In vitro cold storage of Rubus germplasm was investigated using several environmental conditons and types of storage containers. Shoot cultures of Rubus species and cultivars were grown in either tissue culture bags or 20 × 150 mm glass tubes and compared for plant condition and survival under various storage conditions. Cultures stored at 10 C in the dark were in poor condition after 6 months. Cultures kept at 4 C were in much better condition and had higher survival rates after 18 months when stored with a 12 h daylength rather than total darkness. Overall there were no differences in survival or condition between cultures in tubes and bags. Contamination rates were 15% in tubes and 0% in bags. Plants in tissue culture bags could be stored for 9 months at 25 C with 16 h light when the nitrogen level of the MS medium was reduced to 25% and the medium volume was increased from 10 to 20 ml per bag. Genotype differences were apparent under all conditions tested. The best storage condition for Rubus germplasm was 4 C with 12 h light. Plastic tissue culture bags were preferred over tubes due to lower contamination rates.
Barbara M. Reed
Dario Ramirez and Harvey J. Lang
Production of holiday cactus has been limited by the common occurrence of marginal chlorosis of the phylloclades, which can lead to losses in crop quality. This work was conducted to determine if poor growth and phylloclade yellowing could be correlated to applied Fe concentration. Rooted cuttings of Schlumbergera truncata `White Christmas', `Twilight Tangerine', 'Christmas Charm', and `Lavender Doll' were transplanted into a modified Hoagland's solution, adjusted to a pH of 6.3, containing Fe-EDTA at either 0,10,20,30, or 40 mg·liter–1 Fe. Plants were grown in a controlled environmental chamber under 16 h daylength for 16 weeks at 22/18C day/night temperature. Plants grown under 0 and 10 mg·liter–1 Fe had significantly greater fresh weight, height, and root length than plants grown under higher Fe concentrations for all cultivars. Comparison of tissue analysis results revealed a direct correlation between poor growth and levels of Fe within the tissue. There was no correlation, however, between Fe concentration and phylloclade edge yellowing, as yellowing occurred sporadically in all treatments. Comparison studies in the greenhouse of plants grown in peat: perlite medium showed similar trends.
Milton E. Tignor, Frederick S. Davies, Wayne B. Sherman, and John M. Davis
Poncirus trifoliata (L.) Raf. seeds were germinated in perlite under intermittent mist at about 25 °C and natural daylight in a greenhouse. Two-week-old seedlings were then transferred into a growth chamber at 25 °C and 16-hour daylength for 1 week. Tissue samples were collected at 0, 6, 24, 168, and 504 hours after temperature equilibration at 10 °C. Freezing tolerance at –6.7 °C, as determined by electrolyte leakage, and stem (leaves attached) water potential (ψx), measured using a pressure chamber, was recorded for a subset of seedlings for each time interval. Red coloration (apparently anthocyanin) developed at the petiole leaflet junction and buds after 48 hours at 10 °C and gradually occurred throughout the leaves during further exposure. Complementary DNA clones for phenylalanine ammonia lyase (PAL), 4-coumarate: coA ligase (4CL), and chalcone synthase (CHS) were used to probe RNA isolated from the leaves. No increase in steady-state messenger RNA level was detected. Increases in freeze hardiness occurred within 6 hours in the leaves, and continued for up to 1 week. Water potential initially decreased from –0.6 to –2.0 MPa after 6 hours, then returned to –0.6 MPa after 1 week. Thus, Poncirus trifoliata seedlings freeze-acclimate significantly after only 6 hours at 10 °C.
Jeffery K. Iles and Nancy H. Agnew
Nine herbaceous perennial species were evaluated for use as flowering pot plants for late winter and early spring sales. Plugs of Achillea `King Edward', Arabis sturii, Armeria `Alba', Bergenia `New Hybrid', Chrysogonum virginianum, Dianthus `War Bonnet', Phlox `Chattahoochee', Platycodon `Sentimental Blue', and Veronica `Sunny Border Blue' were established in 14-cm (0.8-liter) round plastic containers, grown for one season, and covered with a thermoblanket for winter. Five plants of each species were transferred to a 21 ± 3C glasshouse for forcing under natural daylength at six 10-day intervals beginning 1 Dec. 1993. By this date plants had experienced approximately four weeks of temperatures below 5C. Ambis, Chrysogonum, and Phlox, species that naturally flower in spring, were the most floriferous. Days to first flower for Arabis decreased from 30 to 26 while flower number increased 44% by the 20 Dec. forcing date. For Phlox, days to first flower decreased from 36 to 31 by 20 Dec., but flower numbers were similar regardless of forcing date. Chrysogonum averaged eight flowers throughout the study, but days to first flower increased from 25 (1 Dec.) to 31 in all following forcing dates.
Erika Szendrák and Paul E. Read
The temperate native terrestrial orchids are endangered species. Their propagation from seeds poses specific problems. It is well known that orchid seeds are devoid of endosperm and in nature they need microscopic fungi in a symbiotic relationship for germination. We developed a successful asymbiotic in vitro culture method for germinating seeds of several temperate orchid species and for maintaining the cultures of young plantlets. The medium used for both germination and seedling culture was a modified FAST medium. Seeds were surface-disinfested for 10 minutes in a 10% calcium hypochlorite solution. After sowing, the cultures were kept under dark condition at 10–12°C for 4 weeks. After that the cultures remained in the dark, but the temperature was raised to 25–26°C until germination occurred. Thereafter cultures required alternating seasonal temperatures: 25–26°C from the beginning of April to the end of September and 17–19°C from October to March. For the development of the young plantlets natural dispersed light and prevailing day-length was favorable. After 2 years of aseptic culture they were suitable for transfer ex vitro. Different stages of seed germination and plant development were observed using a scanning electron microscope and will be included in this presentation. Further observation of the effects of different environmental factors is currently under investigation.
