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Sven E. Svenson, Fred T. Davies Jr. and Sharon A. Duray

Gas exchange, water relations, and dry weight partitioning of shoot tip cuttings of `Eckespoint Lilo Red' (`Lilo') and `Gutbier V-10 Amy Red' (`Amy') poinsettia (Euphorbia pulcherrima Wind. ex Klotzsch) were studied during the initiation and development of adventitious roots. Net photosynthesis (A) and stomatal conductance (g) of cuttings were initially low and remained low until root primordia formation. Foliar relative water content (RWC) and osmotic potential (ψπ) increased upon formation of root primordia. Following formation of root primordia (2 days before visible root emergence) and concurrent with increasing RWC and ψπ, g increased. As roots initially emerged, A and g increased rapidly and continued to increase with further root primordia development and subsequent emergence of adventitious roots. Cutting stem and leaf dry mass and leaf area increased during the first few days after sticking cuttings. During primordium development and initial root emergence, the highest percent increase in dry weight was accounted for by basal stem sections. AU cuttings of both cultivars rooted and had similar root numbers after 23 days, but `Lilo' cuttings had 15% better rooting and 44% more roots than `Amy' after 15 days. This research supports the hypothesis that formation and elongation of root primordia coincides with increased gas exchange in poinsettia cuttings, and that gas exchange can be used as a nondestructive indicator of adventitious root development.

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Panayiotis A. Nektarios, Serafim Kastritsis, Nikolaos Ntoulas and Panayiota Tsiotsiopoulou

measurements. Plant growth rate measurements included the following: 1) shoot length; 2) shoot number; and 3) flower number. At the end of the study, plant dry weight partition was determined and included the following: 1) the main stem; 2) the lateral stems; 3

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Juanita Popenoe

`Heritage', `Titan', and `Boyne' red raspberries (Rubus idaeus L.) were grown for 3 years and plots were sampled annually for changes in growth. `Heritage' is a primocane- and floricane-fruiting, strongly suckering cultivar; `Boyne' is a floricane-fruiting, strongly suckering cultivar; and `Titan' is a floricane-fruiting, weakly suckering cultivar. Each year in October, plants of each cultivar were dug from two 0.5-m2 plots in each of four rows, separated into roots, crowns, canes (primocanes were harvested in October and floricanes were harvested in July), and leaves, and dried. Fruit were harvested, yields were recorded, and dry weights of subsamples were used to estimate total fruit dry weights. `Heritage' fruit included the primocane and floricane harvests. `Heritage' was more yield-efficient than `Boyne' or `Titan' in that it allocated a higher percentage of total dry weight to fruit and a lower percentage to vegetative parts. Although `Titan' had fewer canes, cane diameter and length were greater. `Boyne' allocated higher percentages of total dry weight to roots than other cultivars. The percentage of total dry weight allocated to fruit was similar for `Boyne' and `Titan' in 1992, but lower for `Boyne' in 1991. Within the cultivars tested, phenotype for suckering did not indicate productivity.

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T. L. Robinson, W. C Stiles and A. N. Lakso

In two field studies with `Redchief Delicious'/MM.106, 'Empire'/M.9/MM.106 and 'Mutsu'/M.9/MM. 106 trees on fertile silt loam soils, trickle irrigation increased vegetative growth during the first three years and resulted in a 16%-20% increase in cumulative yield over the first five years. When fertilizer was injected into the irrigation water weekly from mid-April until the end of June, tree growth was further increased and cumulative yield was improved an additional 11%-15% for a total of 27%-35% greater yield than the non-irrigated trees. In these studies, ground fertilization did not improve growth or yield unless trickle irrigation was also applied. However, ground fertilization was not as effective as fertigation.

Irrigation and fertigation increased the dry weight of roots by 23% and that of shoots by 36% in the first year resulting in a 10% reduction in the root/shoot ratio. Total tree dry weight was increased by 30% if trees were planted early (April 14) but only 14% if trees were planted late (June 10).

Early planting resulted in 17% greater cumulative yield than trees planted late. Initial tree caliper also had a significant effect on early growth and yield with large caliper trees yielding 12% more than the small caliper trees. The interaction of planting date, tree caliper and fertigation resulted in a 50%-70% increase in yield during the first five years.

