Host-plant nutritional status may affect the incidence and development of western flower thrips (WFT; Frankliniella occidentalis Pergande). Two greenhouse experiments were conducted to determine the responses of WFT population levels on impatiens (Impatiens wallerana Hook.f.) when plants were fertilized with commercially practiced rates of nitrogen (N) and phosphorus (P). Impatiens `Dazzler Violet' were grown with nutrient treatment combinations of 2 N rates (8 and 20 mm) by 2 P rates (0.32 and 1.28 mm). Individual plants grown in thrips-proof cages were inoculated with WFT at 2 or 4 weeks after transplant, in separate experiments, representing vegetative or reproductive stages of plant growth, respectively. Plants were destructively sampled weekly for 4 weeks following inoculation. Plant tissue N and P concentrations were significantly different across treatments: 8 and 20 mm N resulted in 4.9% and 6.3% N in tissue, respectively; 0.32 and 1.28 mm P resulted in 0.37% and 0.77% P in tissue, respectively. Nitrogen rates had no effect on WFT population levels. However, 4 weeks after inoculation with adult female WFT during the vegetative growth stage, plants fertilized with 1.28 mm P had more adult WFT than those fertilized with 0.32 mm P. Feeding damage varied depending on whether plants were inoculated in the vegetative stage with adult WFT or during reproductive growth with immature WFT. Plant size and number of flowers were lower in plants inoculated during the vegetative growth stage with adult WFT but were not affected when inoculation with immature WFT occurred during the reproductive stage, as most WFT were found feeding inside the nectariferous spurs of the flowers. Tissue N was lower in WFT-inoculated plants compared to noninoculated plants in both experiments.
Yan Chen, Kimberly A. Williams, Brent K. Harbaugh, and Michelle L. Bell
Jaemin Lee and Lowell C. Ewart
Most seed produced impatiens today are F1 hybrids. The seed of F1 hybrids is produced by hand-emasculation of the seed parent or the use of some types of male sterility system. The male sterility systems used in impatiens breeding have never been reported, and is proprietary information of seed companies. The objective of this study was to investigate the types of male sterility involved in impatiens. Eighteen inbreds and 14 hybrids were investigated. One sterile inbred line was selected and crossed with several inbred fertile lines for inheritance analysis. The F1 progenies were all fertile, and backcrossed to the sterile parent. The F2 and backcross populations indicate that the inheritance is controlled by a single recessive ms gene. Information concerning with a possibility of cytoplasmic-nuclear gene interaction will be discussed.
William J. Carpenter, Eric R. Ostmark, and John A. Cornell
The role of light on impatiens seed germination and radicle emergence was studied. Seeds having a photodormancy require light for only part of the germination period. Germination ≥85% was achieved after 3, 2, or 1 day of irradiance at 1.5, 15, or 75 μmol·s-1·m-2, respectively. Keeping imbibed seeds in darkness for ≥2 days before light exposure caused reduced total germination percentages (G), delayed achieving 50% of the final germination percentage (T50), and increased the days between 10% and 90% germination (T90-T10). Light for 6 hours daily at 1.5, 15, or 150 μmol·s-1·m-2 promoted high G and rapid and uniform germination, but daily 12 to 24 hours of irradiance decreased G and increased T50 and T90-T10. Estimated rates of decline (increase) in G, T50, or T90-T10 with each added day of light (darkness) or increasing daily hours of light were measured by fitting regression equations. Impatiens seed germination was promoted by the initial 1 to 3 days of light, but light inhibited radicle extension in the latter germination stages.
