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Suppressive Effects of Vermicompost Tea on Root-Knot Nematodes, Meloidogyne SPP

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Title:Suppressive Effects of Vermicompost Tea on Root-Knot Nematodes, Meloidogyne SPP
Authors:Mishra, Shova
Date Issued:Aug 2016
Publisher:[Honolulu] : [University of Hawaii at Manoa], [August 2016]
Abstract:Vermicompost tea (VCT), a water extract of vermicompost (VC), has been documented to suppress several soil-borne pathogens as well as plant-parasitic nematodes (PPNs). Previous research has not showed consistent performance of VCT for suppressing PPNs. Several factors affect the performance of VCT for PPNs suppression. This thesis focused on studying potential factors affecting the VCT in suppression of PPNs and understanding some mechanisms involved in PPNs suppression by VCT. Specific objectives of this thesis were 1) determining the effects of VCT prepared from different curing ages of VC on penetration, reproduction and hatch of Meloidogyne spp., root-knot nematodes (RKs), 2) determining the effective VCT drenching frequency for suppression of RKs, and enhancement of free-living nematodes in a cucumber agroecosystem, and 3) determining if VCT drenching could induces host plant resistance on cucumber (Cucumis sativus).
Three greenhouse trials showed that VCT prepared from uncured and partially cured (cured for 1-1.5 months) VC consistently reduced root penetration and hatch of M. incognita at 1 and 2 weeks after VCT treatment, respectively. However, VCT drenching did not suppress M. incognita reproduction on tomato (Solanum lycopersicon) and cucumber in longer-term greenhouse trials (2.5 months) despite repeated drenching at 2-week interval.
Thus the next logical step was to evaluate drenching frequency for effective management of PPNs in the field. Two cucumber field trials were conducted to examine the drenching frequency of VCT in conjunction with a pre-plant nematode management technique, of a oil radish (Raphanus sativus) cover crop. VCT drenching at 1-week intervals consistently reduced the abundance of RKs in both trials, but oil radish only suppressed the abundance of RKs in Trial II. Weekly VCT drenching also increased abundance of bacterivorous nematodes in Trial I (P < 0.05), indicating an enhancement of bacteria decomposition. VCT drenching could further improve soil health when integrated with oil radish cover crop as indicated by higher nematode richness and abundance of Ecumenicus, an omnivorous nematode. However, this effect of VCT on soil health was not obvious in Trial II. Weather conditions might play a role in the inconsistent performance of VCT drenching on soil health. Although VCT drenching had no effect on cucumber yield, oil radish cover crop consistently increased cucumber yield. Thus, integration of VCT drenching with oil radish cover cropping could offer an economical nematode management practice.
To understand the mechanism on how VCT prepared from uncured VC suppress PPNs, split-root experiments and quantitative real time PCR were used to test the hypothesis on whether VCT drenching induced the expression of plant defense related genes. Split-root experiments showed that drenching VCT prepared from uncured VC on one side of the cucumber roots significantly suppressed root penetration of M. incognita on the other side of the roots compared to the water control (P < 0.05). Plants drenched with VCT showed an increased expression of CHIT-1 at 2 days after M. incognita inoculation, and increased expression of PAL-1 at 2 and 8 days after M. incognita inoculation. VCT drenching resulted in up regulation of LOX-1 at 2 and 5 days and down regulation of PR1 at 5 and 8 d after M. incognita inoculation. CHIT-1, PAL-1 and LOX-1 were known to be involved in Induce Systemic Resistance (ISR) on cucumber. Down regulation of PR1 supporting the hypothesis that VCT did not induce Systemic Acquired Resistance (SAR). This is the first study to demonstrate the ability of using VCT prepared from uncured VC as root drenching to induce ISR on cucumber. Although this induction of ISR was short lived, drenching VCT at a weekly interval could provide consistent suppression of root-knot nematodes for a cucumber crop. Thus, use of VCT prepared from an uncured VC is a viable post-plant nematode
management tool against RK.
Description:M.S. University of Hawaii at Manoa 2016.
Includes bibliographical references.
Appears in Collections: M.S. - Tropical Plant Pathology

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