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Title: Evaluation of Nematicidal Potential of Plant Growth Promoting Rhizobacteria against Meloidogyne incognita
Authors: Anwar ul Haq, Muhammad Shahid, Muhammad Zeeshan Niaz, Kamra Mahmood, Ussama Yaseen, Muhammad Tariq Adnan Khan
Journal: Plant Bulletin
Publisher: Airanam Research
Country: Pakistan
Year: 2022
Volume: 1
Issue: 2
Language: English
DOI: 10.55627/pbulletin.001.02.0222
Keywords: MortalityNematicidesHatchingroot knot nematodePGPRmeloedogyne incognita
Root-knot nematodes have a wide host range, causing damage to many annual and perennial crops. More than 100 species of Meloidogyne are known in which M. incognita (Kofoid and White) Chitwood is one of the most common and important plant parasitic nematode in tropical and subtropical regions of the world including Pakistan. Therefore, the present study was planned to check the effect of PGPRs on juvenile mortality and egg hatching inhibition of M. incognita under lab conditions. Eggs were isolated from egg masses by using NaOCl solution. Rhizobacteria (Bacillus subtilis, Pseudomonas fluorescens, Azotobacter chroococcum, Azospirillum sp., Rhizobium leguminosarum) were multiplied on nutrient broth and kept overnight at 28 ± 2 °C in shaking incubator. Cell free culture filtrates were obtained in falcon tubes by centrifuging PGPRs @ 4000 RPM twice for 30 minutes. Two ml of toxins of each PGPR was poured into each 5cm-dia. petri plate and 100 microliters of egg suspension containing approximately 100 eggs were put in each petri plate. Similar experimental conditions and protocols were used for juveniles’ mortality. In this experiment, instead of eggs, 100 J2s contained in 100 microliters of juvenile suspension were put in each petri plate. The petri plates were placed in completely randomized design in incubator at 28 ± 2 °C with ten replicates. Petri dishes containing distilled water were kept under control. All the PGPRs caused larval mortality and inhibition in egg hatching with varying degrees. The maximum egg hatching was inhibited by Bacillus subtilis while Rhizobium leguminosarum was found the least effective. The other PGPRs i.e. Pseudomonas fluorescens, Azotobacter chroococcum, and Azospirillum sp. showed intermediate results.
To evaluate the effect of Plant Growth Promoting Rhizobacteria (PGPRs) on juvenile mortality and egg hatching inhibition of Meloidogyne incognita under laboratory conditions.
The study involved isolating eggs from egg masses using NaOCl solution. Five PGPRs (Bacillus subtilis, Pseudomonas fluorescens, Azotobacter chroococcum, Azospirillum sp., Rhizobium leguminosarum) were cultured and their cell-free culture filtrates were obtained. These filtrates were tested for their effects on egg hatching inhibition and juvenile mortality of M. incognita. Experiments were conducted in petri plates with 100 eggs or 100 J2 juveniles per plate, with ten replicates, incubated at 28 ± 2 °C. Distilled water was used as a control. Data on egg hatching inhibition and juvenile mortality were recorded at 24, 48, 72, 96, and 120 hours.
graph TD
A[Isolate M. incognita eggs and juveniles] --> B[Culture PGPRs];
B --> C[Obtain cell-free culture filtrates];
C --> D[Test egg hatching inhibition];
C --> E[Test juvenile mortality];
D --> F[Record data at intervals];
E --> F;
F --> G[Analyze results];
G --> H[Draw conclusions];
The nematicidal action of PGPR culture filtrates is attributed to the production of enzymes and toxins that weaken and dissolve nematode barriers. PGPR strains effectively inhibited egg hatching by altering eggshell structures, potentially due to protease, chitinase, and chitosanase activities. The tested bacterial strains show promise as biocontrol agents for future nematode management strategies.
All tested PGPRs demonstrated potential in inhibiting egg hatching and causing juvenile mortality of M. incognita. Bacillus subtilis showed the highest efficacy in inhibiting egg hatching and causing juvenile mortality. Rhizobium leguminosarum was the least effective among the tested PGPRs. Pseudomonas fluorescens, Azotobacter chroococcum, and Azospirillum sp. exhibited intermediate results.
Plant growth promoting rhizobacteria (PGPRs) can effectively inhibit egg hatching and cause mortality of Meloidogyne incognita juveniles, suggesting their potential as eco-friendly bio-control agents for managing root-knot nematodes.
1. Meloidogyne incognita is a common plant parasitic nematode in tropical and subtropical regions: This is stated in the abstract and introduction, supported by numerous citations.
2. Bacillus subtilis showed the maximum egg hatching inhibition: The results indicate that Bacillus subtilis achieved the highest percentage of egg hatching inhibition (e.g., 21.40% at 120 hours, with a calculated inhibition of 99.00% in Figure 1 description).
3. Rhizobium leguminosarum was the least effective PGPR: The data shows Rhizobium leguminosarum had the lowest egg hatching inhibition (e.g., 35.30% at 120 hours) and juvenile mortality (e.g., 75.5% at 120 hours) compared to other PGPRs.
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