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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).

Open Access

Photoperiod is an important environmental signal for regulating developmental patterns in many plant species. In several species, photoperiodic regulation of gibberellin A1 biosynthesis has been implicated as the mechanism by which photoperiod may alter development. To examine this phenomenon in strawberry, Fragaria virginiana plants grown under long day (LD) and short day (SD) conditions with equivalent total PAR were examined to determine changes in vegetative growth and GA1 biosynthesis.

LD conditions (16 hr) promoted vegetative growth. Runner production, total leaf area, area of individual leaves, and petiole lengths, all increased under LD conditions. No runner production occurred under SD conditions (8 hr); however, the number of branch crowns increased.

Gibberellins A44, A19, A20, and A1, all from the GA1 biosynthetic pathway, were identified in plants under both LD and SD conditions. However, SD conditions appeared to affect the 2β-hydroxylation of GA20 to GA1. Whereas levels of most GAs decreased under SD conditions, levels of GA20 increased, and only trace amounts of GA1 were found, indicating a possible blockage of the pathway at this point. As GA1 is considered the active component of the pathway, blockage of GA20 conversion under SD conditions may explain the concomitant reduction in vegetative growth.

Free access

Olive (Olea europaea L.) field experiments involving natural flower and fruit populations are fraught with variability, resulting in large coefficients of variation. We provide evidence that coefficients of variation can be reduced successfully by judiciously selecting four experimental twigs per tree and using only those twigs with an internodal growth ≥2 cm, two inflorescences per node, and that are selected from trees with near-maximum bloom density. Although counting flowers at full bloom may establish the population uniformity, only a single node; e.g., node 5, is needed for analysis. Increasing the number of trees will reduce variance more than increasing the number of twigs or nodes.

Free access

Abstract

Total immersion of Pseuderanthemum atropurpureum L. H. Bailey, Sanchezia speciosa J. Leonard, and Strobilanthes dyeranus M. T. Mast. cuttings in aqueous solutions of the morphactins chlorflurecol and chlorflurenethol prior to propagation retarded plant growth 16 weeks after rooting. Height of Sanchezia and Strobilanthes also was reduced by dips of chlorfluren and dichlorflurecol and chlormequat chloride. Morphactins caused abnormal growth on Pseuderanthemum and Strobilanthes. Dips of PBA reduced the height of Pseuderanthemum and Strobilanthes. Pseuderanthemum height also was reduced by ancymidol and ethephon dips, and height was reduced on Strobilanthes by oxathiin and piproctanyl bromide. Chlorflurecol dips reduced plant dry weight of all species. Plant dry weight of Strobilanthes also was reduced by chlorofluren, chloroflurenthol, oxathiin, and PBA immersion. Ethephon, PBA, and chlorflurenthol dips also reduced Pseuderanthemum dry weight. Chemical names used: 2-chloro-9-hydroxy-9H-fluorene-9-carboxylic acid (chlorflurecol); 2-chlorofluorenecarbonic acid-(9)-methylester (dichloroflurecol); 2-chloro-9-hydroxyfluorene-carbonic acid-(9)-p-chlorophenoxyethylester (chloroflurenethol); 2-chloro-N,N,N-trimethylethanaminium chloride (chlormequat chloride); N-(phenylmethyl)-9-(tetrahydro-2H-pyran-2-yl)-9H purin-6-amine (PBA); α-cyclopropyl-α-(4-methoxyphenyI)-5-pyrimidinemethanol (ancymidol); (2-chlorethyl)phosphonic acid (ethephon); 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (oxathiin); 1-(3,7-dimethyloctyl)-1-(2-propenyl)piperidinium bromide, (piproctanyl bromide).

Open Access

Abstract

‘Redhaven’ peach on 5 seedling rootstocks planted in the spring of 1973 in a water-logged soil exhibited varying degrees of injury by July. ‘Rutgers Red Leaf’ was most tolerant; ‘Lovell’ was least tolerant. These differences suggest the feasibility of breeding for “wet feet” resistance in peach rootstocks.

Open Access

Olive fruit persistence is a crucial component of yield and an important factor in estimating alternate bearing potential.

Unfortunately, measurement of fruit persistence exhibit considerable variation, with coefficients of variation greater than 100. Such a high degree of variation makes field studies on questions regarding flowering and fruiting unmanageable due to the large number of experimental units necessary. To determine the source of this variation and how it might be reduced, comparisons of flower and fruit number per node were made within branches and trees over the course of two seasons. Results show that while the largest population of flowers are most distal on the branch, the central portion of the branch contains the majority of the final fruit population and has the lowest coefficient of variation. Furthermore, variation in the number of flowers and fruits is greater between branches than between nodes or trees. The implications of these data on experimental design are discussed and a design is proposed for reducing variation and labor needs.

Free access

Trees that fruited during 1990 retained 67.3% of the inflorescence buds produced per branch in 1991 compared to 63.1% for trees that were defoliated immediately after harvest in 1990 and 21.3% by trees that were fruiting in 1991. Shading reduced bud retention similar to fruiting.

Defoliation after nut harvest accentuated the delayed costs of reproduction caused by previous season's fruiting whereas shading produced significantly greater immediate costs. Shading effects on the allocation of carbon to buds, leaves and shoots were similar to those of fruiting. Leaf net photosynthesis under shade conditions was reduced to 14.27% of control trees and this led to a significant reduction in the relative growth rates of all the organs surveyed.

Free access

Abstract

Harvesting seed of ‘Manzanillo’ olive (oleo europaea L.) at the end of October, when embryo growth was complete, gave optimum germination and extended storage life with lower germination rates and shorter storage life before or after this date. Optimum germination occurred at 15°C for whole seed and 25° for excised embryos; both grew faster at 25° after germination. Seed and excised embryos germinated equally well in light or dark.

Open Access

Abstract

Spraying 7-year-old citrus trees with film-forming antitranspirants before transplanting increased leaf water potential, thereby reducing “transplant shock.” Leaf water potential decreased rapidly after transplanting, by as much as 21 atm in unsprayed, and as little as 6 atm in sprayed trees. There was little benefit from transplanting in late afternoon rather than the morning.

Open Access

Spring dead spot (SDS), caused by three root-infecting species of Ophiosphaerella, is a destructive disease of bermudagrass (Cynodon spp.L.C. Rich). We tested the effects of incubation temperature and duration, and exposure to decreasing freezing temperatures on bermudagrass shoot survival following inoculation with SDS pathogens. Inoculated plants exposed to freezing temperatures as high as -2 °C following a two month incubation exhibited extensive shoot mortality and had SDS symptoms consistent with those observed in the field. Lowering the freezing temperature from -2 to -8 °C increased disease severity and shoot mortality on noninoculated bermudagrass. Inoculated bermudagrass incubated for 1 month in the greenhouse, then for an additional month at 4 °C had greater shoot mortality following freezing than plants incubated at 25 °C. Although cold acclimation and freezing intensified SDS symptoms, the technique did not reliably distinguish between resistant and susceptible cultivars.

Free access