Seed Info 31, July 2006

S E E D I N F O

Official Newsletter of the WANA Seed Network

No. 31, July 2006

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HOW TO___________________________________________________________________

In this section we provide technical/practical information for technical staff involved in seed production and quality control.

How to No 33: Variety Maintenance in Participatory Plant Breeding
Varietal purity and identity is one of the key seed quality components in a formal seed sector. To ensure such purity, a generation system has been introduced where the variety is maintained and a breeder seed is regularly produced to initiate seed multiplication of later generations (e.g., pre-basic, basic, certified). However, deterioration in seed quality takes place at an increasing rate in a given crop with each cycle of multiplication due to genetic, mechanical, or pathological contamination irrespective of the quality of a starting material or the rate of cross pollination. No crop management practice or post-harvest technology is completely free from seed quality deterioration factors. Genetic impurities resulting from mutation, residual segregation, natural out-crossing with other crop varieties, species or wild relatives; mechanical admixtures through agricultural and processing machinery and volunteer plants of other crops and varieties and contamination with seed and/or soil-borne pests are some of the seed quality deterioration factors. Therefore, production of new breeder seed stock as source for starting new cycle of seed multiplication is necessary as long as the variety is under commercial production.

In participatory plant breeding, groups of farmer breeders are allowed to identify many varieties. The challenges for securing regular stocks of source seed, which can be used for further multiplication, become substantially greater than the capacity of individual resource-poor farmers. Therefore, a well-established formal seed system may be the most appropriate alternative to provide farmers with the variety maintenance services directly or indirectly to the informal community-based seed system as suggested in the "How To" No. 32.

The techniques of breeder seed production vary greatly. They range from selection of seeds, heads, plants or section of field of local cultivars by farmers based on simple morphological, physiological or phenological characters to a complex progeny testing program carried out by plant breeders on pure or multi-line varieties. However, PPB varieties may lack distinctness and uniformity, which may lead to a set of different overlapping plant populations within a single variety. This is more difficult to identify or maintain than a well-defined pure or multi-line varieties. In the former case, the task of proper variety maintenance or quality seed production may be difficult, if not impossible, to accomplish by both the informal community-based or formal seed systems. In the later case where participatory plant breeding varieties are well-defined pure or multi-line cultivars, the approach of multiplying the individual isolines and bulking them based on the farmers' specific needs can be carried out as follows:

•	Select 300-500 heads from cereals or single plants from legumes.
•	Thresh and sow each head or plant individually in 1-2 m rows.
•	Identify the major component lines based on plant characters.
•	Select 20 single plants from each component line, harvest and thresh each component separately, and plant them in adjacent plots for easy comparison.
•	Check carefully for homogeneity within and between the 20 individual plants in each component line and the distinctness between the major component lines throughout the second season.
•	Bulk-harvest the representative plots from each component line as source seed of that particular component at the end of the second season.
•	Put together all or some of the components to form a purposely structured composite variety based on the need of farmer breeders and users.

The involvement of farmer breeders is crucial for the success of source seed production for multi-line varieties from participatory plant breeding. A similar approach has been successfully applied in variety maintenance and breeder seed production of a multi-line blast resistant rice variety Sasanishiki BL in Japan (JARQ 38 (3), 149-154, 2004 http://www.jircas.affrc.go.jp). Abdoul Aziz Niane, Seed Unit, ICARDA, P.O. Box 5466, Aleppo, Syria; Fax: +963-21-2213490; E-mail: a.niane@ cgiar.org.