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D.M. Glenn and R. Scorza

In reciprocal grafts of tall (`Elberta' and `Loring') and dwarf (`Empress' and `Juseito') peach (Prunus persica Batsch.) phenotypes, we measured dry-matter partitioning, resistance to root system water flow, and phytohormone content of xylem exudate. Scion characteristics determined the phenotype and growth characteristics of the tree irrespective of the rootstock. Tall phenotypes had higher dry weight and lower root resistance to water flow than dwarf phenotypes. Cytokinin-like activity and auxin levels in xylem sap were higher in dwarf than in tall phenotypes; whereas gibberellin-like activity was unaffected by either rootstock or scion. The scion of peach influenced phytohormone levels and resistance to water flow in the root system in addition to root and shoot growth.

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D. Giovannini, D.M. Glenn and R. Scorza

The objective was to study selected physiological characteristics of the canopy and examine changes in dry matter partitioning between the root and shoot in two genetically reduced size growth types (dwarf and pillar) relative to the standard growth type. The dwarf phenotype had reduced leaf/root ratio, less allocation of dry matter to woody tissue and more to leaf tissue, high net photosynthesis, and lower leaf respiration compared to the standard and pillar phenotypes. The dwarf and pillar types had greater resistance to water flow than the standard type. Genetic changes in growth habit significantly alter many physiological parameters of peach tree growth and structure.

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D.M. Glenn and D.L. Peterson

An irrigation control valve that uses the suction developed in a tensiometer to start and stop the flow of water to the irrigation system without the need of electricity was constructed. When soil water suction reached –22 cbars at 25 cm, the valve opened and then closed at –18 cbars. Peach trees at 6 × 6 m (three trees per plot) or 4.9 × 3 m (five trees per plot) spacing were irrigated with either pulse microsprinkler or drip irrigation. Evapotranspiration (ET) was calculated from pan evaporation and adjusted for each plot, based on canopy diameter. Flow meters measured water use for each plot in a split plot design with six replications. In Sept. 1995, drip ET was 30%, and pulse ET was 200% of calculated ET for both plant spacings. Spatial variability in actual and calculated plot ET was >200%, and actual plot ET was highly correlated with calculated plot ET. Data for the 1996 field season will be presented. The results indicate that spatial variability in water use is high, and the tensiometer valve is effective and reliable in scheduling irrigation in a heterogeneous environment.

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F. Takeda, M. Wisniewski and D. M. Glenn

In previous work no difference was found in leaf water potential or solute potential between young guttating leaves and older non-guttating leaves of the same plant. This suggested that the absence of guttation in older leaves was associated with a plant resistance component in the hydathodes. Hydathodes of young, folded leaves contained water pores with various apertures and no signs of occlusion.. In expanded, young leaves, production of epicuticular waxes and excretion of some substance through the pores was observed in the hydathode region. By the time leaves had fully expanded the hydathodes had become brownish. The combination of wax deposition and excreted substance had formed plates of solid material covering water pores. These observations suggest that deposition of substances on top of pores contribute to occlusion of water pores in old leaves.

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D. M. Glenn and W. V. Welker

The effect of ground covers on water uptake was studied using peach trees grown in a 4-part split root system. In 1992, one section of the root system was in bare soil and 3 sections were in combination with `K-31' tall fescue. In 1993, K-31 was eliminated in 2 additional sections, leaving 1 section in combination with `K-31'. When grass transpiration was suppressed by covering the K-31, tree water uptake/cm of root length was greater in the presence of grass compared to bare soil under well watered conditions. These data indicate that peach trees compensate for interspecific competition by increasing root hydraulic conductivity.

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D.M. Glenn and W.V. Welker

Our objectives in this study were to measure the effects of low levels of root system carbon dioxide on peach tree growth (Prunus persica L. Batsch) and nutrient uptake. Using soil and hydroponic systems, we found that increased root CO2: 1) increased root growth without increasing shoot growth, 2) increased leaf P concentration, 3) decreased leaf N concentration, and 4) reduced water use relative to air injection or no treatment.

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W.V. Welker and D.M. Glenn

Peach (Prunus persica L. Batsch) trees were grown for five growing seasons in uniform-sized vegetation-free areas arranged in three patterns within a tall fescue (Festuca arundinacea Schreb.) sod. Trees grown in a vegetation-free area arranged in a strip pattern grew better than trees grown either in the center or edge of a square. The distribution pattern of the vegetation-free area influenced growth during the first 4 years; however, at the end of 5 years, differences in canopy width and trunk cross-sectional area were minimal. Thus, there is much latitude in distributing the available vegetation-free area as orchard floor management practices dictate.

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D. M. Glenn and W. V. Welker

Carbon dioxide is produced by microbial and plant respiration and accumulates in the soil. In previous field studies, CO2 levels were higher under a killed sod soil management system, relative to cultivation and herbicide systems (1.8 vs 0.8 and 1.0%), respectively. Our objective in these studies was to measure the effect of elevated levels of root system CO2 on root and shoot growth and nutrient uptake. Using soil and hydroponic systems in greenhouse studies, we maintained root system CO2 levels between 1.5 and 2.5%. Control CO2 levels were less than 1%. Root length density and dry matter partitioning to the root system were increased by root CO2 in soil and hydroponic studies; shoot growth was unaffected. In hydroponic culture, root CO2 increased P uptake, solution pH, root volume and the number of lateral roots/cm root axis. Elevated levels of CO2 in the root system stimulated root growth in both the soil and hydroponic studies.

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W.G. Yang and D.M. Glenn

The osmotic potential and development of apple and peach floral and vegetative buds and tissue were determined pre- and post-bloom. Apple and peach floral and vegetative buds were removed pre-bloom and the osmotic potential and bud development measured pre- and post-bloom. The osmotic potential of vegetative and floral buds was related to the phenology of bud development. Developing buds had a lower (more negative) osmotic potential than dormant buds. Removal of peach floral buds lowered osmotic potential and increased vegetative bud development and early leaf growth rate. Removal of peach vegetative buds, however, reduced fruit bud development, fruit growth, and embryo survival. Osmotic potential was an index of sink activity during the pre- and post-bloom stages of development.