Hector E. Pérez

Germination after simulated rat damage in seeds of two endemic Hawaiian palm species

Seed predation by native and alien rodents can limit plant recruitment and ultimately affect forest dynamics and composition (Campbell & Atkinson 2002, Cote et al . 2003, Hulme 1998, Sanchez-Cordero & Martinez-Gallardo 1998). Even partial consumption of seeds by predators may affect plant community structure, though its importance is poorly understood (Steele et al . 1993, Vallejo-Marin et al . 2006). Despite consumption of relatively large portions of seeds by herbivores, seeds can retain their ability to germinate if the embryo remains intact (Dalling & Harms 1999, Janzen 1972, Mack 1998). Germination of damaged seeds may be accelerated or prolonged (Karban & Lowenberg 1992, Koptur 1998, Vallejo-Marin et al . 2006). Damage by seed pests also facilitates ageing stress; which manifests as decreased seedling vigour, decreased seed viability, lower germination percentages and slower germination rates (Priestley 1986).

Promoting Germination in Dormant Seeds of Pritchardia remota (Kuntze) Beck., an Endangered Palm Endemic to Hawaii

Abstract Pritchardia remota is an endangered palm endemic to the northwest Hawaiian Island of Nihoa. Current management actions include the development of suitable populations for out-planting through seed propagation. However, this action is hindered due to potential seed dormancy. We provide evidence that incorporation of fruits into the soil is necessary for germination in the wild and that seeds possess non-deep, simple, morpho-physiological dormancy. Germination is initiated five wk after sowing and can be spread over 21 wk. Seeds do not require light for germination. Rapid (22 to 34 days) and complete (98 to100%) germination is promoted by removal of the endocarp and/or the operculum followed by incubation at high temperatures (25 to 35 °C).

Examining the interaction of light, nutrients and carbohydrates on seed germination and early seedling development of Bletia purpurea (Orchidaceae)

The effects of carbohydrate availability, carbohydrate source, nutrient availability and illumination on germination and early development of Bletia purpurea (Orchidaceae) seeds were investigated using asymbiotic seed germination. Of special interest was determining the minimum nutritional and light requirements for the completion of germination. Germination and development was limited when seeds were cultured in darkness without sucrose. Seeds were able to germinate under illuminated conditions even in the absence of sucrose and this effect was enhanced when mineral nutrients were incorporated into media. Sucrose, fructose, glucose and trehalose enhanced germination and seedling development while mannitol and sorbitol did not. These data suggest that carbohydrates, either as products of photosynthesis, from symbiotic fungi in situ or as exogenously supplied sugars in vitro, play an important role in regulating seed germination by fulfilling an energy requirement. This hypothesis has been often expressed but rarely satisfactorily tested. Mineral nutrients appear to be less important for germination than carbohydrates. The differential effect of sucrose, fructose, glucose and trehalose at two different concentrations on rhizoid production indicates carbohydrates may play a role in regulating rhizoid production.

Germination Timing and Dormancy Break in Seeds of Summer Farewell (Dalea pinnata, Fabaceae)

Summer farewell (Dalea pinnata) is a legume found in upland ecosystems throughout the southeastern United States. Often used in seed mixes for restoration purposes, it represents an opportunity for the emerging native seed industry in this region. Yet its germination characteristics are not well known. Our objective was to assess the germination timing and potential dormancy mechanisms of summer farewell. We specifically addressed the following questions: 1) to what extent do seeds germinate after shedding? 2) do seeds possess physical dormancy? and 3) can germination be enhanced using dormancy-breaking treatments? Summer farewell seeds germinated to a limited extent upon shedding, and most seeds (> 75%) in the population were shed with water-impermeable coats, or physical dormancy. Germination occurred equally well in light or darkness. Remaining ungerminated seeds displayed a high degree of viability (> 90%) after one year of burial. Thus summer farewell seeds are capable of forming soil seed banks. Scarification followed by incubation at constant temperatures yielded high germination. Germination of mechanically scarified seeds was superior to seeds scarified in acid for 5 or 10 minutes and unscarified seeds. However, incubation at 35°C may be deleterious. We discuss recommendations for restoration practitioners and seed producers.

Preliminary study shows germination of Caribbean applecactus (Harrisia fragrans) improved with acid scarification and gibberellic acid

To determine germination rate and final germination percentage of the endangered Florida endemic Caribbean applecactus (Harrisia fragrans Small [Cactaceae]), we treated seeds with sulfuric and gibberellic (GA3) acids and germinated them under constant temperature regimes. Temperature effect was marginal at best, with only 2% of seed germinating in 50 d in 25 °C. Although there was improved germination with sulfuric acid (H2SO4)alone, significant increases in both germination rate and germination percentage were realized when seeds were scarified with 18 M H2SO4for 15, 30, and 45 s, followed by soaking in 1000 ppm GA3 for 24 h, with 68% germination in 120 d for the 45 s H2SO4treatment. Emergence first occurred on day 18 for seed treated with 1000 ppm GA3 but not until day 70 for the 500 ppm treatment. Control seeds failed to emerge during the observation period. These treatments represent a quick method of meeting Species Level Recovery Actions for Harrisia fragrans in the Multi-Species Recovery Plans for South Florida.

