Genetic Conservation and Importance of Ginger in Ethiopia

Abstract

Ethiopia has conducive agro-ecology and is capable to produce various spices, including ginger. Spices research in Ethiopia with various limitations did a lot on ginger technology development and achieved significant results. Acquiring significant number of ginger accessions from domestic and foreign source, variety development, pre and postharvest management practices including protection parts are available. Ethiopians have high spices consumption culture and significant volume of ginger used locally and this can be considered as one of the opportunities. In addition to this, there is significant export of ginger and generating 22.6 million USD in 2008. Though there is such potential for production and export earnings, still there are lots of challenges that keep the performance of the commodity very low. The local grouping of the ginger materials, and the selection and release of two ginger cultivars from Jimma Agricultural Research center/Tepi Agricultural Research Sub Center, confirmed that the country has a high diversity of germplasm. This chapter reviews the ginger germplasm enhancement, conservation, variety development, status of ginger breeding, diversity of ginger, ginger tissue culture, ginger biotechnology.

1. Introduction

Ginger (Zingiber officinale Rosc) is a monocotyledonous, herbaceous, and tropical plant belonging to the family, Zingiberaceae. It has a long and well-documented history of both culinary and medicinal use throughout the world history, especially in medical care in China, India, and Japan. Ginger is a self-incompatible plant that is characterized by high rates of infertility; thus, its genetic diversity occurs through processes of mutation and natural selection alone. Since ginger is one of the major spices, knowing the diversity in depth can contribute to conservation and its use in breeding programs [1]. In Ethiopia, ginger has been used as a fragrance, carminative, and stimulant and has become a major spice in both the local and export markets. Arabs brought ginger from India to East Africa in the thirteenth century [2], and ginger has since been known in Ethiopia and is cultivated primarily in the humid regions of the Southern Nations (SNNPRS). To a lesser extent, ginger production has expanded to Western Oromia and in Amhara region chilga areas. Commercial production of ginger by smallholder farmers is practiced in South region Kambata-Tambaro, Wolaita, and Hadiya zones. According to statistics from the Ministry of Agriculture and Rural Development, 99% of crop production occurred in the Southern Nations, Nationalities, and People’s States [3, 4].

Ginger prefers a warm and humid climate, and most soils have sufficient water retention and ventilation. It is cultivated in the tropics up to 1500 m above sea level, but partial shade also increases its yield. The base temperature requirement for ginger is 13°C and the upper limit is 32°C/27°C (day/night), whereas the favorable range is 19–28°C. The optimum soil temperature for germination is between 25 and 26°C, and 27.5°C, which is required for growth. Ginger research has been done in Ethiopia for many years. Jimma Agricultural Research Center (JARC) under its sub-center (before), Tepi Agricultural Research Sub-center was responsible for improving ginger’s genetic resources and developing varieties. In this responsibility and action, JARC officially launched two ginger varieties called Yali and Boziab in 2007. The varieties give high yield (200–250 Q/ha of fresh rhizome). Essential oil (1.8–2.5% v/w) and oleoresin (6.01–8.22% w/w) content from these varieties satisfy quality standards. Various technologies on agronomic production and seed rhizome and dried yield rhizome were generated.

Three types of the ginger product known as fresh rhizome, dried rhizome, and extracted rhizome are supplied to the market. Ethiopia used to export fresh ginger to Egypt, Saudi Arabia, and Yemen. Fresh Ethiopian ginger has been reported to be an excellent product with good color and quality and long shelf life [2]. Dried ginger is Ethiopia’s most popular ginger product and is mass exchanged by all market participants at various stages of marketing, from local assembly to the export market. The third type of ginger product on the market is extracted ginger products which include powdered ginger, essential oils, oleoresin, etc. [3].

Ginger production and productivity in Ethiopia was challenged by a number of factors; shortage of varieties with full production packages, postharvest practices, lack of value addition, and poor/limited large-scale investments. Demand for ginger increasing in the domestic and foreign market. Ethiopia’s diverse climate and soil types greatly contribute to ginger production and these all are good opportunities to conserve ginger genetic resources, improve production and productivity and bring significant income and hard currency for the country.

2. Breeding and genetics

2.1 Germplasm enhancement

The first step in doing good breeding research is to obtain a sufficient number of accessions in the relevant or target crop. To achieve this goal in the case of ginger, two key tactics were used: collecting from domestic sources and introduction from abroad. The spices research team started before four and half decades since the start of coffee research as diversification in Jimma Agricultural Research Center (JARC). A few years later, the introduction of ginger accessions began, and at the same time, collecting from several possible ginger-growing sites across the country was undertaken. The collection is always conducted in collaboration with the expertise from Institute of Biodiversity and Conservation (IBC). The significant number of ginger accessions was attained from this activity except that it has been challenged by bacterial wilt of ginger.

