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Temperature is one of the main factors that affects the growth pattern of Gerbera hybrida, which shows vast variation in morphology and stress adaptation among cultivars. However, little is known about temperature responses of plant growth among different cultivars. In this study, four cultivars were planted in different growth temperatures to investigate the effect of temperature on plant growth of Gerbera hybrida during their vegetative growth. Results showed that the optimum growth temperature of the four cultivars was 20 °C, of which plant height, root length, biomass accumulation, leaf area, and photosynthetic rate were enhanced significantly. Different cultivars showed diverse temperature adaptation ranges, which were related with their genetic background, and the temperature adaptability of cultivar Autumn was the best among the four cultivars. Temperature also had significant effects on photosynthetic rate, which was the main factor shaping plant growth. Our research provides the basic guidance for the growth temperature control in the cultivation of Gerbera hybrida.

High-quality young plant production in northern latitudes requires supplemental lighting (SL) to achieve a recommended daily light integral (DLI) of 10 to 12 mol·m−2·d−1. High-pressure sodium (HPS) lamps have been the industry standard for providing SL in greenhouses. However, high-intensity light-emitting diode (LED) fixtures providing blue, white, red, and/or far-red radiation have recently emerged as a possible alternative to HPS lamps for greenhouse SL. Therefore, the objectives of this study were to 1) quantify the morphology and nutrient concentration of common and specialty bedding plant seedlings grown under no SL, or SL from HPS lamps or LED fixtures; and 2) determine whether SL source during propagation or finishing influences finished plant quality or flowering. The experiment was conducted at a commercial greenhouse in West Lafayette, IN. Seeds of New Guinea impatiens (Impatiens hawkeri ‘Divine Blue Pearl’), French marigold (Tagetes patula ‘Bonanza Deep Orange’), gerbera (Gerbera jamesonii ‘Terracotta’), petunia (Petunia ×hybrida ‘Single Dreams White’), ornamental millet (Pennisetum glaucum ‘Jester’), pepper (Capsicum annuum ‘Hot Long Red Thin Cayenne’), and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell trays. On germination, trays were placed in a double-poly greenhouse under a 16-hour photoperiod of ambient solar radiation and photoperiodic lighting from compact fluorescent lamps providing a photosynthetic photon flux density (PPFD) of 2 µmol·m−2·s−1 (ambient conditions) or SL from either HPS lamps or LED fixtures providing a PPFD of 70 µmol·m−2·s−1. After propagation, seedlings were transplanted and finished under SL provided by the same HPS lamps or LED fixtures in a separate greenhouse environment. Overall, seedlings produced under SL were of greater quality [larger stem caliper, increased number of nodes, lower leaf area ratio (LAR), and greater dry mass accumulation] than those produced under no SL. However, seedlings produced under HPS or LED SL were comparable in quality. Although nutrient concentrations were greatest under ambient conditions, select macro- and micronutrient concentrations also were greater under HPS compared with LED SL. SL source during propagation and finishing had little effect on flowering and finished plant quality. Although these results indicate little difference in plant quality based on SL source, they further confirm the benefits gained from using SL for bedding plant production. In addition, with both SL sources producing a similar finished product, growers can prioritize other factors related to SL installations such as energy savings, fixture price, and fixture lifespan.

A greenhouse study was undertaken to investigate whether light-emitting diode (LED) technology can be used to replace high-pressure sodium (HPS) lighting for cut gerbera production during Canada’s traditional supplemental lighting (SL) season (November to March). The study was carried out at the University of Guelph’s research greenhouse, using concurrent replications of SL treatments within the same growing environment. LED (85% red, 15% blue) and HPS treatment plots were set up to provide equal amounts of supplemental photosynthetically active radiation (PAR) at bench level. This setup was used to assess the production of three cultivars of cut gerbera (Gerbera jamesonii H. Bolus ex Hook.f): Acapulco, Heatwave, and Terra Saffier. There were no treatment differences in SL intensity, with average SL photosynthetic photon flux density (PPFD) and daily light integral (DLI) of 55.9 µmol·m−2·s−1 and 2.3 mol·m−2·d−1, respectively. Flowers harvested from the LED treatment had a 1.9% larger flower diameter in ‘Acapulco’; 4.2% shorter and 3.8% longer stems in ‘Heatwave’ and ‘Terra Saffier’, respectively; and 7.7% and 8.6% higher fresh weights for ‘Acapulco’ and ‘Terra Saffier’, respectively, compared with flowers harvested from the HPS treatment. There were no differences in accumulated total or marketable flower harvests for any of the cultivars. The vase life of ‘Acapulco’ flowers grown under the LED treatment was 2.7 d longer than those grown under the HPS treatment, but there were no SL treatment effects on water uptake for any of the cultivars during the vase life trials. There were no SL treatment effects on specific leaf area for any of the cultivars. There were only minimal treatment differences in leaf, soil, and air temperatures. Cut gerbera crops grown with under LED SL had equivalent or better production and crop quality metrics compared with crops grown under HPS SL.

