Redbud (Cercis canadensis) is a small woody ornamental legume that has a hard seed coat, which imposes physical dormancy, typical of many legumes. Redbud also possesses an internal embryo dormancy that must be overcome by stratification. In order to observe the relationship between anatomy and germination, seeds were embedded in JB-4 resin during various developmental and germination stages. The seeds were cut longitudinally with a glass bladed microtome, to observe the radicle, vascular traces and testa. It appears that the vascular traces left from the funiculus serve as a weak point in non-dormant seeds that allows the radicle to rupture the testa during germination.
Rodney Jones and Robert Geneve
Manjul Dutt and Robert Geneve
Impatiens (Impatiens wallerana Hooker F.) and petunia (Petunia ×hybrida Hort. Vilm.) seeds were imaged using a flat-bed scanner interfaced with a personal computer programmed to capture images every hour. Images were used to measure time to radicle protrusion and seedling growth. Time to radicle protrusion was calculated as time to 50% germination or as actual germination for each seed. Seedling growth after germination was calculated from linear regression of growth over time. Radicle protrusion and seedling growth were evaluated as indicators of seed vigor. Both were good indicators of seed vigor in impatiens seed lots. These measurements of vigor were highly correlated for each impatiens seed lot and for pooled seed lots. However, there was little or no correlation between time to radicle protrusion and seedling growth on an individual seed basis. The relationship between germination speed and seedling growth rate observed in impatiens was confirmed in two petunia seed lots. This study supports the use of time to radicle emergence and seedling growth as good indicators of seed vigor. However, it appears that different aspects of seed vigor may be measured by these indicators because there was no relationship between time to radicle protrusion and seedling growth rate on an individual seed basis.
Barry Duncil and Robert Geneve
Wild rye (Elymus) contains several species of cool season grasses that are important components of forest and woodland ecosystems. Little specific information is known about seed dormancy in wild rye species, but cool season grasses generally display endogenous, non-deep physiological dormancy that would normally be satisfied by moist chilling during winter to permit early spring germination. However, few studies have documented the effect of extended chilling stratification on dormancy release in cool season grasses. Therefore, the objective of this study was to document the dormancy condition of representative wild rye species and to observe the impact of chilling stratification on dormancy release. Three species of wild rye (E. virginicus, E. macgregorii, and E. villosus) were selected based on their taxonomic and ecological relationships. All species showed conditional dormancy with respect to germination temperature. At 15 °C, E. virginicus, E. macgregorii, and E. villosus germinated at 75%, 81%, and 40%, respectively, compared to 5%, 3%, and 12% for each species at 20 and 25 °C. Chilling stratification at 10 °C improved germination compared to non-stratified seeds to 95% and 94% for E. m acgregorii and E. villosus, but had no effect or reduced germination in E. virginicus. Stratification at 5 °C was not as effective as 10 °C for dormancy release and appeared to cause chilling injury in E. virginicus and E. macgregorii. The data suggest that these wild rye species express a form of conditional endogenous, non-deep physiological dormancy that is most pronounced when seeds are germinated at non-optimal temperatures.
Robert L. Geneve
Adventitious root formation in debladed petiole cuttings of English ivy proceeds via a direct rooting pattern for the easy-to-roof juvenile phase, while the difficult-to-root mature phase roots through the indirect pattern, Juvenile petiole cuttings treated with NAA (100 μM) plus the polyamine biosynthesis inhibitor, DFMA (1 mM), formed an increased number of roots per cutting initiated through the indirect rooting pattern. The increased formation and the change in rooting pattern were reversed by the addition of putrescine (1 mM). Delaying auxin application to petiole cuttings for 15 days, also induced juvenile petioles to root by the indirect pattern. This could be reversed by rebounding the base of the cutting prior to auxin application at day 15. The data support the use of the terms “pre-competent root forming cells” (PCRFC) and `induced competent root forming cells' (ICRFC) to describe the target cells for the initial events of root formation for the direct and indirect patterns, respectively,
Robert L. Geneve
An interactive multimedia presentation was developed using authoring software (Authorware from Macromedia) to provide information on plant anatomy and cell biology. Our current course in growth and development of horticultural crops has limited time and lab facilities available for these subjects, yet a good foundation in this area is important to understanding growth and development. This software uses a variety of techniques, including color digital images, illustrations, cartoon animation, and video, to teach aspects of cell biology and different plant cell types. In addition, a review session allows students to interactively test their knowledge of the subject. The software was placed on a Dept. of Horticulture server that provided student access to a folder for course work. Students were able to access the software from anywhere on campus via the University network. Multiple students can use the software simultaneously. The approach of using a local server provided easy access and avoided some of the delays involved with viewing large (1 mb) images found when using the World Wide Web. It took students several weeks to complete the software's modules. Then, students completed an independent plant anatomy lab using the software for reference. Students were required to create a virtual notebook of labeled digital images captured from prepared microscope slides using a microscope attached with a digital camera and linked to a computer. Students found this approach to learning to be challenging, and initial feedback has been very positive.
