Nelson's Horse-nettle (Solanum nelsonii)

Mature fruit was collected on 10/16/2018 from approximately 10 plants on Grass Island. Mature fruits were placed in plastic Ziploc bags and transported to the 51-meter transport ship, M/V Imua. Seeds were separated using sieves and dried overnight on paper towels and underfans. Seeds were then placed in small mesh bags and kept in a sealed plastic container with a dessicant until transfer to the Lyon Arboretum Seed Lab on 10/30/2019. Solanum nelsonii collection accession 181031002 #00 contained over 4400 seeds in storage. Results of germination tests indicated viable seeds. A portion of the seeds were submitted for secure backup storage at USDA National Laboratory for Genetic Resources Preservation (NLGRP) in Fort Collins, CO. Threats to the species include habitat modification and destruction by nonnative plants, such as bristly foxtail (Setaria verticillata). The species' habitat on low-lying islets at Pearl and Hermes Atoll is also susceptible to inundation by tsunamis and sea level rise associated with the effects of climate change. Fortini et al. (2013, p. 89) found that, as environmental conditions are altered by climate change, S. nelsonii is unlikely to tolerate or adapt to projected changes in temperature and moisture, and is unlikely to be able to move to areas with more suitable climatic conditions. The low number of individuals may result in reduced reproductive vigor and lower genetic variability associated with small population size, thereby lessening the probability of its long-term persistence. Wagner et al. (1999, pp. 1,273-4) notes a degree of differentiation within the species into four intergrading variants based on leaf size, shape, degree of lobing, thickness, and flower and fruit color; one of which is described from Kure and Midway and another from Midway, Pearl and Hermes, and Laysan (likely extirpated). The two other variants are grouped based on material collected from Moloka‘i, Maui, and Hawai‘i; and plants from Nihoa, Ni‘ihau, and Kaua‘i. The species is most abundant with over 16,000 individuals on Nihoa (USFWS 2016, Plentovich et al. 2017), where plants produce both red and black fruit. Genetic testing to select the appropriate source population for reintroduction efforts may be conducted. Access to Pearl and Hermes is dependent on transportation via ship and small boat operations and availability of qualified staff, making regular monitoring, threat management, and seed collection both costly and infrequent. For these accessions, initial germination was 96% on paper substrate. Longest stored for this species is 2+ years at 4ºC so far but congeners are storable at -18ºC for 15+ years. Seeds stored at -18ºC are scheduled to be tested for long-term viability tests in 5 years.