Crop Genebank Knowledge Base

Sample preparation

Sample preparation in cassava field banks

Contributors to this page: IITA, Nigeria (Dominique Dumet), Bioversity International/ILRI, Ethiopia (Alexandra Jorge); INIA, Peru (Llerme Rios); independent consultant (Clair Hershey).

Source of planting material

Cassava has a typical growing cycle between 9 and 24 months, depending on the genotype and the environmental conditions.

It is best to regenerate within 18–24 months, when most plants complete their growth cycle, to avoid lodging from excessive growth and build-up of pests and diseases.

Visual inspection of plant material

Inspect all plants in the plot to make certain they all appear to be the same clone. If there is a mixture of clones, reconfirm through the standard descriptors, by comparison with the previously recorded genebank descriptors, which of the plants are the true accession and which are the 'contaminants'.
Select plants as sources of planting material based on their apparent health status. Plants should be free of virus symptoms and of other pests or diseases.
Select plants that will provide well-lignified cuttings with well-distributed, healthy buds.
Prepare stakes from healthy plants, identified earlier in the season before leaves drop off when pest and disease (especially virus) symptoms and other foliar diseases are apparent. Also inspect roots for pest and disease symptoms.
Select the mature portion of the stem, avoiding the top green stems and the bottom section of the plants.
Take care to avoid mixing of genotypes.

Preparation of planting material

Cut stakes (stem pieces) at least 20 cm long with at least 4–5 nodes with viable buds to ensure crop establishment. Use well-lignified stems, generally from the middle section of the plant. Cut them at a right angle with a machete or saw to create a smooth cut.
Handle stems with care to prevent bruising and peeling. Do not place the stems on a hard surface to cut them, as this can damage the nodes, reduce their quality and provide entry points for pathogens and insect pests.
Tie cuttings of each accession firmly in separate bundles. At least one cutting in each bundle is labelled, and for extra security it is best to label two stakes (with accession name and number and date of harvest). The label must be sturdy and secure and able to withstand the handling (e.g. packaging and shipping) and treatment of the stake bundles.

Pre-treatments

Treat the bundled stakes with a mixture of broad spectrum insecticide and fungicide.
Add zinc sulphate in regions where zinc is limited in the soil.

Disposal of contaminated material

Incinerate or autoclave contaminated material (to avoid spreading diseases and pests).
Rogue and burn diseased plants regularly during the growth season (if it does not compromise the survival of a specific accession).
After harvest, destroy discarded stems and roots that have disease symptoms or pest contamination

Recording information during sample preparation in field banks

The following information should be recorded for each step:

Site name and map/GPS reference.
Name of collaborator.
Field bank site name (a code to identify the site location).
Plot reference (the plot number at the field site).
Accession number; population identification.
Name of staff (name of staff recording the data).
Source of cuttings.
Number of generations since acquisition of germplasm or date of previous multiplication (if generation is not known).
Preparation of planting material (details of pre-treatments applied).
Details of plants removed or destroyed (due to type mixtures or pest or disease contamination).

References and further reading

Fukuda WMG. 1996. Banco de germoplasma de mandioca: manejo, conservação e caracterização. Cruz das Almas, BA: EMBRAPA-CNPMF. 103 p. (EMBRAPA-CNPMF, Documento, 68).

Hershey C. 2008. A Global conservation strategy for cassava (Manihot esculenta) and wild Manihot species. A consultancy report to CIAT, on behalf of the Global Crop Diversity Trust, Rome. (Final report under review).

IITA Genebank Manual Series, Cassava field bank operations at the International Institute of Tropical Agriculture (IITA). International Institute of Tropical Agriculture, Ibadan, Nigeria.

Mohd SS, Rao VR, editors. 2001. Establishment and Management of Field Genebank, a Training Manual. IPGRI-APO, Serdang. 121 p. Available here.

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