Abstract
Fourteen species of ginger belonging to Zingiberaceae and Costaceae were evaluated for susceptibility to the bacterial wilt pathogen Ralstonia solanacearum (Rs) race 4 (ginger strains) by several methods of inoculation, including tests to simulate natural infection. Twelve of 14 species tested were highly susceptible to all strains of Rs race 4 upon stem inoculation, and susceptible plants wilted within 21 days. In contrast to previous reports that Rs strains from an invasive alien species, kahili ginger (Hedychium gardenarium), are nonpathogenic on ornamental gingers, the kahili ginger strain wilted both ornamental and edible ginger (Zingiber officinale) species within 21 days. Pour inoculation to the base of 11 plant species to simulate natural infection confirmed the ability of Rs to invade all the tested species without root wounds. Shampoo ginger (Zingiber zerumbet) was the most susceptible (wilted in 26 days) whereas pink ginger (Alpinia purpurata) and red ginger (A. purpurata) were the least susceptible and wilted in 71 and 76 days respectively. Pathogen survival in potting medium was evaluated by enumerating viable cells in effluent water from drenched pots with and without infected edible ginger after stem or rhizome inoculation. Ralstonia solanacearum survived in plant-free potting medium for 120 days and for 150 to 180 days in potting medium with infected edible ginger. The ability of Rs race 4 to infect many ginger species without wounding and to survive for long periods indicates that high risks will be incurred if the kahili ginger strain is inadvertently introduced from the forest reserves into ginger production areas.
Bacterial wilt, caused by Ralstonia solanacearum, causes severe wilt in many crops and is widely distributed in tropical, subtropical, and temperate regions of the world (Hayward, 1991, 1994; Kelman, 1953). Ralstonia solanacearum is classified into five races based on the hosts affected, and five biovars based on the ability to use or oxidize several hexose alcohols and disaccharides (Buddenhagen et al., 1962; Hayward, 1964). Race 1 strains (biovars 1, 3, and 4) are pathogenic to a broad range of hosts, including tomato (Solanum lycopersicum), tobacco (Nicotiana tabacum), and peanut (Arachis hypogaea); race 2 strains (biovars 1 and 3) infect banana (Musa acuminata), plantain (Musa paradisiaca), heliconia (Heliconia spp.), and other plants in the Musaceae family; race 3 strains (biovar 2) occur in cool upland areas in the tropics and cause severe wilt in potato (Solanaum tuberosum), tomato, and geranium (Geranium spp.); race 4 strains (biovars 3 and 4) infect ginger; and race 5 strains infect mulberry (Morus alba). The strains in the race 3 group are a select agent under the U.S. Agricultural Bioterrorism Protection Act of 2002 (U.S. Department of Agriculture, 2005). Pathogen diversity and the relationship among races, biovars, and phylotypes have been addressed recently (Alvarez, 2005; Fegan and Prior, 2005).
Edible ginger is a major vegetable and spice crop in Hawaii and in numerous locations in Australia, India, Indonesia, Jamaica, Japan, Malaysia, Nigeria, Sierra Leone, and the Philippines. Hawaii's farmers harvested 4.3 million lb of edible ginger during the 2005–06 season and the total farm value was estimated at $3.0 million (Hudson, 2006b). Plants belonging to the Zingiberaceae and Costaceae families are prevalent in the forests of Hawaii and are grown for cut flowers as well as for the “lei” industry, which is important because of its aesthetic and symbolic value to traditional customs and the local tourism industry. Hawaii's floriculture industry includes numerous economically important gingers from Zingiberaceae and Costaceae. The value of ginger cut flowers in Hawaii was $1.61 million in 2005–2006 (Hudson, 2006a), the predominant flowers being red ginger and pink ginger.
