Seed Desiccation Tolerance and Dormancy of Three Endangered New Zealand Species: Carmichaelia Williamsii, Clianthus Puniceus and Hibiscus Diversifolius
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13 Seed desiccation tolerance and dormancy of three endangered New Zealand species: Carmichaelia williamsii, Clianthus puniceus and Hibiscus diversifolius M.J. PARK1,3, C.R. MCGILL1, W.M. WILLIAMS2 and B.R. MACKAY1 1Institute of Natural Resources, College of Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand 2Margot Forde Forage Germplasm Centre, AgResearch Grasslands, Private Bag 11-008, Palmerston North, New Zealand 3Korea Seed & Variety Service, Anyang-Si Gyeonggi-do, Republic of Korea [email protected] Abstract conventional conditions, the loss of At least one third of New Zealand’s dormancy of C. puniceus at very low indigenous plant species are threatened with moisture contents is of concern. More work extinction and strategies for conserving is needed to confirm the long-term storage endangered flora are urgently required. One behaviour of these species. strategy is to use ex situ seed storage as a Keywords: ex situ conservation, seed complement to in situ conservation. storage behaviour, New Zealand flora Successful ex situ storage of seed requires knowledge of the seed storage behaviour, Introduction optimal storage conditions and germination New Zealand possesses a unique and requirements of the species being stored. diverse flora of 2,300-2,470 taxa, with most For many threatened species, however, this species (80%) being endemic (Dopson et al. information is either incomplete or 1999). Currently 34% of these taxa are unavailable. In this study, preliminary classified as threatened or naturally experiments were conducted with three uncommon, with 11 presumed to be extinct threatened species, Carmichaelia williamsii, (Warmington et al. 1996; de Lange et al. Clianthus puniceus and Hibiscus 2004). In order to combat further species loss, diversifolius, to determine their desiccation a range of conservation solutions including tolerance and dormancy status. Seeds were both in situ protection and restoration and ex tested for germination following desiccation situ conservation is required. and dormancy-breaking treatment. Seeds of In situ conservation aims to conserve all three species could be dried to moisture species within their natural habitat by contents of 2.9-3.7% without losing managing that habitat in a sustainable way. viability. All three species became Ex situ conservation, in contrast, conserves predominantly hardseeded at approximately species outside their natural habitat 10% moisture content. However, C. (Cochrane et al. 2007). This approach is puniceus became permeable to water again most appropriate where populations and/or at moisture contents below 6%. In all plant numbers are small or threatened by species, manual scarification of seeds disease and/or human activities or habitat improved germination to 96-100% change. Ex situ storage provides a resource compared with 5-20% in untreated seeds. that can be used for re-vegetation if in situ Dormancy in these species is a function of storage fails. The two approaches should, the seed coat preventing water uptake by the therefore, be regarded as complementary, dry seed. While seeds of these species are with ex situ storage providing insurance most likely desiccation tolerant and thus can against sudden loss of species in in situ potentially be stored for long periods under storage (Cochrane et al. 2007). 14 Agronomy Society of New Zealand Special Publication No. l3 / Grassland Research and Practice Series No. 14 Seed preservation is one of the most largest populations are known to occur on commonly used methods of ex situ the eastern side of the Te Paki dune wetland conservation (Theilade & Petri 2003). Ex area. This species is classified as ‘nationally situ storage usually requires drying of seed vulnerable’, and is under severe threat from to low moisture content (3-7% fresh weight browsing animals, particularly wild cattle basis), depending on the species, and storage and horses. Some populations at Tokerau at low temperature, preferably at –18°C or Beach have been destroyed by coastal cooler. Temperature and moisture content of housing development (de Lange et al. 2004; the seed are major factors in determining New Zealand Conservation Network 2005c; whether viability is retained in storage Hitchmough et al. 2007). (Hong et al. 2001; Theilade & Petri 2003). In this study, experiments were conducted to For many New Zealand threatened species, determine the desiccation tolerance, however, the information on seed biology, dormancy status and germination of C. seed storage requirements and seed williamsii, C. puniceus and H. diversifolius dormancy release mechanisms is either seed. incomplete or unavailable. Carmichaelia williamsii Kirk (Fabaceae) Methods has a conservation assessment of ‘nationally Seed material endangered’ based on its restricted C. williamsii, C. puniceus and H. distribution and small population size diversifolius seed pods were collected from (Hitchmough et al. 2007). It is restricted to the Auckland Botanic