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Open access

Dennis P. Stimart

Abstract

Excised embryos from Acer griseum (Franch.) Pax., A. mandshuricum Maxim., A. maximowiczianum Mig. (A. nikoense Maxim.) and A. triflorum Kom. germinated within 21 days when incubated in a lighted environment on wick cultures moistened with a solution of 10 mg/liter gibberellic acid (GA3). Cotyledon and epicotyl growth of A. maximowiczianum embryos were greatest when treated with GA3. Embryos of A. maximowiczianum incubated with 6-ben-zylamino purine (BA) or 6-furfurylamino purine (kinetin) developed the longest roots while those treated with indoleacetic acid (IAA) or naphthaleneacetic acid (NAA) remained tightly coiled and dormant. Excised embryos incubated in darkness or intact seeds placed in all treatments failed to germinate. In A. maximowiczianum 3 sites of dormancy delay germination: pericarp, seed coat, and embryo.

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Dianne Oakley, Julie Laufmann, James Klett, and Harrison Hughes

Propagation of Winecups [Callirhoe involucrata (Torrey & A. Gray)] for use as a landscape ornamental has been impeded by a lack of understanding of the seed dormancy and a practical method for overcoming it. As with many members of the Malvaceae family, C. involucrata produces hard seed. In the populations tested, it accounted for 90% of an average sample. Impermeability, however, is not the only limiting factor to germination. Three disparate populations of seed, representing two different collection years have been investigated using moist pre-chilling, boiling water, leaching, gibberellic acid, hydrogen peroxide and mechanical and chemical scarification methods. Scarifying in concentrated sulfuric acid stimulates germination of some seed fractions and causes embryonic damage in others, suggesting variation in seed coat thickness. Similar results were obtained using a pressurized air-scarifier; the hard seed coat of some seed fractions were precisely scarified while others were physically damaged using the same psi/time treatment. Placing seed in boiling water increases germination from 4%, 7%, and 18 % to 23%, 25%, and 77% in the three populations, respectively. Leaching for 24/48 h in cold (18 °C) aerated water or for 24 h in warm (40 °C) aerated water showed only a minor increase over the control. Pre-chilling at 5 °C for 30, 60, and 90 days showed no improvement over the control. Gibberellic acid-soaked blotters improved germination at 400 ppm to 20%, 10%, and 41%; at 500 ppm germination was reduced. Soaking seed for 24 h in a 3% concentration of hydrogen peroxide did not effect germination; at a 30% concentration germination was reduced. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development or seed age.

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James F. Harbage

Micropropagation of three Echinacea species, E. angustifolia, E. pallida, and E. purpurea, was investigated as a potential means of germplasm preservation of species faced with overcollection in the wild and rapid clonal propagation of elite individuals with unique medicinal or ornamental properties. Comparison of explant sources indicated vegetative explants resulted in high contamination rates when collected from shoot-tips (100%),but not when collected from nodal explants (11% to 39). Seed coat removal reduced contamination from 100% in intact seeds to near 0% in excised embryos. Removal of seed coats (pericarp and integument layers) also eliminated dormancy requirement for germination. All species responded with shoot multiplication and loss of rooting when BA or thidiazuron was added to culture medium. Medium with thidiazuron resulted in excessive adventitious shoot formation. Shoot multiplication rates were low (one to three shoots/explant) on medium with BA levels low enough to avoid adventitious shoot formation. Medium containing half-strength MS minerals resulted in more shoots with smaller leaves than full-strength MS minerals. Cultures did not perform well on Woody Plant Medium. Increasing subculture frequency from every 4 weeks to every 2 weeks increased shoot multiplication rates from 1.4 to 1.8 shoots per subculture and total shoots produced after 12 weeks of culturing (per initial explant) from 2.8 to 23.9. Rooting occurred readily on shoots isolated from E. purpurea without addition of IBA. Rooting was low or non-existent on shoots from E. angustifolia and E. pallida, respectively, regardless of IBA level, light conditions, or temperature. Methods described in this study allow rapid multiplication of three Echinacea species and subsequent rooting of E. angustifolia and E. purpurea. Future improvements in root induction treatments will allow more effective use of micropropagation for Echinacea germplasm preservation and multiplication. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine (BA), 1H-indole-3-butyric acid (IBA).

