Induction of resistance against pine wilt disease caused by Bursaphelenchus xylophilus using selected pine endophytic bacteria

Abstract

Pine wilt disease (PWD) is the most destructive disease threatening pine worldwide. The disease is mainly caused by the pine wood nematode, Bursaphelenchus xylophilus, which is vectored by pine sawyer longhorn‐beetles, Monochamus spp. This study aimed to select resistance‐inducing pine endophytic bacteria for management of PWD. To set up a defence‐related genes expression pattern for screening, four chemical inducers (salicylic acid, γ‐aminobutyric acid (GABA), β‐aminobutyric acid and α‐aminobutyric acid) were tested in vitro on pine calli and in vivo on pine seedlings. Treatment with GABA had the greatest reduction in PWD severity on pine seedlings. The pattern of defence‐related gene expression in calli treated with GABA was used to select potential resistance‐inducing bacterial strains. In addition, 92 bacterial strains were isolated from pine tree needles and stems and were tested for expression of defence‐related genes in pine calli in vitro. Among the tested strains, 13 showed a similar pattern to GABA treatment in at least four tested defence‐related genes and were selected for the seedling assay. From the seedling assay, three bacterial strains (16YSM‐E48, 16YSM‐P180 and 16YSM‐P39) showed significant reduction in PWD severity compared to the untreated control. Moreover, among the selected strains, cell‐free culture supernatant of strain 16YSM‐P180 significantly reduced PWD severity in inoculated pine seedlings. The selected strains were identified based on the 16S rRNA sequence as Pseudomonas putida 16YSM‐E48, Curtobacterium pusillum 16YSM‐P180 and Stenotrophomonas rhizophila 16YSM‐P39. These selected strains are suggested as potential alternatives for management of PWD by induction of systemic resistance.

Influence of Resistance-Inducing Chemical Elicitors against Pine Wilt Disease on the Rhizosphere Microbiome

“…Regarding PWN, chemical inducers such as γ-aminobutyric acid, were found to trigger the expression of certain pathogenesis-related genes and, consequently, PWD severity was reduced in treated seedlings. Furthermore, specific pine endophytic bacterial species were utilized for induction of resistance against PWD [ 22 ].…”

“…Distilled water containing 250 μg/mL Tween 20 was used as an untreated control and 5 replicates were maintained for each treatment. Disease severity in treated seedlings was evaluated at 30 days post-inoculation, according to a scale from 0 to 5, in which 0 = healthy seedlings with normal green needles, 1 = < 20% brown needles, 2 = 20–39% brown needles, 3 = 40–59% brown needles, 4 = 60–79% brown needles and bending of the seedlings terminal shoots, and 5 = 80–100% of brown needles and wilting of the whole seedling [ 22 ]. The seedling assay was conducted twice with 5 replicates for each treatment.…”

“…In pine trees, avirulent nematode isolates were shown to induce physiological changes leading to PWN suppression and decreased disease severity [ 10 ]. Recently, Kim et al [ 22 ], isolated pine endophytic bacterial strains and selected three species ( Pseudomonas putida 16YSM-E48, Curtobacterium pusillum 16YSM-P180, and Stenotrophomonas rhizophila 16YSM-P39) with the ability to induce systemic resistance against PWD in callus and pine seedlings as was confirmed molecularly and phenotypically.…”

“…Strict quarantine measures and extensive breeding programs for the selection of resistant trees represent the main effective strategies available for controlling the spread of the disease [ 18 , 19 ]. Yet, several methods have been studied and proposed for the management of PWD, including insect vector eradication, physical chipping, and tree injection with nematicidal compounds [ 20 , 21 , 22 ]. Due to environmental and health risk-related concerns, restrictions have been imposed on the use of nematicides, and the search for safer alternatives such as biological control and induction of resistance, has consequently been encouraged [ 18 , 23 ].…”

Isolation and characterization of Bacillus subtilis strain 1-L-29, an endophytic bacteria from Camellia oleifera with antimicrobial activity and efficient plant-root colonization

“…Endophytes are plant-associated microorganisms that live in plant tissues without negatively affecting the plant host [9,10]. It has been shown that endophytic microorganisms may control plant pathogens [11][12][13], enhance plant growth [14], and improve phytoremediation. However, previous studies of endophytic bacteria have generally focused on model plants, including Arabidopsis thaliana [15], potatoes [16,17], and soybeans [18], as well as oil-producing trees, including olive trees [19,20], oil palms [21], and Vernicia fordii [22].…”