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Respiration of excised Ilex crenata `Rotundifolia' roots as influenced by root-zone growth temperature and buffer solution temperature was measured in the presence and absence of SHAM and KCN. Respiration rates of roots excised from plants grown for three weeks at root-zone temperatures of 30, 34, 38, and 42 C decreased linearly as root-zone temperature increased when the buffer solution was maintained at 25 C. When the buffer solution temperature was the same as the root growth temperature, no differences in respiration rate were found. When plants were grown at a root-zone temperature of 30 C, respiration was maximal at 34 C and decreased to a minimum at 46 C. Above 46 C, stimulation of O2 consumption occurred which was presumed to be extra-mitochondrial. CN-resistant pathway activity decreased at a buffer solution temperature of 46 C which was similar to the critical threshold temperature (48±1.5 C) for `Rotundifolia' holly roots.
Ilex crenata Thunb. `Rotundifolia' split-root plants were grown for 3 weeks at root-zone temperatures of 30/30, 30/34, 30/38, 30/42, 34/34, 38/38 and 42/42. The 38 C root-zone temperature treatment was the upper threshold for a number of growth and physiological parameters. A portion of the root system grown at near optimum temperatures could compensate in terms of shoot growth for part of the root system exposed to supraoptimal root-zone temperatures up to the 38 C critical threshold. Higher root-zone temperatures did not affect photosynthetic rates or root:shoot ratios, but altered photosynthate partitioning to different stem and root sinks. Although no differences were found for total 14C partitioned to the roots, partitioning of the 14C into soluble and insoluble fractions and the magnitude of root respiration and exudation were influenced by treatment. Heating half of a root system at 38 C increased the amount of 14C respired from the heated side and increased the total CO2 respired from the non-heated (30 C) half. Exposure of both root halves to 42 C resulted in membrane damage which increased the leakage of 14C photosynthates into the medium.
Swamp sunflower (Helianthus simulans) is an underused perennial plant native to the southeastern United States that produces an abundance of golden yellow inflorescences in the fall. It is a vigorous grower and tolerates a wide variety of soil conditions, growing in wetland and nonwetland habitats. Swamp sunflower warrants wider use in perennial beds and landscapes, and research on production practices to make plants more suitable for shipping could promote its production. This study evaluated the effects of plant growth regulators (PGRs) on the growth and floral attributes of the swamp sunflower. Treatments were applied to rooted cuttings in 1-gal pots as a substrate drench of 1, 2, 4, or 6 mg/pot paclobutrazol; 0.5, 1, 2, or 4 mg/pot flurprimidol; or water (control)/pot for Expt. 1. A second experiment (Expt. 2) applied 4, 6, or 8 mg/pot paclobutrazol; 2, 4, or 6 mg/pot flurprimidol; or water (control)/pot. Six weeks after treatment (WAT) for Expt. 1, paclobutrazol applied at 4 and 6 mg/pot and flurprimidol at 2 and 4 mg/pot resulted in smaller plants (as reflected by growth index) by 29%, 34%, 22%, and 48%, respectively, compared with the control. Furthermore, at the termination (6 WAT) of Expt. 1, the highest rate of flurprimidol produced the smallest plants, with the exception of the highest rate of paclobutrazol. By 6 WAT, plants treated with the highest rate of paclobutrazol and flurprimidol had lower dry weights and higher chlorophyll measurements than control. All PGR treatments for Expt. 2 resulted in smaller plants than the control by 27% to 36% at 4 WAT and 23% to 41% at 6 WAT. Differences for internode length and flower diameter were observed for Expts. 1 and 2, respectively. Results from these experiments suggest a substrate drench application of 6 mg/pot paclobutrazol or 4 mg/pot flurprimidol can be used for producing smaller plants compared with nontreated plants for swamp sunflower under greenhouse conditions.
In 1991, a cooperative project with the U.S. National Arboretum in Washington, D.C., was initiated in Tifton, Ga. (USDA hardiness zone 8a) to evaluate red maples (Acer rubrum L.) potentially suitable for the coastal plain region of the southeastern U.S. Greatest annual height growth across all cultivars over 6 years was for `Alapaha', a seedling selection from southern Georgia with annual height growth of 35 inches (88.0 cm), and several seedling selections from northern Florida with annual height increases in excess of 33 inches (86.0 cm). Selections showing the least average annual height growth were NA-56024 and NA-57772 (`Red Rocket'). For commercially available cultivars, the most dependable for fall color in Tifton was `October Glory'®. In addition, two new selections from the National Arboretum have also shown excellent fall color—`Somerset' and `Brandywine'.
