Control of Bacterial Wilt Disease of Ginger through an Integrated Pest Management Program
Edible ginger (Zingiber officinale) is a major export crop on Hawaii Island. Bacterial wilt caused by Ralstonia solanacearum is the crop’s most problematic disease. During Year 1, we have:
a) distributed hydroponically-grown, wilt-free ginger seed pieces to commercial growers and backyard gardeners of ginger;
b) provided information to growers on the importance of planting wilt-free ginger seed pieces;
c) begun field trials on cooperator’s farms;
d) begun pot studies to determine whether vermicompost, vermicompost tea or Indigenous Microorganisms (IMO) could help to control ginger wilt; and
e) surveyed commercial ginger growers to determine their current cultivation practices.
The overall goal of this project is to develop and demonstrate sustainable farming practices that control bacterial wilt in edible ginger. Specific objectives are to:
1) demonstrate the importance of clean planting materials;
2) demonstrate procedures to test fields for Ralstonia solanacearum;
3) conduct field studies to determine the effectiveness of green manure crops or rotational crops for pathogen control;
4) conduct greenhouse studies to determine effectiveness of vermicomposts to control R. solanacearum;
5) conduct economic analysis of sustainable farming practices; and
6) disseminate information and enhance farmer adoption of practices through a video and a web site.
During December 2010 through February 2011, hydroponically-cultured, wilt-free ginger was harvested, washed and packed in 30 lb boxes (Figures 1, 2). Ginger seed pieces were distributed to local commercial growers and backyard gardeners.
On Tuesday, February 22, 2011, Drs. Miyasaka, Shintaku and Kratky gave presentations to over 23 people (including commercial growers, their families and agricultural industry representatives) on the importance of planting wilt-free ginger seed pieces, keeping fields disease-free and how wilt-free ginger seed pieces were grown hydroponically (Figure 3). Eleven boxes of clean ginger seed pieces were distributed to commercial growers.
On Saturday, February 26, 2011, Drs. Miyasaka, Kratky and Ms. Ferol White gave demonstrations to over 20 backyard gardeners at the Kinoole Farmer’s Market on “Multiplying Disease-free Ginger in Pots” (Figure 4). Over 20 lbs of hydroponically-cultured, clean ginger seed-pieces were distributed in 0.5 lb bags to back-yard growers so that they could grow and multiply wilt-free ginger in pots.
Since ginger is propagated vegetatively, it is necessary to multiply ginger seed pieces for the next cycle of research trials. Currently, we are conducting greenhouse trials to determine the best hydroponic method of culture for ginger. In addition, hydroponic culture will provide wilt-free ginger seed pieces for next crop cycle. Containers have been constructed using black/white heavy plastic (pond liner) to make a channel or trough. Two-inch high nursery trays were placed on the floor of each trough; on top of them, trays filled with growing medium were placed. Seed pieces from the 2010 crop were planted in each tray (Figures 5, 6). Nutrient solution is continually maintained at three inches of depth in troughs using irrigation tubing that connects to storage tanks containing nutrients.
Polymerase Chain Reaction (PCR) has been utilized as a sensitive detection technique for many pathogens. Until recently, detection of pathogens in soil has been problematic because of soil compounds that inhibit the PCR reaction. We recently adopted a method that includes a crude soil extraction followed by enrichment in selective media and PCR. This method reveals the presence, as well as viability, of the pathogen. We found this procedure to be highly specific and sensitive [as low as 100 colony-forming units (CFU); Figure 7], and we are using it to detect R. solanacearum in field soils and commercial potting mixes, as well as various soil amendments. This testing allows us to evaluate the effects of soil amendments on R. solanacearum populations.
