Lewisia tweedyi (A. Gray) Robinson is an endangered, herbaceous perennial native to the Cascade Mountains of northern Washington state and southern British Columbia. It is highly valued as an ornamental, but has a reputation for being challenging to grow and is only cultivated by alpine specialists. The better known Lewisia species, L. cotyledon, is a minor commercial crop in some areas of Europe and western North America. Lewisias are members of the Centrospermae; a linear peripheral embryo surrounds centrally located perisperm. Lewisia tweedyi seed is distinct from all other lewisias in having a fleshy appendage, or caruncle. Germination practices include stratification for an unspecified period in a garden cold frame. In addition to a long germination period, percent germination is characteristically low. A number of tests, including sowing under axenic conditions, and combinations of prechill periods and liquid N scarification were conducted. Seedcoat-imposed dormancy and germination requirements have been determined.
Christia M. Roberts
Melike Cirak and James R. Myers
The persistent color (pc) trait in snap bean (Phaseolus vulgaris L.) is a member of the stay-green gene family and falls into the cosmetic subclass. Cosmetic stay-green variants remain green but lose photosynthetic competence during senescence. It is an economically useful trait in snap bean as a result of its effects on pod quality. The trait produces a dark-green, uniform appearance of fresh pods, but has other pleiotropic effects, including a light-green seed color, bleached-white cotyledons on emergence, and foliage and pods that remain green even while senescing. One additional pleiotropic effect is reduced field germination and emergence compared with white- and colored-seeded genotypes. Nevertheless, with the aid of seed-applied fungicides, pc types occupy ≈40% of commercial snap bean acreage in the United States. This research project was aimed at understanding why and how germination and emergence is affected in pc beans. The effect is thought to be related to soil-borne pathogens because fungicide treatment of pc seeds increases germination and emergence rates to levels comparable to treated white- and colored-seeded genotypes. For our experiments, we increased seeds of 45 experimental lines and commercial cultivars (25 of which were pc) under uniform growing conditions. Initial experiments documented that, in the laboratory, all seeds analyzed in a tetrazolium test had high viability. Furthermore, untreated seeds of pc and non-pc types germinated in the laboratory showed no difference in germinability, whereas in the field, germination of pc types was reduced significantly. In addition, pc types showed substantially greater infection rates of seeds and seedlings, with the main pathogen being Fusarium oxysporum Schl. f. sp. phaseoli Kendrick & Snyder. Water uptake by green pc seeds was significantly more rapid than white and colored seeds. Measurements of electrical conductivity revealed that pc types had greater solute leakage than other seed types. When seed anatomic structure was examined, pc types had a significantly thinner testa, especially the osteosclereid layer. The reduction in germination and emergence appears to begin with a thinner, more fragile testa showing increased cracking that may happen during seed harvest and conditioning (but certainly does happen during imbibition), allowing more rapid water uptake during germination that leads to testa rupture. Increased and rapid solute diffusion into the surrounding spermosphere stimulates and attracts pathogens to colonize the seeds before seedlings can become established. Seed handling and conditioning processes before planting could be modified to improve field emergence and stand establishment. Selection for thicker testa may also mitigate some of the damage observed during germination of pc cultivars.
Florence Breuillin-Sessoms, Dominic P. Petrella, Daniel Sandor, Samuel J. Bauer, and Brian P. Horgan
a longer period of time during acute drought treatment. Seed number per species For each product, 1.0 g of seed was weighed (three times) and the species were separated using the seed anatomy specific to each species ( Christians, 2007
Alison E. Heather, Hector E. Pérez, and Sandra B. Wilson
to their respective dishes, repeating this measurement at 0.5, 0.75, 1 to 12, 24, and 48 h. Fresh weight increase was calculated using the formula [(W i – W n )/ W n ] × 100, in which W i was the mass of imbibed tissue. Seed anatomy and morphology
Takahiro Tezuka, Hisa Yokoyama, Hideyuki Tanaka, Shuji Shiozaki, and Masayuki Oda
. Sánchez-Coronado, M.E. Gamboa de Buen, A. Baskin, J.M. Baskin, C.C. 2007 Seed anatomy and water uptake in relation to seed dormancy in Opuntia tomentosa (Cactaceae, Opuntioideae) Ann. Bot. (Lond.) 99 581 592 Raghavan, V. 2003 One hundred years of zygotic
Yuliya A. Salanenka, Martin C. Goffinet, and Alan G. Taylor
long-wavelength ultraviolet radiation source (365 nm). For gross seed anatomy, seeds were decoated and observed without further preparations with a stereomicroscope (SZX12; Olympus, Center Valley, PA) equipped with a SPOT Insight camera and software