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Muntubani D.S. Nzima, George C. Martin, and R.W. Breidenbach

Isothermal microcalorimetric measurements of metabolic heat rates of `Kerman' pistachio (Pistacia vera L.) individual inflorescence buds, current-year and 1-year-old shoots were used to investigate the roles of current and reserve photosynthates in the abscission of inflorescence buds. In the early stages of development metabolic heat rates of individual inflorescence buds were two and three times those of individual current-year and 1-year-old shoots respectively. Individual shoot organs (1-year-old shoots, current-year shoots, and inflorescence buds) sampled from “on” trees had higher metabolic heat rates than similar individual organs sampled from “off” trees. Artificial shading of pistachio trees for 14 days in early June depressed metabolic heat rates of individual inflorescence buds within 24 h, but there was a delay of 4 days before the decline in metabolic heat rates of individual current-year and 1-year-old shoots. This suggests that metabolic heat rates of individual inflorescence buds apparently depended on currently fixed photosynthates.

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Tim D. Davis, S.W. George, A. Upadhyaya, and J.M. Parsons

Factors affecting the greenhouse propagation of firebush (Hamelia patens) by leafy stem cuttings during winter were studied. Without bottom heat (BH), mid-day rooting medium temperature was 22 ± 3 C. About half of the auxin-treated cuttings without BH rooted. Maintaining the rooting medium at 29-39 C increased rooting for auxin-treated cuttings to 96-100% and increased root length and visual rating scores several-fold. Rooting percentage, root length, and visual ratings were consistently high in perlite and low in peat. Stem-tip cuttings and sub-terminal stem segment cuttings with basal stem diameters of 3-5 mm rooted slightly better than stem segment cuttings with basal diameters of 6-8 mm. Stem-tip cuttings not treated with auxin but with BH had rooting percentages of 81-86%. Treatment of stem-tip cuttings with auxin generally yielded 90% rooting or above. Despite this, plants grown from auxin-treated cuttings were indistinguishable from plants grown from non-treated cuttings 2 months after the rooting period. Of the variables studied, BH had the most dramatic effect on rooting of firebush cuttings during winter months.

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Tim D. Davis, Daksha Sankhla, N. Sankhla, A. Upadhyaya, J.M. Parsons, and S.W. George

Seeds of Aquilegia chrysantha Gray were germinated under a variety of temperature regimes. Germination was nearly 90% under a day/night cycle of 25/20C, but was reduced to ≤ 40% under constant 25C or a 25/10C day/night cycle. With days between 25 and 29C (night = 20C), germination percentage dropped gradually to ≈ 60% with increasing temperature. With days >29C, germination declined dramatically such that no germination occurred at 31C. Neither kinetin (4.6 to 46 μm) nor ethephon (6.9 to 207 μm) was able to reverse the inhibitory effects of 33C days. Our results indicate that germination of A. chrysantha seed is sensitive to temperature and that germination ≈ 75% can be obtained under a 25 to 27C day/20C night regime. Chemical names used: 2-chloroethylphosphonic acid (ethephon); 6-furfurylaminopurine (kinetin).

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R.R. Tripepi, M.W. George, T. Sripo, S.A. Johnsen, and A.B. Caplan

The objective of this study was to determine if selected strains of Agrobacterium could infect microshoots of Rhododendron catawbiense. Fifteen microshoot stems of R. catawbiense var. album `America', `Joe Paterno', and `Cunningham's White' were inoculated with two drops (about 25 μL) of wild type Agrobacterium tumefaciens strains C58 or B6 or with wild type A. rhizogenes strain E8/73. Five control shoots were inoculated with 1.2 mM KH2PO4 buffer. Microshoots were grown on woody plant medium (WPM) supplemented with 4.9 μM 2iP. Six weeks after inoculation galls that formed were excised from the microshoots and placed on WPM that lacked plant growth regulators but contained 300 mg·L-1 cefotaxime. In another study, these wild-type bacterial strains were genetically modified by inserting the pBINm-gfp5-ER plasmid, which contained genes coding for NPTII and green fluorescence protein (GFP), into the bacteria. These modified strains were inoculated on 15 stems of the three rhododendron cultivars and one variety. Calluses that formed were excised, placed on basal WPM with cefotaxime, and allowed to proliferate. Wild type C58 induced galls to form on `Joe Paterno', R.c. album, and `Cunningham's White' stems, whereas wild type B6 caused galls to form only on the latter two types of rhododendron. Wild-type E8/73 failed to induce gall formation on the rhododendrons. Only genetically modified B6 caused galls to form on only `Cunningham's White' microshoots (seven of 15 inoculated stems). Three of these galls fluoresced green under ultraviolet light. Physical presence of the NPTII and GFP genes in the plant genome was determined by polymerase chain reaction. This study demonstrated that R. catawbiense is susceptible to Agrobacterium infection, and this plant can be genetically transformed.

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W.A. Mackay, S.W. George, C. McKenney, J.J. Sloan, R.I. Cabrera, J.A. Reinert, P. Colbaugh, L. Lockett, and W. Crow

One hundred sixteen rose (Rosa spp.) cultivars were evaluated under minimal input conditions in north-central Texas for 3 years. Plant quality data included overall plant performance, number of flowers, percentage of bloom coverage, final vigor, and survival. Disease ratings for black spot (Diplocarpon rosae), petal blight (Alternaria alternata), powdery mildew (Sphaerotheca pannosa), and aphid (Myzus spp.) infestations were previously reported. Of the original 116 cultivars, 25 had 50% or higher mortality during the trial. Own-root cultivars performed significantly better than the grafted cultivars and had significantly better survival (P = 0.001). As a class, the Polyantha cultivars exhibited the best overall performance, mean bloom percentage, final vigor and survival, while cultivars in the Hybrid Tea class had the worst performance in all measures. Foliar nutrient content, bloom number, and mean percentage of bloom were not good predictors of overall performance. Of the diseases monitored, black spot was the most severe and was closely correlated to overall performance and final vigor, but was not the only factor determining overall performance. The top five cultivars in mean overall performance were RADrazz (Knock Out™), Caldwell Pink, Sea Foam, Perle d'Or, and The Fairy, in descending order.

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W. A. Mackay, C.M. McKenney, P.F. Colbaugh, S.A. George, J.J. Sloan, and R.I. Cabrera

To enlarge the palette of environmentally-responsible landscape plants, 117 garden rose cultivars were evaluated under minimal input conditions. Other than mulching and irrigation, no other inputs were provided, including no fertilization and no pesticide applications. Plants were established in completely randomized blocks with four reps in the spring of 1998 with data collection beginning in 2000 and continued through 2002. Data on overall performance (an index comprised of flower number, percent of plant covered with flowers and plant growth) and relative chlorophyll content were collected the first and third week of each month from April through October. Disease ratings or incidence ratings were collected for Diplocarpon rosae Wolf (black spot), Alternaria sp. (petal blight) and Sphaerotheca pannosa (powdery mildew). Statistical analysis was performed on the mean data for all dates. `Knockout' was the top rose for overall quality with little or no disease observed, high foliage quality, and continuous flowers from spring until late in the fall. `Knockout' also ranked among the top rose cultivars in terms of overall nutrient concentrations (N, P, K, and Fe) in new growth tissue. Most of the hybrid tea roses such as `Peace' and `Double Delight' died in at least three blocks due to disease and a lack of vigor.