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M. Tagliavini and N.E. Looney

Root and shoot growth of peach seedlings was strongly suppressed when the roots were held at 8 to 10C. Shoot and root dry weights and root volume increased linearly with increasing root-zone temperature (RZT) to 22C. GA3 at 5.7 μm (2 ppm) added to the aerated full nutrient solution reversed the effect of low RZT on shoot elongation but inhibited root growth at all RZTs. Paclobutrazol (PBZ) (6.8 × 10-3μm) (2 ppb) inhibited shoot elongation at all RZTs and shoot dry weight at 16 and 22C. However, PBZ had no effect on root dry weight accumulation at any RZT. The shoot growth-promoting effect of GA3, relative to control plants, disappeared at higher RZTs, but GA3 reversed the growth-inhibiting effect of PBZ at all RZTs. PBZ increased mean root diameter at all RZTs and significantly increased root volume at 22C. These results show that growth of peach seedlings is profoundly influenced by a cool root-zone environment. The plant growth regulator effects suggest that seedling roots play an important role in whole-plant gibberellin physiology. Some possible implications for fruit production are discussed. Chemical names used: gibberellic acid (GA3); β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol(paclobutrazol,PBZ).

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Bernadine C. Strik, Gil Buller and Julie M. Tarara

Grow tubes are sometimes used in blueberry (Vaccinium corymbosum L.) to establish plantings or replace dead plants in older fields. Two experiments were conducted at a commercial farm to evaluate the effect of various grow tubes used during planting establishment of highbush blueberry cultivars. The treatments in the first experiment were cultivar (‘Aurora’, ‘Elliott’, ‘Liberty’) and grow tube treatment (no tube, control; opaque cardboard tube in the first growing season; and opaque plastic tube in the first season or first through the second season). The treatments in the second experiment were cultivar (‘Aurora’, ‘Elliott’, ‘Liberty’, ‘Ozarkblue’) and grow tube treatment (control; translucent plastic; opaque plastic; and wire mesh tube over plants in the first growing season). The presence of a grow tube from spring to fall of the first growing season decreased crown dry weight (DW) by an average of 37% to 50% and root DW by 30% (all except translucent plastic in Expt. 2) and increased the aboveground:belowground DW ratio relative to the control by an average of 34% to 67%, depending on the experiment. Plants grown in tubes were taller, had a narrower canopy, and had fewer whips, likely a response to low light levels inside the tubes; the fewest whips were found in the opaque plastic or cardboard tubes and the most in the translucent plastic tube with an intermediate response in the wire mesh tube. Removal of grow tubes during the summer led to plant damage from sudden sun exposure. The opaque grow tubes (present in Year 1) reduced yield/plant in Year 2 for ‘Elliott’ and ‘Liberty’ (cardboard tube only) but not ‘Aurora’. Pruning plants to allow for limited early fruit production (≈0.6 kg/plant) in Year 2 did not reduce yield in Year 3 (≈2.7 kg/plant). Whereas grow tubes reduced root and crown growth in the first season, there appeared to be no longer-term adverse effect on aboveground plant growth or yield.

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Dan TerAvest, Jeffrey L. Smith, Lynne Carpenter-Boggs, Lori Hoagland, David Granatstein and John P. Reganold

Synchronizing the supply of plant-available nitrogen (N) from organic materials with the N needs of apple trees is essential to cost-effective organic apple production. Tree growth and organic matter mineralization are affected by orchard floor management. This study examines the effects of three orchard floor management systems, cultivation, wood chip mulch, and a legume cover crop, on the accumulation and partitioning of compost-derived N in young apple (Malus domestica Borkh.) trees at different compost application dates across two growing seasons. Compost enriched with 15N was applied to apple trees in April, May, and June of 2006 and 2007, and trees were excavated in Sept. 2007 to determine the fate of labeled compost N. Trees with wood chip mulch had significantly greater dry weight and N accumulation in vegetative tree components than trees with cultivation or legume cover. Fruit yields were similar between cultivation and wood chip treatments despite less vegetative growth under cultivation, as these trees partitioned more dry weight into fruit (44%) than wood chip mulch trees (31%). Nitrogen-use efficiency by trees was lower with a living legume cover crop than in other treatments due to competition for resources. In the cover crop aboveground biomass, 20% to 100% of the N was derived from compost. In comparison, only 5% to 40% of N in the decomposing wood chip mulch originated from compost. Tree reserves were an important source of N for spring fruit and leaf growth in all treatments, but significantly more so for trees in the cultivation treatment. Fruit and leaves were strong sinks for compost N early in the season, with trees allocating 72% of spring N uptake into leaves and fruit. In the summer, N uptake increased improving compost N-use efficiency. Summer N was preferentially allocated to perennial tissues (71%), bolstering N reserves. Trees with wood chip mulch performed well and had greater capacity to build N reserves, making wood chips ideal for establishing young organic apple orchards. However, as the orchard matures, it may be beneficial to switch to a groundcover that reduces tree vegetative growth.