Gerbera (Gerbera jamesonii Bolus ex. Hook f.) is one of the most important cut flowers in floriculture industry with high economic value. Short postharvest life is the main barrier for gerbera marketing which is related to water relation disruption resulting from microbial population in preservative solution and exposure to ethylene. Therefore, an experiment was conducted to study the combination effect of an ethylene inhibitor, 1-methylcyclopropene (1-MCP) (0 and 1 μL·L−1), and two antimicrobial agents, ajowan [Carum copticum (L.) C. B. Clarke] essential oil (EO) (0 and 15 μL·L−1) and silver nanoparticles (AgNPs) (0 and 40 μL·L−1), on postharvest life of ‘Pink Power’ gerbera cut flowers. The results showed that stem diameter reduced in both cut stem-end (CSE) and below the flower head (BFH) but the amount of decrease in CSE was more than BFH, and applied treatments had no significant effect on the decrease rate. However, both ajowan EO and AgNPs treatments reduced the number of bacteria at the CSE; ajowan EO was more effective than AgNPs and induced more vase solution uptake. Stem-end electrolyte leakage (EL) was unaffected by 1-MCP treatment, whereas petal EL was lower in 1-MCP-treated flowers. The least wilting percentage and the longest vase life were observed in combination treatment of 1-MCP and either ajowan EO or AgNPs. It could be concluded that 1-MCP combined with ajowan EO or AgNPs, potentially can be used as a preservative solution to enhance postharvest life, delay flower senescence, and prolong vase life of gerbera cut flowers.

Cultivated gerbera (Gerbera hybrida, Asteraceae Dumont) is one of the most important floricultural crops in the United States and worldwide (Behnke, 1984; Rogers and Tjia, 1990). It is well accepted in the cut flower and potted plant markets and can also be grown as a patio, garden, or landscape plant. Gerbera breeding over the past several decades has been focused primarily on developing cultivars for cut flower production or for small flowering pot plants to be used in flower beds (Behnke, 1984; Rogers and Tjia, 1990). Cut flower cultivars require gerbera flowers with long peduncles (greater than 50 cm). The majority of the pot gerbera cultivars have been developed for production in 15-cm-diameter or smaller containers; thus, these cultivars produce compact plants and flowers with short peduncles (less than 30 cm) (Dole and Wilkins, 1999). Recently, interest in producing gerberas in large (20-cm-diamter or larger) containers for indoor or outdoor use has increased [O. Nissen (Sunshine Carnations State, Inc.) and J. Mazat (Ball Horticultural Company), personal communication]. There has been a severe shortage of cultivars suitable for such uses (Channel, 2005). Greenhouse growers and nurseries often rely on two strategies to produce gerberas for this emerging market. One method uses cut flower cultivars and growth retardants to shorten the flower peduncles. However, finished plants often have few flowers and peduncles are still too tall for the pot size. Other growers have tried to use small cultivars, but finished gerbera plants tend to be too small and do not satisfactorily fill up the containers. Previously we developed and released six gerbera cultivars for use in large containers (Deng and Harbaugh, 2010). These cultivars are marketed under the Funtastic series (Ball Horticultural Company) and have displayed exceptional heat tolerance in industry and/or university trials (Siktberg, 2012). Some of these cultivars were selected as ‘‘Best of the Best’’ in the University of Georgia garden trials ( ) and as top performers in the Ohio State University garden trials (Anonymous, 2011). The current series consists of five flower colors (white, light pink, yellow, orange, and orange–red). Additional cultivars are needed to expand the plant palette in this series. Like in other flower crops, continuous introduction of new cultivars with improved or novel horticultural characteristics may serve as a driving force for commercial production and consumer consumption (Behnke, 1984; Rogers and Tjia, 1990). UFGE 7031 and UFGE 7080 were selected and tested specifically for the largecontainer flower market. These cultivars produce large plants with large attractive flowers and appropriate peduncle heights for use in larger containers. These gerberas also express moderate to high levels of resistance to powdery mildew, the most common and important disease in gerbera production and gardening (Chase, 2001; Moyer and Peres, 2008).

