Progress 09/15/04 to 09/14/07
Outputs
OUTPUTS: Effects of the native entomopathogenic nematode (EPN) Steinernema feltiae (MG-14) on Meloidogyne javanica was investigated in heat-treated (4 h at 60C) and antagonist friendly, non-heated soil. Interactions between S. feltiae-infected cadavers, Arthrobotrys oligospora, and cow pea leaf amendment - a source of organic nutrition for nematode antagonists, were also investigated. The use of S. feltiae-infected cadavers provided a level of M. javanica suppression comparable to that of inundated applied S. feltiae juveniles, but superior to that of frozen Galleria and water treatment. Unfortunately, the affect was inconsistent across trials. There was no impact by cadaver age on M. javanica suppression. Stronger affects were observed for nematode-infected cadavers on M. javanica egg production over 35 days, but only in pots containing non-heated soil; with 3-day old cadavers the most effective in reducing egg production. Over 60-days, independent of soil treatment, 3-day, 5-day,
and 8-day cadaver treatments reduced M. javanica egg production by as much as 69%, but the affect was not consistently repeatable. A combined A. oligospora and EPN treatment suppressed M. javanica by an additional 35% over applications of EPN and NTF independently, but the affect was still highly variable. Cow pea amendment did not influence M. javanica suppression in the presence or absence of either NTF or EPNs. Plant biomass was greater for plants grown in heated soil, over non-heated soil, but there was no benefit from applying EPNs or NTF. Steinernema feltiae MG-14 was as effective in reducing M. javanica egg production as S. glaseri NC, a nematode used to bait for NTFs, as well as reducing free J2 stages in the soil, when compared to frozen (non-nematode infected) Galleria. Arthrobotrys oligospora trapped S. feltiae MG-14 and S. glaseri as the number of IJs recovered from soil treated with NTF fell by nearly 70% over 14 days compared to EPN treatments in the absence of A.
oligospora. However, a quarter-strength corn-meal agar bioassay demonstrated little reduction in S. feltiae MG-14 numbers in the presence of either Monacrosporium ellipsosporum or A. oligospora, likely caused by the lack of movement of the IJs on the agar media. Variability in the efficacy of dual EPN and NTF applications in reducing M. javanica may be attributed to a number of factors; notably behavioral interactions between EPN and NTF, time of emergence of IJs from the host, rate of trapping of EPNs by NTF, and relationship in population growth between NTF and EPNs - in addition to abiotic and biotic factors present in the soil, host plant affects, and interactions with the target pest M. javanica. Results from this project have been disseminated by presentations at annual Society of Nematologists meetings.
PARTICIPANTS: Declan Fallon, PI, University of Hawaii, 100% (Full-time) Brent Sipes, Co-PI, University of Hawaii, 5% Harry Kaya, Co-PI, University of California Davis, 5% Donna Meyer, Technician, University of Hawaii, 5% Maggie Love, Student, University of Hawaii, part-time
TARGET AUDIENCES: Researchers developing biological methods to suppress plant-parasitic nematodes
Impacts
Entomopathogenic nematodes (EPNs) are a well established agent for the control of economically important soil insect pests, applied directly to the soil or via irrigation systems. Introducing the infective stage or "IJ" to the soil quickly targets the insect pest, but sometimes the large number of IJs applied can alter the balance of local nematode communities, often to the extent plant-parasitic nematode populations are significantly reduced. The mechanism for this affect is unclear and may be governed by a number of factors; including the release of nematicides produced by the symbiotic bacteria present in the IJ; behavioral interactions between the IJ and the host plant which can block entry sites for the plant-parasitic nematode; and the stimulation of nematode antagonists which can target IJs and plant-parasitic nematodes. Studies were undertaken to investigate factors which can enhance the suppression of plant-parasitic nematodes by EPNs. A native EPN isolate was
tested in a number of greenhouse studies for the suppression of root-knot nematode; a key parasite of coffee, taro, and pineapple in Hawaii. An application of a single nematode-infected cadaver was as effective in suppressing root-knot egg production as the use of inundated IJs, but the affect was inconsistent across trials and not a reliable method for suppressing plant-parasitic nematode populations. The introduction of nematode-trapping fungi (NTF) to the system added another level of suppression, but the affect in combination with EPNs while promising, was unreliable for long term suppression. Treatments were limited to the use of a single cadaver of just two EPN species, applied with a single NTF species, a very small test sample. Experiments are planned to test more effective EPN and NTF combinations - including the application of multiple cadavers over time and increasing the number of cadavers per application. The relationship between controlled variables is likely complex and
initial trials show promise, even if consistency was lacking. Further research will look to unravel some of the complexities between EPNs, NTF and plant-parasites for the development of sustainable plant-parasitic nematode control.
