C. obtusa seedlings 2.0-fold and 1.7-fold compared to control, and fertilizer treatment, respectively. Moreover, B. velezensis CE 100 produced indole-3-acetic acid (IAA) up to 183.7 mg/L, resulting in a significant increase in the growth of C. obtusa seedlings compared to control, or chemical fertilizer treatment, respectively. Therefore, this study demonstrates that B. velezensis CE 100 could simultaneously control Phytophthora root rot diseases and enhance growth of C. obtusa seedlings.

Keywords: antagonistic bacteria; auxin; biocontrol agent; forest seedling production; lytic enzymes; phytopathogenic oomycetes; plant development.

Figure 1

Study area in an experimental greenhouse at the forest nursery (A); seedlings infected by Phytophthora spp. (B); seedlings growth of control conditions, chemical fertilizer treatment and bacterial inoculation with B. velezensis CE 100 (C).

Figure 2

Cell growth curve of B. velezensis CE 100 in PB medium at 30 °C for 10 days. Error bars represent the standard deviation of three replications. Means with the same letter are not significantly different at p < 0.01 when compared using LSD test.

Figure 3

Changes in β-1,3-glucanase (A) and protease (B) activities in the culture supernatant of B. velezensis CE 100. Error bars represent the standard deviation of three replications. Means with the same letter are not significantly different at p < 0.01 when compared using LSD test.

Figure 4

Inhibition effect of B. velezensis CE 100 on mycelial growth of P. boehmeriae, P. cinnamomi, P. drechsleri and P. erythoroseptica (A). Antagonistic activities of B. velezensis CE 100 against P. boehmeriae, P. cinnamomi, P. drechsleri and P. erythoroseptica (B) based on a dual culture method. Error bars represent the standard deviation of three replications. Means with the same letter are not significantly different at p < 0.01 when compared using LSD test.

Figure 5

Inhibition effect of B. velezensis CE 100 on phytopathogenic hyphae morphologies of P. boehmeriae, P. cinnamomi, P. drechsleri and P. erythoroseptica, observed under a light microscope. On the top, the normal growth in the control group and at the bottom, the corresponding effect of B. velezensis CE 100. Arrows indicate hyphal alterations with swelling and deformation structures caused by B. velezensis CE 100.

Figure 6

Changes in indole-3-acetic acid (IAA) concentration with B. velezensis CE 100. Error bars represent the standard deviation of three replications. The means with the same letter are not significantly different at p < 0.01 when compared using LSD test.