Gardens in 2007. The the northern offshore islands (particularly collected pods were couriered to Massey the Poor Knights Islands and the Aldermen University (Manawatu Campus, Turitea Islands) and to two small remnant Site) in paper bags within 12 days of populations near East Cape. Some collection (Table 1). The seeds were populations are at risk from coastal erosion. extracted from the pods by hand and the The species is principally pollinated by New initial moisture content (MC) and Zealand honeyeaters. Loss of these germination determined. pollinators will reduce seed production (Heenan 1996; Brandon et al. 2004; New Determination of moisture content and Zealand Conservation Network 2005a; germination Hitchmough et al. 2007). The moisture content of the whole seed was Clianthus puniceus (G. Don) Sol. ex Lindl. determined using the low-constant- (Fabaceae) is cultivated widely, but wild temperature oven method described in the populations are classified as ‘nationally International Rules for Seed Testing (ISTA, critical’. In 2005 only one naturally 2007). Four replicates of 10 (C. williamsii) occurring plant population was known in the or 25 seeds (C. puniceus and H. wild at a site near the Kaipara Harbour. At diversifolius) were cut in half and weighed this site C. puniceus is threatened by before and after drying in a 103°C ± 2°C summer droughts, browsing animals and oven for 17 h. MC was calculated as the competition from weeds (Shaw & Burns percentage of water on a fresh weight basis. 1997; New Zealand Conservation Network Seed germination was determined using four 2005b; Hitchmough et al. 2007). replicates of 20 (C. williamsii), 25 (H. Hibiscus diversifolius Jacq. (Malvaceae) diversifolius) or 50 (C. puniceus) seeds. appears restricted to the northern most Seeds were placed between moist folded 38 extremity of the North Island (from about lb regular weight seed germination paper Reef Point and Doubtless Bay north) (New (Anchor Paper Company, St. Paul, Zealand Conservation Network, 2005c). The Minnesota) held in closed boxes and Seed desiccation tolerance and dormancy of three endangered New Zealand species (M.J. Park et al.) 15 incubated at 20°C. A seed was considered to Seed dormancy experiment have germinated when a normal seedling Seeds that had not germinated after 3 weeks had developed; a seedling was classified as were counted and manually scarified with a normal when it had a well developed scalpel by cutting the seed coat in the primary root and intact hypocotyl and cotyledon area. Scarified seeds were cotyledons (ISTA, 2007). returned to 20°C to continue the germination process for another 6 days after which Seed desiccation experiment ungerminated seeds were classified as viable Seed samples were dried to target MCs of when they showed no sign of infection and 10%, 5% and 2.5%. Seed from each sample were firm when pressed. Normal seedlings was mixed with an equal weight of silica gel were assessed as previously described. in polythene bags and placed in a desiccator and held at 20°C. Seed samples were Data analysis monitored daily for target weights. The Analysis of Variance (ANOVA) was target weight that corresponded to each conducted on sample means of each target MC was calculated using the treatment. Where significant effects were following formula (adapted from ISTA, detected in the ANOVA (P=0.05), means 2007): were compared using the LSD (Least Significant Difference) test. Prior to Weight of seed (g) at target moisture content = analysis, data were checked for normality. No transformations were necessary. SAS® ⎛ − IMC100 ⎞ for Windows (Release 9.13, SAS Institute, ⎜ ⎟× initial seed weight (g) ⎝ − TMC100 ⎠ Cary, North Carolina) was used for analysis of all data. Where IMC = initial seed moisture content TMC = target seed moisture content Results Initial characteristics Once the target weight was reached seed The initial characteristics of the seeds of the MC and germination were determined as three species used in the experiments are described above. To avoid imbibition shown in Table 1. The moisture content of damage of seed at 10% moisture content and C. williamsii and C. puniceus seeds on below, seeds were humidified before receipt was around 20% and germination germination by placing them above water in over 95%. In contrast, seeds of H. a closed container at 20°C for 24 hours diversifolius had 12.4% MC and low (IPGRI-DFSC, 2004). germination (46%). Table 1 Initial characteristics of Carmichaelia williamsii, Clianthus puniceus and Hibiscus diversifolius. C. williamsii C. puniceus H. diversifolius Collection date 20/12/2007 17/12/02007 31/08/2007 Arrival date 27/12/2007 27/12/2007 12/09/2007 Number of seeds prepared 270 1920 660 Seed weight (mg ± S.E.) 19.8 ± 0.48 22.4 ± 0.32 11.3 ± 0.12 Initial moisture content (%) 19.2 22.8 12.4 Germination (%) 98 94 46 16 Agronomy Society of New Zealand Special Publication No. l3 / Grassland Research and Practice Series No. 14 Desiccation tolerance 41%, respectively. Seeds of C. williamsii, C. puniceus and H. diversifolius tolerated desiccation over silica Seed dormancy gel to 2.9-3.7% MC while maintaining their The proportion of seeds of C.