Soil samples from a ginger field located in Onomea, Hawaii were taken over the growing season to monitor the presence of the pathogen in soil throughout the growing season (Figure 8). Although these samples continually tested positive for the presence of R. solanacearum (Figure 9), disease incidence and crop losses were minimal. A novel soil amendment known as IMO (Indigenous Microorganisms) was applied by the grower to enrich the soil, and it could have acted as a disease suppressant. To test this treatment further, we will conduct greenhouse experiments to evaluate the effects of IMO, as well as vermicompost and vermicompost tea on soil populations of R. solanacearum.
The Enrichment-PCR method is sensitive and accurate in the detection of the pathogen; however, it isn’t available to commercial farmers. To develop a bioassay that farmers could use to determine the presence of ginger wilt, we conducted a preliminary study using soils from fields that had tested positive or negative based on Enrichment-PCR. Either tissue-cultured ginger plantlets or vegetative propagules from red ginger (Alpinia purpurata) were planted into pots containing soil. Unfortunately, soils collected from two fields that had tested positive earlier for ginger wilt did not test positive immediately before this trial. As a result, we lacked a positive control. None of the plants that died during this study tested positive for ginger wilt; apparently they were killed by other disease organisms. In the future, we will ensure a positive control by adding R. solanacearum to the pots containing soil.
To demonstrate the importance of planting wilt-free ginger seed pieces into wilt-free fields, three commercial growers were asked to cooperate in on-farm field trials. Dr. Shintaku and his graduate student, Ms. Sharon Motomura, tested the fields using their enrichment-PCR method and found them to be wilt-free. Wilt-free seed pieces of ginger were planted in two separate farms on the Island of Hawaii (Paukaa and Pepeekeo) during March to April 2011, and their growth is being monitored (Figures 10, 11).
To extend this on-farm research to other islands, an interested commercial grower was contacted on the Island of Maui, and Ms. White visited the farm to collect soil samples and talk to the farm managers. However, due to a decision by higher management, the farm decided not to participate in this trial.
A pot study was set up on May 23, 2011 in a greenhouse at the University of Hawaii at Hilo Farm to determine the effectiveness of vermicomposts to control R. solanacearum. Peat-based potting media (Promix® BX) was substituted with vermicomposts produced from food wastes and shredded paper processed by Eisenia fetida earthworms. The substitution rates were: 0 (control), 20%, 40%, 60%, 80% and 100%. Ginger propagules (approximately 50 – 100 g) were sown into each 1-gallon pot (Figure 12). Each pot received 0.5 pounds of an organic fertilizer, Bioflora®, which contained 6-6-5 % NPK. All treatments were replicated 10 times.
The experiment was divided into two blocks: inoculated and non-inoculated. The treatments (rates of vermicompost substitutions) were randomly arranged within each block. Drip irrigation was set-up to maintain moisture of media at field capacity for all pots. Additional shade cloth was installed over the benches to provide 75% more shade. Half of the pots were inoculated with 108 CFU of R. solanacearum in 5 ml of distilled water 10 days after sowing (Figure 13). Growth and presence of R. solanacearum will be monitored.
Ginger farmers who attended the informational meeting in Hilo on February 22, 2011 were surveyed to determine their current ginger farming practices and their interest in learning more about controlling bacterial wilt of ginger. Six full time farmers and two part-time farmers responded to the survey. The other three respondents were not farmers and their answers are not included here.
Six of the farmers who responded to the survey were affected by the bacterial wilt five years ago. Two of the eight farmers responding to the survey did not plant ginger last year due to the wilt. Of the six remaining farmers, two were not affected by wilt last year and the remaining four were affected. Clearly, wilt has affected ginger production, because only two producers out of eight were not affected last year.
Two of the full-time respondents use the hot water dip method to kill bacterial pathogens, while the remaining six do not. One part-time and two full-time respondents use green manure or rotational crops to control bacteria wilt. Three full-time respondents deep-plow diseased fields to control bacteria wilt of ginger. All respondents were interested in learning more about these treatment methods.
Three full-time respondents use disease-free planting materials. All respondents were interested in using disease-free planting materials. Comments from respondents indicate that these materials are not readily available. A limited amount of disease-free ginger was distributed at the meeting. None of the respondents test their fields for bacterial wilt.