2.2 Conservation

Collected and introduced accessions of ginger were maintained in research plots of Jimma Research Center and mainly in Tepi Agricultural Research Sub-Center before, currently upgraded to Tepi Agricultural Research Center. Despite the threat of the ginger bacterial wilt disease, which destroyed more of the collections, more than 90 accessions have been gathered and some introduced since the research began. Ginger germplasms that have been collected and introduced are evaluated using a variety of criteria. The table below (Table 1) displays a sample of the accessions and their sources. We recently established 45 collections in the JARC research plot, which are being used for various research purposes related to ginger bacterial wilt management.

No.	Entry code	Origin	No.	Entry code	Origin
1	Ging.28/79	Mauritius	24	Ging.30/86	Collected
2	Ging.36/79	Australia	25	Ging.24/86	Collected
3	Ging.41/79	Riodjenero	26	Ging.85/86	Collected
4	Ging.316/73	Surinam	27	Ging.45/86	Collected
5	Ging.296/79	Rafinufa	28	Ging.75/00	Collected
6	Ging.305/73	Collected	29	Ging.61/00	Collected
7	Ging.25/86	Collected	30	Ging.307/72	Collected
8	Ging.28/86	Collected	31	Ging.087/00	Collected
9	Ging.61/86	Collected	32	Ging.15/79	Rafinufa
10	Ging.10/86	Collected	33	Ging.38/79	Australia
11	Ging.48/86	Collected	34	Ging.39/79	Australia
12	Ging.57/86	Collected	35	Ging.180/73	Collected
13	Ging.84/86	Collected	36	Ging.181/73	Collected
14	Ging.70/00	Collected	37	Ging.47/86	Collected
15	Ging.74/00	Collected	38	Ging.53/86	Collected
16	Ging.41/00	Collected	39	Ging.58/86	Collected
17	Ging.16/79	Rafinufa	40	Ging.59/86	Collected
18	Ging.37/79	Australia	41	Ging.56/86	Collected
19	Ging.40/79	Riodjenero	42	Ging.54/86	Collected
20	Ging.141/73	Australia	43	Ging.26/86	Collected
21	Ging.190/73	Collected	44	Ging.86/00	Collected
22	Ging.29/86	Collected	45	Ging.63/00	Collected
23	Ging.52/86	Collected

Table 1.

Germplasms and varieties of ginger in Ethiopia.

Sources: [4, 5].

2.3 Variety development

Rigorous adaptation test of ginger accessions has been conducted in different agro-ecologies, suitable propagation parts, and status to sprouting and subsequent field performance and rhizome yield. Pest reactions and quality were some of the traits used in the evaluation. According to the results obtained [5, 6], the varieties were proved promising and widely employed by users and distributed throughout the potential producing areas. Further evaluation continued to achieve better varieties. Ginger bacteria diseases have been devastating to the materials. This time, more than 45 accessions of ginger are being maintained for future disease management research [7].

2.4 Status of ginger breeding

In Ethiopia, ginger breeding was started as a part of coffee diversification in JARC, since the inception of coffee research in 1969 [8]. Some preliminary research on local and introduced ginger germplasms indicated the existence of genetic variability in their morphological traits, rhizome yield, oil and oleoresin contents [9]. High variability was observed among ginger cultivars and/or accessions for plant height, rhizome yield, oil content, and oleoresin. According to Momina et al. [8] there was high genetic diversity in local ginger germplasms.

2.5 Diversity of ginger in Ethiopia

The introduction of ginger to Ethiopia for a long time (thirteenth century), made the country to have diverse genetic resources. Variability (in morphology and quality) was reported by Momina et al. [8]. Such status of diverse genetic resources is crucial for breeding purpose. Southern Nation and Nationalities regional state are often understood to be major areas of ginger germplasms. Indicating that there is high diversity of ginger in Southern Nation and Nationalities regional state Wolaita zone farmers group local varieties into Masculine and Feminine [3]. Also, farmers in Kambata-Tambaro recognized one local genotype called Hargema (Figure 1). There is some similarity among these materials.

Figure 1.

Feminine Wolaita (left), Masculine Wolaita (right). Source: [3].