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Handell Larco, Bernadine C. Strik, David R. Bryla and Dan M. Sullivan

A systems trial was established in Oct. 2006 to evaluate management practices for organic production of northern highbush blueberry (Vaccinium corymbosum L.). The practices included: flat and raised planting beds; feather meal and fish emulsion fertilizer each applied at rates of 29 and 57 kg·ha−1 nitrogen (N); sawdust mulch, compost topped with sawdust mulch (compost + sawdust), or weed mat; and two cultivars, Duke and Liberty. Each treatment was irrigated by drip and weeds were controlled as needed. The planting was certified organic in 2008. After one growing season, allocation of biomass to the roots was greater when plants were grown on raised beds than on flat beds, mulched with organic mulch rather than a weed mat, and fertilized with the lower rate of N. Plants also allocated more biomass belowground when fertilized with feather meal than with fish emulsion. Although fish emulsion improved growth relative to feather meal in the establishment year, this was not the case the next year when feather meal was applied earlier. After two seasons, total plant dry weight (DW) was generally greater on raised beds than on flat beds, but the difference varied depending on fertilizer and the type of mulch used. Shoots and leaves accounted for 60% to 77% of total plant biomass, whereas roots accounted for 7% to 19% and fruit accounted for 4% to 18%. Plants produced 33% higher yield when grown on raised beds than on flat beds and had 36% higher yield with weed mat than with sawdust mulch. Yield was also higher when plants were fertilized with the low rate of fish emulsion than with any other fertilizer treatment in ‘Duke’ but was unaffected by fertilizer source or rate in ‘Liberty’. Although raised beds and sawdust or sawdust + compost produced the largest total plant DW, the greatest shoot growth and yield occurred when plants were mulched with weed mat or compost + sawdust on raised beds in both cultivars. The impact of these organic production practices on root development may affect the sustainability of these production systems over time, however, because plants with lower root-to-shoot ratios may be more sensitive to cultural or environmental stresses.

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Bernadine Strik and Gil Buller

The effect of early cropping (no removal of fruit buds the first two years) and in-row spacing (0.45 or 1.2 m) on growth and yield of `Duke', `Bluecrop', and `Elliott' northern highbush blueberries (Vaccinium corymbosum L.) was studied. Plants were grown on raised beds for four years. No yield was produced on the control plants in the planting year (year 1) and year 2. Plant growth at the start of year 3 was adversely impacted by early cropping in years 1 and 2. Early cropping reduced the dry weight of the root system, crown, and 1- to 3-year-old wood in all cultivars. `Bluecrop' plants had less total dry weight than those of `Duke' or `Elliott'. Roots accounted for 30% to 45% of the total plant dry weight depending on cultivar. Early-cropped plants had a lower percentage of fruit buds than control plants. Early cropping reduced yield 44%, 24%, and 19% in year 3, compared to control plants, in `Elliott', `Duke', and `Bluecrop', respectively. Cumulative yield (years 1 through 4) was similar between control and early cropped plants in `Bluecrop' and `Duke', whereas early cropping reduced cumulative yield in `Elliott' 20% to 40%, depending on in-row spacing. Plants spaced at 0.45 m produced 62% to 140% more yield per hectare than those spaced at 1.2 m, depending on cultivar. `Elliott' plants seemed less suited to high density planting due to their large root system.

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Frank M. Maas and Edwin J. Bakx

Growth and flowering of shoots of `Mercedes' rose was investigated as a function of the level and spectral quality of photosynthetic photon flux (PPF). Experiments were performed with single-shoot plants decapitated above the two most basal leaves with five leaflets. The development of the two lateral shoots emerging from the axillary buds of these leaves was studied for 4 to 6 weeks. To discriminate between the effects of irradiance and light quality, plants were grown in growth chambers in which PPF and its spectral composition could be controlled. At a photoperiod of 12 hours, the length, weight, and flowering of the shoots strongly increased with irradiance. The growth and number of flowering shoots were always higher for the uppermost than for the second shoot. At the highest PPF (270 μmol·m-2·s-1), flowering occurred in 89% and 33% of the uppermost and second shoots, respectively. At an irradiance level of 90 μmol·m-2·s-1, these percentages were 6% and 0%. Although length and dry weight of both types of shoots were significantly increased by reducing the amount of blue light at constant PPF, flower development was not affected. In a second experiment, plants grown in white light (12 h/day) received a short treatment with low-intensity red or far-red `light at the end of each photoperiod. An end-of-day treatment with red light resulted in significantly more flowering shoots than far-red. The red far-red reversibility of this flowering response indicates the involvement of the photoreceptor phytochrome.