Mark P. Bridgen
Mark P. Bridgen
Traditional and biotechnological breeding techniques are being united to develop exciting new plants and to improve existing cultivated plants by introducing natural variability from germplasm resources. Intervarietal, interspecific and intergeneric crosses can be accomplished by using plant embryo culture techniques, sometimes also referred to as embryo rescue. Embryo culture involves the isolation and growth of immature or mature zygotic embryos under sterile conditions on an aseptic nutrient medium with the goal of obtaining a viable plant. The technique depends on isolating the embryo without injury, formulating a suitable nutrient medium, and inducing continued embryogenic growth and seedling formation. The culture of immature embryos is used to rescue embryos from hybrid crosses that were once thought to be incompatible because they would normally abort or not undergo the progressive sequence of ontogeny. The culture of mature embryos from ripened seeds is used to eliminate seed germination inhibitors, to overcome dormancy restrictions, or to shorten the breeding cycle. New and exciting cultivars of Alstroemeria, also known as Lily-of-the-Incas, Inca Lily, or Peruvian Lily, have been bred by using zygotic embryo culture; these techniques and applications will be discussed.
Mark P. Bridgen and J. Bartok
Red- and pink-flowering cultivars of Alstroemeria were grown with and without cooling tubes placed in the growing medium. Cooling tubes were placed immediately below, 5 cm below, and 10 cm below the surface of the medium. Cooling was obtained by circulating well water (10 to 15C) through polyethylene tubing. Air and media temperatures were recorded every 3 to 10 days in the morning and in the late afternoon to determine if positioning of the cooling tubes had an effect on the medium temperature. The air temperature was warmer than the noncooled medium, which, in turn, was significantly warmer than the cooled medium. There were no significant differences in media temperatures among the three cooling treatments. Flowering of cooled Alstroemeria cultivars continued for 2 months longer at the end of the summer and reinitiated 1 month earlier than the noncooled control. Both cultivars produced significantly more total flowers when grown in cooled medium. Flower production was greatest in the summer for plants with tubes 10 cm below the surface and least for plants in noncooled medium. This trend continued when flowering was reinitiated; however, by April of the following year, all treatments were equal in flower production.
Alessandro Chiari and Mark P. Bridgen
Three Alstroemeria genotypes—A30, ER292, and 16-1-2—developed at the Univ. of Connecticut were grown in vitro on two media: Murashige and Skoog (MS) basal medium and Alstroemeria medium (ALA). Each medium had four levels of 6-benzylaminopurine (BA) added: 0, 9, 18, and 36 μm. Alstroemeria rhizomes initially containing one bud were cultured on the 24 treatments for 12 weeks with transfers onto fresh medium at 4 and 8 weeks. At each transfer and at the end of the experiment plants were scored for the number of shoots produced, number of new buds, fresh weight, and presence of roots. No difference was observed between the MS and ALA media. No interaction was found between medium and hormone concentration. BA inhibited the formation and growth of roots that were observed only in the control without BA. The control was different from 9, 18, and 36 μm BA for the number of buds produced, number of shoots and fresh weight while no differences were observed between the various concentrations of BA. ER292 gave the highest yields in number of buds, shoots and fresh weight of all the genotypes.
Masood Hadi and Mark P. Bridgen
Callus cultures of Torenia fournieri `Compacta Blue' were initiated on a modified Murashige and Skoog salt medium (MS) with 2.26 uM 2,4-dichloro-phenoxy acetic acid. Shoots were regenerated from these cultures using the MS medium amended with 2.46 uM 3-indolebutyric acid and 8.88 uM 6-benzylaminopurine. These shoots were subjected to Tetranychus urticae Koch (twospotted spidermite) and Trialeurodes vaporariorum (Westwood) (greenhouse whitefly) in vitro. Pests were allowed to feed until such time that the pest population started to decrease due to lack of food. Remaining shoot tissue was placed on MS medium amended with 2.28 uM zeatin to -induce shoot formation. Shoots were acclimated to greenhouse conditions and evaluated for resistance to the pest to which they were subjected in vitro. Highly significant differences in pest numbers were found in somaclones when compared to control plants. A wide range of variability was observed within the somaclonal population.
Alessandro Chiari and Mark P. Bridgen
Meristems from three different positions were excised from in vitro plants of Alstroemeria genotype A30. Explants were removed from the most-distal vegetative shoot apical meristems, rhizome tip apical meristems, and rhizome tip axillary meristems. Meristems were cultured on four different media to compare the effect of meristem position and medium on the ability to produce Alstroemeria rhizomes from meristems. The meristem culture media were Murashige & Skoog salts plus 8.39 μM pantothenic acid, 1.19 μM thiamine, and 0.55 mm myo-inositol (MSM), MSM plus 8.88 μM of 6-benzylaminopurine (BA), MSM plus 8.88 μM BA, and 0.72 μM gibberellic acid (GA3), and MSM plus 0.72 μM GA3. Meristems that were removed from the vegetative shoot apices did not develop rhizomes on any medium. Rhizome tip apical meristems developed less than 10% rhizomes when subcultured on media containing BA and GA3. However, rhizome tip axillary meristems developed rhizomes on all media with best results achieved when the medium was supplemented with BA.
Mark A. Smith and Mark P. Bridgen
In vitro growth and development of Alstroemeria `Cornell Pink' were evaluated on media containing different amounts of CaCl2, MgS O4, FeSO4, NO3, or NH4. Six levels of calcium chloride were originally examined (from 0 to 75 mM); the low levels proved to be most beneficial. Subsequent experiments used CaCl2 levels from 0 to 3.0 mM. Again, the low levels were most productive. Two experiments, with different gelling agents, were designed for MgSO4. The levels ranged from 0 to 15 mM. The 15 mM level produced explants with the greatest fresh weight. Three experiments were used to study the effect of FeSO4. The range was the same in all of the experiments (0 to 1 mM), but the increments and the gelling agents differed. In all three experiments, the 1 mM level proved to be toxic. The group with treatments from 0.01 to 0.5 mM had the best response over time. Both experiments with nitrogen found no response to different NO3:NH4 ratios. A positive linear response to rate was found within the range studied (20 to 80 mM).
Chad T. Miller and Mark P. Bridgen
The dormancy mechanism in achimenes (Achimenes hybrids) has not been thoroughly characterized. Rhizomes of five recently developed achimenes cultivars were stored for 0, 4, 8, 12, or 16 weeks at 68 °F. Cultivar A09 demonstrated a strong decrease in the time to root after 4 weeks of storage, rooting after 13 weeks postplanting. The rooting response for cultivars A16, A21, and A22 was significantly less than cultivar A09; they developed roots between 2.6 and 7.6 weeks after 4 weeks of storage. Rhizomes stored longer than 8 weeks resulted in decreased rooting responses for all cultivars. Shoot emergence was delayed in all cultivars with cultivars without any storage period; cultivars A09, A16, and A23 exhibited a stronger delay than other cultivars. After 4 weeks of storage, the number of weeks to shoot development decreased for all cultivars and after each additional 4-week storage period, the number of weeks to shoot development decreased or remained the same. After 16 weeks of storage, shoots developed in less than 4 weeks for all cultivars. Pupation occurred in four of five cultivars on rhizomes given no storage or with only 4 weeks of storage. The results obtained suggest that the dormancy period of some newer achimenes cultivars is abbreviated in comparison with older cultivars.