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Richard A. Criley*

As part of a research study on growth and flower production of 20 commercial heliconia cultivars, plants were established at the Waimanalo Research Farm (Oahu) of the Univ. of Hawaii in July 1999. This report focuses on Heliconia ×rauliniana. Five plants in 7.6 L pots were planted at spacings of 2.5 M in row, with between row spacings of 3 M. Beginning a month later, newly emerged shoots were tagged every four weeks. At flowering, the shoots were harvested and leaf counts made. The information derived from the data include time frame from shoot emergence to flower, rate of shoot production, percentage of shoots from each tag date that flowered and the periodicity of flowering in a two year period. The range of times from shoot emergence to harvest was 208 to 450 days. In the first 12 months following planting, the average cumulative new shoot production since planting was 77 shoots per plant, while more than 58 inflorescences per plant were produced from the tagged stems for a 75% productivity rating. H. X rauliniana evidenced periodic flowering behavior, with peak flowering in the April to June period, that suggested it is a short-day plant for flower initiation.

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R. Jomantiene, J.L. Maas, E.L. Dally, and R.E. Davis

Strawberry fruit phyllody, production of leaves and other vegetative organs from fruit tissue around achenes, has been ascribed to physiological causes due to temperature conditions during transplant cold storage, plant response to changing seasonal conditions at flower initiation time, and to phytoplasma infection. In examination of phylloid fruits from different strawberry clones and from different locations and sources, we found four distinct phytoplasmas associated with phyllody of strawberry fruit: strawberry multicipita (SM) phytoplasma (16S rRNA group VI, subgroup B), STRAWB2 phytoplasma (16S rRNA group I, subgroup K), clover yellow edge phytoplasma (16S rRNA group III, subgroup A), and a new group III phytoplasma. The SM and STRAWB2 phytoplasmas were detected in plants with phylloid fruit that also exhibited stunting and crown proliferation (SM phytoplasma) or stunting and leaf chlorosis (STRAWB2 phytoplasma). In no instances did we fail to detect phytoplasmas in phylloid fruit. To our knowledge, this is the first report to associate strawberry fruit phyllody with the presence of these phytoplasmas and to report that phytoplasmas other than those belonging to 16S rRNA group I (aster yellows group) can also be associated with strawberry fruit phyllody.

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Adriana Beatriz Sanchez-Urdaneta, Raquel Cano-Medrano, and Jorge Rodrl̀guez-Alcazar

The purpose of this research was to investigate the effect of 1% N foliar sprays (0, 2, and 4 sprays at weekly intervals) and girdling (G) on budbreak of three peach advanced selections CP95-1 °C, CP91-8, and CP91-17, and its relationship with both reduced nitrogen (RN) and polyamine contents. Foliar N was applied in July, before flower initiation was detected and girdling was performed 30 days after nitrogen sprays (DAT) The results indicate that 4N+G treatment had the highest content of (RN) with values between 232 and 1000 mg N/g of DW. CP 91-17 and CP95-1 °C selections showed higher RN content than that of CP91-8. Both 2N+G and 4 N+G showed the highest content of putrescine (Put) (908 and 1635 nmol·g-1 FW, respectively). Among peach selections CP91-8 was the one with the highest content of Put. Putrescine content went down as the flower differentiation process evolved. Four N+G treatment promoted budbreak in CP95-1 °C advancing it in 55 days as compared to the control. Budbreak began earlier in the three peach selections treated with 4N+G (11/12/98) followed by 2N+G treatment (7/001/99), and the control (4/02/99). Fruit set was 19%, 12%, and 11% for 4N+G, 2N+G, and control treatments, respectively.

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Carol J. Lovatt

The goal of this research was to identify the role essential nutrients play in the physiology of tree crops, and then to apply the nutrient as a foliar fertilizer to stimulate a specific metabolic process at phenological stages when nutrient demand is high. This approach has proven successful. A single winter prebloom foliar application of nitrogen as low-biuret urea [0.16 kg N/tree (0.35 lb N/tree)] to 30-year-old `Washington' navel orange (Citrus sinensis L. Osbeck) trees during flower initiation significantly increased yield and fruit number per tree for each of 3 consecutive years (P ≤ 0.05). The number of commercially valuable largesize fruit also increased significantly with yield increases (r 2 = 0.88). Sodium tetraborate applied foliarly to `Hass' avocado (Persea americana Mill.) trees at the cauliflower stage of inflorescence development (elongation of inflorescence secondary axes, pollen and ovule development) increased the number of pollen tubes reaching the ovule, ovule viability and cumulative yield (P ≤ 0.05). Additional examples are presented.