To determine the factors affecting airborne conidial concentrations of Podosphaera xanthii Braun and Shishkoff and powdery mildew severity in greenhouse-grown potted gerbera (Gerbera jamesonii H. Bolus), airborne concentrations of conidia were monitored in a glass and polyethylene greenhouse. Temperature, relative humidity, and leaf wetness were recorded onsite, and the percentage of foliage with visible disease was assessed weekly at the glasshouse and every 2 weeks at the polyethylene greenhouse (1 to 10 visual rating scale). Peak airborne conidial concentrations occurred at 0800/1600 and 0900/1400 hr at the glasshouse and polyethylene greenhouses, respectively. Few conidia were sampled between 2200 and 0500 hr at either greenhouse. Worker activity was associated with conidial release in the glasshouse, but not in the larger polyethylene greenhouse, and worker activity may have influenced the daily periodicity of conidial concentrations. Airborne conidial concentrations were not related to environmental conditions in the same hour as conidial detection. An increase in disease severity was positively related to relative humidity and negatively related to leaf wetness at both greenhouses; in addition, temperature was negatively related to an increase in disease severity in the glasshouse. In light of the results of this study, frequent scouting and fungicide applications for powdery mildew are advised. Wide plant spacing and adequate ventilation are also recommended to reduce relative humidity in the microclimate.

Pansy (Viola ×wittrockiana Gams.), petunia (Petunia ×hybrida hort. Vilm.), and gerbera daisy (Gerbera jamesonii Bol. ex Adlam.) plants were grown hydroponically to characterize the deficiency symptoms caused by the absence of calcium (Ca) or boron (B). Primary symptoms occurred on the youngest tissue for both elements, but distinct differences between Ca and B deficiencies were observed. Plants responding to Ca deficiency exhibited discoloration and upward rolling of leaves and ultimately necrosis. Plants responding to B deficiency exhibited minor chlorosis, upward curling, and thickening of leaves, distorted meristems, and strap-like leaves. A second experiment investigated how a temporary disruption of Ca or B affects the plant throughout the crop cycle. Either Ca or B was removed from the nutrient solution for a 7-day period from Day 15 to Day 21, Day 22 to Day 28, or Day 29 to Day 35 after sowing. After the 7-day disruption, the respective element was reintroduced to the plants. Regardless of when the plants were deprived of Ca or B, the symptoms of the respective deficiency were present at the end of the experiment. These studies have shown that a temporary disruption of either Ca or B can cause lasting symptoms throughout the plug production cycle. Also, the symptoms that have been observed in plug production were most similar to those symptoms caused by B deficiency, not Ca deficiency.

This study evaluated the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and plant quality of gerbera (Gerbera jamesonii Bolus `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× or 4× their respective recommended concentration. The insecticides used were abamectin (Avid), acephate (Orthene), bifenthrin (Talstar), clarified hydrophobic extract of neem oil (Triact), and spinosad (Conserve). Photosynthesis and stomatal conductance were reduced in plants treated with neem oil. Plants treated with neem oil flowered later—and at 4× the recommended label concentration had reduced growth, based on lower vegetative dry mass (DM) and total aboveground DM, reduced leaf area, thicker leaves (lower specific leaf area), higher chlorophyll content (basal leaves), and reduced flower production. Plants treated with acephate at 4× the recommended label concentration were of the lowest quality due to extensive phytotoxicity (leaf chlorosis). Plants treated with 1× or 4× abamectin or spinosad were of the highest quality due to no phytotoxicity and no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with 1× bifenthrin had reduced quality because of thrips feeding damage; however gas exchange was not negatively affected.

