Search Results

You are looking at 1 - 10 of 61 items for

  • Author or Editor: R. R. Bruce x
Clear All Modify Search

Abstract

Potted seedlings of white birch (Betula papyrifera Marsh.) and pin oak (Quercus palustris Muenchh.) were grown in the field for 3 months in relatively high- and low-ambient sulfur dioxide air. Biweekly throughout the growing season, plants from each site were harvested, and height and leaf, stem, and root dry weight were measured. The overall growth of white birch, an SO2-sensitive species, was found to be greater in the higher, but sub-phytotoxic SO2 environment. Conversely, the growth of pin oak, an SO2-tolerant species, was greater at the low SO2 site.

Open Access

Abstract

Intraclonal variation in Ulmus americana, American elm and U. pumila, Siberian elm was compared with seedling variation in the same species for the following characteristics: height growth; shoot, root, and total fresh weight; stem, leaf, root and total dry weight; root-shoot ratio, and leaf area. Intraclonal variation was as great as seedling variation for all characteristics in 3-month-old American and 12-month-old Siberian elms and for height growth in 13-month-old American elms. It was significantly less for all other characteristics in the 13-month-old American elm clone.

Open Access

Abstract

The capacity of rhododendron (Rhododendron catawbiense Michx., cv. Nova Zembla) and firethorn (Pyracantha coccinea M. J. Roem. var. Lalandii (Duren) Dipp.) to change ambient SO2 levels in a closed fumigation system was studied. P. coccinea removed greater quantities of SO2 at faster rates than R. catawbiense. Differences in leaf surface characteristics between the 2 species suggest that at least part of the SO2 uptake mechanism may involve a surface-mediated response to the pollutant.

Open Access
Authors: and

The role of spur leaves in bud and fruit development on two spur-type `Delicious' apple strains (Malus domestica Borkh.) and factors affecting spur development were studied. Reducing spur leaf area on vegetative spurs in August reduced the number of spurs that flowered the following year but did not affect flower size. On spurs that did flower, leaf area reduction the previous year did not influence leaf number or area, but the bourse shoot leaf area was reduced. Spur bud diameter, leaf area, size, specific leaf weight (SLW), and leaf dry weight were larger on 2-year-old vegetative spurs than on 1- or 3-year-old spurs. Within each age section of a limb, spur leaf number, area, size, SLW, and bud diameter decreased from the apical to basal positions on the limb. Flower number did not vary within a limb section, but fruit set was lower on the most apical and basal spurs compared to midshoot spurs. Fruit size was largest at the apical end of each limb section and was smallest at basal positions. These relationships were not affected by strain, tree age, or orchard location. Summer pruning at 30 days after bloom tended to increase leaf number, area, size, and spur length compared to unpruned trees or pruning later in the season but did not influence spur bud diameter.

Free access

Light-emitting diodes (LEDs) are a rapidly developing technology for plant growth lighting and have become a powerful tool for understanding the spectral effects of light on plants. Several studies have shown that some blue light is necessary for normal growth and development, but the effects of blue light appear to be species-dependent and may interact with other wavelengths of light as well as photosynthetic photon flux (PPF). We report the photobiological effects of three types of white LEDs (warm, neutral, and cool, with 11%, 19%, and 28% blue light, respectively) on the growth and development of radish, soybean, and wheat. All species were grown at two PPFs (200 and 500 μmol·m−2·s−1) under each LED type, which facilitated testing the effect of absolute (μmol photons per m−2·s−1) and relative (percent of total PPF) blue light on plant development. Root and shoot environmental conditions other than light quality were uniformly maintained among six chambers (three lamp types × two PPFs). All LEDs had similar phytochrome photoequilibria and red:far red ratios. Blue light did not affect total dry weight (DW) in any species but significantly altered plant development. Overall, the low blue light from warm white LEDs increased stem elongation and leaf expansion, whereas the high blue light from cool white LEDs resulted in more compact plants. For radish and soybean, absolute blue light was a better predictor of stem elongation than relative blue light, but relative blue light better predicted leaf area. Absolute blue light better predicted the percent leaf DW in radish and soybean and percent tiller DW in wheat. The largest percentage differences among light sources occurred in low light (200 μmol·m−2·s−1). These results confirm and extend the results of other studies indicating that light quantity and quality interact to determine plant morphology. The optimal amount of blue light likely changes with plant age because plant communities balance the need for rapid leaf expansion, which is necessary to maximize radiation capture, with prevention of excessive stem elongation. A thorough understanding of this interaction is essential to the development of light sources for optimal plant growth and development.