The genus Pavonia is one of the largest genera in the Malvaceae species; it is mainly distributed in South America. Three species of Pavonia were identified based on different flower colors and potential for landscape use in the southeastern United States. These species produce a large amount of seed at the end of the blooming season, which is not ideal for ornamental use. To reduce the seed set, gamma irradiation was used for mutation induction and propensity to induce compactness and sterility. A preliminary study indicated that the seed of Pavonia hastata would germinate at irradiation rates up to 2000 Gy. Seeds of three species were treated with six different dose rates ranging from 0 Gy to 1000 Gy to determine the ideal rate for Pavonia breeding and how gamma irradiation affected seed germination. M1 (the first mutant generation) P. lasiopetala and P. missionum were sown in 2018 and planted in the field at the University of Georgia Durham Horticulture Farm on 1 May 2019, as were M2 (the second mutant generation) seeds of P. hastata. Seed germination in 2019 showed no significance due to treatment but significance due to species and species by treatment interaction. Field evaluation performed in 2019 indicated that height was not influenced by irradiation for any of the three species but that the width index was. Flower diameter and leaf area of P. missionum became smaller as the irradiation rate increased, but the other two species showed no trends. Chlorophyll mutations were observed on P. hastata at the 1500 Gy level, which has attractive traits for ornamental use.
Genome size estimates and chromosome number information can be useful for studying the evolution or taxonomy of a group and also can be useful for plant breeders in predicting cross-compatibility. Callicarpa L. is a group of ≈140 species with nearly worldwide distribution. There are no estimates of genome size in the literature and the information on chromosome numbers is limited. Genome size estimates based on flow cytometry are reported here for 16 accessions of Callicarpa comprising 14 species in addition to chromosome counts on six species. Chromosome counts were conducted by staining meristematic cells of roots tips using modified carbol fuchsin. Holoploid genome size estimates ranged from 1.34 pg to 3.48 pg with a mean of 1.74 pg. Two tetraploids (2n = 4x = 68; C. salicifolia P'ei & W. Z. Fang and C. macrophylla Vahl GEN09-0081) were identified based on holoploid genome size and confirmed by chromosome counts. There was little variation among species for monoploid genome size. 1Cx-values ranged from 0.67 pg to 0.88 pg with a mean of 0.77 pg. Chromosome counts for six species revealed a base chromosome number of x = 17. Callicarpa chejuensis Y. H. Chung & H. Kim, C. japonica Thunb. ‘Leucocarpa’, C. longissima Merr., and C. rubella Lindl. were confirmed as diploids (2n = 2x = 34). Cytology supported flow cytometry data that C. salicifolia and C. macrophylla GEN09-0081 were tetraploids. The two accessions of C. macrophylla included in the study were found to be of different ploidy levels. The presence of two ploidy levels among and within species indicates that polyploidization events have occurred in the genus.
Salvia coccinea is a valuable flowering annual that attracts hummingbirds and bees to the garden, but few cultivars are commercially available. There is a limited range of petal colors and no leaf variegation. This research aimed to improve the ornamental value of S. coccinea by inducing mutations with ethyl methanesulfonate (EMS). The standard, red-flowered species was selected for treatment by exposing seeds to 0%, 0.4%, 0.8%, or 1.2% EMS for 8, 12, or 24 hours. The optimal treatment rate was determined to be 1.2% EMS for 8 hours, which generated desirable mutations near the median lethal dose (LD50). The M1 population had a 53% germination rate and was completely morphologically uniform. By the M2, mutations included differences in leaf shape and flower size in addition to albina, chlorina, virescens, and chimeral chlorophyll changes. A 1% mutation rate was achieved in this breeding program with seven unstable mutations and six stable mutations. The normalized difference vegetation index (NDVI) values were measured to determine differences in chlorophyll content between lethal albina mutations, chartreuse chlorina and virescens mutations, and typical leaf color. Future work will investigate the stability and heritability of chlorophyll variegation by hybridizing these selections with coral-flowered accessions of S. coccinea.
Salvia is a genetically diverse genus in the Lamiaceae family, with hundreds of species distributed globally. With base chromosome numbers ranging from 6 to 19 and ploidy levels ranging from diploid to octoploid, the genus has been proposed to be subdivided based on molecular data rather than morphology. However, little is known about total DNA content across the genus. The DNA content of 141 Salvia genotypes were analyzed using flow cytometry. Samples of Salvia were stained with propidium iodide and compared with the internal standards Pisum sativum ‘Ctirad’ and Solanum lycopersicum ‘Stupické’ to generate estimations of DNA content. Holoploid 2C genome sizes of the analyzed Salvia ranged from 0.63 pg to 6.12 pg. DNA content showed a wide distribution across chromosome number, ploidy, and clade. The wide distribution of DNA content across the genus further indicates the diversity of Salvia and may be useful for future breeding efforts.