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E.W. Pavel and T.M. DeJong

Dry weights of whole fruit and of different fruit tissues, such as the mesocarp (with exocarp) and the endocarp (with seed), were accumulated on early (`Spring Lady'), midseason (`Flamecrest'), and late-maturing (`Cal Red') peach [Prunus persica (L.) Batsch] cultivars during the 1988 growing season. Seasonal relative growth rate (RGR) patterns of whole fruit showed two distinct phases for `Flamecrest' and `Cal Red'; however, `Spring Lady' did not exhibit two distinct RGR phases. The shift from phase I to phase II of the whole fruit RGR curve was related to an intersection of mesocarp and endocarp RGR curves, indicating a change of physiological sink activities in those fruit tissues in the later-maturing cultivars, but not in the early cultivar. Nonstructural carbohydrate compositional changes in concentration or content were similar in the three peach cultivars. Sucrose accounted for most of the seasonal increase in mesocarp nonstructural carbohydrate concentration. A sudden rise of sucrose was associated with the phase shift of the fruit RGR curves of the midseason and late-maturing cultivars, but not of the early maturing cultivar; however, in the early maturing cultivar, mesocarp compositional carbohydrate changes and, particularly, the sucrose increase, indicate that the physiological processes normally associated with the two phases exist in very early maturing fruit but are not associated distinctly with two separate RGR phases.

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Zhongchun Wang and Gary W. Stutte

Greenhouse grown 2-year-old potted `Jonathan' apple trees (Malus domestica Borkh.) were subjected to various levels of water stress in February. Midday leaf water potential (ψW), leaf osmotic potential (ψS), soluble sugars, and starch contents of mature leaves were measured throughout the development of water stress to determine whether active osmotic adjustment could be detected and whether carbohydrates were involved. Active adjustments of 0.6 MPa were observed 3 and 5 days, respectively, after water stress was initiated. Leaf turgor potential (ψP) could not be maintained through the osmotic adjustment when ψW dropped below -1.6 MPa. Sorbitol, glucose, and fructose concentrations increased while sucrose and starch levels decreased significantly as water stress developed, strongly suggesting that sugar alcohol and monosaccharide are the most important osmotica for adjustment. Sorbitol was a primary carbohydrate in the cell sap and accounted for > 50% of total osmotic adjustment. The partitioning of newly fixed W-labeled photosynthates in mature leaves was not affected by water stress immediately after the 30-min 14CO2 treatment. All the W-labeled carbohydrates decreased in the labeled leaves very rapidly after 14CO2 labeling. The decrease in 14C-sorbitol was greater than the decrease in other carbohydrates under both well-watered and stressed conditions. After 24 hours of water stress, however, the percentage of 14C-sorbitol increased while the percentages of sucrose, starch, glucose, and fructose decreased significantly with increasing levels of stress. The ratio of 14C-sorbitol in leaves with ψW = -3.5 MPa to leaves with ψW = -0.5 MPa was significantly higher than that of 14C-sucrose, 14C-glucose, W-fructose, or 14C-starch.

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Logan S. Logendra, Thomas J. Gianfagna, David R. Specca, and Harry W. Janes

Limited-cluster production systems may be a useful strategy to increase crop production and profitability for the greenhouse tomato (Lycopersicon esculentum Mill). In this study, using an ebb-and-flood hydroponics system, we modified plant architecture and spacing and determined the effects on fruit yield and harvest index at two light levels. Single-cluster plants pruned to allow two leaves above the cluster had 25% higher fruit yields than did plants pruned directly above the cluster; this was due to an increase in fruit weight, not fruit number. Both fruit yield and harvest index were greater for all single-cluster plants at the higher light level because of increases in both fruit weight and fruit number. Fruit yield for two-cluster plants was 30% to 40% higher than for singlecluster plants, and there was little difference in the dates or length of the harvest period. Fruit yield for three-cluster plants was not significantly different from that of two-cluster plants; moreover, the harvest period was delayed by 5 days. Plant density (5.5, 7.4, 9.2 plants/m2) affected fruit yield/plant, but not fruit yield/unit area. Given the higher costs for materials and labor associated with higher plant densities, a two-cluster crop at 5.5 plants/m2 with two leaves above the cluster was the best of the production system strategies tested.

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Marianna Hagidimitriou and Teryl R. Roper

`Searles' (low yielding) and `Stevens' (high yielding) cranberry (Vaccinium macrocarpon Ait.) tissues were collected in 1990 and 1991 to determine the concentration of nonstructural carbohydrates in above-ground (uprights, woody stems) and below-ground tissue. Uprights had the highest total nonstructural carbohydrate (TNC) concentration, followed by woody stems, while below-ground tissue contained the lowest TNC concentration. Total nonstructural carbohydrate concentration in uprights increased early in the season, reached a maximum in late May, decreased as flowering approached, and remained low from late June to late August. The latter period corresponds to flowering, fruit set, floral initiation, and fruit development stages. In late August, when fruit were full size, TNC levels increased, reaching highest concentration in November as the plants were entering dormancy. Most TNC increase in the early season and the subsequent decrease were due to changes in starch. The increase of TNC late in the season was primarily due to increases in soluble carbohydrates. Total nonstructural carbohydrate concentration was greater in vegetative than fruiting uprights for the entire growing season. The lower TNC concentration in fruiting than vegetative uprights during flowering and fruit set was due to greater starch depletion in fruiting uprights. Seasonal changes in TNC in the two cultivars were similar; however, `Stevens' had generally higher TNC concentration and total dry weight as well as more fruiting uprights, fruit, and fruit weight per ground area. The low TNC concentration observed during fruit set and development suggests that the demands for carbohydrates are highest during that period and supports the hypothesis that competition for carbohydrate resources is one factor responsible for low cranberry fruit set.

