In plant germplasm conservation, “orthodox” seed (i.e. seed that survives drying down to low moisture content) is the most suitable propagule for long-term storage. In general, high quality seeds of around 5% seed moisture content can be stored for 5-15 years at 2°C and 15-50 years at -18°C. Globally, there are some 1,300 genebanks and 6.1 million accessions of food and industrial crops in conservation. When collecting and conserving plant germplasm, seed science and technology have to be applied during germplasm collection; seed regeneration-germination, seedling establishment, flower synchronization, pollination, harvesting, drying, processing and packaging; seed storage and conservation; characterization and evaluation; and finally, distribution. Some of the seed science knowledge and technology skills encompass seed sampling strategy, sample size, seed health, germination and vigor testing, dormancy breaking, scarification, stratification, vernalization, photoperiod treatment, isolation and pollination techniques, harvesting, threshing, drying, hermetic packaging, storage facility design, etc. The goal is to produce seed lots that fulfill the required genetic, physical, physiological and health quality. A summary was presented to relate germplasm conservation activities to seed science and technology. Some of the seed production, processing and testing equipment used were highlighted. Seed research in germplasm conservation is therefore crucial to streamline the operation and management of a genebank to make it more cost effective and attractive for funding.
Flower seed threshing and cleaning are challenging because many flowers have tiny seed, e.g., the 1000-seed weight of Begonia is 0.01 g, and others have odd-shaped seed, e.g., Tagetes has pappus-bearing seed and Fibigia has winged seed. There is a lack of information on the threshing and cleaning of flower seeds. At the Ornamental Plant Germplasm Center, a small-plot grain belt thresher was modified by disengaging its winnower and a special chute installed to collect the threshed seed and chaff together for cleaning. A custom-made threshing board is used for small samples. The seed with chaff is passed through screen with mesh size that allows all the seed to pass through so that the big pieces of chaff are retained and separated, i.e., scalping. Accurate selection of the next scalping screen (SS) is critical so that the mesh size is just right for at least 95% of the seed to pass through to remove all the chaff larger than the seed. The seed is then sieved on a grading screen (GS) of mesh size that retains at least 95% of the seed to remove all the chaff smaller than the seed. A seed blower is used to further separate the remaining chaff and empty seed based on weight and surface area by adjusting the blowing velocity (BV). A vibratory separator (VS) is used for species with round seed, e.g., Antirrhinum. An X-ray machine is used to monitor the cleaning process. The SC, GS, BV, and VT are given for Agastache, Anisodontea, Antirrhinum, Aquilegia, Aster, Astilboides, Begonia, Belamcanda, Bergenia, Cleome, Coreopsis, Dianthus, Eupatorium, Gaillardia, Geranium, Gypsophila, Iris, Lilium, Lysimachia, Myosotis, Nothoscordom, Oenothera, Passiflora, Penstemon, Petunia, Platycodon, Ranunculus, Rudbeckia, Silene, Stokesia, Synnotia, Tagetes, Talinum, Thalictrum, Verbena, Veronica, and Zinnia.
David Tay and Xiaolei Hu
Radiography is a simple and nondestructive technique to detect empty, immature, and insect- and mechanically damaged seed during seed processing and testing. However, there is a lack of information on the effect of X-ray on seed quality despite recommendations by the Association of Official Seed Analysts for testing agricultural and forest tree seeds since 1979. Two experiments were carried out using lettuce seed of Seed Dynamics, Inc. (No. 52694) and Faxitron MX-20 cabinet X-ray unit set at 20 kilovoltage (kV) for 20 seconds, a standard setting to observe many species of flower seeds. In both experiments, the focus-object distance was 34 cm with no image magnification. The treatments in Experiment 1 were 0 (control), 4, 8, and 12 times of X-ray exposures and Experiment 2 were 0 (control), 15, 30, and 60 times of X-ray exposures on non- and 5-hour imbibed seed. In Experiment 1, germination was done in 288-cell seedling trays in soilless potting mix under greenhouse conditions with four replications of 50 seeds per replicate to observe germination rate, and cotyledon and young leaf discoloration and deformation. Experiment 2 was analyzed using computerized seedling imaging system on germination paper to examine seed vigor and germination rate. There were no significant differences in germination rate in both the non- and imbibed seed in the two experiments. The mean germination rates were 77.75% in Experiment 1 and 94.81% in Experiment 2. No cotyledon and young leaf discoloration and deformation were observed in Experiment 1 and no significant differences in vigor index were found in Experiment 2. The conclusion is that there was no observable effect of repeated X-ray exposures up to 60 times at 20 kV and 20 seconds on a seed lot for both non- and imbibed lettuce seed.
