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- Author or Editor: S. A. Weinbaum x
Leaf retention, uptake kinetics, total uptake (per unit leaf area), export kinetics, and the total export of foliage-applied, labeled B (]0B-enriched boric acid) were determined for apple (Malus domestics Borkh.), pear (Pyrus communis L.), prune (Prunus domestics L.), and sweet cherry (P. avium L.). Foliar uptake of labeled B by shoot leaves was 88% to 96% complete within 24 hours of application. More than 50% of the B retained on shoot leaf surfaces following application was absorbed and exported within 6 hours of application. Genotypic differences in shoot leaf surface characteristics among the species tested greatly influenced the amount of solution retained per unit leaf area. Leaf retention capacity was the primary determinant of the quantity of B absorbed by and exported from shoot leaves following foliar application. On average, apple shoot leaves retained, absorbed, and exported at least twice as much labeled B per unit leaf area as prune and pear shoot leaves and three to four times as much as sweet cherry shoot leaves. The sink demand of nearby, mature apples did not affect the export of labeled B when applied to adjacent spur leaves, but the fruit imported 16% of their total B from the applied solution during a 10-day period. Despite extensive documentation for the immobility of B accumulated by leaves naturally (e.g., from the soil), the B accumulated by leaves following foliage application was highly mobile in all four species tested.
Ethephon applied to peach (Prunus persica L., cv. Andross) and French prune (Prunus domestica L., cv. Agen) at fruit developmental stages sensitive to ethylene-induced abscission reduced peach enlargement and the l4C-IAA transport capacities of excised peach pedicel segments. Sensitivity to (2-chloroethyl)phosphonic acid (ethephon) was inversely related to peach size prior to treatment. Triiodobenzoic acid (TIBA) increased abscission of control and ethephon-treated prunes.
Accumulation of label by fruit tissues of ethylene pretreated prune explants following xylem transport of 14c-sugar was reduced despite the absence of competing sinks and continued availability of sugar. These results provide evidence of a direct effect of ethylene on fruit tissues.
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.
This study was designed to characterize the mechanisms of N-stimulated peach Prunus persica (L.) Batsch productivity. The effects of N fertilization on potential assimilate availability (source capacity) and on the growth capacity of individual fruit (sink capacity) were assessed. On heavily thinned trees, fertilization did not stimulate fruit growth rates relative to those on nonfertilized trees, suggesting that fruit growth rates were not assimilate-limited throughout the period of fruit development. However, N fertilization resulted in a longer fruit development period and increased the growth potential of individual fruit by 20% (fresh mass) and 15% (dry mass) vs. controls. In unthinned trees, N fertilization increased total fruit yield by 49% (fresh mass) and 40% (dry mass) compared to the unthinned, nonfertilized controls. N fertilization increased total fruit yield per tree in unthinned peach trees by extending the fruit development period and thus increasing the amount of assimilate accumulated for fruit growth. The fruit development period was prolonged both by assimilate deprivation associated with increasingly higher crop loads and by N fertilization. Thus, the prolongation of the peach fruit development period by N-fertilization appears inconsistent with the role of N in increasing assimilate availability for fruit growth. We conclude that N fertilization stimulates peach yields by increasing the period for fruits to use assimilates (sink capacity). The effect of N on assimilate availability was not directly evaluated. The timing of fertilizer N availability did not influence fruit growth potential.
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.
Translocation of 15N from foliar-applied urea to vegetative and reproductive sinks of avocado (Persea americana Mill, cvs. Fuerte and Hass) was evaluated during inflorescence development and the early stages of fruit set. Urea (2%) increased the number and the total dry weight of the lateral inflorescence per shoot. The concentration of 15N in avocado inflorescences increased proportionately to the concentration of urea applied to the old leaf surface. The amount of 15N translocated was not affected by the proximity of the source leaf to the “terminal” inflorescence. 15N translocated to developing fruit and to new sprouting leaves in similar amount. Urea N was translocated basipetally from current flush leaves to developing fruit. Removing the vegetative sink reduced N influx to the reproductive tissue and increased initial fruit set by a factor of 1.7 to 2.1 in urea-treated and -untreated shoots, respectively. These data indicate that shoot growth does not limit fruit set in avocado via competition for N.
Nucellar and zygotic offspring of ‘Satsuma’ mandarin (Citrus reticulata Blanco) were differentiated by gas chromatographic analysis of gaseous emanations from fragmented leaves of 6-month-old seedlings. Analysis was rapid (< 3 minutes/sample), could be performed on individual leaves, and required virtually no tissue processing. Thus, the method is amenable to the screening of large progeny at the young seedling stage.
Nonbearing Myrobalan 3-J (Prunus cerasifera Ehrh.) plum trees were maintained at 35 klx, 25°C, and 70% relative humidity in aerated nutrient solutions. Net nitrate uptake (NU) was not reduced during 10 hours of darkness. With defoliation, NU declined within 20 hours, reaching about 50% in 50 hours. The metabolism required for nutrient uptake was presumably supported during darkness by substrate reserves. The lower NU following defoliation is consistent with the view that leaves are important reservoirs of substrate and/or hormones.
Excised fruiting branches of French prune (Prunus domestica L.) were treated with 15 μl/liter ethylene (ETH), which inhibited fresh weight increase and caused abscission of immature fruit. Inhibition of fresh weight accumulation was much greater 30 days after full bloom than 44 days after full bloom. Abscisic acid (ABA) in fruit pericarp and seed was extracted, purified for determination by gas chromatography, and identified by gas chromatography-mass spectrometry. ETH treatment significantly increased ABA concentration of pericarp and seed. The inhibition of growth by ETH was similar for pericarp and seed while the increase in ABA was much greater in pericarp than in seed. The trans, trans-ABA was detected only in the seed and the cis, trans-ABA: trans, trans-ABA ratio was reduced by ETH.
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.