Open access

Faisal A. Al-Mukhtar and Dermot P. Coyne

Abstract

The accessions, PI 255960 (P1) (purple flowers, colored seed, curved pod tip, large seed) and G-19007 (P2) (white flowers, straight pod tip, white seed) of Phaseolus vulgaris L., both late maturing with many ovules and seeds per pod, were crossed with each other and with 2 early maturing, white flowered, white seeded, straight pod tip, low ovule number/pod parents, ‘Great Northern (GN) Emerson’ (P3) and ‘GN UI#59’ (P4). P1 and P2 appeared to possess the same genes for high ovule number/pod. The continuous distributions of ovule number/pod, seed number/pod, and seed weight in the F2 generations of the other crosses indicated quantitative inheritance. However, segregation data in their F3 generations suggested that ovule number/pod may be determined by additive action of the alleles of a single major gene. Moderately high broad sense heritability estimates were obtained for these traits. Purple flower color and seed-coat color were controlled by 2 different complementary dominant genes. Striped pod color and curved pod tip shape (Ct) were each controlled by different single dominant genes. Days to flowering was controlled by a single completely dominant gene; pod maturity was controlled by a single incompletely dominant gene for lateness. Linkage occurred between genes for flower color and pod color pattern, flower color and pod tip shape, and flower color and maturity. High seed number/pod was associated with purple flowers, colored seeds, and late maturity in the F2 of P3 × P1. Late maturity and high seed number/pod were also associated in the F2 of P4×P1, P3× P2 and P4 × P2. Moderately large negative correlations were found between number of seeds/pod and seed weight in all crosses involving P1 and P2. High ovule number/pod was associated with indeterminate growth habit and moderately late flowering in the F2 progeny from the indeterminate cultivar ‘G.N. Nebr. # 1’, crossed with a determinate isoline. No association between seed weight & seed-coat color was observed in the F2 of P3 × P1, and P4 × P1, but there was association between large seed and both late maturity and flower color.

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Gregory E. Welbaum

Muskmelon (Cucumis melo L.) seed crops sometimes contain seeds with split coats that expand to twice their normal water content. These expanded seeds are often referred to as “fishmouth” seeds, because the split seed coat resembles an open fish's mouth when viewed longitudinally. “Fishmouth” seeds are dead seeds. However, little is known about why death occurs inside the fruit before harvest. Hermaphroditic flowers were tagged at anthesis and fruits were harvested at various intervals during the later stages of development and decay. Seeds were removed from the fruits and incubated in water on germination blotter paper for 14 days. The percentage of germinable, dead and “fishmouth” seeds were averaged for each Harvest date. Fruit pericarp samples were analyzed for pH, ethanol, and acetic acid content. At 50 days after anthesis (DAA), just past edible maturity, 100% of the seeds germinated. However, at 60 and 78 DAA germination dropped to 60 and 17%, respectively, while the occurrence of “fishmouth” seeds increased from 2 to 54% over the same period. The ethanol content of the tissue increased from 0.11 to 0.28%, the pH dropped from 6.2 to 5.1, and acetic acid concentration increased from 3.0 to 3.7 mM from 50 to 60 DAA, respectively. However, when dried seeds were incubated in the laboratory under conditions similar to those within the fruit, the formation of “fishmouth” seeds was related to the ageing effects of long term hydration and was not correlated with any chemical product within the fruit.

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Richard L. Fery, Blair Buckley, and Dyremple B. Marsh

The USDA, Louisiana State University, and Lincoln University have released a new southernpea cultivar named WhipperSnapper. The new cultivar is the product of a plant breeding effort to incorporate genes conditioning superior yield and seed characteristics of Asian vegetable cowpeas into American snap-type southernpeas. The new cultivar was developed for use by home gardeners and market gardeners as a dual-purpose cultivar that can be used to produce both fresh-shell peas and immature, fresh pods or snaps. Typical ready-to-harvest WhipperSnapper snaps are green colored, 6.4 mm in diameter, 7.6 mm in height, and 24 cm long; the pods are slightly curved at the attachment end. Typical mature-green pods suitable for fresh-shell harvest exhibit an attractive yellow color, are 25 cm long, and contain 14 peas. Fresh peas are cream-colored, kidney-shaped, and weigh 24.5 g/100 peas. Dry pods exhibit a light straw color, and the dry peas have a smooth seed coat. The quality of WhipperSnapper seed is excellent. In replicated field trials, WhipperSnapper produced significantly greater yields of both snaps and peas than the snap-type cultivar Bettersnap. WhipperSnapper has potential for use as a mechanically-harvested source of snaps for use by food processors in mixed packs of peas and snaps. Protection for WhipperSnapper is being sought under the Plant Variety Protection Act.

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N. Mutlu, D.P. Coyne, S.O. Park, and J.R. Steadman

Common bacterial blight (CBB) in common bean (Phaseolus vulgaris L.), caused by Xanthomonas campestris pv. phaseoli (Xcp), reduces bean yields and quality throughout the world. Pinto `Chase' is a high-yielding variety with moderate resistance to Xcp derived from great northern Nebraska #1 selection 27, whose resistance is derived from an unknown tepary (P. acutifolius) bean source. XAN-159 is a black mottled small seeded breeding line with different genes for high resistance to Xcp derived from a different tepary source (PI 319443). Our objective was to pyramid different genes for Xcp resistance from the donor parent XAN-159 into the rust-resistant recurrent parent Pinto `Chase' using the classical back-cross breeding method with confirmation of resistance using RAPD molecular markers. Resistance was confirmed in some BC2F2 generation plants. Seven RAPD markers and the V locus (flower color) previously identified were confirmed in the BC1 and BC2 populations. Smaller seed size, purple flower color, and black mottled seed coat color were coinherited with resistance to Xcp. However, a recombinant plant with enhanced CBB resistance and moderate-sized pinto seed was identified. Backcross breeding is being continued.

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S. Grange, D.I. Leskovar, L. Pike, and G. Cobb

Triploid watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] consumption is increasing in the United States However, some of the original problems, poor and inconsistent germination, still exist. Seeds of several triploid and diploid watermelon cultivars were subjected to a variety of treatments to improve germination. Control and scarified seeds, by nicking, were incubated at 25 or 30 °C in either 5 or 10 mL H2O or hydrogen peroxide (H2O2). Triploid seed germination was strongly inhibited in all cultivars when seeds were at 10 mL of H2O or H2O2; both nicking and H2O2 increased germination but not equal to rate of the control in 5 mL H2O or H2O2. Germination of diploid cultivars was unaffected by any treatment. Seed morphological measurments indicated that triploid seed has a smaller embryo with a large and highly variable (cv = 105%) air space surrounding the embryonic axis as compared with the diploid seed. These data suggests that triploid watermelon seed germination is not inhibited by the seed coat thickness alone. Seed moisture plays a significant role in germination, emergence, and stand uniformity.

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Tim D. Davis, Wayne A. Mackay, and Daksha Sankhla

Seeds of Lupinus havardii Wats. (Big Bend bluebonnet), a potential cut flower crop, were subjected to a variety of scarification and temperature treatments. Without scarification, only 10-20% of the seeds germinated within one week. Germination percentages increased sigmoidally as scarification time in concentrated sulfuric acid increased. Nearly 100% germination was obtained within one week after seeds were placed in sulfuric acid for 120 min. Nicking the seed coat with a razor blade also resulted in near 100% germination. Soaking the seed in water for 24 h failed to enhance germination. Soaking the seed in ethanol, methanol, or acetone for 2 h likewise failed to enhance germination. Total germination of scarified seed was >90% between 21 and 33C within 28 h. The most rapid germination occurred within a range of 24-29C. Above or below this range germination was delayed. At 35C, seedling, mortality was observed and total germination was reduced to <50%. Our data indicate that seed of this species requires scarification for optimum germination but the seed can germinate over a relatively wide temperature range.

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Haim Nerson

Fruits of four cucurbit crops, cucumber, melon, watermelon. and squash, were harvested 25, 35 and 45 days past anthesis (dpa) and their seeds were extracted immediately or after 10 or 20 days of pre-extraction storage. Upon extinction, the seeds were subjected or not subjected to fermentation, washing and drying, The effects of these procedures on terminability was examined immediately after extraction or after up to 48 months of storage. Cucumber, melon and watermelon reached full germinability by 35 dpa, but squash required a longer period. Fermentation and drying were important for improving terminability of immature seeds of cucumber, melon and watermelon. Fermentation had a deleterious effect on immature squash seeds, but drying and washing improved terminability of squash seeds. Washing of cucumber, melon and watermelon seeds increased the rate of germination but not the percentage. Pre-extraction storage had a positive effect on terminability but was less effective than leaving the fruit on the vine for a comparable period of time. The seed coat completed its growth earlier than did the embryo.