Exploring storage protocols for yam (Dioscorea spp.) pollen genebanking

Implementation of pollen genebanks allows the conservation of plant genetic resources at the haploid level, pollen genetic manipulations, scheduling of hybrid seed production and improvement of breeding efficiency. To establish pollen storage protocols for various genotypes of West African yams, laboratory experiments were conducted on fresh pollen and pollen stored under various conditions at the Genetic Resources Unit International Institute of Tropical Agriculture Ibadan, Nigeria (IITA). The storage treatments examined were air-dried storage, freeze-drying followed by storage in liquid nitrogen and hermetic cold storage without previous drying ("wet-cold" storage). Pollen maintained under dry conditions (dry-air and freeze-dried) maintained aceto-carmine stainability up to 400 days but drastically lost germination capacity, most notably under dry-air storage. But pollen samples maintained at "wet-cold" conditions under -80 degree C retained germination capacity after 2 years. The results provide evidence to suggest recalcitrance of yam pollen grains in view of poor pollen survival with drying. Therefore, the "wet-cold" storage procedure appears to be the most promising method for the sustainable implementation of yam pollen genebanks. Pollen storage protocols for active and base collections were proposed, based on these findings.