Bacterial wilt disease of edible ginger causes severe economic damage in many countries, including China, India, Indonesia, Japan, Malaysia, Mauritius, the Philippines, and the United States (Hawaii) (Alvarez et al., 2005; Kumar and Sarma, 2004). In Hawaii the disease was first reported on the island of Oahu in the early 1960s (Ishii and Aragaki, 1963; Quinon et al., 1964). Crop losses of edible ginger resulting from bacterial wilt exceeded 50% in 1998 and 1999 (Yu et al., 2003), and in 2005, the area harvested was reduced by 13% (Hudson, 2006b). In India, bacterial wilt is widespread on edible ginger and 100% yield losses have been reported (Dohroo, 1991; Mathew et al., 1979; Sarma et al., 1978; Sharma and Rana, 1999). Bacterial wilt has been reported for other members of the Zingiberaceae family, including Alpinia [Alpinia spp. (Hayward, 1994)], turmeric [Curcuma longa (Vellupillai, 1986)], galanga [Kaempferia galanga (He, 1986)], siam tulip (Curcuma alismatifolia), and mioga [Zingiber mioga (Tsuchiya et al., 2004, 2005)]. The pathogen was isolated from yellow ginger (Hedychium flavescens), white ginger (Hedychium coronarium), and kahili ginger plants growing at a single location on the island of Oahu in Hawaii (Aragaki and Quinon, 1965).
A ginger strain of Rs originally isolated from edible ginger has been used in a biocontrol program to reduce populations of kahili ginger, an invasive Zingiberaceae species in the tropical forests of Hawaii. The ginger strain was reportedly specific for kahili ginger and nonpathogenic to important ornamental gingers and common plant species in Hawaii (Anderson and Gardner, 1999). Based on this premise, the pathogen was introduced into Hawaiian forests, including Hawaii Volcanoes National Park on the island of Hawaii (Anderson and Gardner, 1996, 1999). However, other studies indicated ornamental ginger species were susceptible to the ginger strain (Paret et al., 2006). Thus, further studies were needed to assess the host range using a representative set of the Rs strains isolated from edible ginger and kahili ginger.
Survival of Rs races 1, 2, and 3 in water, soil–sand mixtures, and roots of symptomless solanaceous hosts has been documented (Elphinstone et al., 1998; Granada and Sequeira, 1983; Hayward, 1991), but there is a lack of information on survival of race 4 ginger strains in soil or potting media that are commonly used in Hawaii to produce rhizomes in bag culture (Hepperly et al., 2004). Because the industry has increased the use of potting media for production of ornamental gingers (Criley et al., 2005; Kuehny et al., 2005a, b), survival of Rs race 4 populations in the potting medium may be a factor in disease spread.
The objective of the current study was to assess the pathogenicity of Rs race 4 strains on plants belonging to the Zingiberaceae and Costaceae families, and to determine the ability of the pathogen to survive in a potting medium commonly used for ginger culture in Hawaii.
Materials and methods
Pathogenicity and host range studies.
Ralstonia solanacearum strains used for the experiments (A4515, A5192, and A3450) were selected from a larger collection of 55 well-characterized ginger and tomato strains to represent the genetic diversity observed in the local population (Yu et al., 2003). For host range studies we selected two edible ginger strains (A4515 and A5192; isolated from farms on the island of Hawaii), one kahili ginger strain (A4679; isolated from the island of Hawaii), and three tomato strains (A5370, A3450, and A5345; isolated from Hawaii, Trinidad, and Florida respectively). A nonpathogenic strain of Enterobacter cloacae (Ecl) A5149, an endophyte of the ginger rhizome (Nishijima et al., 2004), isolated from the island of Hawaii was used as a negative control. Bacterial strains were streaked on a modified tetrazolium chloride (TZC) medium (Norman and Alvarez, 1989) and incubated for 48 to 72 h. One to two colonies of Rs were transferred to 3.0 mL distilled water (dH2O), vortexed, and adjusted spectrophotometrically to A600nm = 0.1, which corresponds to 108 cfu/mL. Seeds of important ornamental gingers such as red ginger, pink ginger, white ginger, red ginger lily (Hedychium coccineum), siam tulip, white turmeric (Curcuma zedoaria), Globba (Globba spp.), yellow ginger, shampoo ginger, kahili ginger, beehive ginger (Zingiber spectabile), torch ginger (Etlingera elatior), and edible ginger belonging to the Zingiberaceae family; and spiral ginger (Costus barbatus), belonging to the Costaceae family, were collected from the Waimanalo Farm and Lyon Arboretum (University of Hawaii at Manoa, Manoa, HI) and planted in plastic pots (2 L) filled with potting medium (Sunshine Mix 4 Aggregate Plus; Sun Gro Horticulture Canada Ltd, BC, Canada). Two- to three-month-old plants were inoculated into the stem using a syringe to deliver 1.0 mL of the inoculum for each strain tested. Wilt symptoms including flagging and yellowing of leaves were recorded for 5 to 21 d after inoculation (DAI). The Ecl strain (A5149), used as a negative control, was inoculated at the same cell density as Rs strains. All strains were tested on one to nine plants per species depending on plant availability. The pathogenicity assessment was based on the percentage of severely wilted plants up to 21 DAI.
