Seed Processing

• Regenerating accessions in base collections should take priority over regenerating those in active collections. Preparation of regeneration plots Soil • The regeneration plot should be as uniform as possible. • The field should have good drainage. • Consider the need for soil analysis and apply treatments appropriate for the crop and site (fertilizers, lime, irrigation or solarization). Solarization Solarization consists of heating soil by covering it with polyethylene sheets during the hot summer in the tropics to control soil-borne diseases; it is conducted for at least six weeks during the hottest part of the year. 1. Thoroughly cultivate the land and level it to minimize protrusions. 2. Give 50 mm irrigation before laying the polythene sheets. 3. Use clear transparent polythene sheets, 1–2 mm thick. 4. Insert two edges of each polythene sheet in the furrows and bury the edges in the soil tightly. 5. Place weights to prevent flapping and tearing of polythene sheets in ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

the wind. 6. When planting, leave a buffer zone of at least 0.5 m around the edges of the solarized area for dilution of heat near edges. 7. Do not allow irrigation water to flow in from other areas after solarization and during crop growth. Weeds and soil-borne pests and diseases • Identify weeds, pests and pathogens by inspection and prior experience. • Consider reducing such problems during preparation of regeneration plots by applying the following treatments: • herbicide spray; • sterilizing soil; • ploughing to encourage germination of weeds, followed by herbicide spray; and • deep ploughing to kill emerging weeds. 111 Manual of Seed Handling Cleanliness • Keep the plots absolutely clean from alien seeds and plants. • Consider the risk of contamination with alien pollen and take appropriate measures during plot preparation, and by intercultivation and hand-weeding. • ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Ensure that the method of plot preparation is appropriate for the chosen method of establishing plants (for example, ridges and flat beds). • Prepare the regeneration plot considering: • the number of accessions to be regenerated; • the number of plants per accession; • spacing between rows and between plants; and • mechanical access for weeding. • The method of preparation depends on: • soil structure; • the species to be sown or transplanted; and • the need for plant supports, in the case of climbers. Preparation of seed 1. Dry, thresh and clean the seeds if the samples are newly acquired. 2. For those in storage: a. identify the candidate accessions that require regeneration; b. ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

remove the containers from the genebank and allow them to warm up; and c. draw seed samples, keeping in mind the minimum sample size required for regeneration and the current level of germination. 3. Ensure absolute accuracy in identifying accessions while drawing the seeds from the genebank, packaging, and labelling seed samples. To minimize errors, it is the use of computerbased information management systems to generate labels is suggested. The minimum number of seeds for regeneration can be estimated from the standard sample size used for regeneration and the sample viability according to the following equation: Number of seeds required for regeneration = Desired plant population for regeneration/(Germination%14 x Expected field establishment %15). 14 ( SeedProcessing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Germination and field establishment percentage are expressed as decimals: 95% is expressed as 0.95. 15 Plant establishment is generally 5% less than the germination percentage in poor conditions and 1% less in good conditions. 112 Handbooks for Genebanks No. 8 Meiosis and anthesis are sensitive stages during plant development. Care must be taken to avoid any stresses such as high temperature and drought. Seed pre-treatments Specific pre-treatment may be necessary to improve seed germination and establishment. If the seeds are very dry (moisture content

Sowing and crop management Crop management for regeneration differs from normal commercial practices where interplant variation is not of primary consideration. To avoid large losses of alleles ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

and maximize seed yield: