Genetic markers have not yet been described for Lesquerella fendleri (Gray) Wats. a potential new industrial oilseed crop. Seeds of this species are also utilized as a primary component in some desert wildflower seed mixes. Allozyme variation was analyzed for aconitase (ACO), phosphoglucomutase (PGM), and phosphoglucose isomerase (PGI). Four codominant loci, useful as markers, were clearly resolved. In an open-pollinated population, an outcrossing rate and pollen gene frequency was obtained from 20 random families, using these loci. This initial estimate indicated that seed production primarily resulted from outcrossing. Male sterility was discovered in six bulk populations derived from single plant selections. The frequency of this trait, which could affect the outcrossing rate, was found to occur in 15 percent of the plants. Additional populations will be analyzed for validation.
David A. Dierig, Anson E. Thompson, and Earl R. Johnson
A.A. Abdul-Baki, H.H. Bryan, G.M. Zinati, W. Klassen, M. Codallo, and N. Heckert
Prolific flowering is essential for economic seed production in sunn hemp (Crotalaria juncea L.). Since flowers appear as racimes on the distal portions of secondary branches and since the branching is restricted by a strong apical dominance, lifting the apical dominance by cutting the tops of plants should induce more branches and more flowers per plant. We evaluated this concept in a field experiment conducted in 1999 at the Tropical Research and Education Center, Univ. of Florida, Homestead, by cutting main stems of 100-day-old plants in a dense stand (113,000 plants/ha) at 30, 60, and 90 cm above the soil surface. Cutting at all heights induced more branching and flowering than the control. The highest positive response was in plants in which the main stem was cut at 90 cm above soil surface.
F.J. Sundstrom, P. Guzman, and R.F. Stewart
Pathogen free seed has long played a critical role in reducing or eliminating the severity of various diseases in commercial fields. The California Crop Improvement Association (CCIA) provides quality assurance services to the seed industry that are designed to promote the production, distribution and use of high quality seedstocks for agricultural production. To that end, CCIA has developed a Disease Inspection Program to assist vegetable seed producers in eliminating the bacterium, Acidovorax avenae subsp. citrulli (AAC), from cucurbit (Cucurbitaceae) seedstocks. This program utilizes recommendations and standards beginning at parent seed production of hybrids through the production of commercial seedlots. Training of field personnel, field inspections and tissue tests, followed by growouts of at least 30,000 seedlings are used as components of this quality assurance program.
Kenneth W. Mudge and Chin-Chang Chu
In vitro asymbiotic seed germination, subculture, and outplanting of orchids is presented as a laboratory exercise suitable for students of plant propagation or tissue culture. Dendrobium antennatum (Lindley), Phalaenopsis (Blume) white hybrid, or both, are used in this exercise because they flower predictably in the greenhouse, are reliable for seed production, and germinate and grow rapidly in vitro. The exercises can be used to instruct students in the skills involved in orchid seed sterilization, sowing, and culture, as well as instruct students in the unique features of orchid reproductive biology and symbiosis. A schedule is suggested for stock plant flower pollination, capsule harvest, seed sowing, and seedling subculture so that the necessary plant material is available for students to sow, subculture, and outplant seedlings during a single laboratory session.
Pablo A. Goldschmied, Martha A. Mutschler, James W. Lorbeer, Dave P. Loparco, Leroy A. Ellerbrock, and Edward Cobb
All current onion cultivars are susceptible to Botrytis squamosa (BLB), in varying degrees. The wild onion relative Allium roylei possesses strong BLB resistance. To control this disease, BLB resistant onion populations are being created through backcross breeding using A. roylei. Interspecific sexual barriers reduce fertility and seed set, impeding gene transfer. It is relatively easy to make the interspecific F1 between A. roylei and Alliumcepa; however, sexual barriers severely limit seed production in subsequent generations. Nevertheless, we were able to select BC1F2 plants capable of generating high levels of BC2F1 seed. The BC2F1 plants had horticultural characteristics much closer to onion, and segregated for both BLB resistance and fecundity. One particular BC2F1 population gave the highest proportion of resistant plants in a field screen, and nearly all plants of this population produced true bulbs. 120 selected BC2F1 bulbs were retested for BLB resistance in a chamber assay and the most resistant plants were used to advance the transfer of BLB resistance. In 2004, BC2F2 and BC3F1 populations derived from the BC2F1 selections were screened for BLB resistance and used for seed production. 132 plants were selected in the field screen. The level of resistance in BC2F2 and BC3F1 is similar to BC1F2 and BC2F1, with no evidence of reduction in level of resistance with generations. Molecular screens for markers associated with resistance are routinely used in vegetable crops to transfer resistance genes. The creation of a molecular assay for BLB resistance would accelerate its transfer and release of resistant varieties. We are using AFLP and SSRs in a search for DNA markers associated with BLB resistance in our materials.
