Abstract
Genebanks maintaining seeds for long-term genetic resources conservation monitor seed lots to detect early loss in viability. Monitoring is costly and depletes valuable seed. Three decades of genebank seed germination test results of diverse forage species from 50 legume genera in the International Livestock Research Institute’s medium-term store (circa 8 °C with 5% moisture content) were analysed to determine whether advice on seed monitoring intervals could be derived. Cumulative normal distributions were fitted by probit analysis for each seed lot and compared within each genus. Six patterns of within-genus variation were identified: no detectable trend in germination test results during storage (4 genera); detectable trends, but variable (positive to negative) amongst lots (5); consistent slope of loss in viability amongst lots (17); consistent slope of increase in ability to germinate amongst lots (21); common loss in viability amongst lots (2); common increase in ability to germinate amongst lots (1). Seed lot monitoring intervals for the medium-term store were derived for each of 19 genera with consistent loss in viability across seed lots: three genera provided comparatively rapid deterioration, five met the general expectations for a medium-term store (2–10 years’ maintenance of high viability), whilst 11 provided much better survival. Moreover, 26 further genera provided no evidence as yet of seed deterioration; of these, 22 improved in ability to germinate during storage indicating confounding of hardseededness with viability in germination tests.
Highlights
Each decision to store seeds, whether for example by farmers or commercial seedsmen to establish subsequent crops or by genebanks for long-term genetic resources conservation, implies a predictable response of seed survival to storage duration and environment
Each seed lot stored in a suitable environment requires sampling to monitor seed viability over time in order to be able to regenerate the accession before substantial loss in viability has occurred; 85% is the minimum value before regeneration is required in order to avoid loss in genetic integrity (IBPGR 1976), a lower alternative of 85% of initial viability was subsequently adopted (FAO/IPGRI 1994; FAO 2013)
The genebank at International Livestock Research Institute (ILRI) operates two seed stores: one long- and one medium–term store in which seeds are maintained in sealed laminated-aluminium packets at circa (c.) 5% moisture content with c. -18 and 8 °C, respectively
Summary
Each decision to store seeds, whether for example by farmers or commercial seedsmen to establish subsequent crops or by genebanks for long-term genetic resources conservation, implies a predictable response of seed survival to storage duration and environment. Seed survival varies greatly amongst species (Harrington 1972; Hong et al 1996) It is affected by storage period and environment, whereby orthodox seeds (Roberts 1973) stored air-dry show greater longevity the cooler and/or drier the storage regime. The quantitative relationship of both variables (i.e. temperature and moisture content) with seed survival period, and the considerable effect of seed lot thereon, has been described by the improved viability equation (Ellis and Roberts 1980a), parameterised for several crops Monitoring tests should be as infrequent as prudent management allows, and so estimates of longevity in long- and medium-term stores are required for the effective management of a genebank (Hay et al 2015), Genet Resour Crop Evol in wild species where the risk of losing the genotype may be high (Probert et al 2009). Published information on procedures to break dormancy and suitable environments to promote the germination of dormant and non-dormant seed remain limited (Hay and Probert 2013), and dormancy is a particular problem for genebanks holding wild species (Perez-Garcıa et al 2007)
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