Simulation of natural infection by Ralstonia solanacearum race 4.
The ability of the pathogen to enter nonwounded roots was evaluated by a method to simulate natural infection. In our preliminary studies we noted that both ginger strains and kahili ginger strain wilted edible ginger and ornamental gingers 7 to 10 DAI (data not shown), and hence we selected Rs kahili ginger strain A4679 for our experiment. Twenty-five milliliters of the bacterial suspension containing ≈108 cfu/mL of the strain was poured onto the base of 2- to 3-month-old disease-free red ginger, pink ginger, white ginger, red ginger lily, yellow ginger, shampoo ginger, kahili ginger, beehive ginger, spiral ginger, shell ginger, and edible gingers (planted in 2-L plastic pots filled with Sunshine Mix 4 Aggregate Plus potting medium). Three plants of each ginger species were inoculated and monitored for wilting symptoms up to 3 months. Pathogen identity in infected tissue samples was confirmed using samples of Rs-specific immunostrips (Agdia Inc., Elkhart, IN). A 1-g plant sample (≈1 cm3), was excised from the collar region of the infected plant, surface sterilized with 0.6% sodium hypochlorite (NaOCl) for 2 min, rinsed with dH2O three times, and ground with a mortar and pestle in 1 mL dH2O. One hundred microliters of BEB1 buffer (Agdia Inc.) was mixed in a microfuge tube with 100 μL of the sample extract and tested with the immunostrip assay.
Survival of Ralstonia solanacearum race 4 in potting medium.
The potting medium used for bag culture (Hepperly et al., 2004) was inoculated by pouring 25 mL of an aqueous suspension containing 108 cfu/mL of ginger strain A4515 into each of four pots (2 L) containing single 5-month-old edible ginger plants. The plants were watered daily with 200 mL water for 240 d. Each day, 50 mL effluent water was collected and vortexed; a 1-mL subsample was taken to initiate a 10-fold dilution series (10−1 to 10−7); 100 μL of each dilution was plated onto modified SMSA medium (Engelbrecht, 1994) to assess the viable Rs population. The same method was used to assess the bacterial population in the potting medium. A 1-g soil sample was vortexed for 10 s in 10 mL dH2O, and allowed to settle. One milliliter of the supernatant was diluted to enumerate colony counts by the previously mentioned methods. The effluent water and potting medium samples from this experiment were analyzed until 240 DAI.
