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.
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.
Mature almond trees [Prunus dulcis (Mill) D.A. Webb] growing on a very light-textured (Delhi sand) soil were fertilized with 15N-depleted ammonium sulfate during 1980. Although uptake of labeled N from the soil N pool had ceased by 1982, label persisted within the trees at least until 1984. This label presumably represented the residual portion of the organic pool of storage N absorbed by the trees several years before. Leaf, pericarp, and embryo (kernel) samples were collected over a 2-month period during embryo maturation, and samples were processed for mass spectrometric analysis. Total leaf N did not decrease during embryo maturation, but labeled N in leaves decreased by 25%. These data are consistent with the concept of N turnover and flux through mature leaves and transport of N from leaves to fruit. These data indicate also that the N stored overwinter in perennial tissues of almond trees is redistributed within the trees throughout the growing season to support the development and function of annual plant organs such as leaves and fruit.
Fruiting branches of French prune (Prunus domestica L.) were exposed to ethylene or the ethylenegenerating (2-chloroethyl)phosphonic acid (ethephon) and subsequently 14C-uptake and ion leakage patterns of excised mesocarp disks were determined. Ion leakage was increased by these treatments, and the magnitudes of variances associated with ethephon-treated samples indicated differences in sensitivity among treated fruit. Under laboratory conditions electrolyte loss was associated with senescence of mesocarp tissue but was not a prerequisite of fruit abscission.
Non-bearing prune (Prunus domestica L. cv. Agen) trees were fertilized with 15N-KNO3 for 10 days during 9 phenological periods. Nitrate uptake efficienty (NUE) and the distribution of absorbed 15N in the trees were determined for each of these application periods. Nitrate uptake was dependent on presence of leaves, and NUE was low from the period of natural leaf fall until shoot growth had commenced the following spring. NUE increased dramatically during the rapid phase of shoot elongation, and remained high until leaf fall. Nitrogen absorbed from fertilizer was rapidly mobilized by swelling buds and rapidly elongating shoots. The spring flush of vegetative growth utilized both the currently available fertilizer (15N) nitrogen and tree nitrogen reserves. Rapid shoot elongation was primarily dependent, however, on the redistribution of storage N.
Mature almond trees [Prunuis dulcis (Mill) D.A. Webb] growing on a very light-textured soil (Delhi sand) were “pulsed” in 1980 with a soil application of 15N-depleted ammonium sulfate. Leaching of labeled N from the soil and dilution (with unlabeled N carriers) of residual label in the soil minimized uptake of labeled N from this soil in subsequent years. The percent annual depletion (PAD) of labeled N in tissue samples was 50% and represented the percent annual influx of tree N from the soil N pool. Nitrogen assimilated in previous years also represented 50% of total tree N. The fractional contribution of N absorbed in any prior year, relative to the total pool of storage N, may be expressed as 1/(2)x, where x represents the number of years prior to the current year. The PAD, as measured in tissue samples, was greater in trees growing in the Delhi sand than among comparable trees growing in a heavier-textured soil (Yolo silty clay loam). A hyperbolic depletion function was fitted to the data to predict endpoints of tissue labeling. These endpoints were estimated to be 8.5 and 86.1 years on the light- and heavy-textured soils, respectively.
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.
Abortion of distillate flowers (PFA) in a protandrous cultivar of walnut (Juglans regia L. cv. Serr) was increased by N deficiency. Starch and N concentrations in wood of 2-year-old twigs decreased to minimal levels during abortion of distillate flowers. Nitrogen reserves in woody tissues were reduced by foliar N deficiency, as were concentrations of sugars and N in vacuum-extracted xylem sap. Abortive distillate flowers ceased growth before spur leaves reached 50% of full expansion. PFA may result from transient deficiencies of C and N during the spring flush of growth. Depletion of storage C and N was accentuated before maturation of distillate flowers in this cultivar by the metabolic demands of many catkins, spur growth, and leaf expansion.
Localized and carry-over effects of light exposure [as inferred from specific leaf weight (SLW)] on spur viability, flowering, and fruit set were monitored in selected spurs throughout walnut (Juglans regia, cvs. Serr and Hartley) tree canopies. Shaded spurs (i.e., average SLW <4 mg·cm-2) were predisposed to die during the winter, and spur mortality was accentuated among spurs that had borne fruit that season. More catkins and distillate flowers per spur were characteristic of the more exposed positions within the canopy (as indicated by SLW) during the previous summer and following an “off” year. In exposed `Serr' canopy positions (SLW >5 mg·cm-2), catkin and Pistillate flower maturation was reduced in fruiting spurs by 60% and 30%, respectively, in the subsequent year relative to vegetative spurs. In `Hartley', the number of distillate flowers was also reduced by 35% on spurs that fruited the previous year relative to spurs that had been vegetative. Maximum rates of return bloom and fruit set were evident in spurs exhibiting the highest SLW and N per unit leaf area (NA), specific to each cultivar. Among spurs of both cultivars, distillate flower development was more sensitive to shading in the previous season than was catkin development. Shell weight of `Serr' varied positively with SLW, but kernel weight, fruit N, and oil concentration did not vary “with SLW in either cultivar.
Experiments were conducted to determine if differential responses of walnut pollen germination to temperature, previously observed to occur among genotypes, were genetically fixed or expressions of phenotypic plasticity representing adaptive responses to temperatures experienced during pollen development. Individual branches of a single walnut (Juglans regia L. cv. Serr) tree were warmed above ambient conditions during the final stages of pollen differentiation by directing a stream of moist, heated air into polyethylene enclosures, each containing an individual branch unit. Pollen was collected at staminate anthesis and incubated in germination medium on a temperature gradient apparatus. Model curves fitted to the in vitro pollen germination data were used to determine optimum germination temperatures. We found adaptive responses of pollen germination to temperatures experienced during pollen development. The optimum temperature for in vitro germination for pollen from branches maintained under ambient conditions was lower than that of pollen from branches with elevated temperature, and optimum germination temperature increased as a log function of integrated daily temperature (degree-days) experienced during pollen development.