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Gina E. Fernandez and Marvin P. Pritts

A 2-year study was conducted to investigate the influence of the light environment on source-sink relationships in `Titan' red raspberry. Treatments imposed included flower and cane removal in conjunction with partial or whole canopy shading. Raspberry plants were remarkably resistant to a reduction in carbon supply. Yields and primocane production were maintained even when canopies were shaded. Furthermore, if raspberry plants were prevented from producing a full crop in one year, yields the following year tended to be higher than normal. These data, and other studies demonstrating that raspberry roots are strong carbon sinks, suggest that raspberry plants may rely on stored carbohydrate to mature the current crop of fruits when current photosynthate is inadequate. This trait is characteristic of some perennial species adapted to progressively changing environments, but may not be optimal for horticultural situations where growing conditions are relatively constant from year to year. A large root storage capacity and excessive primocane production likely contribute to the relatively low yields that are typical of this species.

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Rajeev Arora, Michael Wisniewski, and Lisa J. Rowland

Seasonal pattern of cold tolerance and proteins were studied in the leaves of sibling deciduous and evergreen peach (Prunus persica). In contrast to deciduous peach that undergoes endodormancy in fall, evergreen peach does not (leaves are retained and shoot tips elongate under favorable conditions) (Arora et al., Plant Physiol. 99:1562-1568). Cold tolerance (LT50) was assessed using electrolyte leakage method. Proteins were separated by SDS-PAGE. Electroblots were probed with anti-dehydrin (Dr. T. Close) and anti-19 kD, peach bark storage protein (BSP) antibodies. LT50 of leaves successively increased from about -7C (18 Aug.) to -15C and -11.5C (23 Oct.) in deciduous and evergreen genotypes, respectively. The most apparent change in the protein profiles was the accumulation of a 60-kD protein during cold acclimation in the leaves of deciduous trees; however, it did not change significantly in evergreen peach. Immunoblots indicate that 60-kD protein is a dehydrin protein. PAGE and immunoblots indicated that 19-kD BSP disappeared progressively during summer through fall in the leaves of deciduous peach, but accumulated to large amounts in bark tissues. Similar inverse relationship for its accumulation in leaf vs. bark tissue was not evident in evergreen peach. Results indicate that BSP expression may be regulated by altered source/sink relationship.

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Richard J. Heerema*, Ted M. De Jong, and Steven A. Weinbaum

Spurs are the primary bearing unit in mature `Nonpareil' almond (Prunus dulcis (Mill.) D.A. Webb) trees. Our objective was to determine whether almond spurs behave autonomously with respect to various biological activities throughout the season. If autonomous, a spur's carbohydrate demands are met primarily by its own leaves and, therefore, the sink to source ratio of the spur itself is expected to be closely linked to its growth and development. In these experiments almond spurs differing in leaf area and/or fruit number were monitored for leaf development, fruit set, floral initiation, spur survival and carbohydrate storage. Previous-season spur leaf area had no relation to the number of leaves preformed within the dormant vegetative bud or final spur leaf area in the current season, but spurs which fruited in the previous season began spring leaf expansion later and current-season spur fruiting was associated with lower spur leaf area. There was little or no relationship between final percentage fruit set at the spur level and spur leaf area in either the current or previous seasons. Current-season spur leaf area was positively related to both spur flower bud number and spur winter survival. Carbohydrate storage in dormant spurs increased with increasing previous-season spur leaf area. These data are consistent with the concept of spur autonomy especially with regards to spur activities late in the season. The relationships of some of these same spur parameters to spur light exposure are currently being investigated.