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Hazel Y. Wetzstein and Charles S. Vavrina

Tomato (Lycopersicon esculentum Mill.) transplants can be affected by an intermittent physiological problem manifested by loss of apical meristem function and retarded growth rates, referred to herein as apical meristem decline (AMD). Production losses associated with this condition can be substantial. Similar abnormal and arrested development of the shoot apex has been observed in a number of other species, and referred to as blindness, budlessness, toplessness, blindwood, and bud abortion. A developmental study using scanning electron microscopy was conducted in `Agriset' tomato during an occurrence of AMD to evaluate and compare normal and afflicted plants. The AMD condition was associated with cessation of leaf primordia development and lack of flower initiation. The shoot apex of plants with AMD remained vegetative compared to normal plants which at the same age had well-differentiated flower primordia. No evidence of abortion, die back, or necrosis of the shoot apex was observed. The effects of mineral nutrient additions on symptom development varied with year. In year 1, N fertilization reduced the incidence of both AMD and retarded bud growth (i.e., the percentage of normal plants increased from 29% to 97% with N applications). Preplant applications of P, alone or in conjunction with CaCO3 and trace elements, also ameliorated AMD. In year 2, AMD was observed only at very low levels, i.e., 4% or less, and mineral nutrition had no apparent effect on AMD or normal plant number.

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Charlotte M. Guimond, Preston K. Andrews, and Gregory A. Lang

Flower initiation and development in `Bing' sweet cherry (Prunus avium L.) was examined using scanning electron microscopy. There was a 1- to 2-week difference in the time of initiation of flower buds on summer pruned current season shoots (P) compared to buds borne on unpruned shoots (U) or spurs (S). By late July, this difference was obvious in morphological development. The P buds had already formed floral primordia, while the S and U buds showed little differentiation in the meristem until early August. In general, buds from unpruned shoots were similar developmentally to spur buds. By late August, primordial differentiation was similar in the buds from all the wood types; however, buds from pruned shoots were significantly larger (838 μm) than buds from spurs (535 μm) and unpruned shoots (663 μm). Early summer pruning may shift allocation of resources from terminal shoot elongation to reproductive meristem development at the base of current season shoots. The similarity in reproductive bud development between spurs and unpruned shoots, given the difference in active terminal growth, might suggest that developmental resources are inherently more limiting in reproductive buds on spurs.

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Jean-Pierre Privé, J.A. Sullivan, J.T.A. Proctor, and O.B. Allen

Climatic elements (solar radiation, daylength, water supply, growing degree days (GDD), corn heat units (CHU), soil, and air temperatures) were monitored to determine which elements could account for the variability in yield of primocane-fruiting red raspberry (Rubus idaeus L.) cultivars. The climatic elements were classed as either having a major or minor influence on the vegetative and reproductive components, based on the frequency of the significance of the multiple regression coefficients. Soil temperature and water supply had a major influence, while daylength, solar radiation, and aboveground temperature (i.e., air, GDD, or CHU) had a lesser influence on these components. Soil temperature had the largest influence during April and May, while water supply was equally influential at all times during the season. Air temperature and solar radiation had their largest influence during the period of flower initiation and development (i.e., June and July), while daylength was most influential from June to October. Berry count, weight, and yield had the highest frequency of associations among the climatic elements, indicating the complexity of the association between these yield components and climate. Total number of nodes/cane, length of the fruiting section/cane, and the harvest period showed the fewest number of associations. Not all cultivars responded similarly to changes in their yield components. `Autumn Bliss' was less sensitive to climatic variation than either `Heritage' or `Redwing'. When `Redwing' was the anomaly, it was usually related to air or soil temperatures.

