DefinePK

Research Objective

To investigate the interactions between plant hosts (tomato, eggplant, okra) and the biocontrol agent Pasteuria penetrans on the development and reproduction of the root-knot nematode Meloidogyne javanica at different harvesting times, measured in degree days.

Methodology

The study involved inoculating tomato, eggplant, and okra plants with Meloidogyne javanica juveniles encumbered with Pasteuria penetrans spores. Control groups received nematodes without P. penetrans. Plants were harvested at three intervals corresponding to 422, 595, and 767 degree days after inoculation. Parameters measured included eggmasses per plant, root galling index, and eggs per eggmass. The presence and developmental stage of P. penetrans in infected females were also assessed. Data were analyzed using Analysis of Variance, with t, LSD, and x² tests for comparisons.

Methodology Flowchart

                        graph TD
    A[Inoculate Plants with M. javanica and P. penetrans] --> B[Harvest Plants];
    B -- 422 Degree Days --> C[Measure Nematode Parameters];
    B -- 595 Degree Days --> D[Measure Nematode Parameters];
    B -- 767 Degree Days --> E[Measure Nematode Parameters];
    C --> F[Assess P. penetrans Infection];
    D --> F;
    E --> F;
    F --> G[Statistical Analysis];
    G --> H[Conclusion];                    

Discussion

The study highlights the complex interplay between plant hosts, nematodes, and biocontrol agents. While P. penetrans demonstrated efficacy in reducing nematode populations and damage, its effectiveness and the rate of its own development were influenced by the plant host and the duration of the cropping cycle. The low rate of parasitism observed, especially at earlier harvest times, suggests that longer periods (at least 767 degree days) are necessary for P. penetrans to complete its life cycle and exhibit significant infection, particularly for the formation of mature endospores. The differential susceptibility of plant hosts, with okra being more favorable for nematode development, also plays a crucial role.

Key Findings

- There were significant interactions between plant hosts and P. penetrans on nematode development, particularly in eggmass production and root galling.
- P. penetrans significantly reduced eggmasses and root galling across all harvesting dates and plant hosts compared to control treatments.
- Plant hosts significantly differed in their susceptibility to nematode damage, with okra generally showing higher eggmasses and root galling.
- The rate of P. penetrans parasitism was low, with vegetative stages observed after 595 degree days and mature endospores only after 767 degree days. Okra-reared females showed higher infection rates by P. penetrans at later harvest times.
- A significant interaction between plant host and P. penetrans was observed for eggs per eggmass on tomato at the third harvest.

Conclusion

Plant hosts significantly influence the development of Meloidogyne javanica and the efficacy of Pasteuria penetrans as a biocontrol agent. While P. penetrans effectively reduces nematode damage, its parasitic activity and development are slow, requiring extended periods to manifest fully. Understanding these host-parasite-biocontrol agent dynamics is crucial for developing effective integrated pest management strategies.

Fact Check

- P. penetrans significantly reduced root galling from 5.53 in control to 3.13 in treatments with P. penetrans after the first harvest. (Confirmed in Results and Discussion section).
- After 767 degree days, females reared on okra were infected by P. penetrans in greater numbers (25) than those reared on tomato (15) and eggplant (10). (Confirmed in Table 12).
- The study used 422, 595, and 767 degree days for harvesting. (Confirmed in Materials and Methods and Results sections).

Mind Map