Publications
- No publications reported this period
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Progress 10/01/05 to 09/30/06
Outputs
Interactions between entomopathogenic nematodes (EPNs), locally isolated nematode trapping fungi (NTF), and cowpea amendment for the suppression of Meloidogyne javanica were investigated in cowpea. Galleria mellonella cadavers infected with indigenous Steinernema feltiae MG-14 were more effective than frozen non-nematode-infected cadavers, but comparable to S. glaseri NJ, in the suppression of M. javanica egg production in cowpea after 35 days (F = 3.32 df = 2, 49, P = 0.0467). Eight-day old cadavers were more effective than 5-day old and 3-day old cadavers in the suppression of M. javanica egg production in cowpea, and reducing free-living J2 numbers in the potted soil for up to 60-days post-application; but all three aged EPN-infected cadavers were able to suppress M. javanica egg production from plants, and J2 numbers in soil, compared to a frozen G. mellonella cadaver (P < 0.05). In the presence of Arthrobotrys oligospora; S. feltiae- and S. glaseri-infected
cadavers reduced M. javanica egg production by 35-36% compared to EPN treatments in the absence of the NTF (P > 0.05). While A. oligospora in the presence of frozen G. mellonella increased M. javanica egg production by 13% compared to plants treated with G. mellonella alone (P > 0.05). There was no benefit from amending the soil with cut cowpea leaves at a rate of 10% v/v. Different combinations of NTF and EPNs were investigated for effects on root penetration by M. javanica. Independent of EPNs, A. oligospora reduced M. javanica root penetration (df = 2, 64 F = 82.95 P < 0.0001), but there was no interaction between A. oligospora and S. feltiae or S. glaseri, even though A. oligospora and S. feltiae together reduced M. javanica penetration by 75%, and S. glaseri and A. oligospora reduced penetration by 23%, versus EPN treatments in the absence of A. oligospora (P > 0.05). The presence of NTF reduced populations of EPNs over time in a sand:soil mix (df =1, 23 F = 4.47 P = 0.0465; day
35). But combinations of NTF and EPNs were only weakly suppressive on M. javanica J2 numbers in the same media (P > 0.05). However, in a corn-meal-agar assay, NTF: A. oligospora and Monacrosporium sp. failed to trap indigenous S. feltiae MG-14 in large numbers, but were effective in trapping non-native S. feltiae SN and S. glaseri NJ; exposure to Monacrosporium for 11 days had no effect on S. feltiae MG-14, but reduced S. feltiae SN populations by 59%; exposure to Arthrobotrys reduced S. feltiae MG-14 numbers by 19%, but S. feltiae SN by 78%. The lack of activity by indigenous S. feltiae MG-14 in the corn-meal agar may have protected infective juveniles (IJs) from predation by NTF. But when S. feltiae MG-14 and A. oligospora were present together in potted sand:soil mix, the presence of the NTF reduced S. feltiae MG-14 numbers by 69% after 14-days of exposure. Future work will introduce multiple EPN-infected cadavers over time to enhance initial positive affects by EPN-cadavers on M.
javanica suppression. In addition, repeat experiments will confirm if there is an interaction between NTF and EPNs on M. javanica suppression using existing and newly isolated NTF species.
Impacts
Suppression of plant-parasitic nematodes by insect-parasitic nematodes is a contentious subject given the disparity in final hosts and thus, potential for direction interaction. However, numerous studies have demonstrated negative impacts on plant-parasitic nematodes by insect-parasitic nematodes. Pin-pointing the cause and effect has been difficult and numerous ideas, some conflicting, have been proposed in explanation. It is likely the whole is greater than the sum of its parts; with no one factor dominating. Our research has used nematode-killed insect cadavers as a cost-effective (cadavers can be tilled into the soil during pre-plant, no need for irrigation or excess water), environmentally compatible delivery system (over chemical control methods); encompassing the parts likely responsible for the suppression of plant-parasitic nematodes. Nematode-killed cadavers also allow for traditional benefits, including the control of, and/or as a preventative measure
against, soil insect pests. We have found a more consistent level suppression of plant-parasitic nematodes using nematode-killed cadavers over other methods, but there is still room for improvement. Introducing nematode trapping fungi to the system has helped; but as yet, there has been no direct interaction to enhance the suppression of either. Our studies have focused on the use of a single-application of a nematode-killed insect cadaver, but stronger control may be obtained by a more frequent application schedule, perhaps with or without nematode-trapping fungi. This will be our strategy for the coming year.
Publications
- Fallon, D.J., Kaya, H. K., Sipes, B. S. (2006) Enhancing Steinernema spp. suppression of Meloidogyne javanica. Journal of Nematology 38: 271-272.