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Conny W. Hansen and Jonathan Lynch

Whole-plant biomass accumulation, P dynamics, and root-shoot interactions during transition from vegetative to reproductive growth of `Coral Charm' chrysanthemum (Dendranthema ×grandiflorum Ramat.) (Zander, 1993) were investigated over a range of P concentrations considered to be deficient (1 μm), adequate (100 μm), and high (5 mm). In nondeficient plants, transition from vegetative to reproductive growth resulted in reduced relative growth rate and root and shoot biomass accumulation. Reproductive plants showed a higher commitment of the whole plant to the production of developing flowers than to leaves and roots, whereas, in vegetative plants, the highest component production rate was in leaves. This indicates changes in the source-sink relationships during transition from vegetative growth making developing flowers stronger sinks for photoassimilates than roots. Phosphorus allocated to developing flowers was predominantly lost from leaves. Phosphorus-deficient plants showed characteristic P-deficiency symptoms and favored root growth over shoot growth regardless of growth stage. Phosphorus availability in nondeficient plants affected root growth more than shoot growth. No substantial differences in shoot biomass production, relative growth rate, and CO2 assimilation rates were observed in adequate-P and high-P plants. However, the root component production rate, root to shoot ratio, root length ratio, specific root length, specific root area, root mass to leaf area ratio, and root respiration increased in adequate-P plants compared with high-P plants, which indicates that high root activity was maintained without affecting shoot biomass in buffered P conditions. Our results suggest that the high P concentrations used in many horticultural systems may have no benefit in terms of shoot growth and may actually be detrimental to root growth.

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Barbara C. Poole, Terril A. Nell, and James E. Barrett

Premature flower bud abscission imposes a serious limitation on longevity of potted Hibiscus in interiorscape situations, Ethylene is known to be one causative factor. Past research has suggested that carbohydrate depletion of buds may also be involved,

A series of experiments was conducted to examine the relationship between carbohydrate levels and ethylene sensitivity of flower buds under low irradiance levels. Two cultivars were used: `Pink Versicolor', which is very susceptible to bud abscission, and the more resistant `Vista', In the first experiment, plants were harvested twice weekly after placement in interiorscape rooms (8.5 μmol m-2 s-1 for 12 hrs per day; 26.5°C day/night) until all buds had abscissed. At each harvest, buds from four size groups were collected for analysis. In the second experiment, source/sink strength of buds was manipulated by selective daily removal of certain sized buds. Remaining buds were collected just prior to abscission for analysis. In two additional experiments, `Pink Versicolor' plants were treated with either silver thiosulfate or ethephon prior to placement in interiorscape rooms. Plants were harvested twice weekly and buds collected. For all experiments, bud dry wt, total soluble sugars and starch content were determined.

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Barbara C. Poole, Terril A. Nell, and James E. Barrett

Premature flower bud abscission imposes a serious limitation on longevity of potted Hibiscus in interiorscape situations, Ethylene is known to be one causative factor. Past research has suggested that carbohydrate depletion of buds may also be involved,

A series of experiments was conducted to examine the relationship between carbohydrate levels and ethylene sensitivity of flower buds under low irradiance levels. Two cultivars were used: `Pink Versicolor', which is very susceptible to bud abscission, and the more resistant `Vista', In the first experiment, plants were harvested twice weekly after placement in interiorscape rooms (8.5 μmol m-2 s-1 for 12 hrs per day; 26.5°C day/night) until all buds had abscissed. At each harvest, buds from four size groups were collected for analysis. In the second experiment, source/sink strength of buds was manipulated by selective daily removal of certain sized buds. Remaining buds were collected just prior to abscission for analysis. In two additional experiments, `Pink Versicolor' plants were treated with either silver thiosulfate or ethephon prior to placement in interiorscape rooms. Plants were harvested twice weekly and buds collected. For all experiments, bud dry wt, total soluble sugars and starch content were determined.

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Victor N. Njiti, Qun Xia, Leonna S. Tyler, Lakeisha D. Stewart, Antione T. Tenner, Chunquan Zhang, Dovi Alipoe, Franklin Chukwuma, and Ming Gao

leaves, stems, and storage roots in proportion to their growth rates. Bouwkamp (1983) noted that sweetpotato may be source- or sink-limited depending on cultivar, environment, or canopy management. It has been reported that long days enhance vegetative

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Yehoshua Saranga, Avishag Levi, Pavel Horcicka, and Shmuel Wolf

