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- Author or Editor: Sharon Kester x
Early seedling growth rate can be used to estimate seed vigor for small-seeded vegetable and flower seeds. However, hand measurement of small seedlings is tedious and difficult to reproduce among analysts. Computer-aided analysis digital images of seedlings should improve accuracy and reproducibility. A flat-bed scanner fitted with base and top lighting provided high resolution images of even small-seeded species like petunia [Petunia ×hybrida `Blue Picotee' (Hort) Vilm.] and lisianthus [Eustoma grandiflorum `Mariachi Pure White' (Raf.) Shinn]. Uniform lighting was provided and images were captured and analyzed in less than 2 minutes. A clear, cellulose film was used as the germination substrate in petri dish germination assays to facilitate capturing images with a flat-bed scanner. The transparent medium permitted seedlings to be imaged without removal from the petri dish and also allowed for repeated measures of the same seedlings in order to calculate growth rate. Six species evaluated in this study included cauliflower (Brassica oleracea L., var. Botrytis), tomato (Lycopersicon esculentum Mill. `New Yorker'), pepper (Capsicum annuum L. `North Star'), impatiens [Impatiens walleriana Hook. f. `Impact Lavender'], vinca [Catharanthus roseus (L.) G. Don. `Little Bright Eye'], and marigold (Tagetes patula L. `Little Devil Flame'). For germination and early seedling growth, the cellulose film compared favorably with other standard germination media (blue blotter and germination paper) for five of the six species tested. Computer analysis of seedling length was possible for all six species and was statistically similar to hand measurements averaged for three analysts.
Standardized seed vigor tests must be developed for greenhouse-grown flower species. Current vigor tests used to evaluate large-seeded agronomic crops are generally not useful for evaluating smaller-seeded flower species. One alternative is to use radicle length in seedlings grown under controlled environments as an indicator of seed vigor. For that purpose, a seed vigor test was developed that uses digital images taken using a flat bed scanner to measure radicle length in small-seeded flower species. A novel, cellulose substrate was used for germinating seeds. It provided similar moisture-holding properties to standard germination blotters used by commercial seed analysts, but is clear. This has allowed for quick image acquisition without removing seedlings from the petri dish. Correlations were made between seedling growth (radicle length, total seedling length, and total seedling area) with other vigor tests (saturated salts accelerated aging) and greenhouse plug flat emergence. For several seed lots of impatiens that varied in initial seed quality, radicle length after 4 days showed good correlations (>R 2 = 0.79) with other measures of seed vigor for describing seed quality. This system is an improvement over other attempts to use computer-aided assessment of digital images because it provides digital images that do not vary due to external lighting; it uses software that can evaluate radicle length in a petri dish assay that does not require a slant-board for straight radicle growth; it relies on standard germination technics used by every seed lab; it uses a clear substrate to replace the opaque blotter to allow digital images to be taken within the petri dish; and accurate measurements of seedling parts is performed in under 2 min per petri dish.
Quercus falcata acorns were cold-stratified for 120 days and then sown in vermiculite under greenhouse conditions. When radicles were 7 cm long, the root tip was either removed (physically pruned) or dipped in a copper hydroxide solution (copper-treated). Intact root systems were used as control. Seedlings were then moved to a root box to observe root system architectures. The box was built of clear plexiglass 2.5 mm thick, and each face was 25.7 × 35.7 cm. Styrofoam spacers were used to separate faces, and nuts and bolts were placed along edges to hold the root box together. To permit observation of the entire root system, plants were grown in a plane between the plexiglass surface and a nylon sheet that separated roots from the medium (MetroMix 510). At 7, 9, and 11 days after treatment, the entire root system was traced on an acetate sheet, and number of internal and external links and number of secondary and tertiary roots were recorded. Total length, internal and external root links length, were obtained using digital analysis (MacRhizo). Dry weight of roots and shoots was collected at the end of this experiment (day 11). Treatment effects were evident 11 days after treatment. Copper-treated plants had statistically more secondary roots and larger internal link length than control or physically pruned plants. Also, copper-treated plants had smaller mean external link length, showing a more branched root system. Root biomass was similar for all treatments; however, copper-treated plants had smaller root: shoot ratio. This suggests that copper was acting as more than a pruning agent because copper-treated plants showed a different root system architecture compared to physically pruned plants.
Root and shoot development in Marigold `Little Devil Flame' was studied after being grown for varying lengths of time in 392-count plugs before transplanting to six-pack cells. Seedlings were grown for 0, 5, 10, 15, 20, and 25 days before transplanting to six-packs. All plants were measured at day 25. There was no significant difference in total root length, area and dry weight per plant or in leaf area and shoot dry weight per plant for seedlings transplanted from 0 to 15 days. Both total root dry weight and total shoot dry weight of seedlings transplanted on day 20 was reduced by 32% compared to seedlings that were not transplanted. Total root dry weight of seedlings transplanted at day 25 was reduced by 60% while total shoot dry weight of seedlings was reduced by 56% from those not transplanted. In a separate experiment, the growth rate of seedlings grown in plugs was sigmoidal (r 2 = 0.98). Growth rate was significantly reduced between 20 and 25 days in the plug. These results suggest that root restriction in the plug may be a factor in the reduction of seedling growth following transplanting.
