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Janine G. Haynes, Wallace G. Pill and Thomas A. Evans

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.

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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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Derek N. Peacock and Kim E. Hummer

We contrasted the effect of liquid nitrogen (LN2), sulfuric acid (H2SO4), and a nontreated control on the germination of six Rubus species. We also were interested in determining if LN2 could be an effective mechanical scarifying agent for these species. Seeds of each species were treated with three 3-minute dips in LN2 with alternating 10-minute thaws, with H2SO4 for 30 minutes, or left untreated. The percent germination of R. multibracteatus A. Leveille & Vaniot, R. parviflorus Nutt., R. eustephanos Focke ex Diels, R. leucodermis Douglas ex Torrey & A. Gray, R. ursinus Cham. & Schldl., and R. chamaemorus L. treated with LN2 was not significantly different than the control. Germinated seedlings from the LN2 treatment of each species showed normal development upon planting, indicating that long-term cryogenic preservation of these Rubus species seeds may be possible. The H2SO4 treatment significantly increased the rate and percentage of germination in R. parviflorus, R. eustephanos, R. leucodermis, and R. ursinus over that of the control and the LN2 treatment. The alternative LN2 application techniques that have been attempted thus far have not significantly improved Rubus seed germination compared with that of the control.

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John R. Duval and D. Scott NeSmith

Production of triploid watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] transplants is hindered by low and nonuniform emergence, and seedcoat adherence. Seedcoat adherence leads to weakened and slow-growing plants. High seed costs are prohibitive to many transplant growers. Improvement of emergence would lower financial risks to growers and transplant producers. Mechanical scarification was examined as a means to decrease the impact of both problems. Seeds of `Genesis' triploid watermelon were placed in a cylinder with 100 g of very coarse sand and rotated for 6, 12, 24, and 48 hours at 60 rpm. Nontreated seeds were used as a control. Data were taken daily on emergence and seedcoat adherence. The experiment was repeated at three temperature regimes. No significant differences were observed in seedcoat adherence. Scarification, however, did significantly improve emergence under test conditions.

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Remi Bonnart, Anthony Koski and Harrison Hughes

Native turfgrasses have received greater attention in recent years because of their usefulness in growing in areas where many other grasses cannot. Saltgrass (Distichlis spicata) has good salt tolerance, but the natural germination rate for the seed is low. This is most likely due to the thickness of the seed coat inhibiting normal imbibition of water. Previous research in our laboratory has demonstrated increased germination with hand-scarification. The purpose of this research was to compare germination rates of machine-scarified, hand-scarified, and nonscarified seed. Scarifying the seeds by hand results in greater uniformity, but the operation is tedious and time-consuming. Machine scarification is quick, but the seeds have reduced uniformity. Two seed lots, one designated “Modoc” and one designated “Granite,” were compared in laboratory and field germination tests. Preliminary observations have shown that “Granite” seed had somewhat higher viability and vigor than the “Modoc” seed. Significantly greater germination occurred with scarification when seeds were germinated at 14 h of light at 30 °C and 10 h of darkness at 20 °C in the laboratory. Although scarification treatments were similar with the “Granite” seeds, near 80% germination, there were significant differences between hand and machine scarification with the”Modoc” seeds; hand scarified seed had greater germination. The field germination experiment had similar results to the laboratory experiments with “Granite” seed. However, scarification did not aid germination of “Modoc” seed. This is thought to be due to low vigor and associated death of seedlings prior to emergence. Preliminary data confirm the low vigor of the “Modoc” seed as compared to “Granite” seed.

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Katherine L. Vasquez and Wayne A. Mackay

Lupinus havardii and L. texensis are two commercially important species of lupines (bluebonnets) in Texas. There is no current information for the storage requirements of these two bluebonnet species seeds. A study was undertaken to examine the effects of relative humidity, temperature, and scarification on seed germinability. Seeds of the two bluebonnet species were stored under five relative humidity treatments (11%, 23%, 52%, 75%, and 95%) and two temperature treatments (3°C or 22°C) either scarified or nonscarified in factorial combination. Seed samples were removed monthly. Nonscarified seed were scarified and all seed were placed in a seed germination chamber and germinated in petri dishes containing moistened filter paper. All samples of seed stored under 95% relative humidity were lost to seed-borne contamination. Germinability of scarified seed of both species decreased within 5 months in the 22°C/75% RH treatment. Other treatments had no effect on germinability during 7 months of seed storage.