The cause for the differences in germination ability of large and small confection sunflower (Helianthus annuus L.) seeds was investigated over 3 years. The source-sink relationship was manipulated to better explore the differences between seeds of various sizes and to study the role of the embryo and the pericarp (hull) in controlling germination ability. Percent germination of large seeds was significantly lower than that of small seeds when tests were performed at 15 °C. Increasing the ratio of leaf area to number of developing seeds caused an increase in mean seed mass, but resulted in a lower percentage of germination. Seed vigor, as measured by mean time to germination or to emergence of hulled seeds or by rate of root elongation, was negatively correlated with embryo mass, indicating that the low vigor of large seeds is not due to the mechanical barrier imposed by the hull. Analysis of electrolyte leakage confirmed the hypothesis that the low quality of large seeds results from a disturbance during the process of seed development.

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P.I. Garriz, G.M. Colavita, and H.L. Alvarez

Crop load and the genetic biological carrying capacity (source–sink relationships) determine the potential for fruit size development on apple; however, the environment within which the fruit grows attenuates this potential. The effects of different crop loads on the growth pattern and the progress of maturity in apples were evaluated at the Comahue National Univ., Argentina (lat. 38 56'S long 67 59'W), during the 1998–99 growing season. Our experiment was conducted on 6-year-old `Braeburn'/Malling Merton 111 apple (Malus domestica Borkh.) trees spaced 4.0 × 2.3 m and trained to palmette leader. Treatments were 1) light crop load (LC), 2.5 fruit/cm2 trunk cross-sectional area (TCSA), 2) moderate crop load (MC), 6.5 fruit/cm2 TCSA (standard commercial crop load) and 3) high crop load (HC), minimum 8 fruit/cm2 TCSA, no fruit removed from tree. Whole trees were hand-thinned 19 days after full bloom (DAFB). Fruit diameter (FD) was taken at two weekly intervals (n = 24 per date and treatment) and maturity indexes were determined at harvest. Analysis of variance was used and mean separations were computed with Student's t test. From 38 DAFB until harvest, fruit size was significantly reduced (P < 0.01) in the HC trees, indicating that they were source-limited during growth. At 166 DAFB, FD was 7.48, 7.14, and 6.89 cm for the LC, MC and HC treatments, respectively. Adequate carbon was apparently available to support a commercial crop load since no differences were found between LC and MC trees. Crop level influenced flesh firmness; at 173 DAFB, it was significantly lower in HC trees than MC and LC trees (84.33, 92.51, and 91.57 N, respectively). These results suggest some goals of thinning for ensuring sizable `Braeburn' fruit.

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Jingwei Dai and Robert E. Paull

The growth and development of Anthurium andraeanum Andre cv. Kaumana flower before and after emergence from the subtending leaf base was studied. Eighty days before emergence, the anthurium flower was =0.3 cm long, enclosed by two tightly rolled stipules at the base of the subtending leaf petiole. During the rapid elongation stage of the leaf petiole, the flower (0.8 to 1.0 cm long) entered a period of slow growth 40 to 60 days before flower emergence. After the subtending leaf blade unfurled and had a positive photosynthetic rate, flower growth resumed. Spathe color development started =28 days before emergence when the flower was =50% of the emergence flower length (4.5 cm). At flower emergence, the spathe, excluding the lobes, was =75% red. The lobes did not develop full redness until 7 to 10 days after emergence. Peduncle growth was sigmoidal with the maximum growth rate 21 days after emergence. Spathe growth is characterized by a double sigmoid curve. The young, growing, subtending leaf blade had a negative net photosynthetic rate. Removal of this leaf blade advanced flower emergence by 18 days. The soft green leaf (25 to 30 days after leaf emergence) had a slightly positive measured net photosynthetic rate, and the removal of this leaf resulted in flower emergence 11 days earlier. A mature subtending leaf had the highest measured net photosynthetic rate, and its removal had little effect on flower emergence. The subtending leaf acted as a source of nutrients required for the developing flower. Altering the source-sink relationship by leaf removal accelerated flower emergence, probably by reducing the slow growth phase of the flower.