Morphological traits were examined in an F3 generation derived from a cross between C. lanatus var. lanatus [(Thunb.) Matsum. & Nakai] and C. lanatus var. citroides. At least three genes, C (yellow) vs. c (red), i (inhibitory to C) vs. I (non-inhibitory to C), and y (yellow) vs. yw (white), with epistatic and inhibitory actions were found to govern the inheritance of fruit flesh color. The high frequency of yellow-fleshed fruit and low frequencies of white and red fruits can be explained by the presence of a new allele (yw recessive to y) in the multiple allele series at the Y locus. The low frequency of tan colored seeds in segregating populations could be explained by at least three genes governing inheritance of seed-coat color. Single factor analysis of variance was conducted for each pairwise combination of random amplified polymorphic DNA (RAPD) locus and fruit or seed characteristics. Several RAPD loci were identified to be loosely linked to morphological characteristics.
Leigh K. Hawkins, Fenny Dane, and Thomas L. Kubisiak
I.E. Yates, W.L. Tedders, and D. Sparks
Severe economic losses in pecan crop productivity result from phytophagous stink bugs and coreid bugs (Hemiptera) feeding on the kernel. Discriminating hemipteran damage from other late seasonal kernel disorders is often inconclusive. Two additional markers of hermipteran damage have been distinguished and can be used as unequivocal evidence of the feeding activity of these insects regardless of the source of the nuts. Staining pecan nuts with red fluorescent dye differentiates the microscopic hemipteran punctures from the natural markings on the shell. Additional confirmatory evidence can be obtained by recognition of the stylet sheaths connecting the packing material on the shell interior to the seed coat of the kernel. These anatomical evidences of hemipteran feeding should facilitate research studies to evaluate the role of hemipteran attack with late seasonal pecan kernel disorders.
Sharon Sowa and Eric E. Roos
Infrared spectroscopy was used to measure biochemical changes during bean (Phaseolus vulgaris L.) seed imbibition. Transmission spectroscopy of excised embryonic axes revealed changes in lipid phase (gel to liquid crystalline) and protein secondary structure within the first 15 min of hydration. Spectral changes in seed coats, cotyledons, and axes during the first 2 hr of imbibition (measured in vivo) were detected using photoacoustic sensing. Onset of seed respiration could be detected as early as 15 min after addition of water. CO2 production, demonstrated by the appearance of a double peak centered at 2350 cm-1, increased with time of imbibition. Infrared photoacoustic spectroscopy of intact seeds holds promise as a method for non-invasive viability assessment.
Orlando Balboa-Zavala and F. G. Dennis Jr.
c,t-Abscisic acid (ABA) was identified in methanol extracts of mature apple (Malus domestica Borkh.) seeds by gas chromatography-mass spectrometry, and concentrations of both free and base-hydrolyzable (bound) ABA in immature and mature seeds were quantified by electron capture gas chromatography. Immature embryos failed to germinate regardless of time of sampling unless seed coats were removed. Germination of excised embryos reached a maximum in early August, then gradually declined to nil in mid-September. Although ABA content of the embryonic axes rose sharply at maturity, the rise occurred only after germination capacity declined. Premature defoliation reduced ABA content of the axes, but did not prevent the induction of embryo dormancy. ABA content of mature seeds declined during stratification at both 5° and 20°C, with maximum differences occurring in the embryonic axis, but dormancy was broken only at 5°. Induction of secondary dormancy by high temperature (27°) was accompanied by a slight decline in ABA content of whole seeds.
P. A. Bonamy and F. G. Dennis Jr.
cis, trans-Abscisic acid (ABA) was identified by combined gas chromatography-mass spectrometry (GC-MS) in a partially purified methanol extract of mature seeds of peach (Prunus persica (L.) Batsch). No germination of intact seeds occurred during seed maturation. Germination of excised embryos increased with maturity, but ABA content of embryonic axes and other seed parts was not related to germination potential. Drying and storage of seeds increased both free and bound ABA in the embryonic axes, but did not significantly affect ABA content of other seed portions. Free and bound ABA decreased on imbibition except for free ABA in the seed coat and bound ABA in the embryonic axis, Levels of free and bound ABA paralleled one another, suggesting that although the former may be converted to the latter, bound ABA is not a major source of free ABA.