The cultivated gerbera daisy (Gerbera hybrida (G. jamesonii Bolus ex Adlam × G. viridifolia Schultz-Bip)) often contracts powdery mildew (PM) when grown under conditions of high humidity. During fi eld and greenhouse performance trials conducted with gerberas of the North Carolina State University collection, two half-sib fi eld plants and two of their greenhouse-grown progeny were identifi ed as being highly resistant to PM caused by Podosphaera (Sphaerotheca) fusca (Fr.) Blumer emend. Braun & Taka- matsu. These plants were also unusual in having smooth glossy leaves with very low numbers of bristle macrohairs (MHs) on the adaxial leaf surface compared to wild type. The primary objectives of this investigation were to determine the mode of inheritance of PM resistance and MH density traits and determine if there was a causal relationship between the phenotypes. Parental genotypes were determined by testcrosses to wild-type, PM-susceptible and MH-high-density leaf cultivars. For each trait, a series of crosses were made to produce P A , P B , F 1 , F 2 , BC 1A , and BC 1B progeny. Linkage relationships among PM resistance and MH density loci were examined by testcrosses. Phenotypic segregation ratios suggested the presence of a dominant allele, Pmr1, determining PM resistance and an unlinked dominant allele, Mhd, determining low density of adaxial bristle MHs and moderate reduction in abaxial smooth MHs. The Pmr1 allele appeared to be incompletely dominant in some heterozygotes where one parent was from a highly PM susceptible background. Modifying genes may have some affect on the level of PM resistance or sus- ceptibility. The Mhd allele appeared to be incompletely dominant in some heterozygotes. Segregation ratios indicated that the wild-type alleles were recessive to the PM-resistance and MH-low-density alleles and given the designation pmr1 and mhd, respectively. Density of leaf MHs did not affect PM resistance. Cultivated gerberas, given the provisional name Gerbera hybrida (Asteraceae), are dip- loids resulting from crosses of G. jamesonii × G. viridifolia (Bremer, 1994; Hansen, 1999). They are ornamentals widely used by fl orists and nurserymen throughout the world. Produc- tion in the United States has been mainly by growers in Florida and California (Rogers and Tjia, 1990). Development of disease resistant gerbera cultivars has progressed slowly due to lack of genetic information available on resistance to specifi c pathogens. One of the most common diseases of gerberas is pow- dery mildew (PM). It is caused mainly by Podosphaera (Sphaerotheca) fusca (Braun, 1995; Braun et al., 2002: Cunningham, 2003; Shin, 2000) and/or Golovinomyces (Erysiphe)

High relative humidity (RH) can cause lower concentrations of boron (B) accumulating in plants. The common greenhouse practice of controlling excess temperatures by applying mist irrigation to young plants (plugs) can result in elevated RH levels, especially with plugs grown in high heat and humidity conditions of summer. ‘Dynamite Yellow’ pansy (Viola ×wittrockiana Gams.), ‘White Storm’ petunia (Petunia ×hybrida Vilm.), and ‘Festival Apricot’ gerbera (Gerbera jamesonii Bolus) plugs were grown in high or ambient RH conditions to determine the effect RH had on B uptake. Results indicate that an increase in RH decreased the amount of water the plant lost as a result of transpiration resulting in lower concentrations of B in shoot tissue. Boron concentrations in leaf tissue were 9.43, 10.56, and 17.81 mg·L−1 in pansy, petunia, and gerbera plants, respectively, grown in high RH conditions. These values were significantly lower than pansy, petunia, and gerbera plants grown in ambient RH conditions (19.94, 25.49, and 42.71 mg·L−1, respectively). Leaf distortion, consistent with B deficiency symptoms, was present in petunia and gerbera plants. Similar trends were observed when the experiment was repeated and leaf distortion was present in all species. This provides convincing evidence that the distorted growth observed in pansy, petunia, and gerbera plug production is the result of limited B caused by excessive humidity.

