Control of Bacterial Wilt Disease of Ginger through an Integrated Pest Management Program

Control of Bacterial Wilt Disease of Ginger through an Integrated Pest Management Program

Summary

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 3 of this project, we have: a) grown and distributed over 700 pounds of wilt-free ginger seed pieces to commercial growers, educators and backyard growers; b) completed our ginger wilt website that also houses all of the project’s educational videos; c) demonstrated that planting wilt-free ginger seed pieces into a field that tested free of R. solanacearum can result in good yields, although there are other pests that can reduce marketable yields; d) conducted a pot study on the use of vermicompost to control ginger wilt; e) started isolation of antagonistic microorganisms (e.g., Pseudomonas fluorescens and bacteriophages) that could provide bio-control of R. solanacearum; f) conducted an informational meeting for growers; g) published an extension paper on effects of shading on hydroponically grown ginger; h) published a second extension paper on a simplified method to multiply wilt-free ginger in pots; and i) completed a master’s thesis on the effects of soil amendments on the survival of R. solanacearum in Hawaiian soils.

Objectives/Performance Targets

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 the 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.

Accomplishments/Milestones

Ginger rhizomes that had been cleaned earlier of R. solanacearum during tissue-culture were multiplied in a disease-free medium using hydroponic culture during May through December 2012. They were harvested during January to February 2013, and 29 boxes (25 pounds each; total of over 700 pounds) were distributed to commercial or educational growers.

Informational meeting for growers

On March 13, 2013, we held an evening meeting for commercial ginger farmers, back yard ginger growers and students (Figure 1). There were 33 growers in attendance. Presentations were made by: a) Junior Extension Agent Ms. Sharon Motomura; b) Junior Researcher Ms. Ferol White; c) Dr. Susan C. Miyasaka; d) Dr. Linda Cox; and e) Dr. Bernard Kratky. Ms. Motomura gave an introductory talk about “Bacterial Wilt caused by Ralstonia solanacearum;” Ms. White talked about “Tissue-culturing ginger plantlets;” Dr. Miyasaka talked about “Planting wilt-free ginger seed pieces into wilt-free soil;” and Dr. Kratky talked about “The effects of aluminet shading on ginger grown in the same soil for two consecutive years.” Dr. Cox talked about various sustainable farming practices for ginger, conducted a survey of commercial growers, and then led a discussion of practices to control ginger wilt.

Effect of silicon on hydroponic production of ginger.

Currently in the greenhouse, we are conducting a second trial to determine whether the addition of silicon will improve hydroponic production of ginger. The first trial did not indicate any improvement of yield due to the addition of silicon.

Continued selection of tissue-cultured ginger

In addition, we are continuing the process of tissue-culturing disease-free ginger plants by growing them in pots, followed by selection for size and uniformity of rhizomes during hydroponic culture.

Extension articles published

Dr. Kratky published an article on how shading reduces yields of edible ginger grown using hydroponics (Kratky et al., 2013). Ms. White published an article on how to multiply wilt-free ginger using a simplified method of pot culture (White et al., 2013).

This objective has been completed. We have shown that our methodology of bacterial extraction from soil followed by Enrichment-PCR is sensitive, reliable and cost-effective. This methodology has been adopted by the Agricultural Diagnostic Service Center at the University of Hawaii at Manoa, in Hilo, Hawaii. The center now offers testing of R. solanacearum in soil and other media, in addition to Enzyme-Linked Immunoassay (ELISA) testing of tissue samples.

Wilt-free ginger seed pieces were planted on April 16, 2012 into a cooperator’s field that was tested to be wilt-free; rhizomes were harvested on February 11, 2013 (Figure 2). Total fresh weight yields in four plots ranged from 62,800 to 86,600 kg per ha (55,900 to 77,100 pounds per acre); marketable fresh weight yields ranged from 44,100 to 69,200 kg per ha (39,300 to 61,600 pounds per acre). The large percentage of unmarketable rhizomes (ranging from 21 to 30% of total fresh weight yield) were primarily due to damage caused by root-knot nematode (Meloidogyne incognita) (Figure 3) and red rot caused by the fungus Pyrenochaeta sp. (Figure 4). This field planting did not have any occurrence of ginger wilt that reduced fresh weight yields in one plot by 67% during the 2010-2011 season; however, other pests and diseases reduced fresh weight yields in all four plots by 21 to 30%.