D. J. Gray
Orthodox seeds enter an arrested growth phase during their final stages of development that follows closely after seed coat hardening, reduction of water content, and maturation of embryonic and storage tissues. This resting phase may last for a number of years, depending on species and environmental conditions (2), and is the major factor accounting for the efficient storage and handling qualities of seed. A similar resting phase induced in synthetic seed will be essential for propagation of many annual crop plants, especially those grown at high density over large areas (e.g., com, soybean, wheat, etc.) where planting efficiencies must be optimum. Additionally, a resting phase will be needed if synthetic seed is to be used for germplasm preservation.
P. A. Hughes and R. F. Sandsted
Seed of Phaseolus vulgaris L. cv. California Light Red Kidney was stored at 1, 12, and 24°C and 30 and 80% relative humidity for 1 year. The higher temperatures accelerated darkening of seed coat color. High relative humidity at 24° resulted in the darkest colored beans, a complete loss of germination, a 4-fold increase in fat acidity and a nearly 2-fold increase in the time required to cook until tender when compared with beans stored at 1° and 30% relative humidity. Beans stored at 1° and 30% relative humidity very nearly retained their original color, germination percentage, and fat acidity in addition to retainment of their cooking time requirements. Ultraviolet and cool-white light also darkened beans in storage, but in contrast to the darkening caused by high humidity and temperature, light promoted darkening was not associated with loss in quality factors.
S. L. Kitto and Jules Janick
Synthetic seed coats were applied to asexual embryos of carrot (Daucus carota L.) by mixing equal volumes of embryo suspension and a 5% (w/v) solution of polyethylene oxide (Polyox WSR-N 750) and dispensing 0.2 ml drops of this mixture onto teflon sheets. Drops dried to form detachable wafers consisting of embryo suspension embedded in Polyox. Embryo survival after drying was determined by redissolving wafers in embryogenic medium and culturing the rehydrated embryo suspension on filter paper supports in petri dishes for 2-3 weeks. When dried to constant weight (6.5 hr) 3% of asexual embryos coated with 2.5% Polyox survived encapsulation, whereas survival of uncoated embryos was nil. Pretreating the embryogenic suspension with 10−6 m abscisic acid (ABA) during the 14 day embryo induction phase increased coated embryo survival to 40% of the initial number of embryos.
W. Stienswat, L. H. Pollar, and W. F. Campbell
We investigated the areas of water penetration and the anatomical structures of hilar regions of permeable and impermeable seed coats of lima beans (Phaseolus lunatus L.). Results indicate that water can enter permeable seeds through the hilum, raphe, and micropyle. In impermeable seeds water cannot pass through any of these areas. Anatomical data confirm that there were no structural differences in the testae of permeable and impermeable seeds, but a noticeable difference was apparent in the hilar region. In permeable seeds the palisade layer did not connect evenly in the hilar canal. By contrast, the hilar canals of impermeable seeds had connected palisade layers that were uniformly coated with a cuticular layer. Micropylar openings were clearly visible in permeable seeds, but these openings were occluded and well covered with cuticle in impermeable seeds. Visible differences were evident in the raphe.
Pamela J. Myers and Peter D. Ascher
Dehiscence of a mature orchid fruit releases a multitude of seeds — more than a million per capsule in some species. Air currents carry the seeds, but few land on a site permitting germination; even fewer chance upon an environment suitable for development of a mature plant. The seed is microscopic and consists of the bare essentials: a seed coat modified for buoyancy, an embryo of from 8 to 100 cells, and, rarely, a small amount of undeveloped endosperm (2). All orchids require an external source of organic molecules for seed germination or seedling development. After germination, many exist for long periods, the entire life cycle in the case of true saprophytes, deriving carbohydrates and other organic molecules from exogenous sources. Various fungi, in mycorrhizal association with the orchid, provide these complex molecules.