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Wayne A. Mackay

Seeds of Lupinus havardii Wats. and L. texensis Hook. were subjected to scarification, storage temperature (4 or 22 °C), and relative humidity (RH) treatments (11%, 23%, 52%, 75%, or 97% RH) for 12 months. Seed moisture increased as relative humidity increased with scarified seed having the greatest increase in seed moisture content regardless of storage temperature. For both species, the combination of seed scarification before storage, 75% RH, and 22 °C storage temperature resulted in a significant and rapid decline in germinability beginning at 4 months. Scarified L. texensis seed stored at 52% RH and 22 °C also exhibited a significant decline in germinability following 6 months storage. Seed of both species stored under all other conditions germinated similar to or higher than the initial germination rate after 12 months. These results clearly show that scarification can be performed before seed packaging as long as the seed packets are stored at ≤23% RH under 4 or 22 °C with no loss in germinability for at least 1 year.

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S.M. Javad Feghahati and R. Neil Reese

Echinacea angustifolia DC., the common coneflower of the western Great Plains, is difficult to propagate by achenes due to inherent seed dormancy. The effects of light and prechilling on seed germination were examined, alone and combined with scarification (mechanical, acid) and ethylene (ethephon) treatments. The results showed that a 2-week prechill treatment combined with ethephon and continuous light, followed by a 2-week germination period in light (16 hours per day) at 25C, could induce >95% seed germination in E. angustifolia. This was a significantly higher percentage of germination over a shorter period of time than any other method examined or previously described. This treatment also synchronized germination, with most viable seeds germinating in <1 week after being placed at 25C in the light. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Richard L. Hassell and Dale W. Kretchman

Seed from six species of the Apiaceae and six parsley (Petroselinum crispum L.) cultivars with three seed lots of each parsley cultivar were tested for the presence of germination inhibiting substances. Aqueous leachate from seed of all six species inhibited germination of lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.). Leachate from root parsley seeds (P. crispum tuberosum) were least inhibitory, while leachate from celery and celeriac (both Apium graveolens L.) seeds were most inhibitory. Inhibitory concentrations in leachate varied by seed lot within a cultivar. Aqueous leachate of seeds from the primary umbels caused less inhibition of germination than did leachate from tertiary umbels. Washing parsley seeds in aerated water for 3 hours or more removed some of the germination inhibitory substance as indicated by the germination bioassay. An aqueous extract prepared from seedcoat tissue, removed during mechanical scarification, inhibited radish seed germination; inhibition was proportional to the duration of scarification and the amount of seedcoat tissue extracted. Parsley seeds scarified ≤60 minutes germinated at rates comparable to washed seeds, but longer scarification time reduced germination. Washing seeds of Apiaceae prior to commercial drying and cleaning may be a practical solution for removal of inhibitors.

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Milton E. Tignor Jr. and Courtney A. Weber

Current efforts in the study of citrus freeze hardiness including gene mapping and elucidating early induction processes require large populations of uniform seedlings. Related genera and intergeneric hybrids are often used in these studies and little is known about factors effecting their seedling emergence. We tested a total of 8 genotypes including Poncirus trifoliata `Rubidoux', Citrus grandis, C. sinensis `Pineapple', C. jambhiri `Schaub', C. paradisi `Duncan', C. aurantium (Brazilian), Carrizo citrange (P. trifoliata × C. sinensis), and Troyer citrange. A total of seven pre-planting treatments were used to evaluate seedling emergence rates. Expanding on the work of previous researchers, treatments were seed coat removal, hydrating in water (96 hours) at either 4, 25, or 35°C, acid scarification, or boiling. Generally, seed coat removal resulted in the most uniform emergence as compared to untreated controls. Presoaking at each temperature enhanced emergence in most varieties tested and 25°C was the best hydrating temperature. Acid scarification greatly delayed emergence in all genotypes tested except Troyer citrange and `Pineapple' orange which had enhanced emergence rates as compared to controls. Preplanting treatment with 100°C water was lethal in all varieties. Pretreatment of citrus seeds can enhance uniformity of germination, although optimum treatments for individual genotypes vary.