B. Bejie Herrin and Daniel F. Warnock
Western flower thrips are an ever-increasing problem in greenhouse floriculture crops. Thrips resistance to pesticides as well as tighter regulations on pesticide use are making thrips management in the greenhouse more difficult. To improve host plant resistance, a study was conducted to determine if impatiens cultivars varied in their susceptibility to western flower thrips feeding damage. In a replicated study, nine impatiens cultivars were inoculated with about 30 thrips. Thrips were allowed to feed on individual plants during an 8-week period of growth. During plant growth, visual evaluations to estimate thrips feeding damage were conducted every 2 weeks. At the conclusion of the experiment, a final visual evaluation was made and thrips numbers were determined. Cultivars varied in estimates of thrips feeding damage. Several cultivars exhibited significantly reduced levels of thrips feeding damage. Of these cultivars, some had high thrips population levels, indicating tolerance, while other cultivars had low thrips population levels, an indication of antibiosis. One cultivar was determined to be highly susceptible to thrips feeding damage. This cultivar was so damaged by the end of the study, remaining plant material was unable to support thrips populations. Variability was found in the levels of thrips feeding damage and thrips population levels indicating the presence of tolerance and/or antibiosis. Because of detected variability, the potential for improving impatiens resistance to thrips feeding damages exists.
Gary F. Polking, Richard J. Gladon, and David S. Koranski
Germinated Impatiens wallerana Hook. f. `Super Elfin Salmon Blush' seeds were exposed to subatmospheric O2 concentrations for 12, 24, or 48 hours at 25C. Suppression of radicle growth during a subsequent 24-hour simulated shipping period was monitored, as was plant growth during a subsequent growth cycle. One percent to 2% O2 for 12 or 24 hours limited radicle elongation to <1.0 mm during the simulated shipping period (darkness, ambient O2) and caused no permanent damage to seedlings. Suppression of radicle elongation with low O2 was greater with a 24-hour than a 12-hour exposure. Oxygen at 0% for 24 hours or at 0% to 1.5% O2 for 48 hours damaged seedlings irreversibly. These results show that specific subatmospheric O2 treatments can restrict radicle elongation of germinated seeds during subsequent shipment to a grower and that the low O2 treatment does not decrease subsequent plant growth.
Bejie Herrin and Daniel Warnock
Western flower thrips (WFT) [Frankliniella occidentalis (Pergande)] are an ever-present problem in greenhouse floricultural crops. To determine if host plant resistance varied in impatiens [Impatiens wallerana Hook. f.] nine genotypes were evaluated for resistance to WFT feeding damage. Individual insect-free plants of each genotype were inoculated with ≈30 laboratory-reared WFT. Thrips were allowed to feed on individual plants for a 4-week period during which visual evaluations were conducted every 2 weeks to estimate feeding damage. Feeding damage varied among genotypes and increased with time. At 4 weeks after inoculation, `Cajun Carmine' and `Super Elfin Lavender' had significantly less feeding damage than all other genotypes. The San Vito Wild-type germplasm was determined to be highly susceptible to thrips feeding damage based on visual evaluations. Because WFT feeding damage varied among genotypes, the potential for improving impatiens resistance to WFT exists within commercially available germplasm.
Daniel F. Warnock
Western flower thrips (WFT) [Frankliniella occidentalis (Pergande)] is a pest of greenhouse-grown floriculture crops worldwide. To determine if plant resistance varied in three populations of impatiens (Impatiens wallerana Hook. f.) collected near San Vito, Costa Rica, 59 genotypes were evaluated for resistance to feeding by WFT. Individual insect-free plants of each genotype were inoculated with 20 laboratory-reared WFT. Thrips were allowed to feed on individual plants for a 4-week period followed by visual evaluations to estimate feeding damage. Feeding damage varied among genotypes. Thirty-seven genotypes had feeding damage levels similar to the susceptible control, while 22 entries were significantly more resistant than the susceptible control. Of the 22 genotypes with some level of resistance, six genotypes were commercially acceptable, having mean visual ratings below 4.0 on a 1 to 9 evaluation scale. Five of these six genotypes were seedlings from a single population and represented 13.9% of the seedlings in that population. The remaining seedling was from a second San Vito population. The plants in these populations identified as having acceptable levels of damage may be useful in a breeding program designed to enhance resistance to WFT feeding damage. Because WFT feeding damage varied among genotypes, the potential for improving impatiens resistance to WFT exists within available germplasm.
