Mexican petunia (Ruellia simplex Wright) is a non-native plant that was introduced to Florida sometime in the 1940s and since then has naturalized in most of the state and in other southern states. Since 2007, we have developed at the University of Florida/Institute for Food and Agricultural Science in Gainesville the first Ruellia L. breeding program aiming to develop fruitless plants with different flower colors and growth habits that will not be invasive by seed dispersal. A combination of polyploidization and hybridization methods was used. In 2011, a total of 15 plants were selected and grown in southeastern, north–central, and northwestern Florida (Fort Pierce, Citra, and Quincy) using a randomized block design with three blocks and three plants per plot at each site. Plants were evaluated monthly for landscape performance, flowering, and fruiting. Two hybrids (R10-102 and R10-108) had outstanding potential as new fruitless cultivars for the plant industry having improved landscape performance and flowering.
Rosanna Freyre, Adam Moseley, Sandra B. Wilson, and Gary W. Knox
Mathews L. Paret, Aaron J. Palmateer, and Gary W. Knox
Bacterial leaf spot on roses caused by a Xanthomonas sp. is a new disease affecting commercial rose production with the potential to cause major economic losses. In the past few decades, antimicrobial photocatalyst technology has emerged from basic research and development to provide convenient formulations of titanium dioxide (TiO2) nanoparticles, which have the ability to destroy bacteria on surfaces in the presence of light. In this study, a TiO2 nanoparticle formulation containing zinc (TiO2/Zn) was tested for management of bacterial leaf spot on Rosa ‘Noare’. TiO2/Zn caused significant reduction in the survival of Xanthomonas sp. strain Xr-1 on glass coverslips coated with the nanoparticles on exposure to light at 3 × 104 lux for 10 minutes. There was no reduction of bacterial viability in non-coated or non-illuminated controls. Field applications of TiO2/Zn at ≈500 to 800 ppm on Rosa ‘Noare’ significantly reduced bacterial spot severity compared with the untreated control. TiO2/Zn activity was better or on par with the ornamental industry standard for management of rose diseases.
Jyotsna Sharma, Gary W. Knox, and Maria Lucia Ishida
Certain cultivars of magnolia are desirable in landscapes for their uncommon yellow flowers. While cultivars derived from Magnolia acuminata L. (cucumbertree magnolia) are difficult to propagate by stem cuttings, some with mixed parentage appear easier to propagate in this manner. We propagated six yellow-flowered cultivars vegetatively by applying 0, 8, 16, or 30 g·kg–1 (0, 8,000, 16,000, or 30,000 ppm) indole-3-butyric acid (IBA) in talc to bases of terminal stem cuttings collected 5, 7, 9, or 11 weeks after budbreak. Mean rooting percentage over all cultivars increased from 12% (in the absence of IBA) to 34% (after application of 30 g·kg–1 IBA). Rooting percentage and basal stem diameter of a cutting did not seem related. For each collection date, more cuttings of `Ivory Chalice' and `Yellow Lantern' developed roots than the other cultivars. More roots (mean = 5) developed on cuttings of `Yellow Lantern' collected 5 weeks after budbreak or when treated with 30 g·kg–1 IBA than the other cultivars. `Butterflies' largely remained unresponsive, whereas rooting of `Golden Sun,' `Hot Flash,' and `Maxine Merrill' collected 5 weeks after budbreak was 31%, 22%, and 28%, respectively. When data were analyzed separately for selected cultivars, 63% rooting was observed among cuttings of `Ivory Chalice' collected 7 weeks after budbreak. Rooting percentage was higher (22%) among cuttings of `Hot Flash' collected 5 or 7 weeks after budbreak in comparison to later collection dates, but harvest date did not influence rooting of `Yellow Lantern,' which ranged from 44% to 59%. Collection of stem cuttings early in the growing season (5 weeks after budbreak) was beneficial (31% rooting) for inducing rooting among cuttings of `Golden Sun.' We conclude that `Ivory Chalice' and `Yellow Lantern' are promising choices for growers interested in clonal propagation of yellow-flowered cultivars of magnolia. To maximize rooting among these cultivars, terminal cuttings should be collected within 5 to 11 weeks after budbreak and treated with 16 or 30 g·kg–1 IBA in talc. Early collection dates (5 to 7 weeks after budbreak) improved rooting among cuttings of other cultivars but these, particularly `Butterflies,' remain variably recalcitrant and merit further study.
Sandra B. Wilson, Gary W. Knox, Keona L. Nolan, and James Aldrich
Chinese privet (Ligustrum sinense) and glossy privet (L. lucidum) have been classified as Category I invasives in Florida. The closely related japanese privet (L. japonicum) has escaped cultivation but is not considered a problem species in Florida. Plant growth, visual quality, flowering, and fruiting were assessed for the resident species (wild-type form) and selected cultivars of chinese privet, glossy privet, and japanese privet planted in northern and southern Florida for 132 weeks. Visual quality varied by site, month, and cultivar. With the exception of ‘Swift Creek’ chinese privet (which did not survive in southern Florida), all cultivars survived the study. All plants fruited in northern Florida. In southern Florida, fruiting was less abundant and not observed for ‘Jack Frost’ japanese privet, ‘Rotundifolium’ japanese privet, ‘Swift Creek’ chinese privet, ‘Suwannee River’ hybrid privet, and glossy privet within 132 weeks. In northern and southern Florida, the growth index rate was lower for ‘Lake Tresca’ japanese privet, ‘Rotundifolium’ japanese privet, and ‘Suwannee River’ hybrid privet than other cultivars. There was a significant interaction between temperature and species for seed germination. Germination in incubators set with a 12-hour photoperiod ranged from 51% to 78.5% for chinese privet, japanese privet, and glossy privet among temperatures, with the exception of glossy privet at 35/25 °C, where only 2.0% of seeds germinated. Germination in complete darkness ranged from 39.5% to 80.5% for chinese privet and glossy privet among temperatures, with the exception of glossy privet at 35/25 °C, where only 0.5% of seeds germinated.