Free access

The transmission of plum leaf scald or phony peach, Xylella fartidiosa, Wells is compared by the slip and chip budding with peach and plum scions on two peach rootstocks, `Lovell' and `Nemaguard'. ELISA was used to determine mean concentrations of the bacteria in scion leaf petioles. There was a greater level of transmission of the pathogen using chip budding over slip budding in plums but not in peach. Further analysis of slip budding showed no difference to unbudded rootstocks wheras chip budding caused a significantly higher incidence of transmission.

Free access

The recessive leaf trait, fused vein (fv), in Cucurbita pepo L. is expressed by the sixth leaf stage and then throughout vegetative growth. It is characterized by the partial fusion of the lateral leaf veins to the main central vein. Consequently, the dorsal leaf surface is distinctively puckered. Use of fv as a genetic marker in hull-less seeded pumpkin lines is hampered, however, by a low recovery of fv plants in segregating populations. Homogeneity Chi Square analysis of 11 F2 (3:1 X2 = 72.05 P < 0.005) and 16 BC (1:1 X2 = 120.12 P < 0.005) populations indicated significant heterogeneity between populations for fv recovery. Recovery ranged from 0 to 35.5% for 11 F2 populations and from 6.8 to 75.4% for 16 BC populations. There was a significant reduction, 35%, in seed yield/fruit when fv pollen was used to hand pollinate fv, normal (N), and F1 flowers as compared to pollinations with N pollen. In pollen competition studies, reduced competition at low levels of F1 or 50:50 fv/N pollen increased fv recovery in F2 and BC populations. These results are consistent with the hypothesis that the fv trait confers gametic subvitality resulting in distorted Mendelian segregation.

Free access

Observations of net assimilation rates (`A') by pecan sun and shade leaves in relation to various levels of solar irradiation, the light adaptation characteristics of these leaf types, the role of clouds in suppressing the penetration of solar irradiation, and the abundance of cloud cover in the southeastern U.S. during the growing season, suggest that nut production throughout the U.S. pecan belt is being limited by insufficient sunlight with the southeastern U.S. (comprising about 2/3 of the commercial U.S. pecan production) being especially impacted. In support of this hypothesis, regression analysis showed cultivar-type nut production for Georgia from 1977-1989 to be significantly (P<.0001, R2 = 0.79) associated with sunlight levels ≥ 3000 Wh m-2d-1 from mid August to early October for the same year. This is taken as evidence that the amount of sunlight reaching the canopy seems to be a major factor that should be considered in relation to orchard site selection and canopy management techniques.

Free access

Three experiments were conducted to delineate gametophytic selection of the fused vein trait in Cucurbita pepo L. Gametophytic subvitality was verified by comparing fused vein and normal pollen tube growth. Microscopic examination of partitioned, co-pollinated flowers revealed fewer and slower growing fused vein tubes than normal. The effects of gametophytic subvitality on seed yield and inheritance were shown by manipulating the severity of reproductive competition. Fused vein, normal, and F1 lines were pollinated with fused vein, normal, 50:50 mix, and F1 pollen at three different pollen loads. Analysis showed that fused vein pollen generated significantly fewer seed per fruit in all lines. In ensuing F2 and testcross populations, a reduction in load and thus competition significantly increased the number of fused vein individuals. Leaf number and area for normal, fused vein, F1, F2, and testcross plants were assessed to test pleiotropic effects on growth common to gametophytic subvitals. Although normal and fused vein lines differed in leaf number and size, their total leaf areas were not significantly different. F2 and testcross plants showed no difference between normal and fused vein individuals; leaf size and number were independent of leaf morphology.

Free access

Genetic experiments were initiated to assess the potential for combining large seed size from PI 285611, a large-fruited, hullless seeded accession, with small fruit size from a hullless seeded breeding line (NH29-13-5-4). An F2 population and parental line were field-grown during Summer 1993 to determine inheritance and heritability of large seed size and the relation between fruit and seed size. Seed size variables of weight, width, length, and thickness were regressed against fruit weight. There was a moderate, positive correlation between large fruit and seed length (R2 = 0.46). However, seed thickness, a major determinant of seed weight, was not correlated with fruit size. In an F2 population of ≈450 plants, there was a small number of plant selections with fruit under 1.5 kg and seed size approaching that of PI 285611.

Free access