To determine whether currently used commercial nutrient solution concentrations can be reduced during the final stage (last 4 to 5 weeks) of production of potted gerbera (Gerbera jamesonii `Shogun') under recirculating subirrigation conditions, plants were grown under one of four nutrient levels (10%, 25%, 50%, and 100% of full strength). Nutrient concentration levels did not affect leaf area, flower number and appearance, and plant total dry weight. There were no significant differences in the greenness (as measured by SPAD meter) of leaves from plants that received the 50% and 100% strength nutrient solutions. However, leaves from plants that received the 10% and 25% strength solution showed significantly less greenness than that of the plants that received 50% and 100% strength nutrient solutions. There were interveinal chlorosis symptoms on the younger leaves of some plants in the 10% and 25% strength nutrient treatments. It is suspected that this interveinal chlorosis was due to iron (Fe) deficiency caused by the increased substrate pH. It is concluded that the nutrient solution concentrations typically used for potted gerbera production in commercial greenhouses at the final stage (4 to 5 weeks) under recirculating subirrigation conditions, can be safely reduced by at least 50% without adversely affecting crop production. Nutrient salts accumulated in the top section of the growth substrate under all treatments levels; however, no phytotoxic effects were observed. No differences in water use (141 mL per plant per day) were observed amid the various nutrient levels. Fertilizer inputs were reduced in the 50%, 25%, and 10% treatments by 54%, 75%, and 90% respectively, relative to the 100% treatment. After 4 weeks under recirculating conditions, the qualities of the nutrient solutions were still within acceptable limits.

The effects of flooding (3 days) and recovery (3 days) on leaf gas exchange parameters (stomatal conductance, net photosynthetic assimilation rate, and leaf transpiration rate) were studied in five, 1-year-old gerbera (Gerbera jamesonii Bolus) cultivars under greenhouse conditions. Flooding reduced the measured parameters in all cultivars, which had not recovered 3 days after flooding ceased. A more detailed study was conducted with the `Beauty' cultivar, in which leaf water potential (Ψw); root hydraulic resistance (Rh); and hormonal concentrations of ABA, IAA, and CK were measured in leaves and roots. Plants were flooded for 2 days, then allowed to recover for 4 days. After 2 days of flooding, Ψw had decreased and Rh had increased. Leaf ABA content increased and IAA and CK content decreased from the start of flooding and did not change during recovery. In roots a transient increase in root ABA levels occurred during flooding and a sharp decrease was measured during recovery, which was related to root death. Similar patterns were observed in root CK concentrations. The IAA concentration in roots remained constant throughout the experiment. The results suggest that ABA and CK may act as signals of flooding stress. Also, the marked intolerance of gerbera to flooding could be a serious barrier to its culture under anaerobic conditions, and hence careful irrigation management is required. Chemical names used: abscisic acid (ABA); indoleacetic acid (IAA); cytokinin (CK).

The financial effectiveness of the soilless culture system (SCS) of gerbera (Gerbera jamesonii Bol. ex Adlam.) production was compared with that of the soil culture system in heated greenhouses in northern Greece. Evaluation was based on budgeting procedures that assumed a project life of 9 years. The decision to accept or to reject the investment was based on the following criteria: 1) net present value analysis (U.S. $18,414), 2) benefit/cost ratio, and 3) risk exposure ratio. The soilless culture system, particularly the plastic bag system using perlite media, was more profitable. Application of sensitivity analysis illustrated the significance of product price and discount rate in determining the accrued benefits. Over the last two decades, significant changes have occurred in the cultivation of high-value horticultural crops, as new produc- tion techniques have been introduced and evaluated. In principle, the enumeration and description of the inherent technical and hor- ticultural advantages of a new technique should be accompanied by a thorough investigation of its economic efficiency. This evaluation procedure has evoked considerable attention, mainly because worldwide market liberaliza- tion has transformed the floriculture market into a highly competitive one. Nevertheless, few scientific analyses have been made of the economic effectiveness of new horticultural techniques. The introduction of the substrate has brought radical changes in protected orna- mental production and has given producers the opportunity to achieve: 1) a high percent- age of high-quality products, 2) uniform prod- ucts, 3) total control of greenhouse produc- tion, 4) reduction of negative effects on the environment, and 5) significantly lower en- ergy costs (Maloupa, 1993). Despite these advantages, the high initial investment cost of soilless culture and the need for extremely

