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Laban K. Rutto, Myong-Sook Ansari, and Michael Brandt

conditions. N and K were applied at rates equivalent to 15, 45, and 75 g·m −2 and 4, 8, and 12 g·m −2 , respectively. z Fig. 2. Dry matter partitioning as affected by nitrogen (N) and potassium (K) applied at rates equivalent to 15, 45, and 75 g·m −2 and 4

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T.M. DeJong

For the last several years, research in my laboratory has been focused on studying the developmental and environmental control of dry matter partitioning in peach trees based on the concept that plants grow as collections of semi-autonomous, but interacting, organs. This concept assumes that plant genotype, triggered by developmental and environmental signals, determines current organ specific growth potentials and that environmental conditions dictate conditional growth capacity and respiration (both growth and maintenance) requirements of each organ at any specific time. Dry matter partitioning at any given time is then determined by the availability of resources to be partitioned, the conditional growth capacity and maintenance requirements of each organ, and the relative ability of each organ to compete for the resources. In this presentation, I will demonstrate how developmental patterns of various organs influence dry-matter partitioning within the tree over time, how organ number can influence the amount of dry-matter partitioned collectively to an organ type, and propose an hypothesis for how environmental conditions may influence partitioning on a diurnal basis.

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C. Alt, H. Kage, and H. Stützel

Concepts of above-ground dry matter partitioning in cauliflower [Brassica oleracea L. (Botrytis Group)] as dependent on nitrogen (N) supply and light environment are presented. Leaf and stem partitioning depends on a functional relationship between stem dry weight and leaf area, independent of N status. Dry matter partitioning into the inflorescence is sink-limited (potential capacity) at the beginning, and source limited (daily available assimilates) later. The intrinsic specific growth rate of the inflorescence is dependent on leaf N content. The model is parameterized and evaluated with data from field experiments. Applied to an independent data set, the model predictions of proportions of inflorescence, leaf, and stem on total dry matter corresponded with measurements (r = 0.84, 0.92 and 0.22, respectively) for different N fertilization rates and light treatments.

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D.M. Glenn and R. Scorza

In reciprocal grafts of tall (`Elberta' and `Loring') and dwarf (`Empress' and `Juseito') peach (Prunus persica Batsch.) phenotypes, we measured dry-matter partitioning, resistance to root system water flow, and phytohormone content of xylem exudate. Scion characteristics determined the phenotype and growth characteristics of the tree irrespective of the rootstock. Tall phenotypes had higher dry weight and lower root resistance to water flow than dwarf phenotypes. Cytokinin-like activity and auxin levels in xylem sap were higher in dwarf than in tall phenotypes; whereas gibberellin-like activity was unaffected by either rootstock or scion. The scion of peach influenced phytohormone levels and resistance to water flow in the root system in addition to root and shoot growth.

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Thomas H. Boyle

The effects of BA concentration on flowering and dry-matter partitioning in shoots of `Crimson Giant' Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran] were investigated. Treatments were applied 12 days after starting the forcing phase (before flower buds were visible) and included BA at 0, 10, 50, 100, and 200 mg·liter–1. Relative to the controls, BA increased the total number of flower buds per plant and delayed flowering by 2 to 3 days. The percentage of aborted flower buds increased more than 3-fold as BA concentration increased from 0 to 50 mg·liter–1 and increased further when 100 or 200 mg·liter–1 was applied. The number of flower buds that reached anthesis increased quadratically with increasing BA concentration and was maximal when plants were treated with 50 mg·liter–1. As BA concentration increased from 0 to 200 mg·liter–1, total dry weight of phylloclades decreased, whereas dry weight of floral tissue increased by a nearly equivalent amount. BA increases flowering and alters partitioning of dry matter in reproductive plants of `Crimson Giant'. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine (BA).

