An efficient and reliable protocol of in vitro shoot regeneration must be first established to have a successful genetic transformation. As a member of legume family, alfalfa is very difficult for direct shoot regeneration. There is no published information on direct shoot organogenesis, although success has been well documented on embryogenesis, which must go through callus stage. Different plant growth regulators at various concentrations were evaluated for callus initiation, development, and direct shoot regeneration. Multiple shoots were produced directly from each individual explant. This will provide an efficient means for production of transgenic alfalfa plants. Therefore, genetic transformation of Medicago germplasm will be significantly expedited.
Guochen Yang and Marihelen Kamp-Glass
Amanda Bayer, John Ruter, and Marc W. van Iersel
by many growers in an effort to irrigate and fertilize more efficiently. Cyclic irrigation, which applies daily irrigation via multiple smaller applications, can be used to apply reduced irrigation volumes, and can reduce water and nutrient leaching
Wallace G. Pill
Nitrapyrin (NI) incorporation into a peat-vermiculite medium reduced shoot growth of tomato (Lycopersicon esculentum Mill. cv. Marglobe) but this reduction was less pronounced at higher NO3-N fertilization levels. An initial 50 ppm NI application caused less growth reduction than 7, weekly 7.14 ppm applications. While increasing NO3 level had little effect on shoot ion concentration, with the exception of increasing shoot K and NO3 concentration, the increased shoot total N, Mg, and K concentrations with NI were attributed to the concentrating effect of reduced growth. Single and multiple NI applications decreased and increased, respectively, both plant water stress and medium NO3 retention. Nitrapyrin consistently increased medium NO3 concentration at the 2 highest NO3 fertilization levels. With time, however, medium NO3 concentration decreased and increased with single and multiple NI applications, respectively, relative to each other. Nitrapyrin initially decreased leaf xylem pressure potential (ψp), but with time, water stress decreased below that of the control plants with the single NI application but remained consistently high with multiple applications. Since leaf diffusive resistance and ψp were lower and transpiration rate was initially higher with the single NI application relative to the control, and since plants given the multiple NI applications had the lowest ψp and transpiration rate values throughout the study, it is hypothesized that NI reduced water uptake. That NI decreased both NO3 assimilation and uptake was evidenced by decreased shoot total N content, increased shoot NO3 content, and increased medium NO3 concentration.
Walter J. Kender and Stephen Carpenter
Orchard and greenhouse experiments were conducted to determine the influence of foliar applications of 6-benzylamino purine (BA) on branching of young apple trees. BA at 100 and 500 ppm, applied to actively growing shoots stimulated lateral bud growth on these shoots during the current season. The presence of fruit, termination of shoot growth, and the localization and non-persistence of BA reduced its effectiveness in breaking apical dominance. For optimum response to BA, multiple spray applications to actively growing shoots in a non-fruiting condition were required. Spray applications of BA failed to induce lateral bud growth on previous season’s wood.
E. D. Earle and R. W. Langhans
Shoot tips of carnations (Dianthus caryophyllus L. cv. CSU White Pikes Peak) formed multiple shoots on agar nutrient medium containing 0.5 mg/liter kinetin and 0.1 mg/liter α-napthaleneacetic acid. Tissue with shoots was transferred to liquid medium on a culture wheel rotating 1 rpm. Many axillary shoots formed and eventually separated from the parent shoot. Tissue could be subcultured into fresh medium, stored at 4.5°, or rooted, potted and grown to flowering. All 175 plants flowered had normal white flowers with characteristic red flecks, indicating that the chimeral arrangement of the petal tissues had not been disturbed by the culture procedure.
Jacob George, Harsh Pal Bais, G.A. Ravishankar, and P. Manilal
Response surface methodology was utilized in statistical optimization of three quality factors (the number of multiple shoots, shoot length, and number of leaves) pertaining to regeneration of plantlets from leaf calli of Decalepis hamiltonii Wight. & Arn. (swallow root). The variables evaluated were the levels of sucrose, BA, and NAA each at two different concentrations. Response surfaces for shoot length and multiple shoot number were useful in achieving optimal levels of media constituents and in understanding their interactions, but response surfaces for number of leaves were not. The data indicate that sucrose, BA, and NAA levels may be manipulated to increase or decrease quality factors chosen. This approach may be useful in developing a micropropagation protocol for D. hamiltonii. Chemical names used: benzyladenine (BA); napthaleneacetic acid (NAA).
J.D. Norton, G.E. Boyhan, and J.A. Pitts
The dwarfing characteristics of St. Julien and Pixy rootstocks as measured by shoot growth and trunk cross-sectional area (TCSA) was evident. Tree survival was significantly reduced after 3 years on Nemaguard and Pixy rootstocks. None of the elements measured by foliar nutrient analysis were below the minimum for plums; however, significant multiple regression equations for total shoot growth, TCSA, and survivability were evident with R 2 of ≈0.30 in all three cases.
Dennis P. Stimart and James F. Harbage
Stem pieces from expanding spikes of Liatris spicata (L.) Willd. were cultured in vitro on a Murashige and Skoog medium containing BA to establish proliferating cultures for use in comparing BA and IBA effects on shoot proliferation. Both compounds promoted multiple shoot development. The optimum level for micropropagation was 2.7 μm BA without IBA. Greatest rooting was at 5.0 μm IBA without BA.
John A. Driver and Andrew H. Kuniyuki
Apical and lateral meristems of Paradox walnut (Juglans hindsii x J. regia) were used to investigate the possibility of accomplishing in vitro propagation of Paradox rootstock. A walnut specific medium, DKW, has been defined supporting optimum multiple shoot development under 4.5 μm benzyladenine (BA) and 5 nm indolebutyric acid (IBA) treatment. The method of analysis to determine the optimum level of constituents in tissue culture medium is discussed. Also reported is the in vivo rooting of tissue culture derived shoots.
Handan Büyükdemirci and Paul E. Read
Axillary buds of `Valiant' grapevine (Vitis spp.) grown in vitro were transferred onto Murashige and Skoog (MS) medium supplemented with different cytokinin and auxin combinations and concentrations. It was found that culture medium caused statistically important differences in number of nodes, number of fully expanded leaves, number of multiple shoots, number of roots, and length of shoots. MS medium supplemented with 1.0 mg BA/liter in combination with 0.01 mg NAA/L was found to be the best medium for shoot growth and callus production. MS medium supplemented with the combination of 0.5 mg BA/L and 0.01 mg NAA/L was the best medium for explant rooting. The medium containing BA and NAA encouraged better shoot growth than those containing BA alone. When the concentration of BA in the medium was increased, multiple shoot proliferation and teratological structures of explants increased, but the number of small leaves and length of internode decreased. Axillary bud culture led to better shoot growth than was found for shoot apex culture. The presence of leaves positively affected shoot growth from axillary buds. Also placing the axillary buds horizontally onto the medium gave better shoot proliferation and growth than placing them vertically.