Evaluating the Potential of Oyster Mushroom Compost Waste for Plant-Parasitic Nematode Management
Since the beginning of this project we have completed three laboratory, two greenhouse, and two field trials. Summary of our results and outcomes are listed below.
Mushroom compost amendment was evaluated in the laboratory and was found to suppress root-knot nematodes as compared to the water control (P<0.05). However, the mushroom compost needed sufficient soil organic matter to be effective against plant-parasitic nematodes. Thus, it was then used with yard waste compost in other experiments. Mushroom compost water extract (MCWE) reduced 40% of the viability of nematodes in petri dishes. However, the extract did not kill the nematodes, but rather paralyzed them. Based on these laboratory studies, we concluded that mushroom compost can be used as amendment for seedling transplant media as a pre-plant nematode treatment, and the MCWE can be used as a post-plant drenching treatment on basil to reduce plant-parasitic nematodes.
We then conducted two basil trials in the field, one at Poamoho Experimental Station in Waialua and another one at Magoon Teaching Facility in Manoa. HI. To address the need of soil organic matter, we planted buckwheat as a cover crop in the Poamoho Trial, whereas we used yard waste compost mulch as surface mulch in the Magoon Trial. Different performances of mushroom compost against nematodes were observed between the two trials, partly due to different climate weather in both locations. Mushroom amendment and drench treatments increased plant growth in Poamoho and mushroom amendment enhanced overall basil yield harvested. However, at Magoon, only mushroom amendment increased basil yield if applied with organic mulch. Both mushroom amendment and drenching did not suppress total plant-parasitic nematodes in both trials. However, we included soil health analysis using free-living nematodes as indicators. In the Poamoho Trial, this analysis indicated that both mushroom amendment and drenching increased abundance of bacteria feeding nematodes, indicating an enhancement of the bacteria decomposition pathway, and thus, a more enriched soil nutrient condition. In the Magoon trial, adding mushroom amendment tended to increase % omnivorous nematodes and nematode richness only when used in mulched plots, whereas drenching with MCWE did not affect free-living nematodes.
We generated two extension articles in H?nai‘Ai, one student symposium poster, and one scientific conference presentation at the International Congress of Nematology at South Africa; attracted two high school students from McKinley High School to adopt this project as their high school science fair project for two consecutive years; and created a website. We also hosted a display booth during an annual Organic Field Day/Workshop event in the College of Tropical Agriculture and Human Resources (CTAHR) at the University of Hawaii.
The overall goal of this project is to explore the potential of spent oyster mushroom compost for managing M. incognita on basil. Specific objectives are to:
- determine the amendment rate of spent Pleurotus spp. compost in organic potting medium against M. incognita;
- establish a mushroom compost water extract concentration for M. incognita suppression; and
- demonstrate a mushroom-compost based technology for pre- and post-plant nematode management on basil in the field.
The performance targets for this year include experiments addressing each of the objectives. Laboratory tests had been conducted to establish a mushroom compost water extract concentration that would be effective in suppressing the key plant-parasitic nematode in Hawaii, root-knot nematode (Meloidogyne incognita). Two greenhouse experiments were conducted to evaluate different amendment rates and Pleurotus species. The field experiments were conducted in two locations to evaluate the effects of mushroom compost ,as well as the mushroom compost water extract in a field setting.
Objective 1: Laboratory trials for mushroom compost amendment effect
Two greenhouse experiments were conducted to examine the effect of the mushroom compost on plant-parasitic nematodes in a sterile soil:sand mixture. Pots were prepared with a 1:1 sterile sand: soil mix (v/v). Pots were either amended with mushroom compost at 0.25, 0.5, or 1% (w/w) of soil weight. Two additional treatments received either no coffee grounds or 1 % coffee grounds without fungi. Both experiments were arranged in completely randomized design with five replications. Four-week old basil seedlings were transplanted into each pot and inoculated with 200-second stage juveniles (J2) of M. incognita nematode. Basil plants were grown for 2.5 months after nematode inoculation with regular fertilization and irrigation as needed.
The results from the greenhouse experiments show that the mushroom amendment of P. ostreatus in Greenhouse Trial I did not increase basil shoot and root weight but increased reproduction rate of M. incognita instead. Coffee amendment did not contribute to suppression of M. incognita and also increased (P < 0.05) J2/g root as compared to unamended control. However, there was a trend that basil growth was poorest in the unamended soil, but nematode population densities tended to be lowest in this soil. The control had 748 nematodes per gram of root, the lowest of all the treatments. The highest was in the 1% mushroom amendment with 1,347 nematodes per gram of root.
