Search Results

You are looking at 21 - 30 of 45 items for

  • Author or Editor: Gregory A. Lang x
Clear All Modify Search

Seasonal uptake, storage, and remobilization of nitrogen (N) are of critical importance for plant growth. The use of N reserves for new growth in the spring is especially important for sweet cherry (Prunus avium L.), for which new shoot and fruit growth is concomitant and fruit development occurs during a relatively short bloom-to-ripening period. Sweet cherries grafted on precocious, dwarfing rootstocks such as the interspecific (P. cerasus × P. canescens) hybrids Gisela® 5 and 6 tend to produce large crops but smaller fruit when crop load is not balanced with adequate leaf area. Study objectives were to: 1) characterize natural N remobilization during fall and winter to canopy reproductive and vegetative meristems; 2) determine the effect of fall foliar urea applications on storage N levels in flowering spurs; 3) determine whether differential storage N levels influence spur leaf formation in spring; and 4) determine whether fall foliar urea applications affect the development of cold-hardiness. During fall, total N in leaves decreased by up to 51% [dry weight (DW)] and increased in canopy organs such as flower spurs by up to 27% (DW). The N concentration in flower spurs increased further in spring by up to 150% (DW). Fall foliar applications of urea increased storage N levels in flowering spurs (up to 40%), shoot tips (up to 20%), and bark (up to 29%). Premature defoliation decreased storage N in these tissues by up to 30%. Spur leaf size in the spring was associated with storage N levels; fall foliar urea treatments increased spur leaf area by up to 24%. Foliar urea applications increased flower spur N levels most when applied in late summer to early fall. Such applications also affected the development of cold acclimation in cherry shoots positively during fall; those treated with urea were up to 4.25 °C more cold-hardy than those on untreated trees.

Free access

Upright Fruiting Offshoots (UFO) is a novel high-density training system for sweet cherry (Prunus avium L.) that produces fruit on multiple vertical leaders (“offshoots”) arising from a cordon-like trunk. The promotion of sufficient upright shoot number and uniform shoot distribution during establishment are key to development of this training system. Trunk angle, meristem management (selective bud retention and removal), and cordon height at establishment were evaluated for influence on shoot number, shoot distribution, total shoot length, and early fruiting potential. At planting, trunk angles of 45° or 60° from the horizontal resulted in increased shoot growth compared with 30°, and also increased shoot distribution when bud selection was not imposed. A cordon height of 45 cm increased total shoot length by 20% compared with a 60-cm cordon height. Bud selection (retaining buds for optimal upright shoot distribution and removing all others) improved canopy development by reducing the number of shoots in the terminal third of the cordon and increasing the number of shoots in the basal and middle thirds compared with no bud selection. Bud selection reduced fruiting potential in the 2nd and 3rd years compared with unmanaged treatments, but subsequently surpassed those treatments in projected annual yield in Year 4 and cumulative yield in Year 5. Bud selection increased total and average shoot length, and improved distribution while moderating early crop load potential. Planting angle, cordon height, and bud selection significantly impact canopy establishment of UFO trees by affecting shoot number, length, and distribution.

Free access

Abstract

The possibility of using 31P-nuclear magnetic resonance (NMR) spectroscopy to detect ethephon (ET) in olive leaves has been examined. 31P-NMR spectroscopy can be used as a nondestructive technique (tissues excised but not extracted) with the unique attributes of monitoring ET hydrolysis internally and without radiochemicals. A characteristic spectral peak for the parent ET molecule was found 17-21 ppm (a measure of relative frequency, not concentration) downfield from the H3PO4 reference, and a nonreactive, minor contaminant spectral peak was found at 26-27 ppm. Absolute spectral peak location (“chemical shift”) is pH-dependent. The ET hydrolysis product, orthophosphate, produces a spectral peak at 2 to 3 ppm, which coincides with the broad spectral peak attributed to major endogenous phosphate compounds in leaves, such as inorganic phosphate. The lower limit of 31P-NMR detection of ET in solution was 10−3 m; however, spray applications of ET were not detectable in olive leaves unless concentrations of 5 × 10−2 m or more were used, which is far greater than current agricultural use levels for mechanical harvest of olive. Nevertheless, 31P-NMR spectroscopy was useful in following ET uptake and decomposition for more than 48 hr in olive leaves from xylem-fed shoots, and the resolution of the ET spectral peak into separate, adjoining peaks presents the potential to identify and quantify subcellular compartmentalization of ET according to pH-induced chemical shifts. Such knowledge would contribute to understanding long- and short-term in vivo decomposition of ET to ethylene. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).

Open Access

Abstract

A nondestructive system for measuring volatile compounds, specifically ethylene, evolved from intact fruit of olive (Olea europaea L.) in the field is described. Polyethylene cans from 35-mm film cartridges are modified with a rubber septum for sampling. The lid is sealed around the fruit peduncle and remains in the field under all conditions. The can is removable to expose the fruit to normal conditions when sampling is not being done. Samples of the atmosphere inside the can are taken with a syringe for gas chromatographic analysis. Background ethylene evolution from the system is low. The system allows repeated monitoring of the same fruit over the duration of a season. Nineteen glues and sealants are evaluated for bonding, phytotoxicity, and ethylene evolution.