Jonathan M. Lehrer, Mark H. Brand, and Jessica D. Lubell
While japanese barberry (Berberis thunbergii DC.) is an acknowledged invasive plant naturalized throughout the eastern and northern U.S., the danger posed by its popular horticultural forms is unknown and controversial. This work analyzed the reproductive potential and seedling growth of four ornamental genotypes important to the nursery industry. Fruit and seed production was quantified in 2001, 2002, and 2003 for multiple landscape plants of B.t. var. atropurpurea, `Aurea', `Crimson Pygmy', and `Rose Glow'. The average number of seeds produced per landscape specimen ranged from lows of 75 and 90 for `Aurea' and `Crimson Pygmy' to 2968 for var. atropurpurea and 762 for `Rose Glow'. Seed production relative to canopy surface area for `Rose Glow' was similar to `Aurea' and `Crimson Pygmy' and all three cultivars were less prolific than var. atropurpurea in this regard. Cleaned and stratified seeds from var. atropurpurea, `Crimson Pygmy' and `Rose Glow' showed an average greenhouse germination rate of 70% to 75%, while `Aurea' yielded 46% germination. A subpopulation of seedlings from each genotype accession was grown further outdoors in containers for a full season to ascertain seedling vigor and development. The vigor of 1-year-old seedlings, as measured by dry weight of canopy growth, for progeny derived from `Aurea' (0.70 g) and `Crimson Pygmy' (0.93 g) was significantly less than var. atropurpurea (1.20 g) and `Rose Glow' (1.33 g). These results demonstrate that popular japanese barberry cultivars express disparate reproductive potential that, after further study, may be correlated with invasive potential. Some popular commercial cultivars may pose significantly less ecological risk than others.
Neil O. Anderson and Peter D. Ascher
Chrysanthemum [Dendranthema ×grandiflora Tzvelv. (syn. Chrysanthemum ×morifolium Ramat.)] breeding programs have been selecting for reduced expression of self-incompatibility (via pseudo-self-compatibility) to create inbred families with selected genotypes to serve as parents for F1 hybrid chrysanthemum seed production. However, it is not known to what extent inbreeding is affecting fertility in this outcrossing, heterozygous species. The objective of this research was to assess male/female fertility changes (gain/loss) in successive inbred generations of chrysanthemums. Pseudo-self-compatible chrysanthemum parents (n = 41 inbred, noninbred, and recombinant inbred) were chosen for fertility analyses. As many as three generations of inbreds (I1, I2, and I3) from self-pollinations were created using rapid generation cycling. Female and male fertility levels of the parents and all derived inbred populations were assessed using outcross seed set and pollen stainability, respectively. Average seed set ranges were 0.3% to 96.1% (inbred parents), 24.5% to 38.5% (noninbred parents), and 0.9% to 85.1% (recombinant inbred parents); these began decreasing in the I1 and continued to decline steadily into the I3. Statistically significant (P < 0.05) decreases in seed set occurred in n = 23 (56.1%) inbred families; the remaining inbred families had similar or higher fertility than the parents. Pollen stainability was >50% for the parents, but began declining in some inbred families as inbreeding progressed. Fertility reductions were attributed to inbreeding depression. Lack of significant fertility losses in other inbred families demonstrates the opportunity of selection of fertile inbred parents for use in hybrid seed production.