One respondent was female and the rest were male. Two full-time respondents were 33 years old and the rest of the respondents were 50 years-old or older. The part-time respondents reported the highest incomes of $75,000 or higher, as well as the highest educational levels of a bachelor degree.
Bacterial wilt has had a large impact on the behavior of survey respondents because it has caused them to change their behavior in nearly all cases (only one relatively new part-time producer has not changed behavior), and in all cases respondents want to learn more about combating this disease. While the number of respondents was small and the workshop attendance was small, the destructive nature of the disease may have resulted in many producers losing interest in growing ginger. The interest demonstrated by the two young producers who responded to the survey indicates that extending the results of this project holds promise for increasing ginger production over the long-term in Hawaii.
We have had six video shooting sessions with Dr. Kratky, showing various stages of hydroponically-cultured ginger growth. We have had one video shooting session, showing the Enrichment-PCR method to detect the wilt pathogen. In addition, video shots were taken of vermicompost and a pot study using tissue-cultured ginger and red ginger to detect the pathogen. We have recorded the narration for Dr. Kratky’s video using a female professional narrator. We have built a rough draft of Dr. Kratky’s material as an Adobe Premier project. This draft will be reviewed soon and revised if necessary.
- Figure 1. Agricultural research technicians, Mr. Christopher Bernabe and Mr. Earl Arakaki, are harvesting ginger grown in the trough system.
- Figure 3. Dr. Shintaku giving a talk to commercial growers on control of ginger wilt disease.
- Figure 4. Dr. Kratky demonstrating to backyard gardeners how to grow disease-free ginger in pots.
- Figure 10. Agricultural research technician Ms. Dayle Tsuha planting wilt-free ginger seed pieces in April 2011 in cooperating farmer’s field in Pepeekeo.
- Figure 5. Ginger planted using the trough method of hydroponic culture.
- Figure 6. Size of ginger seed pieces that were planted.
- Figure 7. Top row, left to right, 106 CFU to 102 CFU of R. solanacearum were added to soil, followed by enrichment (= 72 hrs) in selective medium. The PCR analysis showed the characteristic band that indicates the presence of the pathogen. Bottom row, this method is able to detect populations as low as 100 CFU.
- Figure 12. Preparation of ginger propagules for sowing by graduate student Mr. Paul Flessner.
- Figure 13. Inoculation of the pots by Dr. Arancon with R. solanacearum.
- Figure 2. Mr. Arakaki, Mr. Bernabe, and Dr. Kratky are exhibiting the harvested, hydroponically-cultured, wilt-free ginger.
- Figure 11. Two-month-old ginger.
- Figure 9. Soil samples from this ginger field were tested using Enrichment-PCR Although samples yielded positive results for R. solanacearum, this field had minimal crop losses due to bacterial wilt.
- Figure 8. Soil samples were collected from a ginger field in Onomea.
Impacts and Contributions/Outcomes
During the first year of this project, we have distributed 11 boxes of wilt-free ginger seed pieces to commercial growers of ginger. In addition, we have distributed over 20 lbs of clean ginger seed pieces to backyard gardeners. We have provided information to both commercial growers of ginger and backyard gardeners on the importance of planting wilt-free ginger seed pieces and multiplying them in pots or hydroponic culture to maintain a disease-free source of vegetative planting materials. We have begun field trials on cooperator’s farms to demonstrate the importance of planting clean ginger seed pieces into fields that have been tested using the Enrichment-PCR method. We have begun pot studies to determine whether vermicompost, vermicompost tea or Indigenous Microorganisms (IMO) could help to control ginger wilt. We have surveyed commercial ginger growers to determine their current cultivation practices and their interest in learning new methods to control ginger wilt. This will provide a base-line so that we can determine whether we have been successful in changing their practices in the future.
F. White and S. Miyasaka. 2011. Now is the time to prepare for planting ginger. West Hawaii Today.
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