Biocontrol of the root‐knot nematodeMeloidogyne incognitaby a nematicidal bacteriumPseudomonas simiaeMB751with cyclic dipeptide

Abstract

BACKGROUND Root‐knot nematodes (RKNs) are harmful plant‐parasitic nematodes that cause serious damage to plant hosts. In the long‐term practice of RKN management, bacterial nematicides have attracted increasing attention as an effective biocontrol means. Here we determined the active substances against Meloidogyne incognita from a nematicidal bacterium, developed a biocontrol agent (BCA) based on optimized culture processes. The effects of the BCA on RKN control and plant growth‐promotion were evaluated in tomato pot trials. RESULTS Pseudomonas simiae strain MB751 exhibiting significant nematicidal activity against M. incognita second‐stage juveniles (J2) with approximately 80% mortality (with culture supernatant, 96% volume percentage) was isolated from a vineyard. A set of purification and identification experiments was performed to determine the main nematicidal component in MB751. A cyclic dipeptide Cyclo(L‐Pro‐L‐Leu) was identified with a lethal concentration necessary to kill 50% of the population (LC50) of 65.3 μg mL−1 against M. incognita J2. Following optimization trials on culture medium/fermentation conditions, such as the single factor test, Plackett–Burman test, steepest ascent, and response surface methodology experiments, the MB751 fermentation broth was then prepared as a BCA via a cold‐air drying process. The BCA and was evaluated in tomato pot experiments for effectiveness in suppressing M. incognita. Significant effects on M. incognita suppression and plant‐growth promotion as well as induced systemic resistance to M. incognita of tomato, were observed. CONCLUSION The cyclic dipeptide‐producing bacterium P. simiae MB751 exhibited high nematicidal activity and performance. Further development of this BCA should be pursued for the management of M. incognita in agriculture. © 2021 Society of Chemical Industry.

Characterization of Nematicidal Activity and Nematode-Toxic Metabolites of a Soilborne Brevundimonas bullata Isolate

“…Currently, the most in-depth studies have been conducted on ma RKN-killing bacteria, particularly those from Bacillus and Pseudomonas, such as B. thur giensis, B. subtilis, and B. cereus, which have been successfully applied in the fields biocontrol of RKNs during the cultivation of certain vegetables, including tomato, p per, and cucumber, and have been listed as one of the most promising biocontrol age [11,15,[41][42][43]. In contrast, some Pseudomonas species are able to produce or secrete va ous enzymes [20,34], nematicidal substances [23,24], nematode-toxic metabolites [44], multiple control mechanisms against RKNs, including the induction of systemic sistance (ISR). In this study, we selected an agriculturally significant RKN, the J2 larvae…”

“…Currently, the most in-depth studies have been conducted on many RKN-killing bacteria, particularly those from Bacillus and Pseudomonas, such as B. thuringiensis, B. subtilis, and B. cereus, which have been successfully applied in the fields for biocontrol of RKNs during the cultivation of certain vegetables, including tomato, pepper, and cucumber, and have been listed as one of the most promising biocontrol agents [11,15,[41][42][43]. In contrast, some Pseudomonas species are able to produce or secrete various enzymes [20,34], nematicidal substances [23,24], nematode-toxic metabolites [44], or multiple control mechanisms against RKNs, including the induction of systemic resistance (ISR). In this study, we selected an agriculturally significant RKN, the J2 larvae of M. incognita, as the target nematode pest with which to screen M. incognita-toxic bacterial isolates with highly active secretory metabolites from M. incognita-incident soils, resulting in the wild-type strain B. bullata MB756, which has been characterized to have highly dual nematicidal activity against both M. incognita and C. elegans.…”

“…These bacteria include Bacillus subtilis [11], Bacillus thuringiensis [12,13], Bacillus amyloliquefaciens [14], Bacillus cereus [15], Bacillus firmus [16][17][18], Bacillus nematocida [19], Pseudomonas aeruginosa [20][21][22], Pseudomonas putida [23], Pseudomonas simiae [24], Pseudomonas syringae [25][26][27], Burkholderia cepacia [28], Streptomyces avermitilis [29,30], and Pasteuria penetrans [31]. These nematicidal bacteria affect the target nematodes through different mechanisms, such as restraining the growth and reproduction of nematodes and direct pathogenesis, which are carried out by the production of toxic proteins [32,33], enzymes [12,26,34], small-molecule metabolites [23,24,35], or invasive parasitization [36,37]. In this respect, bacterial nematicides have shown particular usefulness in terms of their relatively high specificity, their ability to act on the underground parts of plants, and the difficulty in resistance-development in nematodes.…”

“…In the current study, we performed a joint two-round screening of culturable nematicidal bacteria from RKN-incident soils that were collected from different areas of China, with a particular focus on those where the supernatant of the culture suspension (SCS) was toxic to M. incognita. After a preliminary screening process from whole-cell suspension using the model organism Caenorhabditis elegans as the target nematode, which has been proven to be effective and time-saving in terms of facile cultivation processes and the short lifecycle for facilitating bioassays [24,38], the resultant bacterial isolates were rescreened to evaluate the nematicidal activity of their SCS against both C. elegans and M. incognita. Ultimately, an isolate was obtained and identified as Brevundimonas bullata (named MB756) through morphological examination, partial physiological and biochemical assays, and alignment analysis of its 16S rRNA gene sequences.…”

Reproductive Toxicity of Furfural Acetone in Meloidogyne incognita and Caenorhabditis elegans

“…Biological control is a promising environmentally suitable approach to reduce nematode losses. Many microorganisms [8][9][10], plants [11][12][13], or their metabolites [14,15] reportedly possess nematicidal activity. However, most have poor practical application efficiency in field.…”