Seed Processing

• use 100 or more plants in genetically heterogeneous accessions; • take special note of the day-length requirements for the species or they may not flower; • provide suitable conditions for growth to trigger abundant flowering; • eliminate competition by weeding alien plants; and • ensure a stable source of water from irrigation if necessary. Sowing date • Sow at an optimum time so that maturity and harvesting coincide with the most favourable weather conditions. • If there is much variation between accessions in flowering time, sort by early and late maturity based on previous documentation and adjust the planting dates so that all accessions mature in a uniform environment. • Planting on the basis of maturity makes crop management and harvesting convenient. Example: Desired plant population = 150 Percentage germination = 85 ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Expected field establishment = 80 Number of seeds for plating = 150 = 220 seeds 0.85 x 0.80 113 Manual of Seed Handling • Sow in uniformly spaced rows and with uniform spacing between plants within rows. • Avoid competition for light and nutrients by using wide spacing. • Ensure complete control of pathogens and pests using standard plant-protection measures. • Thinning should normally not be undertaken—if required, thin plants at random. • Ensure continued absence of alien plants in the vicinity throughout the regeneration cycle by hand-weeding or using inter-cultivation. Irrigation • Irrigate the field when necessary. • Never subject the crop to water stress. • Ensure adequate drainage and no water-logging. Regular inspection of plants is mandatory to achieve these objectives. Verifying accession identity • Accession identity should be verified while the plants are ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

growing by comparing: • morphological data in the documentation system; or • reference material such as original herbarium specimens or seed. • Roguing must be undertaken with caution and only when it is absolutely clear that the rogue plants are genuine mixtures of other accessions or varieties. • When materials are grown in rows, plants growing off-row may be eliminated. Pollination biology Unless the species is an obligate inbreeder, appropriate pollination control should be implemented. A compendium of breeding mechanisms can be found at www.bioversityinternational.org/ ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

Themes/Genebanks/Species_Compendium/default.asp. For out-breeders, elimination of alien pollen can be achieved through: • spatial isolation (this is not practical when dealing with large number of accessions of the same species but very useful for dealing with a limited number of accessions of many species); • temporal isolation; • natural or artificial barriers—growing accessions in standing crops of tall-growing species like sunflower and hemp; and • bagging selected inflorescences with pollen-proof or pollinatorproof bags made of linen or paper and erecting temporary pollen-proof or pollinator-proof nets around plots. Supplemental hand-pollination is sometimes required to improve seed set. 114 Handbooks for Genebanks No. 8 Insect-pollinated crops may be grown in net or nylon-screened cages with specially designed hives for insect pollinators like bees; one accession of each crop species may be planted in each cage. Insect pollinators are released inside the cage at the time of flowering. Supplemental hand-pollination may be necessary to improve seed set (such as in wild species of tomato and eggplant). Isolation cages can be expensive and shading may affect plant ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

growth. An effective solution could be bagging and controlled pollination by hand. If plants flower during or at the end of the wet season, however, pollination bags may be damaged by rain. Excess moisture and humidity in the bags around the flowers can also lead to increased infection with bacteria and fungi. In wet or humid conditions, it is best to tag the flowers and remove the bag as soon as pollination is complete so that the fruits may develop under normal field conditions. Harvesting and post-harvest management • Harvest at optimum maturity (after the seeds have reached the point of physiological maturity): • when maximum number of seeds are ripe; • when seeds become tolerant to desiccation and can be threshed without mechanical injuries; • before ( Seed Processing, Seed Cleaning, Stone separator, Combo Cleaner, Grading Machine, Gravity Separator  )

deterioration sets in; and • before natural dispersal occurs. • Stagger the harvest if there are differences in maturity of the accessions.