Three methods of inoculation—pouring inoculum into plant-free potting medium, stem inoculation, and rhizome inoculation—were compared in another experiment to determine the effect of the bacterial inoculation method (hence, plant part colonized by the pathogen) and subsequent release of Rs into the potting medium and effluent water. For the first inoculation method, 25 mL of an aqueous suspension containing 108 cfu/mL of the ginger strain of Rs A4515 was poured into pots (2 L) containing potting medium but no plants. For the second method, 1.0 mL Rs was inoculated into each stem (three stems inoculated per plant) with a syringe. For the third method, the rhizome was wounded with a scalpel, followed by pouring 27 mL inoculum into the base of the plant. Two pots (2L) were tested for each method; inoculated plants were 5 months old. The pots were watered daily with 200 mL water for 180 d. Fifty milliliters of effluent water was collected and vortexed each day. A 1-mL subsample was then taken to initiate a 10-fold dilution series (10−1 to 10−7); 100 μL of each dilution was plated onto modified SMSA medium to assess the viable Rs population. We also enumerated the bacterial population in potting medium by removing a 1-g soil sample from the pot, vortexing for 10 s in 10 mL dH2O, and allowing soil particles to settle for 5 min. One milliliter of the supernatant was then diluted to enumerate viable colonies.
Results and discussion
Pathogenicity and host range studies.
The race 4 ginger strains affected nearly all ornamental ginger species tested (Table 1). Symptoms ranged from flagging or wilting to plant death. Although the majority of the plants wilted within 10 DAI, the final pathogenicity assessment was recorded 21 DAI, at which time all affected plants were severely wilted or dead. The Ecl negative control did not wilt any of the plants tested (Fig. 1). Of the three race 1 tomato strains tested, strain A5370 (isolated from tomato in Hawaii) wilted nearly all ginger species, whereas strains A3450 and A5345 (isolated from tomato in Trinidad and Florida respectively) did not wilt any of the ginger species. Most of the infected ginger plants showed moderate to complete wilting of leaves, and none of the ginger species were resistant to the Rs race 4 strains, with the possible exception of torch ginger (Table 1), which showed no symptoms. However, only a few plants of this species were available for testing, so results are inconclusive. In contrast to previously published data (Anderson and Gardner, 1999), our results show that the race 4 strains are pathogenic to many ornamental gingers.
Pathogenicity of Ralstonia solanacearum (Rs) on various species in Zingiberaceae and Costaceae.
Symptoms on six ginger species 5 to 21 d after inoculation (DAI) with Ralstonia solanacearum strains (left to right) A4515, A5192, A5370, and Enterobacter cloacae strain A5149 (negative control). Symptoms noted are yellowing, flagging, and wilting of leaves. From top: row 1, white ginger; row 2, red ginger lily; row 3, yellow ginger; row 4, kahili ginger; row 5, beehive ginger; row 6, shampoo ginger.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Symptoms on six ginger species 5 to 21 d after inoculation (DAI) with Ralstonia solanacearum strains (left to right) A4515, A5192, A5370, and Enterobacter cloacae strain A5149 (negative control). Symptoms noted are yellowing, flagging, and wilting of leaves. From top: row 1, white ginger; row 2, red ginger lily; row 3, yellow ginger; row 4, kahili ginger; row 5, beehive ginger; row 6, shampoo ginger.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Symptoms on six ginger species 5 to 21 d after inoculation (DAI) with Ralstonia solanacearum strains (left to right) A4515, A5192, A5370, and Enterobacter cloacae strain A5149 (negative control). Symptoms noted are yellowing, flagging, and wilting of leaves. From top: row 1, white ginger; row 2, red ginger lily; row 3, yellow ginger; row 4, kahili ginger; row 5, beehive ginger; row 6, shampoo ginger.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Spread of Rs from infected siam tulip to the edible ginger and, subsequently, to mioga fields in the Kochi prefecture of Japan was well documented from 1995 to 1999 (Tsuchiya et al., 2005). Our findings that the Rs race 4 strain from kahili ginger is pathogenic to numerous plant species belonging to the Zingiberaceae and Costaceae families thus has broad implications in Hawaii because of the reported use of this strain as a biocontrol agent for invasive kahili ginger in forest reserves.
Simulation of natural infection by Ralstonia solanacearum race 4.