Temperature, relative humidity (RH), desiccation, and hydration affect gerbera (Gerbera jamesonii H Bolus ex Hook.f.) seed storage and germination. Germination percentages (G) were maximal and about equal at constant 15, 20, or 25C in darkness or light but lower at alternating temperatures having the same mean temperature. The number of days to 50% final germination (T50) and between 10% and 90% germination (T90 – T10) required the fewest days at constant 25 or 30C; longer germination periods resulted with alternating temperatures. Reducing seed moisture from 7.1% to 3.5% had no effect on G, T50, or T90 – T10 values, but at seed moisture levels 50 and T90 – T10 longer. Germination percentages were similar after seed storage from 5 to –5C, but G was lower after storage at –10C or lower. Low-temperature seed storage had no effect on T50 or T90 – T10 values. Seeds had highest G and lowest T50 and T90 – T10 values when germinated at 52% seed moisture, with large declines and delays in germination at lower and higher moisture levels. Seed storage for 12 months without reduction in germination was possible at 5C and 11% or 32% RH. Seeds stored at 52% RH lost G at all temperatures, and no seed germinated after storage at 75% RH and 15 or 25C. Seed stored at 5 or 15C and 11% to 32% RH had the fewest days to T50 and T90 – T10.

The respiration of cut flowers of gerbera (Gerbera jamesonii H. Bolus ex Hook.f. `Vesuvio') and sunflower (Helianthus annuus L.) increased exponentially with increasing storage temperature. Poststorage vase life and negatively gravitropic bending of the neck of the flowers were both strongly affected by simulated transport at higher temperatures. Vase life and stem bending after dry storage showed highly significant linear relationships (negative and positive, respectively) with the rate of respiration during storage. The data indicate the importance of maintaining temperatures close to the freezing point during commercial handling and transport of these important commercial cut-flower crops for maximum vase life.

Gerbera seedlings (Gerbera jamesonii H. Bolus Ex. Hook F.) 'Florist Strain Yellow' were planted on drip-irrigated, plastic-mulched beds at 24,000, 36,000 or 72,000 plants/ha. Nitrogen and potassium fertilizers at 55, 110, or 220 kg·ha -1 were factorially combined with populations. In the 1st year of a 2-year study, the number of marketable flowers increased as N and K increased to 110 kg·ha -1 , but as N and K were increased to 220 kg·ha -1 , cull production increased. In the 2nd year, marketable and cull yields increased with N rate to 220 kg·ha -1 ; K did not affect yield. As populations increased from 24,000 to 72,000 plants/ha, marketable and cull flower production increased in both years. Flower size and quality were unaffected by plant populations. Nitrogen and potassium fertility did not affect flower size, quality, or vase life in either year. The majority of Gerbera cut flowers are grown in temperate zones, such as the Neth- erlands, in heated greenhouses and exported to the United States. The climate in coastal South Carolina is tropical to subtropical in summer and subtemperate in winter. Gerbera daisies do not reliably overwinter outdoors in temperate climates, but overwinter with- out significant loss in subtemperate areas. Unprotected field production of Gerbera daisies may be possible in coastal South Car- olina. Fertility requirements for field production of Gerberas are not fully known. In Florida, ground beds are fertigated through drip tub- ing with 0.8 to 1.2 kg of 18N-6P-12K per 30 m 2 with an additional application of N

Ligule color of a Gerbera jamesonii H. Bolus ex Hooker population was analyzed with a reflectance spectrophotometer having a spectral capability of 400 to 700 nm and a cv

