Methods of conservation
Vegetative bank
Contributors to this section: ILRI, Ethiopia (Jean Hanson); Bioversity International/ILRI, Ethiopia (Alexandra Jorge).
Storing plant propagules using cold storage
Vegetative propagules of several tuber crops, including potato, sweet potato, yam and cassava can be conserved under cold conditions of 4-20°C for several months between one harvest and the next planting season. Cold storage avoids deterioration following the harvesting of fresh tubers or stem cuttings and consequent losses caused by both physiological changes within the plant by reducing respiration and infection by pathogens and pests during storage.
Pretreatment
Storage propagules should be free of damage caused by insects and nematodes and any other visible symptoms of diseases before storage. Any type of wounds, scraping and peeling can affect the storage life of vegetative material by allowing fungi and bacteria to enter the plant and causing rotting. The storage propagules should be disinfected as soon as possible after harvest using either a 5% sodium hypochlorite solution or an insecticide and fungicide solution and soaking the propagules inside mesh sacks or storage containers for 10 minutes.
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Storage
The propagules selected for storage are usually stored in mesh sacks, or open boxes made of wood, or plastic to allow air circulation with duplicated labels with the identification number, both inside and outside the container. Stems are often more robust and can be stored in bundles or in polythene bags with the cut ends covered with wax to prevent excessive drying during storage. The material should be monitored weekly for signs of rotting, insect damage or rodent damage.
Reported methods for storage include:
Sweet potato storage tubers may be cured by placing them in a high temperature chamber (25-30ºC) with a high relative humidity (RH) (85-90%) for 4-7 days in order to heal all wounds and then stored under a controlled temperature of 12ºC and a high relative humidity for up to 7 months.
Potato tubers are usually stored at temperatures from 2 to 14 ºC and a relative humidity around 70% in the dark for up to 6 months.
Cassava stems with viable buds can be stored at 20–23ºC and 70–80% RH in bundles or in polythene bags in drier areas during the dry season.
Yam storage tubers should be allowed to dry in the shade for 4 to 6 weeks and can then stored at 18–20°C in a dry cool area for 3 to 4 months. Chilling damage occurs when tubers are stored below 10°C.
References and further reading
Dumet D, Adeyemi A, Ojuederie O. Cassava in vitro processing and gene banking. IITA, Nigeria. Available from: http://www.iita.org/cms/articlefiles/515-genebank_Cassava_manual.pdf. Date accessed: 24 March 2010.
FAO. 2013. Genebank standards for plant genetic resources for food and agriculture. Food and Agriculture Organization of the United Nations, Rome. Available in English, Spanish, French, Arabic, Russian and Chinese here.
Kushman LJ, Wright FS. 1969. Sweetpotato storage. Agricultural Handbook N° 358. USDA, Washington, D.C.
Huamán Z. Clonal Sweetpotato germplasm management training manual. Section 2.1 Maintenance of sweetpotato germplasm in field genebanks. CIP, Peru. Available from: http://www.cipotato.org/csd/materials/Sweetpotato/Batsect2.1.pdf. Date accessed: 24 March 2010.
Conservation
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Page compiled by: Bioversity International/ILRI, Addis Ababa, Ethiopia (Alexandra Jorge); ILRI, Addis Ababa, Ethiopia (Jean Hanson) including information extracted from: Engels JMM, Visser L, editors. 2003. A guide to effective management of germplasm collections. IPGRI Handbooks for Genebanks No. 6. IPGRI, Rome, Italy.
Conservation of plant germplasm can be done on site (in situ) and off site (ex situ).
In situ conservation
This type of conservation refers to the conservation of germplasm in ecosystems and natural habitats and the maintenance and recovery of viable populations of species in their natural surroundings. In the case of domesticated or cultivated species, it refers to their conservation in the surroundings where they have developed their distinctive properties. This is generally done in protected areas mostly for the conservation of wild relatives, and on-farm or in home gardens for the conservation of cultivated species. This type of conservation is not described further the Crop Genebank Knowledge Base.
Ex situ conservation
This type of conservation is the storage of seeds or plant material under artificial conditions (other than their natural environment), to efficiently and effectively guarantee its longevity viability and availability. It is the type of conservation mostly used in genebanks. It covers a range of methods suitable for various types of seeds or plant materials. It ranges from cold storage of seeds or propagules, in vitro (tissue culture or cryopreservation), field, pollen or DNA conservation.
With ex situ conserveration two types of storage are recognized: storage of samples for long-term security – referred to as base collections – and storage of samples for immediate use – referred to as active collections. The storage conditions and distribution arrangements of these stores vary.
Base collections
A base collection is a set of accessions in which each is distinct and as close as possible to the original sample in terms of genetic integrity. Normally, material is not distributed from base collections directly to users. Base collections are only used to regenerate active collections (FAO, 2013). In seed banks, samples in base collections are stored for long periods at below 0°C – usually at -18° to -20°C – to maintain seed viability and, in cryobanks, specially prepared in vitro culture samples are stored for long periods at -196°C, usually in liquid nitrogen.
Engels and Visser (2003) introduced the term ‘most-original sample’ (MOS) to qualify the samples in base collections. A MOS consists of genetic material that has undergone the lowest number of regenerations since the material was acquired by the genebank; it may be a sub-sample of the original seed lot or a seed sample from the first regeneration cycle if the original seed lot required regeneration before storage or a cryopreserved sub sample of the first in vitro culture cycle.
Active collections
Active collections consist of accessions that are immediately available for distribution. These accessions are accessed frequently and storage of active collections can be in seed banks, vegetative banks, field banks and in vitro banks. Seeds are maintained in conditions that ensure at least 65% viability for 10-20 years (FAO, 2013) and in vitro cultures are maintained in slow growth conditions. Samples in vegetative banks are only stored for a few months but perennial living plants in field banks can be maintained for 20 years or more.
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References and further reading
Engelmann F, Engels JMM. 2001. Technologies and strategies for ex situ conservation. In: Engels JMM, Ramanatha Rao V, Brown AHD, Jackson MT, editors. Managing plant genetic diversity. CABI, UK. 512p.
Engels JMM, Ramanatha Rao V, Brown AHD, Jackson MT, editors. 2001. Managing plant genetic diversity. CABI, UK. 512p.
Engels JMM, Visser L, editors. 2003. A guide to effective management of germplasm collections. IPGRI Handbooks for Genebanks No. 6. IPGRI, Rome, Italy. Available in English (1.4 MB) and Spanish (1.5 MB).
FAO. 2013. Genebank standards for plant genetic resources for food and agriculture. Food and Agriculture Organization of the United Nations, Rome. Available in English, Spanish, French, Arabic, Russian and Chinese here.
Rao NK, Hanson J, Dulloo ME, Ghosh K, Nowel D, Larinde M. 2006. Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, Rome, Italy. Available in English (1.5 MB), Spanish (1.4 MB) and French (1.9 MB).
Watch a great documentary on the importance of genetic diversity, landraces and crop wild relatives, to the future of agriculture in the face of climate change and other challenges:
http://www.seedhunter.com/watch.html#assets/images/gallery/crew-sally-ingleton-phillip-bull-svalbard.jpg