James T. Watkins
Victor M. Sanchez, F.J. Sundstrom, and N. Suzanne Lang
This study investigated the influence of plant size, as determined by plant density, and fruit load variation on the production and quality of bell pepper (Capsicum annuum L.) seeds. Six-week-old `Resistant Giant no. 4' bell pepper seedlings were transplanted 15, 30, 45, and 60 cm apart. Plants spaced 45 cm apart were not thinned or were thinned to one or three fruit per plant. Pepper plants grown at low plant densities produced larger fruit and seeds that germinated faster and at higher percentages than plants grown at higher densities. Assimilate export rate (AER) increased linearly with plant spacing. At harvest, C exchange rate (CER) and AER of plants with nonthinned fruit loads were ≈ 300% and 500% higher, respectively, than those of plants with one or three fruit. Fruit thinning decreased CER and AER; however, seeds produced by plants with one or three fruit had significantly higher germination percentages than plants with full fruit loads. These observations suggest that the high CERS of smaller plants with nonthinned fruit loads may have been insufficient to compensate completely for the higher sink demands. Therefore, crop cultural practices that increase the ratio of pepper plant size to total fruit count may increase the quality of seeds produced by those plants.
G. Hacisalihoglu, D.H. Paine, M.B. Hilderbrand, A.A. Khan, and A.G. Taylor
High-quality seed lots are required for successful establishment of horticultural crops. Testing methods are needed that can detect the early phases of aging prior to a significant loss in germination. Quality was assessed using both germination speed and uniformity on non-primed and primed, as well as non-aged and aged, lettuce (Lactuca sativa L.) seed. Speed and uniformity were quantified using time to 50% (T50) germination and one standard deviation (Tsd), respectively. Embryo elongation was developed as a rapid test by first soaking seeds for 2 hours, then cutting and removing the distal one-third of the seed, and finally observing the percentage of visibly elongated embryos from the seed coverings over time. The mild aging conditions employed in this study (45 °C and 50% relative humidity for up to 21 days) had little influence on viability (germination in all treatments was >98%), but reduced germination rate (increased the time for T50 and Tsd). Primed seeds aged faster than non-primed seeds under the same aging conditions. The percentage of elongated embryos was calculated at hourly intervals after cutting, and treatment differences were observed after a total hydration period of 5 hours. The embryo elongation test detected aging in both primed and non-primed treatments.
Ann C. Smigocki and Iris J. Honeczy
Lycopersicon esculentum cv. UC82b cotyledons were co-cultivated with A. tumefaciens carrying vectors with modified isopentenyl transferase (ipt) genes. The ipt gene was placed under the control of the RUBISCO promoter in both the sense and antisense orientation. Over 50 transformants were recovered on kanamycin-containing media. Seeds from RO plants were germinated on selective media and R1 plants transformed with the ipt gene identified by PCR and Southern blot hybridization. Phenotypes of the R1 plants, whether transformed with the ipt gene in the sense or antisense orientation, were comparable to the control plants transformed with an inactive cytokinin gene. Fruit weights from both were similar to those from control plants, however, yields were reduced and ripening delayed. Most fruit had no seeds or very few small seeds. Cytokinin levels are being determined in order to correlate them to the observed phenotypes.
Lisha He and J.S. Burris
Sweet corn (Zea mays var. rugosa L.) seed with the endosperm mutant shrunken-2 (sh2) often exhibit low seed vigor and poor field emergence. Seed respiration and carbohydrate metabolism during germination of supersweet `Jubilee' (sh2) and sugary sweet `Jubilee' (Sh2) were studied. There were no significant vigor differences expressed by isolated embryos from sh2 and sugary (Sh2) seeds, indicating similar embryo physiology. Respiration rates were higher in the sh2 genotype during early stages of germination (24 hours) while they declined later. The available sucrose originating from the endosperm reserves was depleted by day 4. This insufficiency of a sustained energy source due to rapid consumption and minimal stored reserves may limit subsequent seedling growth in the sh2 genotype.
Yehoshua Saranga, Avishag Levi, Pavel Horcicka, and Shmuel Wolf
The cause for the differences in germination ability of large and small confection sunflower (Helianthus annuus L.) seeds was investigated over 3 years. The source-sink relationship was manipulated to better explore the differences between seeds of various sizes and to study the role of the embryo and the pericarp (hull) in controlling germination ability. Percent germination of large seeds was significantly lower than that of small seeds when tests were performed at 15 °C. Increasing the ratio of leaf area to number of developing seeds caused an increase in mean seed mass, but resulted in a lower percentage of germination. Seed vigor, as measured by mean time to germination or to emergence of hulled seeds or by rate of root elongation, was negatively correlated with embryo mass, indicating that the low vigor of large seeds is not due to the mechanical barrier imposed by the hull. Analysis of electrolyte leakage confirmed the hypothesis that the low quality of large seeds results from a disturbance during the process of seed development.
Highly educated and demanding customers, complex business structures, rapidly changing technology, greater liability, and strong competition bring unprecedented pressures on the vegetable seed industry. An effective quality system involving all of the business functions (breeding, parent seed maintenance, production, processing, testing, seed treatment, packaging, marketing, and customer service) seems to be inevitable. The future of the seed business belongs to companies that can provide continuous supplies of high-quality seed with necessary support and technical services and can afford investment in a rapidly advancing technology.
Optimization of crop production can be accomplished only if successful stand establishment is achieved first, since each plant contributes to the total crop yield. Reduction of plant populations after planting will reduce yield and/or quality, even though plants compensate to some degree for stand losses. Successful stand establishment is achieved if factors that affect establishment are known, evaluated, and modified appropriately at the time of field planting. The factors that affect stand establishment are biotic and/or abiotic. Biotic factors are generally pathogens that attack plants as parasites, while abiotic factors are the environmental and physical conditions to which the plant or seed is exposed at the time of planting. Abiotic factors can be classified under three headings: soil, planting requirements, and environmental stress.
Gary A. Couvillon
Several studies with annual crops have shown that large seeds improve percent germination, seedling growth, and uniformity, yield, seedling vigor, and stress tolerance. Little information is available on the influence of seed size on the resulting seedlings of woody plant species. Cercis canadensis L. seeds were divided into large and small seed size fractions and the seeds scarified, stratified, and planted. A larger percentage of large seeds germinated than did small seeds. Seedlings from large seeds had a greater peak and germination value than small seeds, indicating greater vigor and a more rapid germination rate thus more uniform seedlings. Seedlings from large seeds, as indicated by fresh and dry weights, were larger and contained a greater leaf area than those produced by small seed.
Zhang Jianhua, Miller B. McDonald, and Patricia M. Sweeney
This study examined the use of random amplified polymorphic DNA (RAPD) markers as a means to identify cultivars of petunia (Petunia hybrida Vilm) seedlings and cyclamen (Cyclamen persicum Mill.) seeds and to determine the genetic purity within cyclamen seeds. Bulked samples of six petunia and five cyclamen hybrid cultivars, respectively, produced consistent RAPD marker profiles. Evaluation of individual seeds from a single cyclamen hybrid produced polymorphic banding patterns that were attributed to genetic variability present in the female and male inbred parents. These results show that RAPD makers can be used to quickly assess the genetic purity of selected cultivars of these two flower seed crops.