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Experiments with olive (Olea europaea L.) shoot explants were carried out to determine the influence of winter chilling on the release of axillary buds from dormancy. This investigation was designed to explore an alternative explanation for the confusing concept surrounding the role of chilling in olive floral induction. Leafy explants collected from 10 Nov. to 6 Mar. were grown in a greenhouse under mist at 13/24C (night/day) and in a growth chamber at 10/21C (night/day) to determine the end of dormancy. Growth of floral buds from leafy explants was first recorded from 5 Jan. samples. After that date the percentage of developing floral buds and rate of their development increased. Floral bud abscission, increase in bud fresh weight, and simultaneous decrease of relative bud dry weight were associated with growth initiation of floral buds. Manual defoliation of adult trees during the period of shoot explant collection indicated that leaves play a critical role in development once the floral buds had completed dormancy. Supplementary chilling of isolated shoots collected 20 Jan. demonstrated that 7.2C was sufficient to complete chilling requirements, while 12.5C allowed both the completion of chilling requirements and the proper temperature for subsequent floral bud growth. Winter chilling is required to release previously initiated floral buds from dormancy, and we question the previous concept that the role of chilling is to induce olive floral initiation.
Abstract
In the article “Effect of Light Intensity and Carbohydrate Reserves on Flowering in Olive” by G.W. Stutte and G.C. Martin (J. Amer. Soc. Hort. Sci. 111:27–31, Jan. 1986), the following correction should be noted. On p. 28, under Materials and Methods, the sentence “The 80% methanol insoluble materials were suspended in saturated CaSO4 at pH 12.0 and boiled …” should read “The 80% methanol insoluble materials were suspended in saturated CaOH at pH 12.0 and boiled …”.
Abstract
Experiments were designed to alter the carbohydrate status of olive (Olea europaea L.) leaves during the presumed flower induction period. Bearing and nonbearing ‘Oblonga’ olive trees were exposed to either 850 μmol s-1n-2 PAR for 14 hr daily in a 1000 ppm CO2-enriched atmosphere, 150 μmol s-1m-2 PAR for 14 hr daily in 340 ppm CO2, or maintained in a lathhouse at ambient winter conditions of about 350 μmol s-1m-2 PAR and daily temperature fluctuations from 5° to 20°C. The trees exposed to 850 μmol s-1m-2 had 3 to 5 times the starch concentrations of either the 150 μmol s-1m-2 PAR or lathhouse treatments. There were few and inconsistent differences in sucrose, fructose or mannitol concentrations between treatments. The high levels of starch in the 850 μmol s-1m-2 PAR treatment had no effect on the flowering pattern of bearing or nonbearing trees. Gross levels of carbohydrates do not appear to limit flower induction of olive.
Abstract
‘Nemaguard’ peach seedlings [Prunus persica (L.) Batsch] were grown in nutrient solution cultures containing 0.36 µM 14C-labeled paclobutrazol (0.59 MBq·liter–1) for 9 days. Microautoradiographs of transverse and longitudinal stem sections showed that 14C activity was localized in the xylem. Tissue extracts showed that the total 14C activity in the plants was distributed predominantly between the roots (40.9%) and leaves (49.1%). The majority of 14C activity in stems and leaves was located in the lowest stem and leaf fractions. The concentration of 14C activity was highest in leaves (478 dpm·mg–1 fresh weight), and essentially equal in the roots and stems (141 dpm·mg–1 fresh weight) indicating that transport of the compound was occurring via the xylem. Although 14C-labeled paclobutrazol was relatively stable in the nutrient solution, its degradation in the plant was rapid. By 9 days after treatment, the amount of 14C label remaining as 14C-labeled paclobutrazol was 71.5% in the roots, 41.5% to 68.1% in the stems, and 7.8% to 12.2% in the leaves. Chemical name used: β-(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Abstract
‘Nemaguard’ peach seedlings [Prunus persica (L.) Batsch] were grown for 21 days in nutrient solution cultures containing a range (0 to 3.4 μM) of paclobutrazol concentrations. Shoot growth rate and total extension growth were reduced by all paclobutrazol treatments. Within 2 days of treatment, paclobutrazol at 3.4 μM significantly reduced the growth rate, as did the 3.4 × 10−2 μM concentrations after 5 days. Increases in paclobutrazol concentrations decreased leaf area and leaf, stem, and shoot weights. However, specific leaf weight increased as paclobutrazol concentration increased. Leaf expansion was more sensitive to paclobutrazol treatments than stem elongation. As paclobutrazol concentration increased, root extension growth was reduced, but roots were thicker and produced more laterals near the tip. Compared with the control, paclobutrazol at 3.4 × 10−1 and 3.4 × 10−2 μM significantly increased the root: shoot ratio. Chemical name used: β-[(4-chIorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Abstract
An in vitro laboratory model for the study of leaf abscission induced by (2-chloroethyl)phosphonic acid (ethephon) was developed. Feeding of ethephon through the base of excised shoots of ‘Manzanillo’ olive (Olea europaea L.) resulted in a time- and concentration-dependent sequential increase in ethylene evolution from, and abscission of the leaves along, these shoots. The extent of leaf abscission was correlated with the early rate of ethylene evolution from individual leaves. A minimum induction period of about 50 hr was needed to induce the first leaf abscission. An ethephon pulse of 500 mg/liter for 1 hr or 250 mg/liters for 2 hr was enough to induce about 90% leaf abscission.