The kahili ginger strain of Rs (A4679) wilted all 11 ginger species tested when plants were inoculated without wounding (Fig. 2). Shampoo ginger, beehive ginger, spiral ginger, and kahili ginger were highly susceptible and died within 38 d. Shampoo ginger was the most susceptible and wilted in 26 d, whereas pink ginger was the least susceptible, wilting in 76 d. The presence of the pathogen in stem sections of each species that showed wilting was confirmed by the immunostrip assay. The observation that the pathogen invaded the host even in the absence of a stem or root wound confirms its ability to enter through natural openings. This suggests that the pathogen could spread naturally from the inoculated forest plants to edible ginger and ornamental ginger production areas.
Number of days for severe wilting (100% dead plants) of Zingiberaceae and Costaceae plants in tests to simulate natural infection by pouring Ralstonia solanacearum race 4 kahili ginger strain A4679 into the potting medium at the base of the plant. RG, red ginger; PG, pink ginger; WG, white ginger; RGL, red ginger lily; YG, yellow ginger; SG, shampoo ginger; KG, kahili ginger; BG, beehive ginger; SpG, spiral ginger; ShG, shell ginger; EG, edible ginger. The error bars represent sd from the average of three plants.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Number of days for severe wilting (100% dead plants) of Zingiberaceae and Costaceae plants in tests to simulate natural infection by pouring Ralstonia solanacearum race 4 kahili ginger strain A4679 into the potting medium at the base of the plant. RG, red ginger; PG, pink ginger; WG, white ginger; RGL, red ginger lily; YG, yellow ginger; SG, shampoo ginger; KG, kahili ginger; BG, beehive ginger; SpG, spiral ginger; ShG, shell ginger; EG, edible ginger. The error bars represent sd from the average of three plants.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Number of days for severe wilting (100% dead plants) of Zingiberaceae and Costaceae plants in tests to simulate natural infection by pouring Ralstonia solanacearum race 4 kahili ginger strain A4679 into the potting medium at the base of the plant. RG, red ginger; PG, pink ginger; WG, white ginger; RGL, red ginger lily; YG, yellow ginger; SG, shampoo ginger; KG, kahili ginger; BG, beehive ginger; SpG, spiral ginger; ShG, shell ginger; EG, edible ginger. The error bars represent sd from the average of three plants.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Long-term survival of Ralstonia solanacearum race 4 in potting medium.
Ralstonia solanacearum race 4 survived for 180 DAI and was detected at low levels for 150 to 180 DAI in effluent water (Fig. 3). The pathogen was also detected in potting medium 180 DAI (Fig. 4).
Recovery of Ralstonia solanacearum (Rs) race 4 from effluent water of pots containing infected edible ginger. The edible ginger plants were rhizome wounded and poured with Rs strain A4515, and effluent water from the pots was routinely collected and analyzed to assess the bacterial population for a period of 240 d. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of four samples and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) race 4 from effluent water of pots containing infected edible ginger. The edible ginger plants were rhizome wounded and poured with Rs strain A4515, and effluent water from the pots was routinely collected and analyzed to assess the bacterial population for a period of 240 d. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of four samples and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) race 4 from effluent water of pots containing infected edible ginger. The edible ginger plants were rhizome wounded and poured with Rs strain A4515, and effluent water from the pots was routinely collected and analyzed to assess the bacterial population for a period of 240 d. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of four samples and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Survival of Ralstonia solanacearum (Rs) race 4 in potting medium containing infected edible ginger. The edible ginger plants were rhizome wounded and poured with Rs strain A4515, and potting medium from these pots was collected and analyzed to assess the bacterial population for a period of 240 d. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of four samples and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Survival of Ralstonia solanacearum (Rs) race 4 in potting medium containing infected edible ginger. The edible ginger plants were rhizome wounded and poured with Rs strain A4515, and potting medium from these pots was collected and analyzed to assess the bacterial population for a period of 240 d. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of four samples and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Survival of Ralstonia solanacearum (Rs) race 4 in potting medium containing infected edible ginger. The edible ginger plants were rhizome wounded and poured with Rs strain A4515, and potting medium from these pots was collected and analyzed to assess the bacterial population for a period of 240 d. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of four samples and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