Brian E. Whipker, Shravan Dasoju, Michael S. Dosmann, and Jeffery K. Iles
Double impatiens (Impatiens wallerana Hook.) `Blackberry Ice' (variegated-leaf) and `Purple Magic' (green-leaf) were grown on flood benches and irrigated with 50, 100, 200, or 300 mg·L-1 (ppm) N to study the effect of fertility on growth and development. Electrical conductivity (EC) levels at week 9 were similar for both cultivars at each fertilizer rate, except for the 100 mg·L-1 N where EC levels of `Blackberry Ice' were more than double those of `Purple Magic'. This indicated that the nutrient demands were less for `Blackberry Ice' and fertilization rates lower than 100 mg·L-1 N would be required. After nine weeks, plants grown with 100 mg·L-1 N had a 22% larger plant diameter than plants grown with either 50 or 200 mg·L-1 N. Fertilization rates of 50 mg·L-1 N resulted in plants which were covered with a higher percentage of blooms per unit of leaf area, but the plants were smaller. Plant tissue dry weight (leaf, bud, stem, and total) increased to the highest level at 100 mg·L-1 N, then decreased with further increases in fertilization rate. For maximum shoot growth with flood irrigation, growers should apply 100 mg·L-1 N when growing `Purple Magic' double impatiens and a fertilization rate between 50 and 100 mg·L-1 N for `Blackberry Ice'.
Marc van Iersel
Transplanting can result in root damage, thereby limiting the uptake of water and nutrients by plants. This can slow growth and sometimes cause plant death. Antitranspirants have been used to minimize transplant shock of vegetables. The objective of this research was to determine if antitranspirants are useful to reduce transplant shock of impatiens (Impatiens wallerana Hook.f.) seedlings in the greenhouse. Seedling foliage was dipped in or sprayed with antitranspirant (Vapor Gard or WiltPruf) and shoot dry mass was determined at weekly intervals. Antitranspirants reduced posttransplant growth of impatiens as compared to untreated plants, possibly because of a decrease in stomatal conductance, leading to a decrease in photosynthesis. The two dip treatments also caused phytotoxic effects (necrotic spots) on the leaves. In a second study, leaf water, osmotic and pressure potential were determined at 2, 9, and 16 days after transplant. Application of antitranspirants (as a dip or spray) decreased water and osmotic potential compared to control plants. The results of this study indicate that antitranspirants are not useful for minimizing transplant shock of impatiens under greenhouse conditions.
Mehrassa Khademi, David S. Koranski, David J. Hannapel, Allen D. Knapp, and Richard J. Gladon
Water uptake by impatiens (Impatiens wallerana Hook. f. cv. Super Elfin Coral) seeds was measured as an increase in fresh weight every 24 hours during 144 hours of germination. Seeds absorbed most of the water required for germination within 3 hours of imbibition and germinated at 60% to 67% moisture on a dry-weight basis. Germination started at 48 hours and was complete by 96 hours at 25C. Water stress of -0.1, -0.2, -0.4, and -0.6 MPa, induced by polyethylene glycol 8000, reduced germination by 13%, 49%, 91%, and 100%, respectively, at 96 hours. Under the same water-stress conditions, increases in fresh weight were inhibited by 53%, 89%, 107%, and 106%, respectively. Three distinct groups of storage proteins were present in dry seed; their estimated molecular weights were 1) 35, 33, and 31 kDa; 2) 26, 23, and 21 kDa; and 3) two bands <14 kDa. Major depletion of storage proteins coincided with the completion of germination. Water potentials that inhibited germination also inhibited degradation of storage proteins. During germination under optimum conditions, the soluble protein fraction increased, coinciding with a decrease in the insoluble fraction.