Germplasm Maintenance

Germplasm maintenance

Germplasm maintenance involves seed germination testing and monitoring the viability. Germplasm samples for conservation are multiplied mainly during the post-rainy season to get better quality seed. To minimize genetic drift, an adequate number of plants are grown and sampled equally in constituting new seed stocks. Genetic integrity is maintained by pollination control while regenerating cross-pollinating crops such as sorghum, pearl millet, and pigeonpea. Pre-storage deterioration in seed quality is minimized by harvesting promptly when maturity is reached.

Viability testing

The viability of seeds stored in a genebank decreases gradually during storage. The genebank test seed viability of fresh germplasm samples and monitor the seed viability at regular intervals based on the initial viability, type of storage and the crop. These periods vary from 8-25 years for active collection and 10-30 years for base collection. The seed viability and quantity in active and base collections monitored at regular intervals and regenerate accessions as and when required with appropriate plant population and pollination controls to ensure genetic integrity of accessions.

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Regeneration of germplasm

Seeds lose viability even under good storage conditions and it is necessary to regenerate accessions from time to time, the frequency of regeneration depends on the initial viability, the rate of loss of viability and the regeneration standard, the percentage viability at which it is decided to regenerate the accession. The aim of regeneration is to increase the quantity of seed of any accession where the number of seeds available has been depleted, or to restore maximum viability to a seed lot. Regeneration of germplasm is one of the most crucial processes in genebank management. It is costly in terms of resources and time, and it involves the risk to genetic integrity. The methods employed for regeneration vary considerably according to the crop species and its reproductive system - inbreeding or out-breeding.

Germplasm regeneration is mainly carried out in the post-rainy season (Nov-May) at ICRISAT, Patancheru. Due to low ambient relative humidity and absence of rains, incidences of diseases and pests are low, and consequently the quality of seed produced is high. Regeneration is carried out in precision fields and under good agronomic management for obtaining seeds of good quality and vigor. Optimum plant stand and suitable pollination control measures are required for maintaining genetic integrity in crops like sorghum, pearl millet, and pigeonpea (where out-crossing exists). Germplasm collections contain accessions originating from a wide range of environments and the site of regeneration may not be optimal for all accessions. It would be ideal to regenerate germplasm in near-optimum locations, and meet the requirements of specific cultivars. Efficient management of seed germplasm collections therefore entails minimizing the frequency of regeneration. This can be achieved by maximizing the seed longevity.

Seeds are a product of the seed production environment as well as the genetic constitution of the parent plants. The complex of environmental conditions, including soil and climate, frequently override the expression of genetic characters. Therefore, to improve seed quality, germplasm regeneration programs should stress improved management and production practices. Several pre- and post-harvest and seed drying practices influence initial vigor and subsequent longevity of regenerated seed lots. Wild species and critical accessions with low viability/limited seed stocks are multiplied in the glasshouse under adequate protection.

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Field genebank and Arachis House

ICRISAT mandate crops are photoperiod and temperature sensitive and require appropriate environment for regeneration. Germplasm accessions that do not produce adequate seed for conservation such as wild species of groundnut and pearl millet, perennial species of Sorghum and pigeonpea are maintained as live plants in a Field Genebank (botanical garden) and House of Arachis.

Special facilities were created at ICRISAT Genebank for regenerating all seed producing wild species of genus Arachis and unadapted Arachis hypogaea accessions. Majority of the accessions represented by 41 wild species and six botanical varieties of cultivated groundnut were successfully regenerated in these facilities overcoming the problems encountered during field regeneration. Regeneration was possible round the year in these facilities with minimum operational interference. The seedling establishment, plant growth and pod returns per cycle were significantly higher using these facilities.