Abstract
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°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. Key words: Yams, pollen genebank, preservation protocols.
Highlights
The improvement of yam (Dioscorea spp.) through conventional breeding is constrained by complicated flowering biology characterized by dioecy, unsynchronized male and female flowering and poor and irregular flower production which altogether limit wide hybridization (Akoroda, 1981; Asiedu et al, 1992)
This paper examines potential protocols for sustainable pollen storage based on results from various experiments conducted on the pollen grains of different West African yam genotypes
Functional viability shown by the percentage germination capacity was over 30% for all the species and Pollen fertility index (PFI) estimates ranged between 4 and 6, except for the exotic D. bulbifera accessions that appeared to be sterile
Summary
The improvement of yam (Dioscorea spp.) through conventional breeding is constrained by complicated flowering biology characterized by dioecy, unsynchronized male and female flowering and poor and irregular flower production which altogether limit wide hybridization (Akoroda, 1981; Asiedu et al, 1992). Pollen storage is important for germplasm conservation, exchanges and handling and it enhances improved breeding efficiency (Hanna, 1994). It will allow pollen to be available throughout the breeding period, enhancing wide and controlled hybridization. It will circumvent the limitations to yam hybridization of unsynchronized male and female flowering by making pollen available whenever the stigma is receptive. It will permit crosses across geographical locations. Pollen storage will enhance conservation of the haploid level gene pool as a valuable resource base for biotechnological manipu-lations in yam improvement
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