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Michael R. Sweatt and Jayne M. Zajicek

Castilleja indivisa grows hemiparasitically attached to the roots of various nearby plants. Studies were done using several host plants to determine the effects of the parasitic relationship on the growth of C. indivisa and the host plants. Transpiration rates, and leaf water potentials of C. indivisa, and various hosts, were also measured at various soil moisture levels. Carbon transfer between C. indivisa and each host was examined using a 14CO2 tracing technique.

The various hosts used in this experiment enhanced the growth of C. indivisa by 200-700% compared to non-parasitic controls. Transpiration rates of non-parasitic controls remained relatively low at all soil moisture levels while transpiration rates of parasitic C. indivisa increased rapidly as soil moisture increased, and generally exceeded that of its host at low to medium soil moisture levels. Leaf water potentials of non-parasitic controls were generally more negative than other treatments. Carbon exchange between C. indivisa and its hosts was insignificant and appears not to be a major nutritional factor.

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Jane M. Petitte and Douglas P. Ormrod

Abbreviations: CSTR, continuously stirred tank reactor; PLA, planar leaf area; π osmotic potential; ψ leaf , leaf water potential. 1 Current address: 620 Shadywood Lane, Raleigh, NC 27603. This paper is a portion of a thesis submitted by J.M.P. in

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J. Ryan Stewart, Roger Kjelgren, Paul G. Johnson, and Michael R. Kuhns

Although transplanted trees typically establish and grow without incident in frequently irrigated turfgrass, their performance in precisely irrigated turfgrass in an arid climate is not known. We investigated the effect of precision irrigation scheduling on growth and water relations of balled-and-burlapped littleleaf linden (Tilia cordata Mill. `Greenspire') planted in buffalograss (Buchloë dactyloides [Nutt.] Engelm. `Tatanka') and kentucky bluegrass (Poa pratensis L.). Over 2 years, trees in turfgrass were irrigated either by frequent replacement based on local reference evapotranspiration, or precision irrigated by estimating depletion of soil water to the point of incipient water stress for each turfgrass species. Predawn leaf water potential and stomatal conductance of trees were measured during first-year establishment, and predawn leaf water potential was measured during a mid-season water-deficit period during the second year. Trunk diameter growth and total tree leaf area were measured at the end of each year. Values of predawn leaf water potential and stomatal conductance of trees in precision-irrigated buffalograss were lower (–0.65 MPa, 25.3 mmol·m–2·s–1) than those of trees in the other treatments near the end of the first growing season. The longer interval between precision irrigations resulted in mild water stress, but was not manifested in growth differences among trees across treatments during the first season. During the water-deficit period of the second year, there was no evidence of stress among the trees regardless of treatment. At the end of the second season, total leaf area of trees grown in precision-irrigated kentucky bluegrass (1.10 ± 0.34 m2) was 46% of that of trees grown in buffalograss (2.39 ± 0.82 m2) that were irrigated frequently. Trunk diameter growth of trees in frequently irrigated kentucky bluegrass (1.91 ± 2.65 mm) was 29% of that of the trees grown in buffalograss (6.68 ± 1.68 mm), regardless of irrigation treatment, suggesting a competition effect from kentucky bluegrass. We conclude that frequent irrigation of balled-and-burlapped trees in turfgrass, particularly buffalograss, is more conducive to tree health during establishment than is maximizing the interval between turfgrass irrigation. Regardless of irrigation schedule, kentucky bluegrass appears to impact tree growth severely during establishment in an arid climate.

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Long-Xi Yu, Ann. F. Greer, and Zohreh Tabaeizadeh

We have carried out a comparative study on chitinase gene expression and enzyme activity in Lycopersicon chilense (a drought-tolerant wild tomato) and L. esculentum under water stress. Both enzyme assay and Northern blot analysis revealed that chitinase expression was differentially induced by drought among the different genotypes. Higher induction of chitinase was found in tolerant species compared to the sensitive one. Among genotypes examined, L. chilense LA2747 presented the highest level of the chitinase induction, while the lowest level was found in L. esculentum HR86. Leaves of drought-stressed plants showed the highest expression and roots showed the lowest, with stems being intermediate. Chitinase activity was detected in flowers of both drought-stressed and control plants. The measurement of leaf water potentials of different genotypes revealed a correlation between drought tolerance and the level of chitinase expression during water stress. Our results suggest that the chitinase might be involved in drought tolerance of L. chilense.