Barbara M. Reed
Medium-term in vitro cold storage of Rubus germplasm was investigated using various temperatures, photoperiods, and storage containers. Shoot cultures of several Rubus taxa were grown either in tissue-culture hags or 20 × 150-mm glass tubes. Cultures stored at 10C in darkness were in poor condition after 6 months. Overall survival and condition ratings were significantly better for bags than tubes when cultures were kept at 4C. Contamination was present in 14% of the tubes, but only 3% of the bags. Addition of a 12-hour photoperiod to 4C storage significantly improved both condition ratings and survival percentages of many individual genotypes. Evaluation of the 250-accession germplasm collection after 12 months at 4C (dark) showed 92% of accessions in bags and 85% in tubes in suitable condition to remain in storage. Storage of cold-sensitive genotypes in tissue-culture bags at 25C with a 16-hour daylength was extended to 9 months when the MS-medium nitrogen level was reduced to 25% of standard concentration. Survival of `Mandarin' raspberry stored for 9 months improved from 40% at 4C (100% N) to 90% at 25C (25% N). Results of these studies suggest that most Rubus germplasm can be stored safely at 4C with 12 hours of light. Plastic tissue-culture bags are preferred over tubes due to higher survival and lower contamination rates. Storage at 25C on reduced-nitrogen medium is an alternative method for cold-sensitive genotypes.
Carolyn L. Paynter and Barbara M. Reed
The National Plant Germplasm Repository, Corvallis, houses over 700 different Fragaria genotypes. Many of these produce few or no runners, making propagation difficult by in vitro or conventional methods. Experiments were run to determine the response of non-runnering genotypes to environmental conditions and GA3 treatments. Two groups of plants of 12 genotypes were grown in a 25°C growth chamber (GC) with 24 h light. One group was sprayed twice with 500 ppm GA3, 24 h apart, while a second group was not sprayed. Control plants of each genotype were grown at ambient temperature and long days and were not sprayed with GA3. Both F. vesca L. cultivars and day-neutral genotypes produced significantly more runners with the GA3 GC treatment than the unsprayed GC or the control. Most June-bearing cultivars had improved runnering with both GC treatments. A separate experiment using 30 genotypes with two GA3 sprays (500 ppm, 24 h apart) at ambient temperature and long daylength showed that plants with the GA3 sprays produced significantly more runners than unsprayed controls. In both experiments, GA3 sprays improved runner production by most of the unresponsive Fragaria genotypes.
Elizabeth Will, Terri W. Starman, James E. Faust, and Shane Abbitt
The objective was to study the flowering response of garden cultivars of Dendranthemum × grandiflorum (Ramat.) Kitamura to temperature and photoperiod. Fifteen garden mum cultivars were grown in ten temperature (18 and 24°C constant day and night greenhouse temperatures) and photoperiod (8, 10, 12, 14, and 16 h) combinations. Rooted cuttings were pinched above the fifth node and placed in the temperature/photoperiod treatments. When axillary shoots developed, all but one shoot was removed to produce a single stemmed plant. Photoperiods were provided by delivering 8 h sunlight, then pulling black cloth and providing daylength extension with incandescent bulbs. Days to visible bud, days to first bud color, days to flower, node number, and stem length were measured. By 11 weeks after the start of photoperiod treatments, no difference was measured in days to flower in the 8-, 10-, and 12-h photoperiods at 18°C. Days to flower increased as photoperiod increased from 12 to 14 h. At 18°C, five cultivars flowered in the 16-h photoperiod, while 10 cultivars developed crown buds, i.e., flower buds that initiated but had not developed. At 24°C, there was no difference in days to flower in the 8and 10-h photoperiod, while days to flower increased as photoperiod increased from 10to 12-h treatment. Cultivars formed crown buds but had not reached flowering in the 14and 16-h photoperiods at 24°C. Regardless of temperature, stem length increased as photoperiod increased above 10 h.
Remmie Booij and Bert Meurs
The harvest season for Brussels sprouts runs mainly from September to March. During this period the daylength is relatively short and the light intensity is low. Bud growth occurs, when photosynthesis is low. The question is, whether actual photosynthetic rate or rcdistrubution of earlier fixed photosynthates is the main source for bud growth. The aim of the present experiment was first to determine the gain of C and N and the distribution of these plant constituents within the plant, and second the role of the apical bud. Partitioning of dry matter over the plant parts and the allocation along the stem were determined. Contents of C, N, NO3 and soluble sugars in the dry matter were ascertained, and the total amounts of these components could be determined. From this analysis fluxes were calculated and the role of redistribution was investigated. Redistribution of soluble sugars and N from leaves before shedding contributed substantially to bud growth. The apical bud did not affect total dry matter production, but if removed, more dry matter became available for bud growth in the top region of the plant, resulting in a higher total bud yield.