Cecil T. Pounders, Eugene K. Blythe, Donna C. Fare, Gary W. Knox, and Jeff L. Sibley
This study reports on the performance of 34 clones of crapemyrtle (Lagerstroemia indica L., L. fauriei Koehne, and L. indica × L. fauriei hybrids) grown in field plots at four locations representative of different environments in the southeastern United States. Traits evaluated were spring leaf-out and initiation of flowering in the second season after field planting and plant height after 3 years of growth. Cluster analysis (Ward's method) was used for grouping and comparison of means across locations for each trait. Best linear unbiased prediction was used for estimating random effects in linear and generalized linear mixed models to better determine the general performance of the clones under a variety of environmental conditions. Each clone's trait stability was quantified using the regression of an individual genotype's performance for each of the three studied traits on an environmental index based on the trait mean for all genotypes grown in an environment. Sequence of clone leaf-out and size rankings were more stable across the environments than the sequence in which the various clones initiated flowering. L. fauriei clones and clones originating from the initial cross between L. indica and L. fauriei were generally later to leaf out, earlier to flower, and more vigorous growers than L. indica or the complex L. indica × L. fauriei clones that were evaluated. First flowering was affected by environmental variation more with interspecific hybrids than with L. fauriei and L. indica clones. Performance, particularly with respect to plant height, of several clones did not agree with previously published classifications. Information generated by this study will allow crapemyrtle breeders, landscape professionals, and consumers to better select the most appropriate crapemyrtle clone for a particular application.
Edward F. Gilman, Gary W. Knox, Catherine A. Neal, and Uday Yadav
Lagertroemia indica L. × fauriei Koehne (`Natchez' crape myrtle) crown width increased after 13 months as irrigation frequency increased from every 3 days to every day, and the irrigated area around the fabric container increased from 20% to 100% of the circular area within 20 cm beyond the container. Restricting irrigation to within the fabric container plus 20% of the area 20 cm beyond the container edge resulted in less height and width for crape myrtle, but had no effect on root growth, compared to irrigating 100% of area 20 cm beyond the container. Restricting the pattern of irrigation to the container plus 20% of the area 20 cm beyond the container resulted in greater free-root weight (roots < 5 mm in diameter) within the container for laurel oak (Quercus laurifolia Michx.) compared to irrigating the container plus 100% of the area 20 cm beyond the container. Height, width, and caliper of oak were not different among treatments.
Sandra B. Wilson, Gary W. Knox, Zhanao Deng, Keona L. Nolan, and James Aldrich
A wild-type selection of heavenly bamboo (Nandina domestica) and eight cultivars were evaluated in northern and southern Florida for 144 weeks. Onset of flowering generally began by April and May in southern Florida and 4 to 8 weeks later in northern Florida. Fruit was first noted 4 to 8 weeks after most cultivars began flowering. Landscape performance and fruit production varied widely among taxa and location. ‘AKA’, ‘Firehouse’, ‘Firepower’, and ‘Firestorm’ heavenly bamboo did not flower or fruit in either location. Greater plant growth, survival, and fruiting were observed in northern Florida than in southern Florida. In both locations, the wild-type form of heavenly bamboo produced more fruit than ‘Alba’, ‘Gulf Stream’, ‘Monfar’, and ‘Moyer’s Red’. Seed viability was fairly consistent among fruiting cultivars, ranging from 69% to 89%. Nuclear DNA content and ploidy analysis indicated that all nine nandina cultivars were diploids, suggesting that tetraploidy is not the genetic cause of the non-fruiting trait in ‘AKA’, ‘Firehouse’, ‘Firepower’, and ‘Firestorm’. Results of this study offer insight into future non-invasive heavenly bamboo breeding efforts and emphasize the importance of cultivar and geographic distinctions when regarding the invasive status of a species.
David M. Czarnecki II, Sandra B. Wilson, Gary W. Knox, Rosanna Freyre, and Zhanao Deng
Benjamin D. Anderson, Gary W. Knox, Ann R. Blount, Cheryl L. Mackowiak, and Edward F. Gilman
Rhizoma peanut has the potential for use as an ecologically friendly groundcover or turf alternative. Little is known about height and cover characteristics of this plant, which are important ornamental considerations. The objectives of this field study were to characterize maximum average canopy height, height variability, the time to reach full canopy cover, and the time at full canopy cover of seven released and nine experimental selections of rhizoma peanut grown in full sun or under 30% shade at two North Florida locations. Greater height and a less uniform canopy were observed for shaded plants. Establishment, as measured by full canopy cover, did not occur until the second year after planting. Shade treatment had little effect on the time to reach full canopy cover or the duration of full canopy cover, indicating that rhizoma peanut will perform equally in full sun or under 30% shade. Recommended selections for ornamental use based on these variables include ‘Brooksville 67’, ‘Brooksville 68’, EX3, and EX8.