Abstract
Maximizing seed longevity is important for genebanks to efficiently manage their accessions, reducing the frequency of costly regeneration cycles and the loss of genetic integrity. Research on rice seeds has shown that subsequent longevity in air-dry storage can be improved by drying seeds, which are metabolically active at harvest (moisture contents above a critical value close to 16.5%), for an initial period at a higher temperature (40°C–60°C) than that currently recommended by the current genebank standards (5°C–20°C). The aim of this study was to test whether similar benefits could be achieved in two legume species—cowpea and soya bean—by drying freshly harvested seeds, from two separate harvests, at 40°C and 35% relative humidity, for up to 8 days before equilibrium drying in a drying room (17°C and 15% relative humidity). Improvements in longevity were observed in three of the four accessions of soya bean, with the greatest improvement generally occurring after the maximum duration (8 days) at the higher temperature. However, of the five accessions of cowpea, only seeds of TVu-9698 and TVu-13209 from the first harvest, and of TVu-13193 from the second harvest, showed an improvement in longevity compared with drying following the standard protocol. A negative effect of high-temperature drying was also observed in one accession of cowpea, TVu-11980, but only in seeds harvested later in the season, 13 weeks after planting. This research not only provides evidence of the potential benefits of drying orthodox seeds at an alternative, higher, temperature instead of at the conventional lower temperature, before long-term storage, but also raises awareness of how genebanks can improve the management of their accessions.
Highlights
The long-term preservation of the genetic diversity of orthodox species can be ensured by storing their seeds at a low temperature (-20°C) and moisture content (MC) (3%–7%) in genebanks
The aim of this study was to evaluate whether similar benefits to longevity could be achieved in seeds of cowpea and soya bean when they are dried for an initial period at a higher temperature (40°C) before equilibrium drying at a cooler temperature (17°C which complies with the current genebank standards)
In general, seeds that were exposed to an initial period of high-temperature drying reached a lower final MC compared with when seeds were immediately placed in the drying room (DR)
Summary
The long-term preservation of the genetic diversity of orthodox species can be ensured by storing their seeds at a low temperature (-20°C) and moisture content (MC) (3%–7%) in genebanks. Recommendations for the management of genebank accessions emphasize the importance of initial seed drying to extend the subsequent storage longevity.[2,3,4,6] It has been reported that there is an upper temperature limit for safe drying, which varies between species and depends on the MC of the seeds—as seeds dry, the maximum safe drying temperature increases.[7] the values of safe drying temperatures for seed drying reported in the literature are not consistent. It has been claimed that a safe drying temperature for rice seeds is 48.9°C and 60°C when seeds are at an MC >20% and
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