Production of local ginger materials in Wolaita and Hadiya zones has been since time immemorial and various local landraces were common in different areas (Bilbo and Volvo (Figure 2) introduced to the area recently (in 1998). According to Geta and Kifle [3] seed transfer and distribution as informal ways (farmer-to-farmer) remained very common.

Figure 2.

Subterranean parts of Bilbo with two taproots (left), Volvo with a single taproot (right). Source: [10].

The local grouping of the ginger materials discussed here (Table 2), and the selection and release of two ginger cultivars from Jimma Agricultural Research center/Tepi Agricultural Research Sub Center, confirmed that the country has a high diversity of the germplasm. This needs further research to exploit ginger genotypes with different quality parameters and special traits.

Category	Vernacular	Unique characteristics	Common characteristics
Local	Feminine “Wolaita”	Highly palmated rhizomes Large-sized rhizomes More productive	Drought tolerant Less fertilizer requirement Long postharvest storability (up to 10 years) Suitable for perennial harvesting Less susceptible to mold development when subject to sun-drying at wet weather condition More preferred to dry planting
	Masculine “Wolaita”	High fiber content Highly pungent	High harvesting cost Less productive/unit area Large number of prominent roots High cost of root trimming during rhizome drying
	“Hargema” (Kambatigna)	Highly pungent Large number of prominent roots (‘Amesalgier’)	Late maturing Less preferred for fresh rhizome market Low dry matter content (high degree of shrinkage upon drying) Fast rate of drying Less attractive appearance Much weight loss with prolonged storage period
Introduced	“Bilbo” (Wolaitigna and Kambatiga)	One prominent root/digitally palmated rhizome	Drought tolerant Soil exhaustive Short postharvest storability Less suitable for perenniated harvesting, dries up with extended dry season as a result of less number of prominent roots Highly susceptible to mold development when subject to sun-drying at wet weather condition Less preferred to dry planting Easy for manual harvesting; low harvesting cost More productive/unit area Low number of prominent roots Low cost of root trimming during rhizome drying
	“VolVo” (Wolaitigna and Kambatigna)	2–3 prominent/tap roots/digitally palmated rhizomes Relatively highly pungent	Early maturing Highly preferred at fresh rhizome market High dry matter content (less degree of shrinkage upon drying) Slow rate of drying Highly attractive appearance High demand at the central market Easily peeling off of the skin at frequent overturning during the process of drying, which in turn, increases its susceptibility to mold development Minimum weight loss upon prolonged storage period

Table 2.

Characteristics of different ginger vernaculars cultivated in SNNPRS.

Source: [10].

2.6 In vitro propagation for maintenance of ginger

Propagation of two ginger cultivars by tissue culture is one of the strategy to improve production and productivity by overcoming ginger bacterial wilt. The study was carried out with the objective of assessing the potential of axillary buds and shoot tips as explant sources and determination of suitable growth regulators for in vitro propagation. MS medium with four levels of benzyl adenine (BA) and kinetin was used for shoot multiplication in combination with two explant sources. Shoot tip explants on 2 mg l⁻¹ BA and 1.2 mg l⁻¹ kinetin was found to be better than other explant-media combinations. Consecutively, the plantlets developed an average of 8.75 roots within 4 weeks of the culture period and performed well in greenhouse acclimatization and field operations. In vitro propagation of the Yali and Boziab was proved possible with this explant and media combinations. Parameters such as number of leaves and dry weight of plantlets regardless of the varietal difference in comparison to axillary bud was higher. Similarly, shoots cultured on MS medium with 1 mg l⁻¹ NAA alone developed vigorous roots. Plantlets produced by this propagation protocol were successfully acclimatized within 4 weeks of hardening. The acclimatization procedure has been supported with the application of shade nets (at 30 and 70% shade level) and polythene under the greenhouse condition. Subsequently, the seedlings have survived well under field conditions [12].

2.6.1 Ginger tissue culture

In Ethiopia, infection with Ralstonia solanacearum has resulted in significant losses of ginger rhizomes. To have successful ginger cultivation, disease-free planting material generation is required and practiced. Plant tissue culture technology has proven to be effective in the commercial production of pathogen-free plants as well as the preservation of rare and endangered species’ genetics (Table 3). The initial surface sterilization experiment was effective when 0.7–1.5 cm shoot tips were treated with 70% ethanol for 5 min followed by double sterilization with 5% active chlorine concentration of local bleach (Clorox), for 15 min under aseptic condition. This treatment cleans bacterial contamination more than 95%. Also, antibiotics (tetracycline and streptomycin) reduced the contaminants thereby increase the survival rate of the plantlets.