Isolation of antagonistic microorganisms for potential control of bacterial wilt

Dr. Shintaku has isolated Pseudomonas fluorescens from field soil and is evaluating these bacterial cultures for antagonism towards R. solanacearum. In addition, they detected numerous placque-forming bacteriophages from infested soil and are evaluating these cultures for potential biological control of R. solanacearum.

Dr. Arancon and student Mr. Ronald Santos conducted a second pot study starting April 24, 2013 (Figure 5). Ginger propagules (approximately 2-4 ounces or 50 – 100 g) were sown directly into three gallon pots containing media amended at different rates with vermicomposts produced by Perionyx excavatus from food wastes and shredded paper [0 (control), 20, 40, 60, 80, 100 percent substitution rates]. Potting media (Promix No. 3) and vermicompost were screened for Ralstonia, showing no previous contamination. All pots were fertilized with inorganic and slow nutricote released fertilizers. Half the pots were inoculated with 109 CFU of R. solanacearum race 4 in five ml of water. All 12 treatments (six vermicompost rates x two pathogen rates) were replicated five times and laid out in a randomized complete block design. All pots were raised in a greenhouse with a controlled drip irrigation system to maintain moisture levels at field capacity at all times. Plant height and disease symptoms were recorded weekly. Symptoms of R. solanacearum were assessed on a scale of 0 (no symptoms) to 5 (100% of plant foliage showing symptoms). Initial ginger growth rate varied between treatments, with the highest yields and growth rates found between 20% and 60% vermicompost rates. The lowest yields and growth rates were found in the control and 100% vermicompost rates. This bell-shaped response of ginger growth to increasing vermicompost application rate was evident at both rates of pathogen applications. Initial assessments of the symptoms of R. solanacearum on foliage were evident on all plants grown on all vermicompost treatments, including the control and 100% vermicompost rate. A complete analysis of the data will be presented upon harvest, including rhizome yields from all treatments and other potting media characteristics.

Successful defense of Master’s thesis

Ms. Sharon Motomura’s thesis entitled “The Effects of Soil Amendments on the Survival of Ralstonia solanacearum in Hawaiian Soils” was accepted in April 2013. She graduated with a master’s degree in Tropical Conservation Biology and Environmental Science from the University of Hawaii – Hilo in May 2013. She has been hired by the University of Hawaii as a Junior Extension Agent for food crops on Hawaii Island; her areas of responsibility include ginger production.

At the grower’s meeting held in March 2013, Dr. Cox gave a brief presentation about the cultural practices that will assist producers in managing the spread of bacterial wilt of edible ginger. These practices included the following:

1) Site selection (wilt-free site, not down-slope from another ginger field);
2) Planting (avoid planting during wet weather);
3) Site preparation (use disease-free equipment and prepare site to drain well);
4) Planting disease-free seed pieces;
5) Limiting site traffic;
6) Using organic soil amendments;
7) Crop rotation (rotate ginger with crops that are not hosts to bacterial wilt);
8) Intercropping (interplant with crops that are not hosts to bacterial wilt);
9) Bio-fumigation (growing green manure crops);
10) Controlling other pests; and
11) Harvesting on-time.

Survey Results

Producers were then asked to complete a survey and Dr. Cox later analyzed the survey results. The producers that participated in the survey reported growing ginger for an average of 6.5 years. Respondents were either long time growers reporting ten or more years growing ginger or new producers with five or less years of ginger production experience. Of the 10 respondents, five were not employed off their farm. Of those employed off their farms, two were employed part-time and three were employed full time. All respondents were male with an average age of 42.3. Respondents were either younger than 39 or older than 53. Seventy percent of the respondents attended college and 50% reported having an associate, bachelor or master degree as the highest level of school that they completed. Respondents reported that five years ago, they planted 4.04 acres of ginger, on average. Only one respondent reported being affected by bacteria wilt at that time. Last year, respondents reported planting 4.26 acres of ginger and three reported being affected by bacterial wilt. Only one respondent reported no prior knowledge about bacteria wilt and the disease that it causes. Respondents reported on their use of the recommended practices aimed at managing the spread of bacterial wilt (see Table 1). Only intercropping was used by less than 50% of the respondents, with the other practices being used by at least 67% of the respondents. Seventy-five percent of the respondents said that they were interested in the testing service for seed pieces and soil offered by the Agricultural Diagnostic Service Center, which is part of the College of Tropical Agriculture and Human Resources. Interest in disease-free seed pieces was relatively low and the use of disease-free seed pieces was not among the most widely used cultural practices. Only three respondents were willing to purchase wilt-free seed pieces at an average of $5.33 per pound. Clearly, the majority of producers that responded to the survey are using the recommended practices. This survey result supports the project objective of increasing the adoption of the recommended cultural practices.

