The artichoke, Cynara scolymus, is normally propagated by cuttings from mother plants; however, it is possible to produce some types of artichokes from seed. Methods used for producing open-pollinated seed of onion and carrots may be suitable for producing artichoke seed. Outcrossing in artichokes occurs because of differences in maturity of the staminate and pistillate phases within flowers. Producing artichoke seed by simple inbreeding techniques is usually not successful because of vigor loss and low pollen production, low seed production, and late maturity of progeny. Outcrossing is the preferred method of creating a new variety. The cultivar `Imperial Star' was developed by crossing a thornless French line with an Italian line that had sharp woody spines, and a uniform, olive-green color. The French line was a bright green with some light purple at the base of the bracks. The F1 generation from this cross had good hybrid vigor, and produced abundant seed and pollen. The F2 generation segregated widely with many recombinant types that neither parent showed (e.g., extreme thorniness of leaves and petioles). Two plants were selected for sibling pollination. Subsequent generations of siblings within this type produced higher percentages of the desired type—glossiness, earliness, and high seed yield. Subsequent sibling crossing led to the selection of `Imperial Star', PVP. 9000179.
The physiological mechanisms leading to a decline in sprout-vigor, root growth potential and apical dominance during long-term aging of potato seed tubers are currently under investigation. Malondialdehyde (MDA) and ethane, products of peroxidative degradation of PUFA increase in seed-tuber tissues with advancing age (from 2 to 32 months of storage). MDA is known to react with free amino acids to produce lipofuscin-like fluorescent compounds (FC), which build-up in aging/senescent tissues of plants and animals. With advancing seed-tuber age, an increase in free amino acids, MDA and FC concentrations was evident. Moreover, high levels of MDA have been shown to reduce protein synthesis in both plant and animal cells. We therefore examined the extent to which seed-tuber age affects protein synthesizing capacity of tuber tissues during sprouting. Tissue disks from 6- and 18-mo-old seed-tubers at various stages of sprouting, were compared for their protein synthesizing ability by monitoring the incorporation of radiolabelled amino acids into TCA precipitable products. The rate of incorporation (dpm mg protein-1 min-1) was 1.8 to 5.4-fold higher in tissue from 6-mo-old, as compared to that from 18-mo-old seed tubers, at similar stages of sprout development. Loss in protein synthesizing ability (possibly due to direct peroxidative damage) may be an important factor contributing to loss of sprout-vigor from aged potato seed-tubers.
The propagation of clonal rootstocks for the pawpaw [Asimina triloba (L.) Dunal] has been unsuccessful; therefore, nurseries currently graft cultivars onto rootstock derived from locally available seed of diverse genetic origin. Great variation in pawpaw scion growth and suckering is observed with this seedling rootstock and grafted trees are also slow to come into production, often producing fruit 5 to 6 years after planting. In an effort to develop superior seedling rootstocks for pawpaw cultivars, seedstock was evaluated from the cultivars PA-Golden (#1), Sunflower, Susquehanna, NC-1, K8-2, and commercially available seed (RVT). The objectives of the experiment were to determine if: 1) genotype and seed size influenced vigor of greenhouse-grown container seedlings; 2) graft compatibility and growth rate of scions would vary by rootstock; and 3) scion precocity was influenced by various seedling rootstocks in the field. Greenhouse experiments were conducted in 2002, 2003, and 2004, and each year all seedstocks had a high germination percentage (95%) and uniform size within each seedstock. Seed size was an important factor in determining vigor in container production. Seed of `Sunflower' was large (1.65 g/seed) and consistently produced vigorous seedlings that were able to be chipbudded within 6 months. Seed of the selection K8-2 was smallest (0.94 g/seed) and showed the least vigor. Bud take was similar for the scions `Sunflower' and `Susquehanna' on all rootstocks. Twenty-one weeks after budding, scions of `Sunflower' were about 30% larger than scions of `Susquehanna'; however, source of seedling rootstock did not affect growth of either cultivar. Field evaluations have begun with the two cultivars budded onto the six rootstocks.
Achievement of head size uniformity at final harvest reduces loss and increases profitability for the hydroponic lettuce grower. Shoot fresh weight of `Cortina' lettuce (Lactuca sativa L.) at 7 or 21 days after planting (DAP) was inversely proportional to the number of days required for seedling emergence, and was greater for raw than for pelleted seeds. Head fresh weight at final harvest (61 DAP) was directly proportional to seedling length at 21 DAP, but raw and pelleted seeds produced equal head weights. Thus, initial seed (seedling) vigor differences were maintained to final harvest. Osmotic seed priming (–1.5 MPa KH2PO4, 20 h, dark) led to increased germination rate at 15, 25, and 35C; had no effect on germination synchrony; and increased germination percentage only at 35C. Covering raw or pelleted seeds sown in depressions of the phenolic foam trays with fine (No. 5) vermiculite compared to leaving the seeds uncovered, and soaking the trays in hydroponic solution rather than water, increased seedling shoot fresh weights. Seeds sown on their first day of germination or primed seeds gave greater seedling shoot fresh weights than pelleted seeds. However, the more uniform seedling shoot fresh weights from germinated seeds than from primed seeds was associated with more rapid and synchronous seedling emergence.
Flowering dogwood (Cornus florida) is a popular flowering tree that is a mainstay of the southeastern U.S. nursery industry. Because cultivars of this species are primarily propagated through budding onto seed-propagated rootstock, a reliable source of seeds is needed. Disease- and weather-related problems may sometimes result in a shortage of dogwood seed. The objective of this study was to develop a method of storing dogwood seed that would allow growers to save seed during years in which good flowering and seed set occur for use when insufficient seed is available. Open-pollinated seeds were collected in Fall 1999, dried to 6%, 10%, and 14% moisture, and stored at -20, 5, and 22 °C. After 1, 2 and 3 years of storage, seed was stratified for 3 months and then planted in the greenhouse. Percent germination was compared to that of a subsample of the seed lot that had been stratified and planted following collection in Fall 1999. After 1 year in storage, seed dried to 10% and 14% moisture and stored at 22 °C failed to germinate; germination of the other samples ranged from 55% to 97% of that of the control sample. After 2 or 3 years in storage, all seed stored at 22 °C and the seed dried to 14% moisture and stored at 5 °C failed to germinate. Germination of the remaining samples ranged from 76% to 97% of the control in year 2, and from 72% to 109% in year 3. After 3 years in storage, seed dried to 6% moisture and stored at 5 °C and seed dried to 10% moisture and stored at -20 °C had the highest germination percentage and best seedling vigor. Development of a seed storage method for dogwood will benefit both dogwood producers and germplasm preservation efforts.
Low-vigor seeds of black-eyed Susan (Rudbeckia fulgida Ait.) primed in aerated -1.3 MPa KNO3 for 7 days at 30C in darkness had double the total germination percentage at 30C and one-half the mean time of germination as nonprimed seeds. Priming the seeds in polyethylene glycol rather than KNO3 generally resulted in lower total germination percentage and longer mean time of germination. Osmotic priming increased total germination percentage and germination rate of seeds germinated at 21.9 to 32.2C, but the priming benefit on total germination percentage was greater at ≤27.6C. Total germination percentage of primed and nonprimed seeds was highest at 28.8 to 32.2C.
109 ORAL SESSION 28 (Abstr. 572–579) Fruit Set & Seed Quality–Vegetables
Switchgrass (Panicum virgatum L.) is one of the perennial, native, warm-season grasses recommended as a component of wildflower meadows. Seed treatments to alleviate low seed vigor and seed dormancy of switchgrass would enhance establishment of either plug transplants or seedlings after direct sowing into the meadow. “Heavy” seeds (45.5 mg/50 seeds) of open-pollinated switchgrass stored under cool and dry conditions (average 13 °C, 30% relative humidity) for 24 months had higher germination percentage than “light” seeds (26.0 mg per 50 seeds). In factorial combination, the heavy seeds were subjected to acid scarification (8 M H2SO4 for 5 min), sodium hypochlorite treatment (5.25% NaOCl for 15 min), and moist chilling (prechilling in 0.2% KNO3, for 14 days). Acid scarification followed by NaOCl treatment additively increased germination, a response that was associated with marked corrosion of the lemma margin in the distal region of the caryopsis, as observed by scanning electron microscopy. Prechilling the seeds following acid scarification and NaOCl further increased germination. All three treatments combined (acid scarification, NaOCl, and prechilling) almost doubled the final emergence and greatly increased seedling shoot dry mass in both a warm and cool postsowing environment. However, the effectiveness of these seed treatments was lost after 32 months of dry storage.
Objectives of this study were to determine the effects of lima bean seed size differences and a short chilling period after planting on seedling emergence rate, seedling abnormalities and vigor. Individual seeds of 'Jackson Wonder' lima bean were weighed and placed into one of five size classes: 24-33. 36-41. 44-49, 52-57, and 60-73 g per 100 seed. Seed of each size class were germinated at a constant 23-26C or chilled at 8C for 24 hrs and then moved to 23-26C conditions for the remainder of the study. A 24 hr chilling period after planting had a detrimental effect on subsequent lima bean seedling emergence only from 8 through 11 days after planting. Plant fresh and dry weights were significantly less for the chilled seed treatment. Temperature treatments had no effect on percent normal and abnormal seedlings or primary leaf area. No differences in seedling emergence number or rate were found among seed size classes. Smaller seedclasses had significantly fewer normal and more abnormal seedlings than larger seed size classes. The largest seed class produced seedlings with about two times more fresh and dry weights and leaf area than those from the smallest seed weight class. Plant fresh and dry weights and leaf areas from all seed size classes were significantly different from each other.
Dry heat treatment (DHT), a powerful and agrochemical-free means of inactivating seed-borne virus and other pathogens, has been extensively used for value-added vegetable seeds in Korea, Japan, and some other countries. Since seeds are treated with extremely high heat (75 °C or higher) for a long time (72 h or longer), heat-induced phytotoxicity symptoms are frequently observed. Even though various internal and external factors, such as seed maturity and vigor, maximum temperature and duration of DHT, are known to influence the severity of phytotoxicity, precise control of seed moisture contents during DHT is regarded as one of the most important factors for successful DHT. In an ideal condition using a specifically designed DTH machine, seed moisture content of bottle gourd, initially around 6.20% to 0.64% when stored in a storage room with 50% RH, decreased by 1% after 24 h at 35 °C (5.20% to 0.23%), and further decreased below 4% after 24 h pretreatment at 50 °C (3.64% to 0.37%). The seed moisture content was further reduced down to about 2% after 72 h DHT at 75 °C (2.16% to 0.28%). During the post-treatment conditioning at 50 °C and 70% RH for 24 h, the moisture contents were raised to about 6%(5.94% to 0.45%), thus approaching the initial moisture content of 6% to 7%. During the germination period, treated seeds showed slower absorption of water as compared to the intact seeds, thus suggesting that this slow absorption of initial moisture absorption may be responsible for the slow initial germination frequently observed in treated seeds. Final germination and seedling vigor were not affected by DHT.