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Progress 10/01/04 to 09/30/05
Outputs
The use of Steinernema feltiae (MG-14)-infected Galleria mellonella from Maui, was tested for effects against M. javanica in soybean, cowpea, and tomato, grown in heat-treated and non-heat treated (raw) soils. The effect of soil treatment on plant growth and M. javanica development was variable; in the majority of experiments the difference between treatments was minimal (P > 0.05); in one experiment non-heat treated soils supported lower M. javanica populations; possibly the result of nematophagous organisms, but the reverse was true in a separate experiment, which may have been attributed to background plant-parasitic nematode populations. S.feltiae-infected G. mellonella suppressed M. javanica root penetration in soybean (F = 6.14, df = 6,14 P = 0.0069); egg production over 35 days in tomato (F = 5.89, df = 3,39 P = 0.0026), but not cowpea (P > 0.05); and egg production over 60 days in cowpea (F = 4.58, df = 3,44 P = 0.0081). The age of nematode-infected cadavers
was not a consistent factor in M. javanica suppression. Plant growth was unaffected by the presence of nematode-infected cadavers. Steinernema feltiae-killed insect cadavers did not outperform aqueous suspensions of S. feltiae infective juveniles (IJ) in the suppression of M. javanica penetration (P > 0.05), but provided superior efficacy over 35 days in reducing M. javanica egg production; aqueous suspensions of S. feltiae did not differ to control treatments. Future work will investigate the interaction between S. feltiae-infected host cadavers and nematode-trapping fungi, Arthrobotrys sp. in cowpea amended, and non-amended soils for the suppression of M. javanica.
Impacts
Plant-parasitic nematodes account for an estimated $8 billion loss in failed crops. Current control methods for plant-parasitic nematodes rely on the use of restricted chemical nematicides. Insect-parasitic nematodes are a specialist group of nematodes that are frequently used as bio-control agents. The free-living juvenile stage of the nematode kills its host using a symbiotic bacteria. This bacteria produces antibiotics and nematicidal agents which allows the nematode to complete its life cycle. Our research is focused on using insect-parasitic nematodes as an antagonistic agent to plant-parasitic nematodes. Root-knot nematodes are similar to insect-parasitic nematodes in having a free-living stage which seeks a suitable plant host to infect. Early research in this area applied insect-parasitic nematode juveniles directly to root-knot infested soils; but variable efficacy was attributed to short term persistence in the soil. The use of nematode-killed hosts as a
delivery system for juveniles enabled the suppression of plant-parasitic nematodes for a period up to 60-days. Juveniles emerging over time from nematode-killed host persist longer in the soil and benefit from protection derived from the host cadaver. Considerable potential exists to integrate insect-parasitic nematodes with alternative biocontrol strategies, including cover crops, nematophagous fungi, and antagonistic organic extracts. Future research will investigate these alternatives.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Plant-parasitic nematodes (PPNs) are a significant threat to several important crops grown in Hawaii, including coffee, pineapple, and papaya, and are an acute problem in small-acreage farms of ginger and taro. Effective methods to control PPNs are limited. Chemical methods of control are inappropriate for many growers in Hawaii due to safety, toxicity, and licensing concerns. Studies of synergistic interactions between antagonists have received little attention. To facilitate this, we intend to test combinations of endemic entomopathogenic nematodes (EPNs) and nematophagous fungi against the root-knot nematode, Meloidogyne javanica. In selecting endemic suppressive agents, we eliminate the need to introduce and license exotic organisms, utilizing organisms adapted to the environment and preserving the integrity of the ecosystem as a whole. EPNs are insect parasites with a free-living, soil-inhabiting, life stage. The EPN-bacterium complex is known to suppress PPN
populations. Competition for root space, ammonia production, and metabolites of the symbiotic bacteria contribute to this suppression, but the effect, although significant, remains variable. Synergistic suppression of M. javanica using an EPN and a nematophagous fungus has been demonstrated in a small scale, non-optimized system. Our specific objectives to reach this goal are a) To determine the effect of EPNs on M. javanica in sterile and non-sterile soils; b) To determine synergistic relationships between EPNs and nematophagous fungi on M. javanica suppression; c) To determine effects of EPN-infected insect cadavers on nematophagous fungi and M. javanica; d) To evaluate M. javanica suppressive agents under field conditions. We have initiated a greenhouse trial investigating the benefit of slow release EPN juveniles from nematode-infected insects. EPN suppression of M.javanica can be reduced by watering, and nematode migration. By introducing infected insect cadavers we anticipate a
slow release of EPNs over a period of 9 to 11 days, providing greater potential for PPN suppression than single EPN applications.
Impacts
In the first year we plan to develop an EPN application strategy that facilitates persistance of entomopathogenic nematode (EPN) juveniles around plant roots. We anticipate a greater level of plant-parasitic nematode (PPN) control from our nematode-infected cadavers versus innundative released EPN juveniles as previously published from our laboratory. We then plan to investigate the impacts and interactions of nematophagous fungi on M. javanica in the presence of this EPN-cadaver system.
Publications
- No publications reported this period
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