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- Author or Editor: Jose M. Montano x
The abscission zone of Douglas-fir (Pseudotsuga menziesii var. menziesii Mitb. Franco) was studied throughout needle development. A separation layer one cell thick developed at the needle base when extension growth ceased. Cells of this layer stained positively with safranin and slightly with toluidine blue. A protective layer, which developed in stem tissue adjacent to the separation layer, stained positively with safranin, periodic acid-Schiff's reagent, phloroglucinol-HCL and chlorine sulfite. Abscission was induced by drying cut trees to a water potential below −3.5 MPa. Water-stressed trees segregated into abscising and non-abscising needle groups. Walls of separation layer cells from trees with abscising needles were characterized by shrinkage followed by tearing. Walls of separation layer cells from trees with non-abscising needles were anatomically unaffected by water stress. Mechanical damage of cell walls in the separation layer occurred when water stress was −3.5 MPa or lower. Abscission could be prevented by maintaining a water potential above −3.5 MPa.
Cut coastal Douglas-fir trees (1.0 to 1.5 m) were allowed to dry to various water potentials in a greenhouse. About one-half of the tree population, dried to a water potential (ψ) of −3.5 MPa, lost significant quantities of needles but were otherwise comparable to undried trees. Drying to −4.0 MPa or below resulted in significantly reduced water uptake after rehydration and irreversible damage. Changes in percentage of moisture content and stomatal conductance generally paralleled ψ but were less useful indices of the damage threshold. Bark wrinkling and percentage of broken needles were useful morphological indices of the damage threshold. Subjective ratings of quality were less reliable indices of the damage threshold. Water potential was an appropriate single measurement of Christmas tree water status and a suitable index of the damage threshold.
Various storage treatments were imposed on cut douglas-fir Christmas trees to measure drying relative to the damage threshold ψ of −3.5 MPa. In a greenhouse (day/night 16°/10° ± 5°C, RH 70-95%), cut douglas-fir dried to −3.5 MPa in 4 days. Overhead irrigation under these conditions maintained ψ about − 3.2 MPa for 9 days. Outdoors (day/night 672° ±9°), ψ declined to a range of −2.5 to −3.0 MPa depending on the weather. Overhead irrigation outdoors maintained ψ between −1.0 to −2.5 MPa. The antitranspirants tested did not reduce the rate of water loss significantly in the greenhouse. Outdoors, ψ of Vapor Gard-treated trees was similar to the irrigated trees, but Vapor Gard caused serious cosmetic defects. None of the other antitranspirants tested reduced moisture loss outdoors.
Gibberellic acid (GA) increased bolting from 4.2 to 12.8% in fall-planted ‘Yellow Grano’ onion when applied 5 times at 500 ppm from 3/9 to 5/21. A single GA treatment 4/12 did not affect bolting. GA at 1000 ppm applied 11/1 and 12/9 had no effect on bolting or total seed yields of 3 short-day cultivars, but it limited seed yield per umbel. January 14 and February 21 treatments of 1000 ppm increased bolting percentage from 42 to about 60 and the February 21 treatment increased seed yield. Germination percentage of harvested seed was not affected by treatment. All GA treatments caused leaf growth from lateral buds.
Spring application of 2-chloroethyphosphonic acid (ethephon) at 500 and 1000 ppm, N-6 Benzyladenine (BA) at 100 ppm or succinic acid-2, 2-dimethylhydrazide (SADFI) at 5000 ppm did not affect bolting percentage.
Ethephon treatments inhibited internal scale browning of onions held in common storage for 3 months. October or Nov. ethephon treatments at 2500 ppm reduced bolting from 42 to 29%, and a dual ethephon application 10/8 and 11/1 resulted in only 11% bolting.