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Seed dormancy in Callirhoe involucrata (Torr. & Gray) Gray, (Malvaceae)




Skogerboe, Dianne M., author

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Propagation of Callirhoe involucrata (Torr. & Gray) Gray, for use as a landscape ornamental has been encumbered by a lack of understanding of the seed dormancy and the development of a practical technique for overcoming it. In the populations tested, hard seed accounted for 49 % of an average sample of viable seed. Three disjunct populations of seed, representing two different collection years, were used to investigate practical methods of overcoming impermeability due to hard seed. Methods tested were moist pre-chilling, hot water, leaching, gibberellic acid, hydrogen peroxide, citric acid, potassium nitrate, mechanical and chemical scarification. Standard germination tests were conducted at three-month intervals for 15 months. In addition to hard seed, high percentages of seedless fruit, aborted and unfilled seed were identified. Hand scarification was the most effective means for improving germination in Callirhoe involucrata, resulting in germination as high as 98 %. Scarifying seed with concentrated sulfuric acid was highly effective when a double 60-minute exposure was used, generating germination percentages between 75 - 90 %. Single timed exposure treatments to sulfuric acid stimulated germination in some fractions and caused embryonic damage in others suggesting a 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 treatment. Soaking the fruit in boiling water (100°C) proved to be the most practical means of improving germination (over control) with increases from 12, 22, 30 % to 48, 58 and 91 %, in the three populations respectively. Leaching for 24 and 48 hours in cold (18°C) aerated water showed no improvement over control. A significant increase in germination was established for one lot when leaching occurred for 24 hours in warm (40°C) aerated water. Prechilling at 5°C did not improve germination in unscarified seed. Gibberellic acid, citric acid, and potassium nitrate did not significantly improve germination in scarified seed. Similarly, soaking seeds for 24 hours in 3 % hydrogen peroxide did not increase germination and at a 30 % concentration germination was reduced. Embryo dormancy did not appear to be a factor although some question remains about the presence of chemical inhibitors. The considerable variation in seed dormancy expression may be a function of differences in environmental factors during development. Success was obtained using vegetative stem cuttings dipped in 1.0 % IBA powder and placed under mist. Rooting reached 86 % in some trials.


2001 Fall.
Covers not scanned.
Includes bibliographical references.

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Callirhoe -- Seeds -- Dormancy


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