This research focused on the influence of insecticides on gas exchange, chlorophyll content, vegetative and floral development, and overall plant quality of gerbera (Gerbera jamesonii var. `Festival Salmon'). Insecticides from five chemical classes were applied weekly at 1× and 4× the recommended concentrations. Insecticides used were: abamectin (Avid® 0.15 EC), acephate (Orthene® Turf, Tree & Ornamental Spray 97), bifenthrin (Talstar® Nursery Flowable), clarified hydrophobic extract of neem oil (Triact® 70), and spinosad (Conserve® SC). Phytotoxicity occurred in the form of leaf chlorosis on all acephate treatments, with the greatest damage occurring at the 4× concentration. Photosynthesis and stomatal conductance were significantly reduced in plants treated with neem oil extract. Plants treated with the neem oil extract (1× and 4×) flowered later and had reduced growth [lower shoot dry mass (DM) and total DM]. Plants that received 4× the recommended concentration of neem oil extract had reduced leaf area, thicker leaves (lower specific leaf area), higher leaf chlorophyll content, and reduced flower production, as determined by flower number and flower DM. Plants treated with acephate 4× concentration were the lowest quality plants due to extensive phytotoxicity (leaf burn), which also reduced photosynthesis. The highest quality plants were treated with spinosad and abamectin due to zero phytotoxicity and/or no thrips damage (thrips naturally migrated into the greenhouse). The control plants and plants treated with bifenthrin 1× were not marketable due to thrips damage; however, plant growth characteristics and gas exchange were not statistically different.

Snapdragon (Antirrhinum majus L. `Chitchat'), delphinium (Delphinium ajacis L. `Bellisimo'), chrysanthemum (Dendranthema grandiflora RAM. `Regan'), tulip (Tulipa hybrid `Golden Brush'), gerbera (Gerbera jamesonii H. Bolus `Manovale'), oriental lily (Lilium asiaticum L. `Specisiom Simplon'), rose (Rosa hybrid L. `Carnavale') and iris (Iris hollandica Tub. `Blue Magic') cut flower stems were placed at 20 °C in water containing the NO donor compound 2,2'-(hydroxynitrosohydrazino)-bisethanamine (DETA/NO) at 10 and 100 mg·L-1 and after 24 h, transferred to humidified air containing 0.1 μL·L-1 ethylene. Compared with flowers kept in water, the vase life of all eight flowers was extended by DETA/NO with an average extension of about 60% with the range being about 200% for gerbera to 10% for chrysanthemum. DETA/NO appears to have widespread applicability to cut flowers and offers a simple technology to extend vase life.

The vase life of many cut flowers is often limited by bacterial occlusion of stem bases. In this study, we tested the efficacy of a novel antimicrobial agent, aqueous chlorine dioxide (ClO2), to extend the longevity of cut Gerbera flowers by reducing the number of bacteria in vase water. Commercially mature and freshly cut Gerbera jamesonii `Monarck' flowers were placed into clean vases containing deionized water and 0, 2, 5, 10, 20, and 50 μL·L-1 ClO2. Stems were then maintained in solutions at 21 ± 0.5 °C and 42 ± 11% relative humidity until the end of vase life. Inclusion of 2, 5, and 10 μL·L-1 ClO2 in vase water had beneficial effects on flower longevity. For instance, treatment with 5 and 10 μL·L-1 ClO2 extended flower longevity by 1.4-fold or 3.7 days, as compared to control flowers (0 μL·L-1 ClO2). In contrast, exposure to the higher concentrations of 20 and 50 μL·L-1 ClO2 did not extend flower vase life. Relative to control flowers, treatment with 10 μL·L-1 ClO2 delayed the onset of detectable bacterial colonization of vase solutions from day 3 to day 6 of vase life. However, this ClO2 treatment did not reduce the number of bacteria that subsequently accumulated in vase water as compared to control flowers. Treatment with 10 μL·L-1 ClO2 also increased rates of solution uptake by stems and reduced the loss of flower fresh weight over time. These results highlight the potential use of ClO2 treatments to extend the postharvest longevity of Gerbera flowers.

Pot gerbera (Gerbera jamesonii Var. `Shogun') plants were subirrigated with one of four nutrient solutions (10, 25, 50, and 100% of full strength) in order to determine whether currently used commercial nutrient solution concentrations can be reduced without negative impact on crop production. Nutrient concentration levels did not affect leaf area, flower number and appearance, and plant total dry weight. There were no significant differences in leaf chlorophyll content between the plants that received the 50 and 100% strength nutrient solutions. It is concluded that nutrient solution concentrations typically used in commercial greenhouse, for pot gerbera production, can be safely reduced by at least 50% without adversely affecting crop production. Nutrients accumulated in the top section of the growth substrate under all treatment levels; however, no phytotoxic effect was observed. Fertilizer inputs were reduced in the 50%, 25%, and 10% treatments by 54%, 75%, and 90% respectively. After 4 weeks recirculating, the quality of the nutrient solutions was still within acceptable limits.