Susan M. Stieve* and David Tay
Seeds of herbaceous ornamental accessions conserved by the USDA National Plant Germplasm System (NPGS) are traditionally produced in summer field cages with honey bees (Apis mellifera) when pollinators are required. Efficient methods to produce high-quality seed in greenhouses may allow for year-round seed production. Flower quantities and effects of pollinators on number and weight of seed produced were studied in field cages and greenhouses at the Ornamental Plant Germplasm Center in 2003 in a randomized complete-block experiment. Honey bees, bumblebees (Bombus impatiens), or blue bottle flies (Diptera calliphoridae) were used as pollinators. Field cages and greenhouse compartments with no pollinator were controls. Cultivars used were Antirrhinum majus `Gum Drop', Coreopsis tinctoria `Plains Bicolor', Dianthus chinensis `Carnation' (NPGS accession NSL 15527), Rudbeckia hirta `Indian Summer', and Tagetes patula `Jaguar'. Seeds were harvested, cleaned, weighed, and 100-seed weights calculated. On average Antirrhinum, Dianthus, Rudbeckia and Tagetes produced more flowers in greenhouses, Coreopsis produced more flowers in the field. Coreopsis and Rudbeckia produced more seed per flower on average with field pollination by honey bees, Antirrhinum and Dianthus produced most with bumblebees in the field, and Tagetes produced most with blue bottle flies in the greenhouse. Each genus had similar 100-seed weights on average in all treatments. Results show pollinators other than honey bees are useful for herbaceous ornamental seed production and that seed production in greenhouses may be an alternative method for seed production of herbaceous ornamentals.
Susan M. Stieve and David Tay
Storage of quality herbaceous ornamental seeds is a primary concern of the Ornamental Plant Germplasm Center, a USDA National Plant Germplasm System genebank. In Autumn 2005, 30 accessions, including 10 genera of herbaceous ornamentals, were evaluated for initial seed weight and viability using four replications of 50 seeds except for Begonia, which consisted of two replications of 500 seeds due to extremely small seed size. Seed lots were then recleaned using an Oregon Seed Blower; Begonia were cleaned using the rolling paper method where good, round seeds roll off vibrating paper held at an angle and shrunken seed do not. Heavy and light fractions of all seeds were saved, 50-seed weight calculated, and viability tested. Seed cleaning was assisted by Faxitron X-ray technology to identify the quantity of seeds with embryos in each treatment. Seed cleaning statistically increased the weight for 19 accessions including Actea, Antirrhinum, Oenothera, Penstemon, Ranunculus, Rudbeckia, and Talinum, where the heaviest seed were in the heavy fraction of recleaned seed. Seed weight for some Begonia and Tagetes accessions was statistically increased, while weight of no Petunia accessions was increased. Viability was calculated as the percentage of normal and dormant seeds. Seed cleaning statistically increased the viability of 10 accessions including Actea, Oenothera, Petunia, Ranunculus, and Talinum; seed lot viability was statistically increased for some accessions of Antirrhinum, Penstemon, Rudbeckia; no accessions of Begonia or Tagetes had improved viability. Results suggest that recleaning seed lots to improve seed weight and viability may be effective, but differences between genera as well as species within genera exist.
Samuel Contreras, David Tay and Mark A. Bennett
Among the factors affecting germinability of a seed lot are the environmental conditions under which the seeds are produced. The objective of this study was to determine the effects of temperature during seed development on seed quality of two Asteraceae species. Seeds of lettuce cv. Tango and Helianthus debilis cv. Vanilla Ice and sp. cucumerifolius were produced in a greenhouse under one of two treatments: i) hot (27, 40, and 20 °C temperatures average, max, and min, respectively), and ii) cool (23, 33, and 18 °C temperatures average, max, and min, respectively). In both species, heavier seeds were produced under the cool conditions and no differences were observed in standard germination. In lettuce, germination percentage and rate were both affected by increased levels of exogenous ABA concentrations and reduced water potential (PEG solutions), and, in both cases, seeds from cool treatments were more affected. Germination at 30 °C and constant light was higher for seeds from the hot treatment. Lettuce seed showed a strong light requirement for germination. However, seeds from the hot treatment gave better dark germination at 13 and 19 °C. Seeds of H. debilis did not required light for germination, and the germination percentage and rates were evaluated at 13, 21, and 29 °C. For both lines, seeds from each treatment behave similarly; however, the germination of H. debilis cv. Vanilla Ice at 29 °C was higher when seeds were produced in the hot conditions. The results showed that temperature during seed development affected aspects of seed quality that are not detectable by the standard germination, but by germination at suboptimal conditions. Within the Asteraceae family, differences varied among and within species.
Alice Mweetwa, David Tay and Gregory Welbaum
Orchids are important ornamental, food, and medicinal plants. Orchid germplasm preservation is important because some species are endangered due to loss of habitat and human predation. Very few of the world's genebanks are involved in orchid preservation. Orchid germplasm preservation is a priority for the USDA Ornamental Plant Germplasm Center in Columbus, Ohio. Brassia and Phalaenopsis seeds were harvested at different stages of development and stored at –196 °C (liquid nitrogen), –80, –18, 4, and 25 °C for 6, 12, 18, and 24 months to determine the optimum conditions for long-term seed storage. Phalaenopsis and Brassia seeds adjusted to 45.5% RH over chromium dichromate were able to survive 10-d storage. Seeds frozen in liquid nitrogen for 30 min were able to germinate and produce protocorms 19 d after sowing, just a day longer than control seeds. Liquid nitrogen storage also improved germination of some Phalaenopsis seed lots from 0 (control) to 38%. Storing Phalaenopsis seeds at –80 and 4 °C also improved germination similarly, suggesting dormancy was broken by low-temperature seed treatments. On the other hand, seeds stored at 25 °C did not germinate. Preliminary results suggest that orchid seeds tolerate freezing even in liquid nitrogen and that cryopreservation may be a viable long-term strategy for orchid germplasm preservation.