Antibiotics	Antibiotics concentration (mg/l)	Shoot number mean ± SD
Control	00 mg/l	8.00 ± 2.71abc
Ampicillin	130 mg/l	11.51 ± 1.29a
Ampicillin	160 mg/l	8.75 ± 1.70abc
Ampicillin	200 mg/l	6.74 ± 1.70bc
Ampicillin	250 mg/l	7.00 ± 1.40bc
Gentamaycine	130 mg/l	6.00 ± 1.40c
Gentamaycine	160 mg/l	5.70 ± 1.50c
Gentamaycine	200 mg/l	5.75 ± 1.70c
Gentamaycine	250 mg/l	6.75 ± 0.50bc
Streptomycin	130 mg/l	6.75 ± 1.25bc
Streptomycin	160 mg/l	7.00 ± 0.00bc
Streptomycin	200 mg/l	6.60 ± 0.57bc
Streptomycin	250 mg/l	6.50 ± 0.57bc
Tetracycline	130 mg/l	8.00 ± 1.5bc
Tetracycline	160 mg/l	7.70 ± 0.81bc
Tetracycline	200 mg/l	7.20 ± 0.50bc
Tetracycline	250 mg/l	6.00 ± 1.15c

Table 3.

Antibiotics treatment of plant material results in shoots free from R. solanacearum.

Numbers are mean and SD of four replicates (four plant in each culture jars).

Means followed by the same letter within a column are not significantly different by Tukey’s test at α = 0.05%.

Source: [11].

2.6.2 Ginger biotechnology

Consistent and increasing demand for clean planting material from improved cultivars of ginger is persistent. Providing the required through indigenous techniques of propagation is incompetent owing to inefficient production and transmission of disease. In this regard, to evaluate the potential of shoot tips and axillary buds and to determine the appropriate growth regulators for propagation In vitro was attempted in two ginger cultivars [12]. From the study, it is reported that the better shoot multiplication of average for each explant was 7 shoots after culturing for 6 weeks attained on BA (2 mg/l) and kinetin (1 mg/l) with a huge significant difference in observation between explant source and growth regulator used. Successful root induction (8.75) in 4 weeks of culture and well acclimatization and field survival were noticed in the plantlets generated. Berihu [13] reported on disinfection of ginger sprout buds and disease screening with tests that have resulted in disease-free plantlets of ginger through mass propagation and commercialization to customers. A Series of washing steps with CuSO₄ with Tween 20 with different time intervals and flashing with sterile water has resulted in effective disinfection. Biochemical examination and serological test via NCM-ELISA for cleaning of disease in vitro and mass propagation of ginger for samples tried and yielded successful raising ginger sample. Another study on In vitro micropropagation of shoot tip explants by Selam et al. [14] using Ethiopian ginger cultivar to overcome the problem of unclean and unhealthy ginger planting material is published late. The wilt disease due to Ralstonia solanacearum Biovar 3 Race 4 has resulted in obtaining masses of profuse planting materials free from disease. The study aims at revealing the effect of three sterilization agents namely RBK (0.25% w/v), NaOCl (0.50% v/v) and ethanol (70% v/v) in mixture with HgCl₂ (0.25%). Study of efficacy for 4 antibiotics (broad-spectrum) in combination to control contaminants of bacteria with shoot tip explants of ginger and the effect of antibiotics performance on the shooting of explants of cultivar have been studied. Live explants (70%) with 80% free from contamination were obtained after 3 weeks of incubation from 20 min exposure to 0.50% v/v NaOCl continued by 0.25% HgCl₂. Of all the combinations tried the highest (7.10 ± 0.36 and 7.51 ± 0.27, respectively) mean micro shoots per explant and mean length of shoot (4.2 and 3.56 cm) were obtained at cefotaxime (50 mg/l) and cefotaxime with streptomycin (25 mg/l). The results presented in this study could provide some basic foundation for optimizing protocols in sterilizing explants and can effectively control the bacterial contaminants in ginger cultivar for large-scale micropropagation [15].

3. Conclusion

There is attractive local and foreign market for different types of ginger products; dry, sliced, extracted oleoresin, and essential oil content. Government, research, NGOs, and private sectors need to work on the conservation and maintenance of the ginger germplasms in Ethiopia.

Acknowledgments

The authors would like to acknowledge all the parties working on spices/ginger and contributed for writing of this article.