Pollen cryobanking for tropical plant species

Abstract

Storing pollen for future use is an important tool in species that are wild crop relatives, for conservation of genetic resources. The mature male gametophyte of most plant species is desiccation tolerant which render them ideally suitable for storage. A major impact of pollen cryopreservation of threatened plants will be to maintain genetically diverse stocks of pollen collected from wild for future conservation measures, a strategy which can also accomplish conservation of nuclear genetic diversity (NGD) to conserve genetic variation expressed through pollen. This is the only variability that could be tapped under natural situations, especially when information on their breeding behavior is less known. Long term pollen cryopreservation has been attempted successfully in many species for conservation of NGD. Case studies of pollen from five RET (rare, endangered, threatened) plants which require immediate conservation attention viz., Celastrus paniculatus, Cayratia pedata, Oroxylum indicum and pollenia from Decalepis hamiltonii and Holostemma adakodien were investigated for their suitability to cryogenic preservation. Pollen/pollinia of these species after initial viability assessment were cryopreserved by direct immersion in liquid nitrogen. After 1 week of cryostorage, pollen/pollinia were re-assessed for viability. Three species showed no difference in post cryostorage viability. The remaining two species declined in post-cryostorage viability by way of reduced germination when compared to their fresh counterparts. Among the two species with pollinia there was a delayed post-storage germination initiation by 1 and 2 h, compared to initial germination of fresh pollinia. The results indicate that for RET plants investigated in this study, pollen cryopreservation can be encouraged to conserve nuclear genetic variability which could be used with increased efficiency to improve seed set for species recovery, amplification, etc., for eco-rehabilitation/eco-restoration programs.