In the subsequent experiment, which tested the survival of pathogen after three inoculation methods, the population of the pathogen was no longer recovered from effluent water of plant-free potting medium at 30 d, in comparison with recovery of high populations from effluent water of pots containing stem- and rhizome-inoculated plants (Fig. 5). High populations of Rs were released from infected plants during the early stages of disease development. The pathogen was recovered from effluent water up to 150 DAI with stem- and rhizome-inoculated plants, and 60 DAI from effluent water of plant-free potting medium (Fig. 6). However when potting medium was sampled instead of effluent water, the pathogen survived with stem- or rhizome-inoculated plants for 150 DAI and for 120 DAI in plant-free potting medium (Fig. 7). High populations of Rs were noted when potting medium samples were analyzed instead of effluent water from these pots for all three methods of inoculation. The survival of the pathogen in the absence of host plant debris for 4 months is of particular concern to local growers, because it is an indication that the pathogen may persist in an ecosystem even after infected plants are removed. Pathogen-free edible ginger seed rhizomes are currently produced in potting medium in Hawaii (Hepperly et al., 2004), and many ornamental flower growers use this potting medium for production. The ability of Rs to survive in this medium after it is introduced presents risks to both the edible ginger and floriculture ginger industries. Further studies of long-term survival of Rs in volcanic soil and ginger field soil are in progress.
Recovery of Ralstonia solanacearum (Rs) 1 to 30 d after inoculation from effluent water after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs, and this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) 1 to 30 d after inoculation from effluent water after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs, and this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) 1 to 30 d after inoculation from effluent water after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs, and this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) for 180 d from effluent water after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs; this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) for 180 d from effluent water after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs; this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Recovery of Ralstonia solanacearum (Rs) for 180 d from effluent water after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs; this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Survival of Ralstonia solanacearum (Rs) race 4 in potting medium for 180 d after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs; this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Survival of Ralstonia solanacearum (Rs) race 4 in potting medium for 180 d after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs; this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Survival of Ralstonia solanacearum (Rs) race 4 in potting medium for 180 d after inoculation with three methods: plant-free potting medium (▲), stem inoculation (◆), and rhizome inoculation (■). Plant-free potting medium represents pots filled with potting media and with no plants that were inoculated with Rs; this represents the free-living bacteria. Stem inoculation represents pots with edible ginger, inoculated on the stem with Rs. Rhizome inoculation represents pots with edible ginger, and the rhizome was wounded, followed by pouring Rs inoculum. Viable cells are reported as log colony-forming units per milliliter (1 cfu/mL = 29.5735 cfu/fl oz). Each point is the average of two samples per treatment and the error bars indicate sd from the mean. The strain tested is Rs race 4, A4515.
Citation: HortTechnology hortte 18, 1; 10.21273/HORTTECH.18.1.90
Conclusions
The results of pathogenicity tests, simulation of natural infection, and long-term survival studies indicate that R. solanacearum race 4 can affect negatively both the edible ginger and floriculture ginger industries in Hawaii. Use of Rs as a biocontrol agent against an invasive ginger species is a concern to local agriculturalists, and a thorough evaluation of its spread, and survival on weeds and in watercourses is needed before any application in forest reserves.