Abstract
Leaves, stems, inflorescences and fruits from excised ‘Manzanillo’ shoots of olive (Olea europaea L.) basally fed with (2-chloroethyl)phosphonic acid (ethephon) were used to study the relation between ethylene evolution and abscission. The abscission response of the various organs to ethephon was directly related to concentration and length of exposure to a given treatment concentration. After an ethephon pulse treatment, stem tissues evolved increased levels of ethylene for a longer period than leaves, whereas the effect on petioles was shorter than leaves. Leaf abscission occurred after ethylene evolution from them declined. Inflorescences did not abscise even though induced to evolve high levels of ethylene. The rate of leaf ethylene evolution and abscission was higher in reproductive shoots than in nonreproductive shoots and was influenced by the number of inflorescences present on the shoot. Leaves on shoots with a large number of inflorescences senesced more rapidly than those with fewer inflorescences in our in vitro system and developed a marked chlorosis after 24 hours. Ethylene evolution from fruits on ethephon-fed shoots was low and abscission was erratic. The abscission layer between fruit and stem developed at no specific site along the pedicel or peduncle. Probable reasons for the specific levels and duration of ethylene evolution from the various tissues after an ethephon pulse are discussed.
Abstract
A rapid method was developed for extraction and purification of free abscisic acid (ABA) from leaves of waterlogged seedlings of Juglans. There were significant increases (6-15 fold) in leaf ABA contents of treated plants reaching maximum levels after the first 12 to 18 hours of waterlogging. With the exception of J. nigra, the leaves of which were desiccated at 24 hr after treatment, ABA content rapidly declined to original levels by 30 hours after waterlogging. Changes in ABA concentration in walnut is likely a secondary expression to the stress induced by waterlogging.
Abstract
(2-chloroethyl)phosphonic acid (ethephon) applied at pH 6.8 to 7.0 resulted in fruit loosening which allowed mechanical harvest of at least 85% of the olive crop but there was excessive leaf loss. Inclusion of calcium salts helps offset leaf loss, but also decreases fruit loosening. 2-chloroethyl-tris-(2-methoxyethoxy)-silane (Alsol) and (2-chloroethyl)-methyl-bis-(phenylmethoxy)-silane (CGA 15281) appeared to be more superior looseners than either ethephon or GAF 7767141 (an ethylene generating material) with less leaf loss following treatment.
Abstract
A laboratory system was developed to study olive (Olea europaea L.) organ abscission (21). An improvement of the use of ethylene-releasing compounds in this system is described to provide a model for field abscission responses and characterization of ethylene release. Olive fruit began the separation process as early as 7 to 13 hr after treatment with CGA-15281 (CGA), but not until 19 to 25 hr after treatment with ethephon (ET). CGA is characterized by an immediate, substantial breakdown to ethylene, whereas ET reaches its maximum ethylene release at 12 to 18 hr after application. Ethylene release was much greater from CGA than from equimolar concentrations of ET throughout the abscission initiation period. The relation of ethylene release characteristics to control of olive fruit and leaf abscission is discussed, with the suggestion that fruit respond more rapidly to, and at shorter durations of applied ethylene than do leaves.