Two laboratory experiments were conducted to determine the effect of the mushroom compost on root-knot nematodes using 100-cm3 cone-tainers. Potting media were amended with mushroom compost of Pleurotus ostreatus or Pleurotus eryngii at 50, 33, 2, and 1% (w/w) and compared to an unamended medium. All tubes were inoculated with 200 M. incognita per cone. A zucchini seedling was planted into each cone at time of amendment. At seven days after nematode inoculation, roots were weighted, stained, and processed for nematode eggs extraction, and nematodes were extracted from the media using elutriation and centrifugal floatation methods.
The results showed that regardless of the mushroom amendment rate, the mushroom compost was not able to suppress root penetration of root-knot nematodes, but at 1% or higher, it suppressed nematodes in the growing media. Similar nematode suppression effect was observed for the compost of the two oyster mushroom species. Amendment rate at 2% or greater of either species also produced higher root weight. This result is published in a local Sustainable and Organic Agriculture Program (SOAP) quarterly newsletter, H?nai‘Ai, which is commonly viewed by local farmers. http://www.ctahr.hawaii.edu/sustainag/news/articles/V20-Ching-Wang-MushroomCompost.pdf.
This result was also presented at the 2014 International Congress of Nematology and the power point is uploaded to our website at http://www.ctahr.hawaii.edu/WangKH/Downloads/ChingMushroomCompost.pdf. The graduate student, Ching, presented this result in poster format at the CTAHR Student Symposium and won a third prize for the poster competition. http://www.ctahr.hawaii.edu/WangKH/Downloads/2014_CTAHR_Symposium_Mushroom_Compost_kh.pdf.
Objective 2: Laboratory trials for mushroom compost water extract (MCWE) effect
Mushroom compost was mixed with water and aerated for 24 hours at concentrations of 0, 25, 33, and 50 %. Water was used as an untreated control. Solutions were strained and then tested in petri dishes with 50 Meloidogyne incognita, incubated for 1, 2, 3, 4, or 5 days, and then counted. After counting, nematodes in each sample were washed with water using 32-mm-pore screen to replace MCWE with water and nematodes were incubated for another day and then recounted to examine if the non-viable nematodes were only paralyzed or dead.
The results showed that nematodes were suppressed by all the concentrations tested as long as incubation in MCWE was ≥ 2 days. All of the MCWE concentrations suppressed nematode activity when compared to the water control (P< 0.05). However, after washing with water, most nematodes regained activity, which suggested that the MCWE only had a nematostatic and not nematicidal effect.
This result is also posted in our website at http://www.ctahr.hawaii.edu/WangKH/Downloads/ChingMushroomCompost.pdf.
Objective 3: Field trials for pre- and post-plant nematode management on basil
Two basil field trials are currently in progress. The experimental design was a 2 × 2 × 2 (organic source × mushroom amendment × MCWE drenching) split-split plot design with six replications to examine the mushroom compost effects on the plant-parasitic nematode, Meloidogyne incognita, as well as free-living nematodes. Since our greenhouse experiment showed that oyster mushroom amendment did not suppress nematode in soil with low organic matter, we grew a buckwheat cover crop for two months and incorporated it into soil as an organic source and compared it to no buckwheat in the Poamoho Trial. Basil cuttings were prepared in seedling trays using peat moss potting mix. Half of the basil seedlings were grown in potting mix amended with mushroom compost (50% of Pleurotus ostreatus compost) and the other half were not. At one month after transplanting, half of the buckwheat × mushroom amendment basil plants were drenched with 25% MCWE, and the other half were not. Slight modification in experimental design was conducted for the Magoon Trial, where yard waste compost was used as organic source instead of growing buckwheat cover crop. Plants were drenched with MCWE at an eight-week interval.
In the Poamoho trial, mushroom amendment increased basil yield (P < 0.10) and plant height (P < 0.05) but did not suppress root-knot nematodes. Drenching with MCWE increased plant height (P < 0.05) and chlorophyll content if planted in buckwheat treated plots (P < 0.05). Both mushroom amendment and drenching did not suppress total plant-parasitic nematodes. However, we included soil health analysis using free-living nematodes as indicators. This analysis indicated that both mushroom amendment and drenching increased abundance of bacteria feeding nematodes, enrichment index (EI) (P < 0.05) and decreased the channel index (CI) (P < 0.05), indicating an enhancement of the bacteria decomposition pathway, overall, a more enriched soil nutrient condition.
