Applied pollen conservation research of endangered Hawaiian endemic Hibiscus and Pritchardia species

Storage of pollen allows for gene exchange between geographically isolated individuals, and for controlled pollination when flowering of staminate and pistillate flowers or individual plants is asynchronous. Desiccation of pollen is essential for the retention of high longevity, yet research into pollen storage behavior of wild species is infrequently performed. Hibiscus clayi and Pritchardia minor are Kaua‘i single-island endemic plant species assessed as Critically Endangered and Endangered, respectively, by the IUCN Red List of Threatened Species. With respect to these species we ask; 1) How does pollen germination respond to varying sucrose concentrations (5-40%) and substrates (liquid/solid); 2) What is the pollen germination temperature niche breadth; 3) How does pollen viability respond after desiccating to the international genebank standard of 15-25% RH? If desiccation tolerant, 4) how does viability of previously desiccated then hermetically sealed pollen respond to freezing at conventional (-18ºC) and -80ºC temperatures? Finally, in order to understand relative storage lifespan and the influence of moisture relations, we ask, 5) How does pollen longevity respond to periods of time stored in varying RH environments. To answer these questions, we collected pollen from the National Tropical Botanical Garden’s living collections. Germination was assessed in a modified Brewbaker and Kwak media with 10-40% sucrose in 5% increments. We will desiccate pollen to a range of RHs at ambient temperature (~25°C), hermetically seal, and store at -18 and -80ºC, then test viability via a germination test at each stage. To assess pollen longevity at ambient conditions, survival curves will be determined and compared using p50 (the time for viability to decrease to 50%). Results on the experiments are forthcoming. Research into optimal pollen storage methods by species is needed to better understand the effects of desiccation, freezing, and time on pollen viability and longevity. Considering the current rate of plant extinction in Hawai‘i, pollen storage is an important conservation tool for conducting controlled crosses that might otherwise not be possible.

Key words: desiccation tolerance, ex situ pollen conservation, longevity, pollen banking, pollen germination, pollen storage
Authors: Dustin Wolkis1*, Natalie Blum2, Makoa Elgin2, Cecily Eltringham1, Seana Walsh1, Alina Wood1
1 Department of Science and Conservation, National Tropical Botanical Garden, Kalāheo, HI, USA. 2 School of Life Sciences, University of Hawaiʻi at Mānoa, Honolulu, HI, USA. *corresponding and presenting author; dwolkis@ntbg.org