Soon O. Park, Kevin M. Crosby, Rongfeng Huang, and T. Erik Mirkov
Male sterility is an important trait of melon in F1 hybrid seed production. Molecular markers linked to a male-sterile gene would be useful in transferring male sterility into fertile melon cultivars and breeding lines. However, markers linked to the ms-3 gene for male sterility present in melon have not been reported. Our objectives were to identify randomly amplified polymorphic DNA (RAPD) markers linked to the ms-3 gene controlling male sterility using bulked segregant analysis in an F2 population from the melon cross of line ms-3 (male-sterile) × `TAM Dulce' (male-fertile), convert the most tightly linked RAPD marker to the ms-3 gene into a sequence characterized amplified region (SCAR) marker based on a specific forward and reverse 20-mer primer pair, and confirm the linkage of the RAPD and SCAR markers with the ms-3 gene in an F2 population from the cross of line ms-3 × `Mission' (male-fertile). A single recessive gene controlling male sterility was found in F2 individuals and confirmed in F3 families. Two RAPD markers that displayed an amplified DNA fragment in the male-sterile bulk were detected to be linked to the ms-3 gene in the F2 population from the cross of line ms-3 × `TAM Dulce'. RAPD marker OAM08.650 was closely linked to the ms-3 gene at 2.1 cM. SCAR marker SOAM08.644 was developed on the basis of the specific primer pair designed from the sequence of the RAPD marker OAM08.650. The linked RAPD and SCAR markers were confirmed in the F2 population from the cross of line ms-3 × `Mission' to be consistently linked to the ms-3 gene at 5.2 cM. These markers were also present in 22 heterozygous fertile F1 plants having the ms-3 gene. The RAPD and SCAR markers linked to the ms-3 gene identified, and confirmed here could be utilized for backcrossing of male sterility into elite melon cultivars and lines for use as parents for F1 hybrid seed production.
Rita L. Hummel and Wilbur C. Anderson
Cabbage seed production in western Washington is at risk from freeze damage in the months of November to February. During the 1987-1988, 1988-1989 and 1989-1990 winters, the cold protection efficacy of 5 floating row covers (Agryl P17, Dewitt N-sulate, Reemay 2014, DuPont Typar, VisQueen Porous Row Cover) and straw was tested on field-grown cabbage. Air temperature in the cabbage crown, Tk50 of cabbage leaves, plant winter survival and seed yield were measured. During a severe freeze in February 1989, an average temperature of -11.1 °C was recorded in the uncovered controls while temperatures under the row covers were -6.7°C, -6.8°C and -8.4 °C under the N-sulate, VisQueen and Agryl covers, respectively. When compared to controls in June of 1989, row covers increased the survival of the more cold hardy `Brunswick' plants but did not significantly increase seed yields. The duration and severity of the February 1989 freeze was such that all of the less cold hardy `Golden Acre' plants were killed.
Leslie K. Manning, Robert R. Tripepi, and Alton G. Campbell
Postharvest plant residues from Kentucky bluegrass (Poa pratensis L.) seed production may be useful as an organic amendment in container mixes. Postharvest residues of `South Dakota' bluegrass were composted with and without an N amendment, such as cattle manure (M) or alfalfa seed screenings (As). After composting, all residues were ground to 4- to 6-mm segments and mixed with sphagnum peat and perlite (2:1:1 by volume). Media that contained amended bluegrass residues had higher electrical conductivity (EC) values and lower C: N ratios (<19:1) than media made with other bluegrass residues. Tomato (Lycopersion esculentum Mill. `Laura') seedlings grown in residue composted with As had at least 3.5- and 4-fold more shoot dry weight and leaf area, respectively, than plants grown in any other composted medium. In addition, seedlings grown in composted bluegrass residues amended with As had 34% and 41% more shoot dry weight and leaf area than plants grown in a 75% peatmoss–25% perlite medium. Composted residue amended with alfalfa seed screenings appears to be suitable as a peatmoss extender in container media.