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R. Scott Johnson, Claude Phene, and Charles Medawar

Six irrigation strategies were imposed on a block of O'Henry peach trees irrigated by fanjets. Treatments received different percentages of ET during the various stages of fruit growth and postharvest. ET was estimated by a large weighing lysimeter containing 2 trees and located in the center of the block. Fruit diameters were measured weekly and final fruit weights were determined at harvest. Adjusted fruit weights were estimated by statistically adjusting each treatment to the same fruit load.

Adjusted fruit weight correlated well with soil water content during the month before harvest but not during early stages of fruit growth. Treatments which applied 50% ET during early stages of fruit growth showed reduced fruit size at that time. However, with applications of 150% ET during the final fruit growth stage, fruit size recovered. Adjusted fruit weight also correlated with measures of tree water status including midday leaf water potential and canopy temperature.

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Michael A. Arnold., G. Kim Stearman, and Reed W. Cripps

Rooted cuttings of Acer rubrum `Red Sunset' grown in containers treated on interior surfaces with 100 g Cu(OH)2/liter white interior latex paint, or left untreated, were root pruned or not root pruned and planted in a field plot. A pseudo-bareroot treatment, trees from untreated containers shaken free of media, was included. Height (115 vs. 108 cm) and caliper (12.0 vs. 10.7 mm) at transplant was slightly greater for copper treated trees than for untreated trees. Leaf water potentials (LWP) at transplant were similar for all treatments. Mid-day LWP of trees transplanted from untreated containers tended to be lower than that of trees grown in copper treated containers at days 3, 14, 28, and 53 after transplant. Pseudo-bareroot trees had the most negative mid-day and pre-dawn LWP through day 92. Soil water potentials were from -0.01 to -0.03MPa.

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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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Beth Jez Lawrence and Jayne M. Zajicek

Sap flow rates of three Cercis spp. exposed to supraoptimal root-zone temperatures were characterized in a controlled environment chamber using a water bath to control temperatures. Flow rates of sap in the xylem were measured every 15 sec. and averaged over 15 min. intervals. Sap flow measurements were correlated to root-zone temperatures recorded during the same time intervals. Whole plant transpiration was measured gravimetrically. Root-zone temperatures were maintained at 22C for three consecutive 24-hr cycles and then increased to 45C for an additional three 24-hr periods. All plants, regardless of species, had reduced sap flow patterns when exposed to high root-zone temperatures. Plants maintained at a constant temperature of 22C showed no extreme fluctuations in sap flow rate. Stomatal conductance rates and leaf water potentials showed similar trends to whole plant transpiration.

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Robert M. Frymire and Janet C. Cole

Uniform rooted cuttings of pyracantha (Pyracantha coccinea M.J. Roem. 'Lalandei') were potted into 3.8 liter containers in a pine bark:sand medium. Plants were treated with a medium drench at 0.5 mg ai per container, or a foliar spray at 150 mg ai per liter, or no uniconazole. Plants also were exposed to one of three irrigation regimes: nonstressed, stressed or acclimated. Uniconazole had little effect on leaf water potential, osmotic potential, transpiration or leaf conductance. The uniconazole drench treatments reduced plant growth and increased N, Ca, and Mn concentrations in the leaves. Foliar applications had less effect on plant growth and elemental content Acclimated and stressed plants had lower water and osmotic potentials, transpiration rates and leaf conductance than nonstressed plants on the final day of the stress cycle. Acclimated plants had higher levels of N and Mn with lower levels of Zn in the leaves than either stressed of nonstressed plants.

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Jesse R. Quarrels and Paul G. Thompson

An experiment was conducted to determine the rate and frequency of irrigation needed for optimum yield in sweetpotato (Ipomoea batatas (L.)Lam). A line source irrigation system was used to provide continuously increasing amounts of water at each irrigation. The physiological responses of sweetpotato to water application were measured. There was an increase in leaf water potential with increasing rates of irrigation. Leaf diffusive resistance decreased as total water rate increased to 76% of pan evaporation (Epan) and then increased with higher rates of irrigation. Marketable yields increased as total water rate increased to 76% of Epan and then decreased rapidly with higher irrigation rates. Water relations measurements indicated that reduction in yield with higher amounts of water application was due to low soil oxygen content.