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Thomas Tworkoski and Ralph Scorza

Shoot and root characteristics of four peach tree [Prunus persica (L.) Batsch (Peach Group)] growth habits (compact, dwarf, pillar, and standard) were studied. In compact trees, leaf number (1350/tree) was twice, but leaf area (6 cm2/leaf) was half that of pillar and standard trees. The number of lateral branches in compact trees (34) was nearly three times more than in pillar and standard trees. Leaf area index (total one-side leaf area per tree divided by the canopy cross-sectional area of the tree) of pillar trees was greater than compact, dwarf, and standard trees (13 compared with 4, 4, and 3, respectively) due to a narrower crown diameter. Dwarf trees were distinct with few leaves (134/tree) and less than half the roots of the other growth habits. Compact trees produced more higher order lateral (HOL) roots than pillar and standard trees. More second order lateral (SOL) roots were produced by compact than standard trees (1.2 vs. 0.8 SOL roots per centimeter first order lateral root). Pillar trees had higher shoot: root dry weight (DW) ratios (2.4) than compact and standard trees (1.7 for both) due to lower root DWs. Root topology was similar among compact, pillar, and standard peach trees but root axes between branch junctions (links) were significantly longer in compact trees. Compact trees had more and longer HOL roots in roots originating near the root collar (stem-root junction) (i.e., more fibrous roots) and this appeared to correlate with more lateral branches in the canopy. These results indicate significant differences in root as well as shoot architecture among growth habits that can affect their use as scion or rootstock cultivars.

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Annick Moing, Nathalie Langlois, Laurence Svanella, Anne Zanetto, and Jean-Pierre Gaudillère

Sorbitol is a sugar alcohol, present with sucrose in Rosaceae trees, which seems to have a role in plant response to environmental stress. The aim of this study was to investigate variability in sorbitol : sucrose ratio in source leaves of 53 species or hybrids of Prunus. The studied taxa, representing three subgenera and 11 sections of the Prunus genus, were chosen from the Prunus collection at the Institut National de la Recherche Agronomique, Bordeaux, France. Young mature leaves were sampled on three dates in spring and summer and were analyzed for neutral soluble sugars using high-performance liquid chromatography. There were differences in sorbitol : sucrose ratio according to sampling date and according to taxon. Sorbitol content increased and sucrose content decreased from May to July, leading to an increase in sorbitol : sucrose ratio. For each date, there was a high variability within botanical sections for sorbitol : sucrose ratio. The highest variability between species for sorbitol : sucrose ratio was in July, with P. cocomilia having the lowest ratio (1.15, w/w) and P. fremontii having the highest ratio (5.59, w/w). When species were pooled according to their geographical zone of origin, species originating from Japan showed the lowest sorbitol : sucrose ratio for all sampling dates. In July, species originating from Japan, Europe, and central to western North America had sorbitol : sucrose ratio significantly lower than that of species originating from Europe to western Asia, China to eastern Asia, and central to eastern North America. These results indicate that variability in sorbitol : sucrose ratio exists in the Prunus germplasm and seems to be related to the geographical origin of the species. Moreover, variability in sorbitol to sucrose ratio is high in the germplasm of different Prunus taxa.

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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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Lloyd L. Nackley, Jig Han Jeong, Lorence R. Oki, and Soo-Hyung Kim

Garlic (Allium sativum) is a commercially and culturally important crop worldwide. Despite the importance of garlic, there have been few studies investigating how garlic growth and development will be affected by the atmospheric enrichment of carbon dioxide (CO2). A split-plot experiment with CO2 concentrations as main plot and nitrogen (N) fertilization as subplot was carried out to examine the effects of elevated CO2 at (mean ± sd) 745 ± 63 µmol·mol−1 across three levels of N: high-N (16.0 mm), mid-N (4.0 mm), and low-N (1.0 mm). Three hypotheses were tested: 1) garlic plants will allocate proportionally more biomass to bulb when grown in elevated CO2 compared with the plants grown in ambient CO2; 2) plants will sustain improved photosynthesis without downregulation in elevated CO2, irrespective of N; and 3) elevated CO2 will improve plant water use efficiency (WUE) across N fertilization levels. We found that proportional biomass allocation to bulb was not significantly enhanced by CO2 enrichment in garlic. Overall biomass accumulation represented by leaf, stem, and bulb did not respond significantly to CO2 enrichment but responded strongly to N treatments (P < 0.001). Contrary to our hypothesis, photosynthetic downregulation was apparent for garlic plants grown in elevated CO2 with a decrease in Rubisco capacity (P < 0.01). Instantaneous leaf WUE improved in response to elevated CO2 (P < 0.001) and also with increasing N fertilization (P < 0.001). Finally, our results indicate that bulbing ratio is likely to remain unchanged with CO2 or N levels and may continue to serve as a useful nondesctructive metric to estimate harvest timing and bulb size.

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Carole L. Bassett and D. Michael Glenn

study of Glenn and Puterka (2007) regarding the separation of gene responses; i.e., RPF significantly increased fruit size and also increased MdSot3 expression. Increased sorbitol transport is likely related to increased carbon partitioning to the

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Xuan Liu and Catherine Grieve

. 2G ). While salinity did not alter total carbohydrate content, it did alter carbon partitioning between soluble carbohydrates, as shown by the significant ( P ≤ 0.05) increase in the ratio of chiro -inositol over the sum of fructose, glucose, and