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Justine E. Vanden Heuvel, John T.A. Proctor, K. Helen Fisher, and J. Alan Sullivan

In order to gain an understanding of the capacity of severely shaded leaves to be productive in dense canopies, the effects of increased shading on morphology, dry-matter partitioning, and whole-plant net carbon exchange rate (NCER) were investigated on greenhouse-grown Vitis vinifera L. `Chardonnay' grapevines. Vines were subjected to whole-plant shading levels of 0%, 54%, 90%, and 99% of direct sun 3 weeks after potting. Data were collected 8 to 10 weeks after potting. Nonlinear regression was used to investigate the relationship of leaf morphological traits and organ dry weights to increased shading. Leaf size was maintained with increased shading to approximately the 90% shading level, while leaf fresh weight, volume, density, and thickness were immediately reduced with increased shading. Root dry weight was most affected by increased shading, and root to shoot ratio was reduced. When nonlinear regressions were produced for light response curves, light compensation point was reduced by approximately 49% by moderate shading, and 61% by severe shading. Shaded leaves approached the asymptote of the light response curve more quickly, and had reduced dark respiration rates, indicating that the morphological compensation responses by the vine allow shaded leaves to use available light more efficiently. However, the long-term ramifications of reduced root growth in the current year on vines with shaded leaves may be significant.

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Kirk D. Larson, Douglas V. Shaw, and Jerry Sterrett

Three preplant soil fumigation treatments were applied to a strawberry fruit production field in Summer 1993: 1) a mixture of 67 methyl bromide: 33 chloropicrin (wt/wt, 392 kg·ha–1) (MBC); 2) chloropicrin (trichloronitromethane, 336 kg·ha–1) followed by metam sodium (935 liters·ha–1) CMS); and 3) nonfumigation (NF). Bare-rooted `Camarosa' strawberry plants were established in each treatment on 1 Nov. in annual hill culture. Plant mortality was <1%; thus, differences in growth and productivity among treatments were due to sublethal effects of competitive soil organisms. Fruit yields were recorded weekly from 14 Jan. to 23 May 1994. For the NF treatment, early season (January–March), late season (April–May), and total yields were 86%, 69%, and 72%, respectively, of those of the MBC treatment. Early season yields were greatest for the MBC treatment, but late and total yields were greatest for the CMS treatment. From Jan. through May 1994, 20 plants were destructively harvested from each treatment at about monthly intervals for determination of leaf (LDW), crown (CDW), and root dry weight (RDW). For a given date, LDW, CDW, and RDW of plants in the MBC and CMS treatments were greater than those of the NF plants. From January to March, plants in the NF treatment allocated a proportionally greater amount of dry matter to roots, and proportionally less dry matter to crowns and leaves than fumigated plants. In April and May, root: shoot ratios were similar for all three treatments. These data demonstrate the marked influence of soil fumigation treatment on yield and dry matter partitioning of strawberry, and suggest that combinations of chloropicrin and metam sodium may be a viable, albeit expensive, alternative to fumigation with methyl bromide.

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P. Inglese, T. Caruso, G. Gugliuzza, and L.S. Pace

Effect of crop load on dry matter partitioning was studied on 3-year-old peach [(Prunus persica (L.) Batsch (Peach Group)] trees of the early ripening `Early May Crest' (EMC) grafted on `GF677' and Penta (Prunus domestica L.) rootstock and the late ripening `Flaminia' grafted on `GF677' rootstock [(Prunus persica × Prunus dulcis (Mill.) D. A. Webb] and grown outdoors in 230-L containers, for 2 years. Fruit thinning was carried out 10 days after fruit set to produce different crop loads. Trees were sampled destructively throughout two growing seasons and divided into above-ground and root components, for dry matter and carbohydrate analysis. At the end of the fruit development period, in the first year, total tree dry matter accumulation was related linearly to crop load even when the increase in crop load greatly decreased vegetative and root growth. Total dry matter accumulation was highest in EMC/`GF 677' at any specific crop load, and EMC trees on `GF677' allocated relatively more dry matter than EMC/`Penta' trees to vegetative and root growth, even under increasing fruit sink demand. Two consecutive years of heavy crops resulted in an inverse relationship between crop load and dry matter accumulation of trees, due to a major reduction of vegetative, root, and fruit growth. The percentage of dry matter partitioned to fruit decreased with the vigor of the rootstock, and EMC/`Penta' trees had the lowest harvest index at each specific crop load. The early ripening EMC/`GF677' trees which had twice the harvest index of `Flaminia'/`GF677' trees for any level of crop load. `Flaminia'/`GF677' trees had the largest canopy size. Starch content in the roots was lowest for cropping trees and depended on the rootstock and on the length of the fruit development period, being highest for the late ripening `Flaminia'/`GF677' trees. Individual fruit weight decreased with crop load, and the reduction of fruit size was related to rootstock and time of ripening.

