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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.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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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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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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W.Q. Yang and D.M. Glenn

The osmotic potential and development of apple (Malus domestica Borkh.) and peach [Prunus persica (L.) Batsch] floral and vegetative buds and tissue were determined pre- and postbloom. Apple and peach floral and vegetative buds were removed prebloom and the osmotic potential and bud development were measured pre- and postbloom. The osmotic potential of vegetative and floral buds was related to the phenology of bud development. Developing buds had a more negative osmotic potential than dormant buds. Leaf buds on deflorated shoots had a more negative osmotic potential than leaf buds on shoots with floral buds. However, flower buds on defoliated shoots had a less negative osmotic potential than flower buds on shoots with leaf buds.

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D.M. Glenn, G. Puterka and S. Drake

Particle film technology uses inert mineral particles to envelope a plant in a protective and porous “particle film.” The film appears to protect against insect damage by creating a hostile and unfamiliar environment, causing nonrecognition of the host, acting as an irritant, and giving poor adhesion or gripping of eggs and insects to the plant surface. Being porous, the particle film allows free exchange of water and carbon dioxide from the leaf during photosynthesis. The mineral particles are reflective of infrared radiation and reduce the heat load on the plant. Laboratory, greenhouse, and field trials demonstrate that particle film technology is a viable pest control practice for a wide range of insect and disease problems with additional horticultural benefits due to reduced heat stress. In field studies, reducing heat stress improved red apple color development, increased leaf photosynthetic rates, and increased yield. Particle film technology appears to be a viable alternative to conventional pesticide use in apple and pear production. Particle films have the added benefits of reducing plant heat stress and improving safety to farm workers, consumers, and the environment.

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T.J. Tworkoski and D.M. Glenn

Peach tree size has been restricted when trees were grown continuously with grass after tree planting. However, control of excess vegetative growth of fruit trees was inconsistent when grass was planted beneath mature trees. This research determined the effect of seven grasses on growth, leaf nitrogen concentration, and yield of 8-year-old peach trees and on weed abundance. Two cultivars (`Loring' and `Redhaven') of peach [Prunus persica (L.) Batsch] trees were planted in separate orchards in 1987 in a split-plot design with grass as a main effect and time as the subplot. Nine treatments were installed as ground covers beneath peach trees in 1995: Festuca arundinacea, Lolium perenne var Manhattan II; L. perenne var. Linn; Agrostis gigantea, Dactylis glomerata, Phleum pratense, Bromus carintus, weedy control, and herbicide control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in `Loring' and `Redhaven'. For example, compared to herbicide treatments, orchardgrass reduced sprout length by 27% in `Loring' and by 15% in `Redhaven'. Fruit-bearing branch length was reduced with orchardgrass by 30% in `Loring' and 19% in `Redhaven'. Orchardgrass affected fruit yield more than vegetative growth, reducing yield by 37% and 24% in `Loring' (predominantly in the 2- to 2.5-inch size class) and `Redhaven' (predominantly in the >2.5-inch size class), respectively. All grasses were not equally competitive, `Linn' perennial ryegrass never significantly affected growth or yield. Weedy treatments also did not differ from herbicide treatments in peach tree growth and yield. Grasses and weeds consistently reduced peach tree leaf nitrogen by 17% compared to herbicide treatment, but weed density was not correlated with reductions in yield and vegetative growth. The results indicate that peach cultivars respond differently to grass competition but the relative competitiveness of grass species was similar for both cultivars. Grass competition can reduce growth of mature peach trees but this reduction did not translate to reduced pruning time per tree.

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W.V. Welker and D.M. Glenn

Peach [Prunus persica (L.) Batsch] trees were planted in killed sod developed from five different grasses. Tree growth was evaluated within the killed-sod treatments, as well as between killed-sod and bare soil treatments. Canopy width, tree height, and trunk cross-sectional area were all greater in the killed-sod treatments than in the bare soil treatments. All five grasses tested were acceptable for developing a killed-sod mulch. Chemical names used: N-(phosphonomethyl) glycine (glyphosate); N1(3,4-dichlorophenyl)-N,N-dimethylurea (diuron); 5-chloro-3-(1-1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione (terbacil).

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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.