Discussion Results

The group discussion that followed the presentation during the March growers’ meeting focused on how producers managed bacterial wilt in their operations. Some growers reported that they seek out virgin land that will not be infected and wanted more access to such land. Other growers relied on natural and organic farming methods to increase the disease suppressiveness of their soil. Clearly these two approaches were the most commonly used among the producers.

We completed our ginger wilt website, which also houses all of the project’s educational videos: http://www.ctahr.hawaii.edu/dnn/gingerwilt/Home.aspx.  As of November 1, 2013, the number of views were: 313 views for the first YouTube video “The Ginger Project Overview,” 1,310 views for “Bernard Kratky’s Seed Production,” 149 views for “PCR Soil Testing,” 194 views for “Cultural Practice,” and 412 views for “Pepeekeo Harvest.”

Kratky, B.A., C. Bernabe, E. Arakaki, F. White, and S. Miyasaka. 2013. Shading reduces yields of edible ginger rhizomes grown in sub-irrigated pots. Coll. Trop. Agr. Human Resources, Univ. Hawaii, Honolulu, HI. Root Crops, RC-2. http://www.ctahr.hawaii.edu/oc/freepubs/pdf/RC-2.pdf . Motomura, S. 2013. The effects of soil amendments on the survival of Ralstonia solanacearum in Hawaiian soils. Univ. Hawaii – Hilo, Tropical Conservation Biology and Environmental Science. White, F., S. Motomura, S. Miyasaka, B.A. Kratky. 2013. A simplified method of multiplying bacterial wilt-free edible ginger (Zingiber officinale) in pots. Coll. Trop. Agr. Human Resources, Univ. Hawaii, Honolulu, HI. Plant Disease, PD-93. http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-93.pdf .

• Figure 1. Informational growers’ meeting held on 13 March 2013.
• Figure 2. Unsorted ginger rhizomes harvested from the field trial on 11 February 2013.
• Figure 3. Injury to ginger rhizomes caused by root-knot nematodes.
• Figure 4. Red rot of ginger rhizomes.
• Table 1. Practices used by commercial ginger growers to control bacterial wilt.
• Figure 5. Dr. Norman Arancon conducting a greenhouse study on the effect of vermicompost on ginger wilt.

Impacts and Contributions/Outcomes

During Year 3 of this project, we grew and distributed over 700 pounds of wilt-free ginger seed pieces to commercial growers, educators and backyard growers. We completed our ginger wilt website that also houses all of the project’s educational videos at: http://www.ctahr.hawaii.edu/dnn/gingerwilt/Home.aspx. This website is a resource for ginger growers to access current information on best methods to control ginger wilt. We demonstrated that planting wilt-free ginger seed pieces into a field that tested free of R. solanacearum can result in good yields, although there are other pests that can reduce marketable yields. We have shown that our methodology of bacterial extraction from soil followed by Enrichment-PCR is sensitive, reliable and cost-effective. This methodology has been adopted by the Agricultural Diagnostic Service Center at the University of Hawaii at Manoa, in Hilo, Hawaii. The center now offers testing of R. solanacearum in soil and other media, in addition to Enzyme-Linked Immunoassay (ELISA) testing of tissue samples. We conducted an informational meeting for growers and surveyed them for adoption of recommended practices to control ginger wilt. We published one extension paper on the effects of shading on hydroponically grown ginger and a second one on a simplified method to multiply wilt-free ginger in pots. Graduate student Ms. Sharon Motomura completed her master’s thesis on the effects of soil amendments on the survival of R. solanacearum in Hawaiian soils, and she has been hired as a Junior Extension Agent of Food crops, that includes ginger.

Collaborators: