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.
Abstract
Suitable parents for the production of F1 hybrid seed between almond and root-knot nematode resistant peach were selected. Three of 13 almond selections were found which, when pollinated by ‘Nemaguard’ pollen, produced good sets of seed. When germinated, their seedlings showed good root-knot nematode resistance, hybrid vigor, and exceptional compatibility with almond tops.
The self-incompatibility of almond was used to permit natural pollination between selection CP5-33 and a selected seedling of ‘Nemaguard’, 3-28. The F1 hybrids proved to be very compatible as rootstocks with almond and peach tops and imparted increased vigor to them.
Both ‘Nemaguard’ and a selected seedlings of ‘Nemaguard’ served as good pollen parents. ‘Okinawa’ peach, another rootknot nematode resistant peach type rootstock, was a less satisfactory pollen parent.
Science and Technology is one that gives a good overview of the whole area of seed development, dormancy and germination, including hormonal regulation of seed germination as well as seed quality aspects such as testing, seed vigor, seed-borne pathogens
The commercial pecan [Carya illinoinensis (Wangenh.) K. Koch] nursery industry relies on open-pollinated seed for rootstock production. Current choice of seedstocks by commercial pecan nurserymen was surveyed by telephone. Nurseries were called if they appeared in the directory used for the 1994 release of `Navaho'. Factors influencing the choice of seedstock include seed availability, nut fill, nut size, nut shape, seedling vigor, stand uniformity, and root characteristics. Local availability is important in the choice of seedstock. Those who harvest from their own trees usually credit the seedstock with other valuable characteristics, such as improved germination or vigor. Those who purchase seed usually target a preferred seedstocks for particular reasons but plant available seed in its absence. Well-filled nuts are recognized as being important for good germination. Small nuts are often preferred, especially when seed is purchased because more nuts per pound increases potential production. Round nuts are generally preferred over long nuts due to improved performance in some mechanical planters. Distinct regional preferences are apparent in the choice of seedstocks. Regionally preferred seedstock selections are generally validated by a survey of the research literature. Patterns of selection are consistent with climatic and geographic constraints. Tree procurement patterns have changed: many small nurseries have gone out of business, many large nurseries transport trees far from the nursery for sales, and quarantine restrictions have altered procurement patterns in Arizona. Recommendations are made to nurserymen, pecan growers, and researchers concerning continued progress toward improving regionally adapted pecan rootstocks through seedstock selection.
Soil particle size was found to affect expansion and contraction of soil mass as moisture changed; thus all other seedling emergence stresses changed. Cohesion between soil particles is changed by soil type, content, and particle size, which in turn changes seed energy requirements for survival and emergence. The rates of germinating/emerging; seed/seedlings accelerated or stopped depending on moisture fluctuations and water degradation of aggregates. The same moisture content may be damaging in one soil and not in another. Many seedlings with developed radicals and hypocotyls did not emerge and were found in pockets of fine soil below 0.5mm; or as if their energy had been used up. Stands after emergence frequently varied greatly in vigor and survival by many units. Vigorized seed produced variable results depending on soil stress limitations during emergence. That is, laboratory differences did not always reflect in the field. The least critical stress period was between planting and the emergence of the radical--about 1/3 of the emergence time. Ideal seed beds often produced poor stands when water management and temperature were stressful. Packing density was found a good measure of seed-bed soil quality.
Abstract
Dioecious asparagus cultivars produce seed that traditionally has been saved by growers. This practice had led to the loss of high yield and rust resistance of the original ‘Martha Washington’ and ‘Mary Washington’ cultivars, as well as others, because of random matings among the unselected male and female progeny plants. Even saving seed from vigorous female plants has little value because of random pollination by unselected males. Seed produced by dioecious cultivars causes 2 other problems. One is volunteer asparagus seedlings behaving as weeds in the cutting bed. The other is the diversion of photosynthate that is stored in the seed instead of the roots, thus reducing vigor and spear yield of the female plants.
A radish (Raphanus sativus L. cv. Scarlet turnip white tipped) seedling growth test was developed to examine promotive effects of 2-(3,4-dichlorophenoxy) triethylamine (DCPTA) on seedling vigor and plant development. Compared with controls, seed treatment using 30 μm DCPTA significantly (P = 0.05) enhanced the rates of root and hypocotyl elongation and seedling dry weight. Enhanced hypocotyl development by DCPTA showed a significant linear correlation (r = 0.83) with the increased taproot yield of mature plants grown from DCPTA-treated seeds. The harvestable taproot yield and harvest index of plants grown from seeds treated with 30 μm DCPTA were increased 109% and 38%, respectively, as compared with controls. Incubation of radish seeds in 30 μm DCPTA with actinomycin-D, alpha-amanitin, amisomycin, or cordycepin significantly reduced DCTPA-mediated seedling growth. These results indicate that nuclear gene expression and translation of mRNA on 80S ribosomes are required for the acceleration of seedling development by DCPTA.