Samuel Contreras, David Tay and Mark Bennett
Lettuce seeds (Lactuca sativavar. acephalacv. Tango) were used with the objective of determining the effect of temperature, light, and their interactions in promoting germination. Under standard op-timal conditions (20 °C, light), the seed presented 100% germination (radicle emergence 5 d after sowing). Different treatments evaluated germination under dark conditions, with or without a red light break (LB, 28.8 mmol·m-2) 48 h after sowing, and with different combination of temperatures pre- (soaking temperature, ST) and post- (germination temperature, GT) the LB. Germination at constant 20 °C without LB was less than 5%, and with LB, it was around 30%. However, germination was close to 100% at GT of 20 °C when LB was applied after a ST of 10 °C, and around 50% under the same conditions, but without LB. When GT was 30 °C and LB was applied, germination was less than 3% with ST = 30 °C, less than 10% with ST = 20 °C, and around 100% when ST = 10 °C. With ST and GT of 10 °C and 30 °C, respectively, and no LB, germination was less than 5%. Germination at 10 °C constant, with and without LB, was around 90% and 0%, respectively. When ST was 40 °C and LB was applied, germination was around 40% at GT= 20 °C, but less that 3% with GT= 30 °C. In summary, a severe inhibition of germination was observed when seeds were germinated in dark, which was partially reversed by either a light treatment or soaking at 10 °C, and fully reversed when both treatments were applied together. Inhibition of lettuce germination at 30 °C was observed when this temperature was applied after a light treatment, but not when applied before. Possible implications of these results for the phytochrome mechanism of action are discussed.
Jing Luo, David Tay and John Cardina
Exotic noxious plants, including invasive plants and exotic weeds, have caused huge economic loss and ecological damage around the world. To prevent further introductions of such species as crops or ornamental plants, biological and ecological traits associated with invasiveness and weediness need to be identified so that prediction can be made on the potential of being noxious for proposed species. It was suggested that weeds were usually generalists that can survive and reproduce in a wide range of environments; i.e., they were quite “plastic” in response to different environments. In accordance to this idea, phenotypic plasticity has been recently proposed as an indicator and predictor for weeds and invasive plants. This hypothesis is tested using two exotic dandelion species: Taraxacum officinale (common dandelion), widespread weed, and T. laevigatum (red-seeded dandelion), which occurs in a much lower frequency in Ohio. A greenhouse experiment was conducted in which the two species were grown in two soil moisture levels (dry vs. wet) combined with two light exposure levels (full sun vs. shade). Various traits were measured to see whether T. officinale is more plastic than T. laevigatum in these four environments. The results show that, when using coefficient of variance (CV) as a measurement of plasticity, T. officinale has significantly larger CV than T. laevigatum in plant diameter (P = 0.02), shoot: root ratio (P = 0.04) and soil pH (P = 0.02). This indicates that T. officinale is more plastic in some of the resource-capture-related traits such as leaf morphology and biomass allocation, and presumably also in root exudates, which alter the soil pH.
David Tay, Joseph Tychonievich and Stephanie Burns
The Association of Official Seed Analysts adopted X-ray technology for testing agricultural and forest tree seeds in 1979. It has not been applied on flower seeds. To date, its use is still lacking, despite the relatively simple and nondestructive nature of the test. One of the reasons for the slow adoption is the lack of a simple X-ray unit that gives instant high resolution digital images. The Faxitron MX-20, a cabinet X-ray unit designed for high detail radiographic imaging of medical specimens, fulfills this need. The high magnification capacity of 1×, 1.5×, 2×, 3×, 4×, and 5×, and the low kilovoltage (kV) provide enhanced image performance with good quality contrast. The exposure time and X-ray tube kV can be selected to produce the best images. Its laser locator eases the positioning of a sample under examination accurately and the 2-× 4-inch field of view digital camera with 10 lp/mm resolution provides the instant high quality on-screen viewing of seed sample images. The most useful application at the Ornamental Plant Germplasm Center is not in seed testing as recommended for agricultural and tree seeds, but as a tool during seed cleaning to see in a matter of seconds whether empty, immature, insect-damaged, and broken seed have been removed. It has proven useful in Achillea, Alstroemeria, Aquilegia, Aruncus, Aster, Baptisia, Begonia, Campanula, Chrysanthemum, Coreopsis, Dianthus, Euphorbia, Geranium, Hemerocallis, Impatiens, Iris, Lilium, Lupin, Lysimachia, Narcissus, Pelargonium, Penstemon, Petunia, Phlox, Platycodon, Ranunculus, Rudbeckia, Salvia, Silene, Stokesia, Tagetes, Talinum, Verbena, Veronica, and Viola.