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  • Author or Editor: T.T. Muraoka x
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An average of >20% seedless (blank) fruit are produced annually in Pistacia vera cv. Kerman. The degree of blank production was reportedly not related to individual tree yields and, therefore, was not thought to be resource limited (Crane, J.C., 1973. HortSci. 8:388-390). In two crop years, we studied the variability in percentage blanking among individual shoots characterized by widely varying leaf area to fruit (L/F) ratios. L/F ratios were related inversely to the percentage of blank fruit produced. Thus, individual branches behaved somewhat autonomously with respect to blanking. Our data are consistent with the view that embryo development was resource-limited. Although `Kerman' exhibits the potentiality for parthenocarpic fruit set, the hissed distribution of seedless fruit within the tree presumably indicates that blanking is an example of stenospermocarpy. Blanking does not result primarily from inadequate pollination under typical field conditions.

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Dry matter accumulation by immature ‘French’ prune (Prunus domestica L. cv Agen) fruit was reduced significantly within 7 days by (A) branch girdling plus defoliation (G+D), or (B) 300 ppm ethephon. Ethephon, but not G+D, reduced fruit removal force (FRF) significantly over the same interval. These data do not support the hypothesis that ethylene (C2H4)-induced thinning is initiated by assimilate deprivation. We propose that reduced mobilization of assimilates by ethephon-treated fruit is a consequence of the incipient fruit senescence which precedes abscission rather than the causative factor.

Open Access

Exposure to photosynthetically active radiation and the consequent effect on leaf mass per unit leaf area (SLW) and nitrogen (percent dry weight and μg·mm-2) allocation within tree canopies was investigated in walnut (Juglans regia `Serr' and `Hartley') trees. Percent contribution of discrete light flux densities below light saturation (100-700 μmol·s-1·m-2) to the total light exposure of individual spurs, exposed up to 9 hour·day-1 to saturating light (>700 μmol·s-1·m-2), was minimal (<1 hour), indicating that individual spurs were either exposed or shaded most of the day. SLW and N content per unit leaf area of individual spurs were highly correlated (second-order polynomial curve fit) with light exposure within the tree canopy, indicating uneven allocation of available N for optimal utilization. Nitrogen expressed as percent dry weight was not correlated with light exposure and SLW. Leaf N content per leaf area was highly correlated (linear fit) with SLW.

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Nitrogen (N) deficiency reduced biomass and altered N allocation within large walnut tree canopies (Juglans regia L. cv Serr). N-fertilized control trees contained 2.5 times more N in current year spurs, leaves and fruit than did those of N-deficient trees. The N content and biomass allocated to kernels was reduced in N-deficient canopies to a greater extent than was al location to current year shoots and foliage. N removal in abscised leaves and fruit was 3 times greater in canopies of fertilized trees than in N-deficient trees.

A non-destructive method is described to calculate total spur, leaflet and fruit numbers. Calculations were based on ratios of fruit counts on selected scaffold limbs to total fruit number per tree. Dry weight and N content of representative spurs, leaflets and fruit permitted estimation of whole canopy biomass and N content in these organs. N contained in current year spurs and the N lost from the tree in fruit and leaf litter were calculated for both N-fertilized control and N-deficient trees.

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Leaf dry weight per leaf area (LDW/LA); weight of leaf N per unit leaf area (LN/LA); leaf dry weight (LDW); and fruit quality, particularly sugar per fruit (SF); fruit fresh weight (FFW); and fruit dry weight (FDW) were measured over a range of daily average incident photosynthetic photon flux values (PPF) (50 to 1000 μmol·s-1·m-2) in 7-year-old prune (Prunus domestics L. syn. `Petite d'Agen') tree canopies. Linear or curvilinear relationships between these leaf attributes and fruit characteristics were significant over the PPF range. Analysis of LDW/LA or LN/LA may be used to indicate tree canopy locations in which fruit size and quality is limited by suboptimal PPF.

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Two heavily-cropping, twelve-year-old prune trees (Prunus domestica L., syn. `Prune d'Agen') were compared with two adjacent trees which were defruited during stage II of fruit growth (28 May). Trees were uprooted, dissected, and processed to determine total nonstructural carbohydrates, tree nutrient contents and within-tree distribution at the time of fruit maturity (28 July). Trees defruited 2 months earlier contained 5 times as much starch and 2.5 times as much total nonstructural carbohydrates (TNC) in leaves and perennial tree parts as did cropping trees at the time of fruit maturity.

Cropping trees absorbed about 90 g more K during stage III of fruit growth than did defruited trees during the same interval (28 May -28 July). Vegetative trees parts (i.e., trunk, branches, roots, and leaves) in cropping trees generally had lower K contents than did defruited trees at the time of fruit maturity. Fruit demand for K was associated with increased K uptake from the soil despite reduced levels of TNC in the roots and the probability of reduced root growth. Potassium uptake by heavily cropping trees was not resource limited when K was supplied regularly through the drip irrigation system.

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