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Mokhles A. Elsysy, Michael V. Mickelbart, and Peter M. Hirst

Uniform annual apple (Malus ×domestica) fruit production is highly dependent on consistent flower formation from year to year, as inconsistent flowering can lead to the biennial bearing observed in some high-value cultivars. The presence of fruit on a spur has been considered the main cause of the expression of biennial bearing and the inhibition of flower initiation, with a number of theories being introduced to explain the phenomenon. In the current experiment, individual spurs of annual bearing cultivars (Gala, Ruby Jon, and Pink Lady) and biennial bearing cultivars (Honeycrisp, Fuji, and Golden Delicious) were thinned to a single fruit or completely defruited at petal fall. Spurs were sampled at the end of the growing season. Effects of fruiting on spur characteristics such as spur and bourse leaf area, stomatal density, leaf gas exchange, and flower formation were determined. Across all cultivars, the presence of fruit on a spur did not affect spur characteristics or flower formation compared with nonfruiting spurs. Similarly, flowering was unaffected by those factors associated with greater spur carbohydrate status, such as bourse leaf area and assimilation rate. Cultivars with greater transpiration and stomatal conductance (g s) rates had lower rates of flower formation. Future studies should focus on xylem flow and expression of genes regulating flowering and plant growth regulators in annual and biennial bearing cultivars.

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James E. Faust and Royal D. Heins

The effects of temperature and daily-integrated photosynthetic photon flux (PPFDI) on African violet (Saintpaulia ionantha Wendl.) flower initiation and development were quantified to provide the basis for an inflorescence development model. The percentage of leaf axils in which an inflorescence initiated and continued development increased as the PPFDI increased from 1 to 4 mol·m-2·day-1, while the rate of inflorescence development was a function of the average daily temperature (ADT). The appearance of a visible flower bud (VB) in a leaf axil was related to the growth of the subtending leaf blade. A polynomial model based on ADT and PPFDI was used to describe leaf blade length at visible bud (LBLVB). A nonlinear model was used to describe the influence of ADT on leaf expansion rate (LER). Inflorescence appearance in the leaf axil was predicted by measuring LBL and estimating the time for the leaf blade to develop to the length required for VB. A phasic-development scale was developed to quantify inflorescence development. Days required for an inflorescence to develop from VB to first open flower was described as a function of ADT and either inflorescence height or inflorescence development stage (IDS). Days from leaf emergence to first open flower for the inflorescence initiated in that leaf axil decreased from 86 to 55 as ADT increased from 18 to 26C.

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Andrew B. Ogden and Marc W. van Iersel

Growers interested in producing early, high-quality, southern highbush blueberries (Vaccinium corymbosum L.) in high tunnels face a lack of information regarding appropriate cultural methods. We sought to elucidate the optimal date to close high tunnels to hasten vegetative and reproductive growth of organic southern highbush blueberry cultivars Emerald and Jewel grown in Georgia. The three dates selected to close the high tunnels were 15 Dec., 2 Jan., and 16 Jan. High tunnels raised soil and daytime air temperatures during winter months, but the tunnels did not retain heat at night and did not provide freeze protection without the use of propane heaters. The high tunnel microclimate advanced both vegetative and reproductive growth compared with outdoor plants. Averaged over the 2-year study, the 15 Dec. tunnel closure advanced flower initiation by 38 days for ‘Emerald’ and 39 days for ‘Jewel’ compared with outdoor control plants. Synchronization of flowering of the two cultivars was poor in 2007 when ‘Emerald’ flowered much earlier than ‘Jewel’ and much better in 2008. In 2007, flower and fruit development of ‘Jewel’ were faster than that of ‘Emerald’ with Jewel going from the appearance of individual flowers to ripe fruit in 80 days as compared with 105 days for ‘Emerald’. Total yield was strongly correlated with fruit set (r = 0.94). ‘Emerald’ fruit contained higher concentrations of soluble solids and anthocyanins than ‘Jewel’ fruit, and anthocyanin concentrations increased throughout the harvest period. No fruit matured in 2008 as a result of freeze damage. The biggest obstacle for high tunnel production of southern highbush blueberries appears to be preventing freeze damage and assuring pollination. Cost-effective freeze protection and ways to promote good fruit set will be critical to successful production of early southern highbush blueberries in high tunnels.