Literature cited
Alvarez, A.M. 2005 Diversity and diagnosis of Ralstonia solanacearum 437 448 Allen C., Prior P. & Hayward A.C. Bacterial wilt disease and the Ralstonia solanacearum species complex APS Press St. Paul, MN
Alvarez, A.M., Trotter, K.J., Swafford, M.B., Beresteky, J., Yu, Q., Ming, R., Hepperly, P.R. & Zee, F. 2005 Characterization and detection of Ralstonia solanacearum strains causing bacterial wilt of ginger in Hawaii 471 478 Allen C., Prior P. & Hayward A.C. Bacterial wilt disease and the Ralstonia solanacearum species complex APS Press St. Paul, MN
Anderson, R.C. & Gardner, D.E. 1996 Preliminary evaluation of Pseudomonas solanacearum as a potential biological control agent of the alien weed kahili ginger (Hedychium gardenarium) in Hawaiian forests Nwsl. Hawaiian Bot. Soc. 35 3 6
Anderson, R.C. & Gardner, D.E. 1999 An evaluation of the wilt-causing bacterium Ralstonia solanacearum as a potential biological control agent for the alien kahili ginger (Hedychium gardenarium) in Hawaiian forests Biol. Control 15 89 96
Aragaki, M. & Quinon, V.L. 1965 Bacterial wilt of ornamental gingers (Hedychium spp.) caused by Pseudomonas solanacearum Plant Dis. Rptr. 49 378 379
Buddenhagen, I.W., Sequeira, L. & Kelman, A. 1962 Designation of races of Pseudomonas solanacearum Phytopathology 52 726 (abstr.).
Criley, R.A., Meyer, J., Paz, M.D.P. & Kuehny, J.S. 2005 Tropical gingers as new flowering potted plants 28 32 Leonhardt K.W. & Nakao P. Proc. 2004 Hawaii Floriculture Conference College of Tropical Agriculture and Human Resources, University of Hawaii P-04/05.
Dohroo, N.P. 1991 New record of bacterial wilt of ginger in Himachal Pradesh 16 Proc. Pathological problems of economic crop plants and their management, Indian Phytopathol Soc. North Zone Meet, Central Potato Res. Inst Shimla, India April 29–30
Elphinstone, J.G., Hennessy, J.K. & Stead, D.E. 1998 Detection of Ralstonia solanacearum in potato tubers, Solanum dulcamara and associated irrigation water 133 139 Prior P., Allen C. & Elphinstone J. Bacterial wilt disease: Molecular and ecological aspects Springer-Verlag Berlin
Engelbrecht, M. 1994 Modification of a semi-selective medium for the isolation and quantification of Pseudomonas solanacearum Austral. Centre Intl. Agr. Res. Bacterial Wilt Nwsl. 10 3 5
Fegan, M. & Prior, P. 2005 How complex is the Ralstonia solanacearum species complex? 449 461 Allen C., Prior P. & Hayward A.C. Bacterial wilt disease and the Ralstonia solanacearum species complex APS Press St. Paul, MN
Granada, G.A. & Sequeira, L. 1983 Survival of Pseudomonas solanacearum in soil, rhizosphere, and plant roots Can. J. Microbiol. 29 433 440
Hayward, A.C. 1964 Characteristics of Pseudomonas solanacearum J. Appl. Bacteriol. 27 265 277
Hayward, A.C. 1991 Biology and epidemiology of bacterial wilt caused by Pseudomonas solanacearum Annu. Rev. Phytopathol. 29 65 87
Hayward, A.C. 1994 The hosts of Pseudomonas solanacearum 9 24 Hayward A.C. & Hartman G.L. Bacterial wilt: The disease and its causative agent, Pseudomonas solanacearum CAB International Wallingford, UK
He, L.Y. 1986 Bacterial wilt in the People's Republic of China. Proc. Bacterial Wilt Disease in Asia and the South Pacific Austral. Centre Intl. Agr. Res. 13 40 48