Satin flower (Clarkia amoena ssp. whineyi: syn. Godetia whitneyi) is a cool temperature, high light plant grown as a cutflower in Japan, Europe and California. In preliminary greenhouse cutflower and pot plant trials, satin flower plants flowered in 10-11 weeks when grown under 24hr supplemental HID lighting compared to 20-22 weeks under ambient winter conditions. In Sept. and Nov. 1989, satin flower plants were treated with the following supplemental and photoperiodic lighting treatments ambient light; SD (ambient day, black cloth 1600 to 800 HR); LD (ambient day, incandescent light 1600 to 400 HR, 5 μmol s-1 m-2); SD-SPL (ambient day supplemented with 100 μmol s-1m-2 HPS, black cloth 1600 to 800 HR); LD-SPL (ambient day supplemented with 100 μmol s-1m-2 800 to 400 HR), Node number and days to flowering were significantly different between the treatments. Plants grown under LD-SPL flowered in 10 weeks and had 32 nodes, LD -13 weeks and 37 nodes (weak, spindly, few flowers), SD-SPL - 17 weeks and 70 nodes, SD - 21 weeks and 75 nodes. Strategies for supplemental lighting for greenhouse cutflower production will be discussed.
In vitro shoot multiplication of white Eastern redbud was successful using two-node mature explants from the initial spring flush on a woody plant medium (WPM) supplemented with benzylaminopurine (BAP). Optimal shoot proliferation was obtained at 10-15 μM BAP. Treatment with thidiazuron produced fasciated (stunted) adventitious shoots which failed to elongate. Successive subcultures increased the ability of explants to form shoots. However, shoot tip necrosis became a problem after 7-8 subcultures. Shoot tip necrosis is being studied by comparing shoot multiplication on bacto-agar vs. gelrite, increasing the Ca concentration in WPM and by trying to reduce the phenolic exudate by the explants with PVP or activated charcoal. Microshoots >3 cm long were rooted by pulse treatment on half strength WPM containing 300 μM IBA or NAA before being moved to hormone free WPM. There was a different morphology between IBA and NAA induced roots, although the number of roots were comparable. IBA treated microcuttings developed branched, fine roots, whereas NAA treated plants produced unbranched, coarse roots. Rooted microshoots were successfully acclimated to greenhouse condition.
Ethephon and ethylene gas applied to intact Eastern redbud seed induced germination in 44 or 53% of dormant seed. However, endogenous ethylene production was not found to be correlated with the release from dormancy during chilling stratification (5°C). Seeds stratified in the presence of 6000 ppm 2.5-norbomadicne germinated at the same percentage as control seeds. Isolated embryos treated with 100 to 500 μM AOA or 1000 μM silver thiosulfate germinated at a slower rate than control seeds, but the release from dormancy during stratification was unaffected by either ethylene inhibitor. Ethylene evolution, ACC and MACC content remained at a low level throughout stratification. EFE activity was not detectable in hydrated dormant or non-dormant seed. All ethylene parameters measured increased sharply during germination with peak activity correlated with radicle emergence. These data indicated that ethylene production was linked to germination, but unrelated to dormancy release in Eastern redbud seed.
Warm season annual flowers were trialed as field grown cutflowers in the summer of 1989. Plants were transplanted to the field in early or late May and grown at densities of 40 plants m-2 in beds with black plastic mulch, trickle irrigation and support wires. Tall ageratum, `Horizon Blue'., plants were harvested throughout the summer with total yields of 290 stems m-2with stem lengths over 36 cm long. Stem lengths increased significantly over the summer; 40% of the stems harvested in September were over 56 cm long. Spray asters, `Matsumoto Blue', Matsumoto Red' and `Serene Red', were harvested eight weeks after transplanting with yields of 20 to 30 stems m-2; 60% of the stems were 36-45 cm long and 40% were 46-55 cm long. Tall, crested celosia, `Red Chief', `Gold Chief' and `Fire Chief', plants were harvested 8 weeks after transplanting with yields of 45 stems m-2 over 60% of the stems were 45 cm long or longer. Godetia, `Grace Red' and `Grace Salmon', plants sown March 3 and planted in the field April 10, performed well; later plantings were much less successful. Plants were planted at a density of 5 m-2 and produced 25 to 50 flower stems per plant; stem lengths were 30 to 38 cm long.
Echinacea are North American members of the Asteraceae, and all can show some degree of endogenous physiological seed dormancy that is alleviated by chilling stratification. In some species, ethephon has been shown to substitute for chilling stratification to relieve dormancy. The objective of this research was to investigate the effect of ACC on dormancy and germination in five Echinacea species. Germination for each species was 90%, 59%, 99%, 81%, and 21%, respectively. Germination on 5 mM ACC improved germination in E. tennesseensis, E. paradoxa, and E. simulata to 82%, 99%, and 82%, respectively, but there was no change for E. purpurea and E. angustifolia. Germination rate was dramatically accelerated in all species in the presence of ACC. On average, there were 57% more seeds germinated on ACC after 3 days compared to untreated seeds. Exposing E. purpurea and E. tennesseensis seeds to 1 or 2 days of 5 mM ACC before drying and subsequently re-hydrating the seeds did not have the same effect as continual exposure to ACC. Similarly, there was no clear enhancement of adding ACC during stratification over the improvement gained by chilling stratification alone. Seeds produced more ethylene upon germination following both stratification and ACC treatment. However, significantly more ethylene is produced during germination in ACC-treated seeds. It was clear that ACC-treated seeds showed improvement for enhanced germination speed and in some cases germination percentage. Unfortunately, this enhanced germination was not retained in seeds treated with ACC and dried prior to germination. Additional work is required to develop a commercially viable method of loading ACC into seeds for germination enhancement.
A laboratory exercise is presented that demonstrates the impact of seed coverings and hormones on seed dormancy and release in seeds with endogenous, physiological dormancy. The materials and methods are simple and inexpensive and can be accomplished as an on-campus laboratory or as a distance education exercise. The execution of the laboratory is rapid (≈1 hour), and the results are obtained in 2 weeks. The exercise generates an opportunity for the discussion of a complex subject that involves the interaction of two tissue types within the seed (the embryo vs. the seed coverings) and nicely illustrates their role in seed dormancy maintenance.