Chemical and physical methods were tested to determine their effectiveness in controlling Western Flower Thrips, Frankliniella occidentalis (Pergande), in greenhouses. Comparisons were made between abamectin (Avid); Spinosyn A and D, formulated from the soil Actinomycete, Saccharopolyspora spinosa (Spinosad); azadirachtin (Margosan-O); and diatomaceous earth, a physical control aimed at deterring pupation. Results based on the number of thrips counted in gerbera (Gerbera jamesonii L.) flowers indicate that the chemical treatments were significantly more effective in reducing populations than the diatomaceous earth. Over time, the population of thrips in both the Avid and Spinosad treatments was reduced to zero. Diatomaceous earth treatments reduced populations almost 50% as compared to the control, while reductions from Margosan-O ranged 50-90%.

The frequency distribution of gerbera flower hue in the Davis population of gerbera appears continuous and bimodal. This suggests that a gene of large effect may be segregating in a background of polygenic variation. CSA is a statistical technique developed in genetic epidemiology for investigating such complex traits without the need of inbred lines. The REGC program of SAGE (Elston, LSU Medical Center, New Orleans) uses the regressive models of G. Bonney (1984) through pedigree analysis to provide estimates of major gene parameters and residual correlations among relatives. Pedigrees obtained from generations 14, 15, and 16 indicate that a major dominant gene for hue is segregating and accounting for -0.66 of the total variation. The genotypic means are 32 degrees and 71 degrees for the aa and bb genotypes, respectively. The a allele is dominant to the b allele and has a frequency of 0.55. The residual parent-offspring correlation estimate is 0.2 and measures the genetic contribution to the remainder of the variance.

The effects of long-term genetic improvement are measured by selection response predicted from estimates of narrow-sense heritability. However, changes of population mean must be partitioned into genetic and environmental components-in order to accurately estimate selection response. A long-term selection experiment for cut-flower yield in the Davis population of gerbera (Gerbera hybrida, Compositae) was conducted for sixteen generations. Breeding value was estimated for individual plants in the population using Best Linear Unbiased Prediction (BLUP). Genetic change was calculated from breeding values of individual plants in each generation. The results of this study indicate: the long-term selection experiment was successful and necessary for genetic improvement. Genetic change over sixteen generations was 33 flowers. Mean breeding values increased monotonously with an “S” shape pattern. Environmental effects fluctuated from generation to generation. Cut-flower yield in the Davis population of gerbera will continuously respond to selection.

Inbreeding depression is found in most flower crops. Limited population size can cause inbreeding even in outcrossed populations. The Davis population of Gerbera hybrida has been selected for increasing flower yield for 15 generations. The mean yield per plant of the population has been increased from 14.2 to 28.0 flowers per winter six-month period. In each generation 23 to 80 selected parents have been crossed at random. Inbreeding coefficients were estimated from the pedigrees of each of the 6199 plants in the 16 generations. The inbreeding level in this population was found to increase in each generation and currently is 16.5%. Mean yield and inbreeding per family have a statistically significant negative correlation in generations 13 to 16. The results indicate that inbreeding is increasing in this randomly outcrossed population because of its finite number of parents, and that yield is reduced by 3.9 flowers per six-month due to inbreeding.

Additive genetic components of variance and narrow-sense heritabilities were estimated for flowering time and cut-flower yield for generations 8-13 of the Davis population of gerbera, using the least squares (LS) and restricted maximum likelihood (REML)methods. Estimates of heritability for flowering time were 0.54 and 0.50 using REML and LS, respectively, indicating a close agreement between the two methods. However, estimates of heritability for cut-flower yield were 0.30 and 0.46 from REML and LS. This may result from the fact that cut-flower yield was selected in each generation; flowering time was not. Realized heritability for cut-flower yield was estimated to be 0.26 which agreeded more closely with the heritability estimated from REML. The advantages of REML, and its applications in the estimation of components of genetic variance and heritability of plant populations are discussed.