In the Magoon trial, yard waste compost was used as organic source instead of cover crop. Similar split-split plot experiment to the Pomaoho Trial was conducted. The performance of mushroom compost was less effective in Magoon trial than the Poamoho Trial. Although mushroom amendment (P<0.10) and mulch (P<0.05) increased basil yield, drenching with MCWE only increased chlorophyll content but not the yield. In general, yard waste compost mulch improved soil health conditions. Adding mushroom amendment tended to increase (P < 0.10) % omnivorous nematodes, structure index (SI), nematode richness, and diversity only if used in mulched plots. In this trial, drenching with MCWE did not affect free-living nematodes.
These field trials suggested that mushroom compost (amendment or drenching) was acting more like compost that increased the bacterivores or omnivores if yard waste compost with high C: N ratio was associated. Lack of enhancement of fungivorous nematodes suggested that Pleurotus ostreatus in the compost was not active. Despite the fact that mushroom compost does not manage plant-parasitic nematodes in our field trials, its enhancement on soil health is promising. Our field trials were also complicated by the infestation of downy mildew. We plan on repeating another field trial with Thai basil that is more tolerant to downy mildew.
Impacts and Contributions/Outcomes
On July 26, 2014, we hosted a display booth on the use of mushroom compost for nematode management during the CTAHR Organic Field Day Event that was attended by >200 people. Most of the visitors were small-scale farmers located on Windward side of Oahu, as well as home gardeners. A survey conducted at the workshop shows that 87.5 % participants are highly interested in growing their own oyster mushrooms. Most participants gave a positive reaction to this project and think it is a useful tool that they can use and pass on to others. Participants also look forward to learn about the benefits of this project will have on the farmers in the community.
This project is especially supported by the largest oyster mushroom producer in Hawaii, Robert Stanga at Hamakua Heritage Farms, LLC, in Laupahoehoe, Hawaii. The company donated mushroom compost substrate for us to conduct the field trials. They appreciated the publications we produced and are sharing that with their clients and visitors.
Although the mushroom compost has not been effective in suppressing plant-parasitic nematodes, there has been improvement in soil health. Plants were more tolerant of the plant-parasitic nematodes with the mushroom compost, and beneficial nematodes were also more abundant. Basil yield was also increased in the mushroom treatments, especially for treatments with mushroom as amendment.
Overall, we generated two extension articles in H?nai‘Ai, one student symposium poster, and one scientific conference presentation at the International Congress of Nematology at South Africa, and attracted two high school students from McKinley High School to adopt this project as their high school science fair project for two consecutive years. They have won an award for their district science fair competition and are currently working on their second year’s science fair competition. We also created a website for the public to view on our results from this project. Updated findings can be found on our website at the link below.
Specific outcomes of this project are listed below:
- Ching, S. and K.-H. Wang. 2014. Mushroom compost to battle against nematode pests on vegetable crops. H?nai‘Ai Newsletter August 2014. http://www.ctahr.hawaii.edu/sustainag/news/articles/V20-Ching-Wang-MushroomCompost.pdf
- Wang, K.-H. and S. Ching. 2014. Rhizosphere inoculum and amendment. H?nai‘Ai Newsletter March 2014. http://www.ctahr.hawaii.edu/sustainag/news/articles/V19-Wang-RhizoInoculum.pdf
- Ching, S., and K.-H. Wang. Evaluating the potential of oyster mushroom compost waste for plant-parasitic nematode management. International Conference of Nematology, Cape Town, South Africa. May, 2014.
- Ching, S., K.-H. Wang, and B.S. Sipes. 2014. Evaluating the potential of oyster mushroom compost waste for plant-parasitic nematode management. CTAHR Student Research Symposium, Honolulu, Hawaii (Abstract #33).
- Wang, K.-H. and S. Ching. Organic Field Day. Waimanalo Research Station, July 26, 2014.
High School Science Fair Project:
- Au, Vivian Hiu Shan, and Liang, Yumi. 2013. The effect of oyster mushroom compost on nematode-infested soil. McKinley High School. High School Science Fair Project (3rd place at the Honolulu District Science Fair; Best of Category award in Environmental Sciences at the Hawaii State Science Fair; win recognition from the Hawaii Agricultural Research Center; as a result, the students traveled to Los Angeles to observe the National High School Science Fair Competition).
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