Open Access

Dye transport through vascular pathways was examined in tissues surrounding the graft union of second-leaf, field-grown trees of `Lapins'/Gisela 5 (`Gi 5') (dwarfing) and `Lapins'/'Colt' (nondwarfing). Excavated, intact trees were allowed to take up xylemmobile dye via transpiration for 6 h before sectioning the tree into scion, graft union, and rootstock tissue. `Lapins'/'Gi 5' had a significantly larger stem cross-sectional area in the central graft union than did `Lapins'/'Colt'. Per unit cross section, dye transport of both `Lapins'/'Gi 5' and `Lapins'/'Colt' was significantly less in the graft union than in rootstock sections, with still less transported to scion tissues in `Lapins'/'Gi 5'. `Lapins'/'Gi 5' had a tendency to produce vascular elements oriented obliquely to the longitudinal axis of the tree. Dye was distributed more uniformly axially and radially across the graft union in `Lapins'/'Colt' than in `Lapins'/'Gi 5', with an apparent accumulation of dye in `Lapins'/'Gi 5' graft union. Xylem vessel diameters and vessel hydraulic diameters (VDh) were smaller overall in `Lapins'/'Gi 5' than in `Lapins'/'Colt'; however, graft unions in both had smaller VDh than did rootstock sections. These observations suggest reduced transport efficiency of xylem vessels in the graft union in `Lapins'/'Gi 5' may be due to smaller vessels, vascular abnormalities and/or increased amounts of callus and parenchyma tissue.

Free access

Flower initiation and development in `Bing' sweet cherry (Prunus avium L.) was examined using scanning electron microscopy. There was a 1- to 2-week difference in the time of initiation of flower buds on summer pruned current season shoots (P) compared to buds borne on unpruned shoots (U) or spurs (S). By late July, this difference was obvious in morphological development. The P buds had already formed floral primordia, while the S and U buds showed little differentiation in the meristem until early August. In general, buds from unpruned shoots were similar developmentally to spur buds. By late August, primordial differentiation was similar in the buds from all the wood types; however, buds from pruned shoots were significantly larger (838 μm) than buds from spurs (535 μm) and unpruned shoots (663 μm). Early summer pruning may shift allocation of resources from terminal shoot elongation to reproductive meristem development at the base of current season shoots. The similarity in reproductive bud development between spurs and unpruned shoots, given the difference in active terminal growth, might suggest that developmental resources are inherently more limiting in reproductive buds on spurs.

Free access

Of eight genotypes of cayenne pepper (Capsicum annuum L.) examined, two were identified that differ significantly in ease of fruit detachment force. Greenhouse and field-grown plants of these genotypes, Cajun 1-9027 and Cap-9004, were investigated for differences in cell type and organization at the fruit and receptacle junction. Scanning electron microscopy revealed that mature Cajun 1-9027 fruit that did not separate exhibited a distinct region of sclerified cells that extended from the periphery of the fruit into the receptacle for 25 to 30 cell layers. In contrast, mature fruit of the more readily detachable Cap-9004 had 10 to 15 layers of sclerified cells at the region of detachment. Histochemical and stereological techniques indicated that Cajun 1-9027 had a greater volume of sclereids than Cap-9004. Cajun 1-9027 exhibited smaller cortical cells in the detachment region than Cap-9004. Neither genotype exhibited a well-defined abscission zone at maturity in the detachment region. The presence of more sclerified cells and increased lignification in Cajun 1-9027 compared to Cap-9004 probably contributed to the differences in ease of detachment between the two genotypes.

Free access

Abstract

The cotyledons of pecan [Carya illinoensis (Wang.) K. Koch] seed remain fleshy and turgid throughout an attachment period of several weeks after germination. The growth (dry weight) of the developing seedling was dependent on the cotyledons for the first 3 weeks of the 6–10 week attachment period.

Open Access

Cayenne pepper fruit adhere tightly to the calyx/receptacle, increasing the cost of hand harvest and restricting mechanical harvest. Eight (8) cayenne pepper genotypes were selected from field observations to characterize fruit detachment forces(FDFs) and examine potential relationships between FDF and other fruit parameters. A preliminary greenhouse experiment revealed two genotypes with consistently lower FDFs and two with consistently higher FDFs over several progressive harvest. A field experiment confirmed these characteristics. No correlation between any fruit parameter and FDF was found to be consistent over the genotypes studied.

Free access

Year-round production of the florist azalea cv. Gloria is limited by non-uniform flowering in fall-produced, endodormant-budded plants. To examine the effects of the standard dormancy-breaking chilling treatment (six weeks at 3.5 C) on carbohydrate metabolism, single-cutting plants were chilled in low light (10 μmol·m-2s-1) or in continuous dark Treatment effects were studied by destructively harvesting canopy organs for dry weight and carbohydrate analysis at two week intervals during treatment and at five day intervals during greenhouse forcing. Flowering performance was also evaluated. No differences were found between the low light or continuous dark chilling treatments for canopy organ dry weights, days to initial flowering, or days to 50% flowering. Leaf dry weight decreased 22% during chilling, and did not recover to pre-treatment levels through 15 days of forcing. Stem dry weights did not change during treatment or forcing. Floral bud dry weights were maintained during treatment and increased during forcing. Analysis of soluble carbohydrates indicated that the low light treatment influenced carbohydrate metabolism, resulting in Increased concentrations of sucrose, fructose, and glucose in all canopy organs compared to the dark treatment Maltose concentrations were higher in the light for leaves and stems, but not buds. The potential significance of these changes, with respect to dormancy-breaking treatments and uniform flowering performance, will be discussed.

Free access