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T. Caruso, P. Inglese, F. Sottile, and F.P. Marra

Vegetative growth, fruit yields, and dry matter partitioning within above-ground components were assessed during three growing seasons for trees of an early ripening peach (Prunus persica L. Batsch `Flordaprince' on GF 677 rootstock) trained either to a free standing central leader (930 trees/ha) or to Y shape (1850 trees/ha). Individual trees trained to central leader gave higher fruit yield, had a significantly greater leaf area and accumulated more dry mass in above-ground components per tree than Y shape trees. The training systems did not differ in terms of yield efficiency (yield per trunk cross-sectional area) and leaf area index (LAI), but Y shape trees had a higher harvest index and fruit dry mass per ground area than central leader. Four years after planting, Y shape had 35% higher yield per hectare than central leader. The relative contribution of 1-year-old wood, shoot and leaf to the dry mass of the tree decreased with tree age. Four years after planting the dry matter partitioned to the >1-year-old wood components represented 60% of the total tree mass (excluding fruit) in both the training systems. Central leader trees had the highest relative vegetative growth rate during stage III of fruit development. Most starch depletion occurred from dormancy to pit hardening from the canopy main storage pools (>1-year-old wood), and was higher for central leader than Y shape trees. For the ease of management and the high crop efficiency, the Y shape can be successfully used for peach high density planting systems.

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Carl J. Rosen and Cindy B.S. Tongn

Two on-farm field studies were conducted in 1996 and repeated in 1997 to determine the effects of soil amendments and scape (flower stalk) removal on yield, dry matter partitioning, and storage quality of hardneck garlic (Allium sativum L.). One study site was on a loamy sand soil with low organic matter and fertility and the other site was on a sandy loam soil with high organic matter and fertility. Soil amendment treatments tested at both sites were: 1) no amendment, 2) composted manure, and 3) inorganic fertilizer according to soil test recommendations. A fourth treatment, dried, composted turkey-manure-based fertilizer, was included at the low organic matter site. Scapes were removed at the curled stage from plants in half of the harvest rows. Scapes from the remainder of the harvest row plants were allowed to mature until harvest. In 1997, bulbs from each treatment were stored at 0 to 3 °C or 19 to 21 °C for 6 months. Soil amendment treatments had no effect on total garlic bulb yield, dry mass partitioning, or stored bulb weight loss at the sandy loam, high organic matter site. Manure compost, fertilizer, and composted turkey manure soil amendments reduced the yield of smaller bulbs compared with the control at the loamy sand, low organic matter site. The proportion of bulbs >5 cm was highest with the manure compost treatment. At the low organic matter site, scape removal resulted in a 15% increase in bulb yield and an increase in bulb size compared with leaving scapes on until harvest (P = 0.05). At the high organic matter site, scape removal increased bulb yield by 5% (P = 0.10). Scape removal increased dry matter partitioning to the bulbs, but had no effect on total (scape + shoot + bulb) aboveground dry matter production. The increase in bulb dry mass when scapes were removed was offset by an increase in scape dry mass when scapes were left on. Bulb weight loss in storage was less at 0 to 3 °C than 19 to 21 °C. Soil amendments only affected bulb storage quality at the loamy sand, low soil organic matter site. The effect of scape removal on bulb weight loss was nonsignificant at either location.