Genetic differentiation in natural populations of a Keystone Bunchgrass (Aristida stricta) across its native range

Aristida stricta Michx. (Poaceae) is a perennial bunchgrass native to the Southeastern Coastal Plain of North America where it is a keystone species in the longleaf pine savannas and slash pine flatwoods from southeastern North Carolina to Florida, and westward to the coast of Mississippi. We examined genetic relationships within and among ten populations of A. stricta by using eight inter-simple sequence repeat (ISSR) markers to generate band frequency data for 32 individuals from each sampled population. An analysis of molecular variance showed that 38% of the variation resided among populations while 62% was attributable to variation within populations. Grouping the populations by habitat or by geographic location did not show significant differentiation between the groups. Overall, pair-wise geographic and genetic distances were not correlated. Data indicate that while individuals within each population are genetically diverse, there seemingly are barriers to gene flow across populations leading to their divergence. Each population contains several exclusive loci suggesting that limited gene flow and/or genetic drift are likely leading to this pattern of localization. Our results, coupled with those of the previous studies that presented evidence for local adaptation and phenotypic differences among populations, suggest that there is sufficient differentiation among populations of this species to warrant: (1) maintenance of the existing genetic diversity at individual sites, and (2) use of local seed and plant sources for conservation projects.

A New Method of Wiregrass (Aristida stricta Michaux.) Viability Testing using an Enhanced Forceps Press Test

ABSTRACT: Wiregrass (Aristida stricta Michx.) is a keystone species in fire dependent pine ecosystems throughout the southeastern United States and is often re-introduced into sites via broadcast seeding. Using seed lots of high quality may enhance these restoration efforts. However, parameters that determine seed lot quality, such as viability, have not been studied in detail. Moreover, methods for determining wiregrass seed viability have not been reported. Here we describe a new method for determining wiregrass seed viability using forceps and a microscope. This method is relatively rapid, requires no specialized training in seed biology or chemical viability assay analysis, and is as accurate and precise as chemical viability assay methods. The new forceps press test approach can be exploited by wiregrass propagators and practitioners to gain a better understanding of seed lot quality that may augment their restoration efforts.

Dose–response of germinating Rudbeckia mollis (Asteraceae) seeds exposed to various thermal scenarios

Temperature is a key environmental signal regulating germination. A thorough understanding of how seed populations respond to various temperatures can inform end-users regarding effective establishment strategies and forms the basis for questions related to a taxons thermo-biology. Although abundant information exists regarding germination responses of economically important crops to several temperature scenarios, much less is known concerning the seed biology of wild germplasm. To address this, we examined the germination response of non-dormant Rudbeckia mollis seeds to various doses of constant or simulated seasonal diel temperatures. Germination response was sigmoidal. Seeds of R. mollis were capable of germinating within a few days to high percentages (>95%) at relatively cool constant (15–25°C) or 12-hour alternating (22/11–33/24°C) temperatures, with optimum temperatures for germination occurring at 25°C or 29/19°C. Germination was inhibited as temperatures increased to 30°C or 33/24°C with early and late germinating phenotypes displaying differential responses at these temperatures. No germination occurred at 35°C. Results are discussed in terms of seedling establishment of R. mollis outside its natural range and implications of climate change on germination.

Mass-based germination dynamics of Rudbeckia mollis (Asteraceae) seeds following thermal and ageing stress

Seed mass is an important plant functional trait linked to germination. For instance, higher-mass seeds often display greater germination compared to lower-mass seeds when exposed to non-stressful conditions. Yet, knowledge pertaining to germination dynamics for different mass-based seed fractions following exposure to abiotic stress is lacking. Here, we assess the germination response of relatively fresh, mass-separated Rudbeckia mollis (Asteraceae) seeds to various simulated seasonal temperatures, supra-optimal temperatures and increasing ageing stress duration. Air density separation yielded three mass-based classes, called light (393 ± 35 μg), intermediate (423 ± 29 μg) and heavy (474 ± 38 μg). Water uptake kinetics indicated that imbibition (0–6 h) and germination lag (6–24 h) were independent of seed mass. Similarly, germination and viability loss of fresh seeds following exposure to seasonal and supra-optimal constant temperatures were independent of mass. However, seed mass influenced germination following increasing ageing stress, with light seeds germinating to a significantly greater extent than intermediate or heavy seeds. For example, final germination per cent in light-class seeds was about 1.7 times greater than intermediate or heavy seeds after 20 d of saturated salt accelerated ageing (SSAA). Seeds stored for 1 year in the laboratory displayed mass-dependent germination patterns similar to seeds following SSAA. Mass-independent germination responses may be a strategy to maintain an annual life history in otherwise difficult environments when R. mollis seeds are relatively fresh. However, differences in germination response between aged and unaged seeds suggest that mass-dependent viability loss may occur in R. mollis .

Do Habitat and Geographic Distribution Influence Decreased Seed Viability in Remnant Populations of a Keystone Bunchgrass

Wiregrass (Aristida stricta) is an important species for restoration of imperiled pine-grassland ecosystems. However, in situ and ex situ seedling establishment is problematic due to highly variable germination. I assessed seed lot quality with respect to the production of viable and non-viable seeds from seven remnant wiregrass populations occurring in xeric or mesic habitats throughout Alabama, Florida, Georgia, and South Carolina. Additionally, I investigated the incidence of contamination and germination following surface sterilization. Approximately 55 to 90% of seeds were non-viable due to lack of seed fill and fungal contamination. The number of empty seeds always outweighed that of infected seeds. Populations were similar for seed lot quality when grouped by habitat. Alternatively, populations were heterogeneous for seed lot quality when grouped by geographic region. Seeds from all populations were infected with Curvularia and most were infected with Sorosporium. Surface sterilization with up to a 10% bleach solution did not eliminate pathogens on otherwise viable, healthy seeds suggesting that internal seed tissues may have harbored infection. The high level of non-viable seeds implies that large quantities of seeds are required in order to meet restoration objectives and that caution should be exercised if inter-population seed movement is needed.