Introduction

As an adjunct to seed storage for genome preservation, orchid pollen storage has much to offer: to the hybridist wishing to overcome flowering asynchrony in species and/or to introduce wild genome contributions into cultivated taxa; to the gene bank manager seeking to preserve a large quantity of genetic material in a small facility; and to the conservationist anxious to preserve species, even if this can only be achieved through the pollination of plants held ex situ in orchid collections with stored pollen. Pollen storage may also be of considerable future importance to the biotechnologists, if the process of haploid plant production via embryo development from pollen grains (i.e. androgenesis) can be extended to orchids.

The literature on orchid pollen germination is surprisingly limited with previous studies concentrating on optimising the composition of the germination medium, particularly the sugar level. Pfundt (1910), working with two European species and a range of sugar levels from 5–20%, observed a preference for 5–10% sugar. Miwa (1937) similarly found orchid pollen generally germinates best when using cane sugar at around 3–10%. Although more exacting studies on the optimal chemical composition of the germination medium have been performed, particularly with reference to plant hormones (Curtis & Duncan 1947; Rao & Chin 1972), sugar level remains the most important single chemical factor in stimulating orchid pollen germination on artificial medium; its action being osmotic, preventing grain bursting whilst avoiding plasmolysis, rather than as a heterotrophic source of carbon (see Stanley & Linskens 1974).