Variability in response of seeds to liquid nitrogen exposure in wild coffee (Coffea arabica L.)

In order to investigate the intraspecific variability for tolerance to liquid nitrogen (LN) exposure of coffee (Coffea arabica) seeds, seed and embryo viability after desiccation or desiccation and cooling to −196°C, with or without controlled rehydration of seeds after thawing, has been studied within a core subset of 30 accessions of the CATIE field genebank. A high variability for seed sensitivity to LN exposure was observed: seed viability after cryopreservation varied from 0 to 74% among the accessions studied (0 to 100% when expressed in percentage of the desiccation control) and was not correlated to seed size, seed water content after desiccation, or seed and embryo viability after desiccation. By contrast, no variability was found between the genotypes studied for embryo viability after LN exposure. Viability of embryos after cryopreservation was always very high, indicating that, when occurring, the decline or loss of seed viability after LN exposure was due to damages to the endosperm only. Controlled post-thaw rehydration of seeds, through a 6-week osmoconditioning treatment with a −1.25 MPa polyethylene glycol solution, dramatically increased viability of frozen seeds. However, this effect was variable within the accessions studied and independent of seed viability after desiccation or desiccation and LN exposure.