Hepperly, P., Zee, F., Kai, R., Arakawa, C., Meisner, M., Kratky, B., Hamamoto, K. & Sago, D. 2004 Producing bacterial wilt-free ginger in greenhouse culture Soil and Crop Management, Cooperative Extension Service, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa 8 1 6
Hudson, M.E. 2006a Annual summary: Hawaii flowers and nursery products U.S. Dept. Agr., Natl. Agr. Stat. Serv., Hawaii Field Office, Hawaii Dept. Agr Honolulu, HI
Hudson, M.E. 2006b Annual summary: Hawaii ginger root U.S. Dept. Agr., Natl. Agr. Stat. Serv., Hawaii Field Office, Hawaii Dept. Agr Honolulu, HI
Ishii, M. & Aragaki, M. 1963 Ginger wilt caused by Pseudomonas solanacearum E.F. Smith Plant Dis. Rptr. 47 710 713
Kelman, A. 1953 The bacterial wilt caused by Pseudomonas solanacearum North Carolina Agr. Expt. Sta. Tech. Bul. 99 194
Kuehny, J.S., Criley, R.A. & Paz, M.D.P. 2005a Jump-starting ginger Ornamental Outlook 14 18 19
Kuehny, J.S., Criley, R.A. & Paz, M.D.P. 2005b The joy of gingers Ornamental Outlook 14 16 17
Kumar, A. & Sarma, Y.R. 2004 Characterization of Ralstonia solanacearum causing bacterial wilt in ginger Indian Phytopathol. 57 12 17
Mathew, J., Abraham, K., Indrasenan, G. & Samuel, M. 1979 A new record of bacterial wilt of ginger incited by Pseudomonas solanacearum E.F. Smith from India Curr. Sci. 48 213 214
Nishijima, K.A., Alvarez, A.M., Hepperly, P.R., Shintaku, M.H., Keith, L.M., Sato, D.M., Bushe, B.C., Armstrong, J.W. & Zee, F. 2004 Association of Enterobacter cloacae with rhizome rot of edible ginger in Hawaii Plant Dis. 88 1318 1327
Norman, D. & Alvarez, A.M. 1989 A rapid method for presumptive identification of Xanthomonas campestris pv. dieffenbachiae and other xanthomonads Plant Dis. 73 654 658
Paret, M.L., de Silva, A.S. & Alvarez, A.M. 2006 Ornamental plants in the Zingiberaceae and Costaceae families susceptible to Ralstonia solanacearum, race 4 biovar 4 Phytopathology 96 S89
Quinon, V.L., Aragaki, M. & Ishii, M. 1964 Pathogenicity and serological relationship of three strains of Pseudomonas solanacearum in Hawaii Phytopathology 54 1096 1099
Sarma, Y.R., Indrasenan, G. & Rohini, I. 1978 Bacterial wilt of ginger (Zingiber officinale) Indian Arecanut Spices Cocoa J. 2 29 31
Sharma, B.K. & Rana, K.S. 1999 Bacterial wilt: A threat to ginger cultivation in Himachal Pradesh Plant Dis. Res. 14 216 217
Tsuchiya, K., Sawada, H., Yoshida, T. & Takahashi, M. 2004 Invasion, transmission, and adaptation of new race strains of Ralstonia solanacearum, causal pathogens of bacterial wilt of Zingiberaceae plants in Japan Phytopathology 94 S104 (abstr.).
Tsuchiya, K., Yano, K., Horita, M., Morita, Y., Kawada, Y. & d'Ursel, C. 2005 Occurrence and epidemic adaptation of new strains of Ralstonia solanacearum associated with Zingiberaceae plants under agro-ecosystem in Japan 463 469 Allen C., Prior P. & Hayward A.C. Bacterial wilt disease and the Ralstonia solanacearum species complex APS Press St. Paul, MN
U.S. Department of Agriculture 2005 U.S. Agricultural Bioterrorism Protection Act of 2002: Possession, use, and transfer of biological agents and toxins, 7 CFR part 331 and 9 CFR part 121 Fed. Register 70 52
Vellupillai, M. 1986 Bacterial wilt in Sri Lanka. Proc. Bacterial Wilt Disease in Asia and the South Pacific Austral. Centre Intl. Agr. Res. 13 57 64
Yu, Q., Alvarez, A.M., Moore, P.H., Zee, F., Kim, M.S., deSilva, A.S., Hepperly, P.R. & Ming, R. 2003 Molecular diversity of Ralstonia solanacearum isolated from ginger in Hawaii Phytopathology 93 1124 1129