Robert L. Geneve
Seed dormancy in Eastern redbud (Cercis canadensis var. canadensis L.) can be overcome by seedcoat scarification to allow water imbibition, followed by chilling stratification to permit germination. During chilling stratification, there was an increase in the growth potential of the embryo as indicated by the ability of the isolated embryo to germinate in osmotic solutions. Penetration resistance of the testa also decreased after chilling stratification. The combination of seedcoat alteration and the increase in embryonic growth potential was associated with overcoming dormancy in redbud seed. GA3 or ethephon (50 μm) stimulated germination (28% and 60%, respectively) and increased the growth potential of treated embryos. Chemical names used: gibberellic acid (GA3), (2-chloroethyl) phosphoric acid (ethephon).
Robert L. Geneve
Jennifer Marohnic and Robert L. Geneve
Marigold seedlings were grown in four containers that differed in both volume and shape. Seedlings grown in 1.5-gal containers showed the greatest potential for shoot and root development 20 days after sowing. These seedlings had greater leaf area, shoot and root dry weight, and total root number and length compared to seedlings grown in 406 plug trays, 72-cell packs, or 6-inch containers. There was a positive correlation (r 2 = 0.81) between cell volume and seedling growth as well as a positive correlation (r 2 = 0.89) between container height with seedling growth. An attempt was made to separate the impact of container volume vs. container height on seedling growth. Containers were designed using acrylics to vary the container height while keeping the volume constant at 1500 cm3. There was a positive correlation (r 2 = 0.87) between shoot and root dry weight with container height. The data suggest that both container volume and height contribute to overall seedling growth in marigold, but when container volume is not limiting, container height has a large impact on seedling development.
Carrie DeVier and Robert L. Geneve
The influence of flowers on root formation in mum cuttings was evaluated for stock plants grown under long (LD) or short (SD) days. SD plants showed visible flower buds after 20 days and color after 30 days. Cuttings were taken from LD or SD plants at 10-day intervals until flowers were fully open. Cuttings from LD plants rooted at 100% throughout the study, with 24 or more roots per cutting. Cuttings from SD plants showed a gradual reduction in rooting percentage and number as flower development increased. After 30 days, roots per cutting for SD plants was reduced by 85% compared to LD cuttings and only 30% of SD cuttings rooted. In a separate experiment, cuttings were taken from stock plants after 40 long or short days. Partial or all flower buds were removed from SD plants prior to sticking. SD cuttings (regardless of flower bud removal) rooted at <47%. LD cuttings rooted between 23.6 to 43.8, while SD cuttings rooted between 3.1 and 8.5 roots per rooted cutting. The data indicates that cuttings taken from flowering plants show reduced potential for rooting and that this effect was not influenced by removal of flowers prior to sticking cuttings.
Karsedis Distabanjong and Robert L. Geneve
Somatic embryos from Eastern redbud show a high degree of malformation during development and a low conversion rate to seedlings. This problem is common with somatic embryo systems, especially with legume species. A procedure for multiple shoot formation from somatic embryo explants of Eastern redbud was developed that bypasses the need for germination to recover plantlets. Somatic embryo explants cultured on DKW medium containing benzyladenine (BA) and thidiazuron (TDZ) produced more shoots than either treatment alone. The highest number of shoots (3.3 to 3.4 shoots per explant) was obtained from partially desiccated and wounded explants treated with a combination of 5 or 10 M BA and 0.5 or 1.0 M TDZ for 20 days before being transferred to the same medium without TDZ. The number of shoots formed was increased from 1.5 to 3.2 shoots per explant by cutting through the cotyledonary node prior to culture. In addition, the frequency of explants forming shoots was increased by desiccation of somatic embryo explants to ≈50% moisture and by using somatic embryos with two well-formed cotyledons as explants.